^y^s/oe>s-^f/ CO o O CQ O O c £3 U •l-l ^ a. t^ cc 1^ . LLI o — • J^ a E \ ^ ^ C/3 O c li c 1) c o 00 iZ a: 5 ^5 CO Ti; Ci3 ti: o o o o o o o o d S o o u c xi O (1> O o o s: o. •a c ca "ca o '5b "o u l-l O ■J? c o o ca Pu o System of Interest Prey B ingestion Predator Plant I D Figure 1-4. Graphic symbols used in ecological modeling (Odum 1967). Figure 1-5. A diagrammatic systems model of an aquatic habitat. mE VOLUME I Narrative Report 1.0 The Ecological Characterization Pi-ocess 2.0 Chenier Plain Ecosystem 3.0 Chenier Plain Basins 4.0 Chenier Plain Habitats 5. Chenier Plain Animal Species :";i>'■iv-Vfei^■■■:'J^^;^^•';^^i~^r^>:^i^■■^l^;/;^^.:;;:v-^'V-^^ X2 VOLUME II Appendixes 6. Introduction 6. 1 Chenier Plain Data Sources 6. 2 Chenier Plain Socioeconomic Data 6. 3 Chenier Plain Biological Data 6. 4 Chenier Plain Hydrological and Habitat Data 6. 5 Literature Cited VOLUME III Atlas Plates: lA and IB - Index Maps 2 -The Pleistocene Erosional Surface 3A and 3B - Chenier Plain Habitat Groups 4A and 4B - Chenier Plain Wetland Habitats 5A and 5B - Canals and Point Source Discharges 6A and 6B - Special Features S...> ■■■■.- .■■■■■.iT^-rr 1 Viri-.i Vl'-i'-li'^l'i .'.r;.'i''.'.'v,vi.',-' ■"•.•■•.■;s-> Sy Figure 1-6. Contents of the Chenier Plain Ecological Characterization Study. 2.0 The Chenier Plain Ecosystem 2.1 INTRODUCTION The Chenier Plain ecosystem is a rich and complex mixture of wetlands, uplands, and open water that extends about 322 km (200 mi) from Vennilion Bay, Louisiana to East Bay, Texas (fig. 2-1). The lengthwise boundaries cf the ecosystem are the 9 m (30 ft) depth contour along the sliore of the Gulf of Mexico and the 1.5 m (4.9 ft) land elevation contour. These boundaries are separated by distances ranging from 16 km (10 mi) to 64 km (40 mi) and encompass a total area of over 1,295 km (5,000 mi^). Several systems of rivers and lakes cross the Chenier Plain from north to soudi and divide it into six fairly distinct drainage basins. Pleistocene-age deposits, which forni the geologic substrate of the Chenier Plain region, are found at the surface a few kilometers inland from the coast and dip gently seaward to .include the slope of the Continental Shelf which is delineated by the 10 m (33 ft) bathymetric line that lies about 8 km (5 mi) offshore and by the 20 m (66 ft) line lying some 45 km (28 mi) offshore. These Pleistocene deposits are ovedain at the coast by geologically Recent sequences of inland stranded beaches that align the topographic grain parallel with tlie coast. Near sea level marslies interlaced with tidal channels lie between successive ridges. The coastline is breached by inlets tliat connect estuaries extending inland up river basins. The exception is the East Bay Basin in Texas, whose long axis parallels the coast. Although geo- graphically part of the Chenier Plain, the topography of this basin is similar to that found in basins of the Strand Plain ecosystem to the west. Water- riverine, Gulf, and subsurface-is the single most important medium for transporting and mixing sediment, and nutrients. Rivers function as arteries transporting sediments and nutrients from inland catchrnent basins to the mixing and receiving basins of estuaries, marshlands, and the Gulf of Mexico. Meteorological forces interact with tides and waves to generate currents along the coast and in estuaries. Although highly variable from year to year, climate exerts a long-term influence sustaining major repetitive water movement patterns. Onshore winds associated with summer sea breezes and offshore winds that accompany the passage of winter cold fronts raise or lower water levels, and drive surface water. Landforms and accompanying habitats result from the complex interaction, through time, of geological, hydrological, and meteorological processes. Parts 2.2 through 2.5 focus on these processes which are relevant to understanding the development, variability, and interaction of habitats. The basins that compose the ecosystem function as discrete units but are also subject to similar regional forces. These basins, as the primary functioning units of this study, are discussed in part 3.0. 2.2 GEOLOGICAL PROCESSES Tliis section discusses the sedimentary and erosional processes associated with land gain or loss, and habitat development. Changes that have occurred since the sea reached its present level, approximately 3,000 to 4,000 years ago are of primary concern. The relation between events that occurred during the last few decades and those presently underway are also of significance. However, this record is framed against coastal plain development processes (e.g., alluvial, deltaic, and marine sedimentary processes) that occurred during the last ice age when the sea level was dramatically lower, as well as during the time when the sea was rising to its present level. 2.2.1 SEA LEVEL CHANGES The last continental glacial advance lowered the sea level approximately 135 m (443 ft) below its present level (Fisk and McFarian 1955, Gould 1970), and the shoreHne was at a point approximately 200 km (124 mi) seaward of its present position (RusseU 1936). Receding seas exposed the Pleistocene surface (known as "Prairie" in Louisiana and "Beaumont" in Texas) to erosion and weathering. With lowered base levels, coastal streams along the Chenier Plain cut valleys into the Pleistocene deposits (plate 2). Subsequently during sea level rise with glacial retreat, sequences of sediments were deposited on the eroded Pleistocene surface (Saucier 1974). These sediments consisted of sequences of open Gulf, bay, lake, marsh, and swamp deposits. Each habitat can be described from borings by the composition of flora and fauna and the quantities and bedding characteristics of sands, silts, and clays contained in the deposits (Byrne et al. 1959). The depositional phase ceased when the sea reached its approximate present level. At that time the shoreline was landward of its present position, as evidenced by the inland location of former beach ridges of Recent age (fig. 2-2a and b). Subsequently the shoreline advanced, by sediment accretion, some distance seaward of its present loca- tion. At present much of it is retreating again. The entrenched valleys that were drowned during sea level rise have not been filled with sediments but form shallow inland lakes. 2.2.2 LAND SUBSIDENCE Wlren combined with wave attack, loss of sedi- ment supply, and sea level fluctuations, land subsi- dence occurs. Tills process is lughly complex and includes regional crustal downwarping of the Gulf coast geosynchne, tectonic processes of folding and faulting, and compaction of sediment tlirough de- watering. Compaction, which is the major cause of land subsidence, includes: differential consolidation because of sediment textural variability; consolida- tion of underlying sediments from weight of levees (natural and artificial), beaches, buildings, piles, and fills; lowering of the water table through extraction of ground water, salt, sulfur, oil, or gas, or reclama- tion practices; and extended droughts and marsh burning that cause surface dehydration and shrink- age in highly organic soils. In comparison with other causes of subsidence, crustal downwarping has a minor effect on the Chenier Plain region. The Pleistocene surface lies only about 10 m (33 ft) below tlie Recent surface at the present shoreline (plate 2). Below the Mississippi River delta the depth of the Pleisto- cene surface is over 300 m (984 ft) (Fisk and McFarlan 1955, Gould 1970). Land subsidence caused from de- watering processes is usually less dramatic in the Chenier Plain than farther east because of the rela- tively thin section of Recent deposits that overlie the Pleistocene surface. Nevertheless, the overall net rate of subsidence (or sea level rise) is signifi- cant and averages about 1.75 cm (0.69 in) per year on the Chenier Plain. 2.2.3 RECENT SEDIMENTARY ENVIRONMENTS During the geologic formation of the Chenier Plain, the Mississippi River occasionally constructed deltas close to its eastern flank, just as the Atchafa- laya River, located between the Mississippi River and the Chenier Plain, is presently doing. The west- ward movement of reworked former delta sediments combined with sediments from adjacent active Mississippi River distributaries are thought to be the main source of sediments for the Chenier Plain. It is also evident that the rivers within the region contributed sediments to the coast (Howe et al. 1935, Van Lopik and Mclntire 1957). Deposits of marine origin are represented in the lower part of the Recent sedimentary wedge. Although not deUneated in every core examined, they exist in theory based on an understanding of processes that must have been operating during sea level rise. Thus, they may only be distinguishable from overlying nearshore, marsh, bay, or beach deposits by their relationship to the erosional Pleistocene surface (Byrne et al. 1959, Gould and McFadan 1959). Gulf bottom, marsh, lake, and bay deposits cap the marine deposits and comprise sequences of sand, silt, clay, and organic deposits representing open Gulf, bay, lake, .and marsh or swamp habitats (Byrne et al. 1959, Kane 1959, Coleman 1966). The open Gulf marine deposits are highly variable depending on their proximity to the sediment source and to the offshore energy conditions. They inter- finger with marsh, bay, or lake deposits close to the shoreUne where erosion or accretion has occurred. The open Gulf deposits are distinguished by the marine fauna, distinctive sedimentary structures, and absence of accumulations of organic detritus. Bay, lake, and marsh deposits are closely con- nected both vertically and laterally. As a result of small changes in rates of sea level rise and subsi- dence, and in current patterns, what was a coastal marsh became a lake or bay within a relatively short time. Types of marsh habitat also changed in this dynamic setting. Marsh deposits fomied organic layers that can be dated by their radiocarbon con- tent to reconstruct the depositional history of the area (Byrne et al. 1959, Gould and McFadan 1959, and Coleman 1966). Swamp deposits are confined to river valleys and do not represent a major depositional element in the Chenier Plain. Bay and lake deposits differ from each other chiefly in their exposure to varying degrees of river and tidal influence. They can be recognized in the subsurface by their hthologic, faunal, and sedimentary properties. Virtually every water body in the Chenier Plain is subject to some tidal influence except where engineering projects disrupt the natural process. The inland water bodies resulted from the drowning of reUct Pleistocene entrenched valleys, as was the case for East Bay, Sabine Lake, and Calcasieu Lake along the coast, and for White Lake and Grand Lake, located inland from major Gulf connections (Fisk 1944). Many small lakes originated as marsh ponds diat enlarged when sahnity changes or other stresses interrupted the marsh building processes. Many irregularly shaped lakes represent old river or tidal stream courses that were abandoned. 2.2.4 CHENIER RIDGES The Chenier Plain is characterized by sand and sheU fragment ridges that parallel the shoreline (fig. 2-2a and b). These ridges are of three basic origins: barrier islands, river mouth accretions, and recessional beach ridges. The cross sections of sediment facies in figure 2-3 were constructed from unpublished data in the Louisiana State University Coastal Studies Institute files. Barrier islands or spits are progradational features produced by longshore transport of sand-size or larger particles. Barrier islands represent accumulation of sediments that develop seaward of embayments that are usually connected with the Gulf by inlets. They are usually connected with the Gulf by inlets. Barrier islands are nourished by sediments from physiograpliic structure while undergoing erosion and retreat. Growth usually occurs downdrift and landward by spit and accretion ridge fomiation. Bolivar Peninsula (fig. 2-3, cross sections A and B) is the single example within the study area. How- ever, barrier islands probably existed along other coastal sections of tlie Chenier Plain during sea level rise. River mouth accretion ridges are another feature of the Chenier Plain created by progradation. These multiple bars fonn concavely seaward where the excess of sand-size particles deposited at river mouths are reworked by waves and currents into complex accretionary patterns (fig. 2-3, outlet of Sabine Lake). Multiple rivemiouth ridges converge to fonn a single recessional ridge extending between the river inlets. The fanning pattern at river mouths differ from barrier spits that fomi broad single ridges or multiple ridges with less seaward concavity. River-mouth ridges are well-developed at tlie mouth of the Sabine River, with less extensive development occurring at the mouth of the Calcasieu River (fig. 2-2a). A series of tliese accretion ridges, representing older shore- lines occur as far north as Little Pecan Island and 10 o u c ■a c U o CO X) X (>1 3 M 11 3 O. -a c CO ^ :3 60 tl- 13 - o n '^ 1 ) 1 1- / V ?^ - / 1, "^ >r 1/) ^ • ;•.'••.■■'■•■.■.' K\> J::;^^;///>;: s^i ^ ( "■ ■ VW > t. - 1 > o ° - < ) " (1> -^ ^-^ on in c -^ '3 i- o <" -J E M 3 S = 2§ ^•« •5 2 ^ 6 C I- ■3 t« 00 C o o on CQ C o ^ •- ca ^ 13 00 ^3 ''^ -r-l k. Si ■S = ? o. ^ 5 00 3 03 4-. 3 c .■*=: a> ■»-> . .^ eg ca 515 3 6 3O •o w5 "2 ja 3 ca .H c ^ =^ ca c ^'OO u >> a. .ti i) Ui i2-!= ca S -s > > c 09 ■V 3 00 a, 14 I Little Chenier. There has been a progressive west- ward shift of river mouths through time in response to tlie dominant littoral drift to the west. The sedi- ment buildup at Hackberry Beach was shifting the Memientau River moutli westward until con- struction of the navigation channel (through lower Mud Lake) and the jetty system at the coastline interrupted nonnal riverine and littoral processes. Recessional beach ridges, the most common sand ridges, are the characteristic type in the Chenier Plain (fig. 2-2a and b). These ridges were constructed by erosional processes but may be laterally continuous with progradational ridges at bay or river mouths. The ridges were formed along sections of the coast undergoing coastal retreat, and their development coincides with Mississippi River shifts eastward and the resulting lack of sediments to maintain coastal buUdout. As a consequence, existing beach front and nearshore deposits are eroded and are deposited landward over marsh or bay deposits. Storm con- ditions accelerate this process. Most of the present shoreline in the Chenier Plain is experiencing re- treat; the existing beaches are pushing back over marshes. As evidence of this process, exliumed peat and marsh plant remains are exposed along the strand- Une. It is likely that sediments being transported westward from the Atchafalaya delta will reverse the erosional trend along the coast in the eastern section of the Chenier Plain. The present coast- line contains many examples of seaward buOdup of progradational ridges at river mouths over near- shore deposits that grade laterally into recessional ridges overlying marsh deposits. 2.2.5 NEARSHORE TOPOGRAPHY Turbidity is high along the nearshore zone when waves are breaking, and each breaking wave injects plumes of fine-grained sediment into the water column. On long stretches of the coast, water energies are essentially working against shoal mud bottoms. Coarse-grained sediments are deficient except at locations where the strandhne is either holding its own or experiencing slight buildout. Coarse- grained sediments are winnowed westward and accumulate at inlets or river mouths. Thus, pro- gradation is occurring on the shores fronting Chenier auTigre, at river mouths, and along the Bolivar Peninsula. The remainder of the coast is experiencing retreat over marshlands and bay bottoms that provide the source of fine-grained sediments and much of the broken shell that makes up the beach. The Atchafalaya Bay is becoming an increasingly im- portant source of fine-grained material, which drifts westward and enhances the sediment supply. Evi- dence indicates that Atchafalaya suspended sedi- ments extend westward to the Sabine River (Wells 1977). Deficiencies of course -grained sediments are also reflected in the general absence of extensive dune fields along the coast and of well-developed offshore bars. Hackberry Beach and Bolivar Peninsula con- stitute the only areas of important dune activity. Offshore bars that constitute conspicuous features along most coasts are only subtly developed along the Chenier Plain. Where sand is more plentiful, such as along the Bolivar coast, offshore bars are well- developed. Depending on offshore conditions, there may be two or more sequences of bars seaward paraUeUng the shore. 2.3 HYDROCLIMATE CUmate combines with the biological and physical components of the ecosystem to determine the character of the physical environment. At the regional level, emphasis is placed on the dynamic aspects of climate that interact with water and water movement. Climate is highly variable and exerts both short- and long-term influences on the region. Time scale is important when considering vari- ability and climatic trends such as the long-term variability of global temperature (fig. 2-4). The Chenier Plain's development has spanned approxi- mately the last 3,000 to 4,000 years, and the cli- matic variability associated with that time period has influenced conditions in the study area. Sea level rise to its approximate present position resulted from long-term climatic influences. Note that the global temperatures of the mid-1970's were warmer than the mean when one views temperatures over both the last 1,000 or 10,000 years; during the last 100 years the temperatures have not shown as large a variance. The most important aspects of cUmate in the study area are precipitation, temperature, and wind. A generalized hydrologic cycle across the Chenier Plain is depicted in figure 2-5. The parameters illus- trated are in a constant state of flux and the move- ment of water between the ground-water aquifers and tlie overlying marshes is known to occur but has not been quantified. Winds are of primary importance in water movement. Several of the basins in the area align in a north-to-south direction that gives maximum exposure to southerly and northerly winds. Southerly winds drive Gulf waters shoreward into the estuaries, resulting in raised water levels. The magnitude of rise in water levels depends on the strength and duration of the winds, on tidal conditions, and on the amount and duration of rainfall. Southeasterly winds are dominant throughout the study area (Atturio et al. 1976, Murray 1976). The frequency of southeasterly winds are higher in the spring, when they occur approximately 30% of the time, and decrease in winter to a low of 17% (fig. 2-6). These winds cause the dominant westerly longshore drift. Coastal land- fonns in this area indicate that winds from the southerly and easterly quadrants were prevalent during the past 3,000 to 4,000 years. North winds occur, on the average, 16% of the time from October through March, and decrease to less than 5% of the time during the summer months. Winds are usually strongest during the winter, coinciding with the high frequency of north and northeasterly winds. These winds, which are associated with the passage of cold fronts, lower 15 AIR TEMPERATURE a < (A OC < COLD WARM 1960 _ 1920 1880 _ COLD WARM 1900 1700 1500 (D ) 73^ a < ® V) cc 1300 - ^^ ) < UJ 11001 ~ c ? >- \Eas\ern 900 - J ^Europe C.2 OA 06 A°C THE LAST 100 YR LEGEND 1 THERMAL MAXIMUM OF 1940'S 2 LITTLE ICE AGE 3 YOUNGER DRYA5 COLD INTERVAL -1.5 C THE LAST 1000 YR MIO- LATITUDE COLD WARM O O < en < (/) o z < (/) o -10 C THE LAST 10,000 YR Figure 2-4. Major trends in global climate during the past 10,000 years (National Academy of Sciences 1975). 16 a, 0) c Q o :S o o O s (1) •i-i O U5 I (N 0) ■r-4 17 Wind speed Iknotjl SUMMER direclion 3 4-10 1121 22 33 34-47 48* ^ N ^^X-- 36 NE 1% 5-7 E / / 18 1 SE 1 'l3%\o%] 25-7 S \ V y/j 25 9 SW \ \ ^ 4 10-3 W l», L>/ 7 1 NW \^ 3 5 % 86 56 3 28. S 1,5 ° Wind speed Iknoli) FALL Wind direction 0-3 4-10 11 21 22 33 34 47 48+ % CAIM 5.1 % N ^^'^ \ 14 5 NE zii^^ 4% 18 6 E Mr :Cio;:^ / 23 7 SE 3\SZ7..^Kf 18 6 S \ *v 1 K/ 11.5 SW ^ 1% 3.4 W J y ^^ 3-1 NW \ k 4.7 % 4 9 41 9 434 7.0 9 .0 CALM 2 5% Wind speed Iknolsl WINTER Wind direclion 0-3 4-10 11-21 22 33 34-47 48+ % N ,^ '' > >^ 16 1 NE / r \ 4% ' 15 7 E / \ V / 1% 17 3 SE / / / 17 4 S 1_- ^ 13 8 SW \ >i / 4.7 W \ 1 4 3 NW 1 \ 8.9 % 4 2 38 3 44.9 9.7 08 .2 Wind speed Iknolsl SPRING Wind direclion 0-3 4.10 11 21 22-33 34-47 48« % CALM 2.0% N /f ^ S / 10 2 NE / '-'l 7 2 E /)^^2o^=^ 17 6 SE ( IGZ^jj 30 3 S \^^S;t^a^ 11.7 SW \ r 4.1 W V 1% 3 3 NW \ \ 5 3 % 4 9 39 9 38.7 5.7 0.5 .0 ^1 CALM 27% Figure 2-6. Bivariate frequency distribution of wind speed and wind direction offshore of Sabine Pass by season. Percentages of occurrence are given in the margin. inland water levels. The response is strongest over lakes, bays, and surrounding marshes and is weakest in or near the uplands in constricted river basins (Wax 1977). If the same weather pattern continues for an extended period, the response weakens as steady-state conditions are approached (Part 3.3). The prominence of north-to-northeast and south- to southeast winds coupled with the lack of westerly components cause unequal erosion along the shore- hncs receiving the impact of wind-driven waves. Generally southern shorelines experience the highest rate of erosion, reflecting the strength of the northerly winds. Northern shorelines experience somewhat less erosion, reflecting the high frequency but low intensity of southerly winds. Eastern and western shorelines experience the least amount of erosion (Adams et al. n.d.). The Chenier Plain has a warm, humid climate. The seasonal precipitation based on a 30-year average (fig. 2-7) is fairly unifonn, with the months of October, November, and March being somewhat drier than other months; July typically receives the greatest amount of precipitation. Precipitation, ahuost always in the form of rainfall, supplies water for groundwater recharge, soil moisture recharge, and surface water runoff. Runoff differs considerably from the precipi- tation distribution because of the seasonality of solar radiation and temperature (fig. 2-7). Changes in temperature lag behind changes in solar radiation by approximately one month. eoo 500 400 300 200 lOoL Soter Radiation O N Figure 2-7. Seasonal fluctuations in solar radiation, air temperature, precipitation, and rain surplus at Lake Charles, from National Weather Service records. 18 I Gulf tropical disturbances are important erosion factors; approximately one-half of the shoreline erosion on lakes in the Calcasieu area over the past 25 years, as deduced from maps and photos, was the result of Hurricane Audrey (Adams et al. n.d.). Tropica] disturbances cause both wind and water erosion. Storm surges and heavy rains produce an abnormally large volume of water that must exit to the Gulf through restricted passes. Tropical disturbances are low frequency events; however, Muller (1977) included them as one of eight synoptic weather events that, when combined, represent the climate of the northern Gulf coast. The probability that a tropical disturbance will cross the Chenier Plain in any given year is 0.5% based on data reported by Cry (1965). However, tropical disturbances centered outside the Chenier Plain may also cause dramatic changes in the area. Annual precipitation decreases from east to west in the study area from a mean of 144 cm (57 in)/yr in Vermilion Basin to 113 cm (44 in)/yr in the East Bay Basin. The temperature pattern is not as evident; how- ever, it may be slightly warmer in the western portions of the Chenier Plain. On a seasonal basis a strong temperature gradient is found in a south-to-north (coast-to-inland) direction. Sea and land breezes tend to moderate the climate, cooling it in summer and wanning it in winter. Table 2.1 shows the inter- regional differences that can be expected in the average number of freeze days between Rustin and Hackberry, Louisiana. Rustin is about 261 km (162 mi) north of Hackberry. Freezes in the coastal environment are more moderate, occuring later in the fall and earher in the spring. Table 2.1. Average number of freeze days annually at various places in Louisiana (U.S. De- partment of Commerce, Weather Bureau 1964, 1965). Station Area Freeze days Hackberry Chenier Plain 13 Alexandria Central Louisiana 27 Rustin Northeast Louisiana 46 2.3.1 WATER BUDGET The climatic water budget originally developed by Thomthwaite (1948) combines the effects of precipitation and temperature into an accounting system for water. Although it was devised for upland agricultural areas, the model has been modified for wetland situations (Wax et al. 1978). The water budget of wetlands differs from that of the uplands in the following ways: 1. Since soils are always saturated, a soil moisture storage term is not necessary in the wetlands; more water is available to the plants. Thus, the model predicts that plants in the wetlands will have higher transpiration rates. 2. In the uplands, water surplus in the form of runoff flows away from the area through constricted streams, whereas the same runoff in coastal areas flows into the wet- lands and provides an additional source of water. Rain surplus is the amount of water available for surface runoff and ground-water recharge. Evapora- tion and transpiration rates are low during the winter, thus a high percentage of the precipitation is sur- plus. Throughout the Chenier Plain, average con- ditions show tliat the surplus period extends from December through April. The effect of this surplus on the streams and eventually on the marshes varies with the size, slope, watershed area, and substrate of the individual streams. Small streams will respond almost immediately to rain surplus; however, in rivers such as the Calcasieu, it may take several months before all of the surplus generated from rainfall has drained into tlie marshes. Rain deficits occur when evaporation and transpiration exceed precipitation; this is common during May, June and July (fig. 2-7). 2.3.2 SYNOPTIC WEATHER TYPES Synoptic climatology classifies all observed weather in a region into designated types. Muller (1977) devised a synoptic climatology for the north- ern Gulf of Mexico based on data from the New Orleans weather station. Muller and Wax (1977) extended this synoptic analysis to Lake Charles, Louisiana. Table 2.2 lists the weather types, and enumerates and contrasts the averages for several parameters for four Januaries during 1971 through 1974. A strong seasonal pattern for many of the weather types is apparent (table 2.3). Cold fronts occur frequently on the Chenier Plain during winter. The weather type sequences associated with these fronts begin with the Frontal Gulf Return, when the cold front is still several hundred miles to the west or north but is affecting the weather by lifting the warm Gulf air. Rain is common at this time. Frontal Gulf Return accounts for 31% of the average annual precipitation although it occurs only 1 1% of the time. As a cold front passes through, it often stalls out in the northern Gulf (Frontal Overrunning), bringing on precipitation from the western Gulf. This weather type accounts for 32% of the average annual precipitation. After the front has passed, 19 clearing skies, cool temperatures, and northerly winds dominate (Continental High). With this sequence, water levels and salinity generally fall. As the cold front continues to move east to northeast, the Coastal Return situation is initiated, and winds shift from northeast to southeast. Continued movement of the front away from the basin brings about a stronger flow of maritime tropical air (Gulf Return), with an accompanying increase in water level and salinity. As another cold front approaches from the north- west, Gulf Return changes to Frontal Gulf Return, and the series of events is repeated. In contrast, summer weather is dominated by a southerly flow of air. The frequent occurrence of the Gulf High is the result of the displacement of a Bemiuda High pressure cell south and west over the Gulf of Mexico but still east of the Chenier Plain. The relatively weak clockwise circulation accom- panying the Gulf High causes gentle winds in the Chenier Plain to come from the soutli to south- west. The Gulf Return has a somewhat stronger circu- lation with winds coming from the southeast. The Table 2.2. Mean values of parameters of synoptic weather types at Lake Charles during each January from 1971 to 1974; number of observations in parenthesis. Synoptic weather type Parameter* Pacific high (8) Continental high (25) Frontal overunning (43) Coastal return (10) Gulf return (24) Frontal gulf return (12) Gulf tropical disturbance Gulf high (1) .\ir temperature (°C) 8.3 8.3 7.2 10.0 17.2 17.2 12.8 Dew-point temperature (°C) 7.2 0.6 4.4 10.0 16.7 17.2 12.8 Relative humidity (%) 92 85 87 98 97 99 100 Wind direction (azimuth) 06 02 01 12 17 17 15 Wind speed (kn) 7 7 11 6 9 8 5 Cloud cover (%) 80 30 90 70 100 100 100 Parameters recorded at 0600 CST. ^Where = North, 9 = East, 18 = South, 27 = West. Table 2.3. Synoptic weather types and percent of hours recorded at Lake Charles, 1971 through 1974. Percent of h jurs, by month Synoptic weather types 1 F M A M .1 J A S O N I) Pacific high 8 15 9 9 9 4 10 6 9 Continental high 18 22 18 21 28 19 10 21 16 40 27 25 Frontal overrunning 31 19 19 13 11 11 5 7 14 13 29 30 Coastal return 9 13 11 13 7 5 7 21 16 19 10 9 Gulf return 20 16 24 29 26 25 29 18 18 11 15 10 Frontal Gulf return 13 15 19 15 14 10 2 2 6 8 13 19 Gulf tropical disturbance 1 2 5 6 24 Gulf high 1 4 28 44 28 3 2 20 Continental High occurs fairly regularly. Its charac- teristics during tlie summer are not as noticeable as in tlie winter; however, it generally brings cooler, somewhat drier air with fair skies. The Gulf Tropical Disturbance, which includes hurricanes, occurs infrequently from late spring through early fall. Winds can be extremely strong and can approach from any direction except northwest through northeast. This weather type is associated with the most dramatic environmental responses. 2.4 NEARSHORE HYDROLOGIC PROCESSES The coastal waters of the Chenier Plain area are kept in constant motion by the driving forces of wind, waves, tide, atmospheric pressure gradients, and semipermanent currents. Wave -driven currents control the circulation patterns in the immediate nearshore zone. Rainfall and freshwater inflows from rivers, such as the Atchafalaya, mix with Gulf waters to bring about density gradients and buoyancy effects that are important in the circulation at tidal passes and estuary moudis. Nearshore waters are very turbid during high discharge periods of the Atchafalaya River and when waves are breaking along the coast. Wind direction and intensity are the primary fac- tors controlling orientation and size of wave trains approaching the coasthne and consequently the over- all circulation pattern. Winds along the Louisiana and eastern Texas coast generally come out of the east and southeast, at velocities of 4 to 10 kn (8 to 19 km/hr) (5 to 12 mi/hr) in summer, and at slightly higher velocities in winter (fig. 2-6, Murray 1976). These winds drive longshore currents toward the west. Prevailing southeasterly winds often develop swells that contact the bottom of the smooth, gently sloping sliallow shelf and shoreface, causing wave trains and currents that control deposition and ero- sion along the coast. Investigations along muddy coasts indicate that highly turbid waters have a dampening effect on waves (Wells 1977). Approximately 92% of the waves along coastal Louisiana are 1 to 2 m (3.3 to 6.6 ft) in height and have a period of 4.5 to 6 sec when wind speeds are greater than 10 km/hr (6.2 mi/hr) (Louisiana Superport Studies 1972). Waves greater than 2.5 m (8.2 ft) in height occur approximately 30% of the time during winter but only 2% of the time in mid summer. Thus, the Chenier Plain coast is a relatively low-to- moderate energy coastline in temis of offshore waves. The shallow slope of the Continental Shelf apparently attenuates the offshore wave power sufficiently to yield the low energy environment of the coast. Winds associated with winter frontal passages or hurricanes produce large and sustained waves off- shore. Hurricanes usually have a net drift toward the northwest. They can cause considerable modification to the shelf waters and generally drive oceanic waters onto the shore and into estuaries. The intense wave action associated with hurricanes reworks the slielf sediments and can transport large quantities of sedi- ments shoreward. The significant inflow of fresli turbid water from the Atchafalaya River reduces nearshore salinities. During the flood season, the saUnity levels along the entire open coast of the Chenier Plain are similar to salinity levels in the estuaries, i.e., 10°/oo to 20°/oo (part 3.3). Tides along the western section of the Chenier Plain, especially in the vicinity of Sabine and Cal- casieu lakes, are as high as 0.7 m (2.3 ft) and are capable of producing significant tidal currents. Currents of 3.3 kn (6.1 km/hr, 3.8 mi/hr) flood and 4.3 kn (8.0 km/hr, 4.9 mi/hr) ebb develop in re- stricted passes in the Galveston Bay area, particu- larly between Galveston and West Bay and between Christmas Bay, Bastrop Bay, and West Bay (Murray 1976). Mudflats result from the net effect of sedimen- tary input from local rivers, the Atchafalaya River and its general westward drift, and the erosional forces of the coastal waves and longshore currents. When sedimentation exceeds erosion, mudflats may develop offshore of the beach. During severe storms the mud, along with whatever beach material is present, may be driven landward over the adjacent marshes. 2.5 GROUNDWATER Rain surplus coupled with favorable geologic conditions have enabled extensive ground-water aquifers to develop in the Chenier Plain. These aquifers are part of a regional ground-water area that extends throughout most of the northern coast of the Gulf of Mexico. Sands and gravels with over- and under-lying clays have been deposited through geologic time along the northern coast of the Gulf of Mexico. The tre- mendous weight of these sediments has caused the downwarping known as the Gulf Coast Geosyncline. Two favorable conditions for ground-water develop- ment are associated with this downwarping. First, the resultant slope aOows for a gravity flow of water from the outcropping areas in the north (the princi- pal recharge areas) to the Chenier Plain. Second, faults associated with the downwarping generally parallel the coast and therefore transect all major surface flows. This allows for additional ground- water recharge from surface streams during periods of higli surface flows and a discharge of ground water to surface streams during periods of low flow. This discharge maintains a minimum baseflow in surface streams and acts as a buffer against drought con- ditions for riparian vegetation. A third major source of ground-water recharge is by downward seepage through the large surface 21 area of the wetlands. According to Zack (1973). max- imum seepage occurs when surface water levels are highest, i.e., during the spring, and late summer to early fall. Less important recharge sources are through fractures associated with faulting from salt domes, and inter-aquifer exchange in localized areas where separating clay layers become thin or non- existent. The most important ground-water aquifer in the Chenier Plain is the Chicot Aquifer, which was formed during the Pleistocene age. I'his aquiter supplies more than 90% of all ground water pumped in the Chenier Plain (Guevara-Sanchez 1974). in the hydraulic center of this aquifer, Calcasieu Parish and vicinity, extensive clays separate the Chicot Aquifer into three distinct layers: 60 m (197 ft), 150 m (492 ft), 210 m (689 ft) sands. Massive beds of sand and gravel ranging from 15 to 250 m (49 to 820 ft) in total thickness are over- lain by extensive, impermeable clay beds. Alternating, interfingering lenses of sand and mud are found in the shallow subsurface of southeastern Texas. The verti- cal and lateral distribution of sand in this region suggests that the Chicot Aquifer may comprise several local aquifers separated by mud intervals that are locally well-developed (Guevara-Sanchez 1974). The deposits slope gently gulfward 1 to 3 m/km (2 to 6 ft/ mi) and increase in thickness from less than 30 m (98 ft) in northern Louisiana to more than 2,150 m (7,054 ft) beneath the Gulf of Mexico. Thickness increases from Lake Calcasieu east to Wliite Lake and then decreases to the Atchafalaya Basin. To the west the beds become thinner, although localized vari- ability is much greater than to the east of Lake Cal- casieu. Aquifers of the Chicot reservoir have been tapped by offshore wells and contain freshwater beneath the Gulf of Mexico near the shoreline be- tween Cameron and the Atchafalaya river. Older Miocene and Phocene aquifers, although large, are used only indirectly. The Pliocene aquifers are directly connected to the Chicot reservoir in many areas; therefore, an indirect withdrawal is taking place. Due to the numerous interconnections in south- east Texas, the PHocene and Pleistocene aquifers are collectively known as the Gulf Coast Aquifer. 2.5.1 USAGE OF GROUND WATER Cyclical, and continuous ground-water pumping takes place in the Chenier Plain. Irrigation require- ments are cychcal (spring and summer): municipal and industrial needs are continuous. Ground-water withdrawal volumes by activity are presented in parts 3.2.3 and 3.2.6. In the Chenier Plain and immediate vicinity the total withdrawal is 2 x lO'm^ (7.06 x lO^'ft ) per yr, with irrigation accounting for 74% of the usage, industry 17%, and municipalities and rural areas 9% (Louisiana Department Pubhc Works 1971, Baker and Wall 1976). Pumping has been in- creasing annually: in the Lake Charles area the rate of increase is about 2.8 x lO^m^ (9.89 x 10''ft^) per yr (Harder et al. 1967, fig. 2-8). Based on the esti- mated freshwater recharge rate for aquifers currently being pumped in southwestern Louisiana (Jones et al. 1956) and extending this rate to the Texas area of re- charge, use exceeds recharge by 1 x lO'm^ (3.53 x 10''ft^)peryr. 160 120_ o c e 80_ 40_ O U- . -.^'700»oot" Sand ..1210ml :V 2 00 foo t" Sand 160 ml •^ *- It \ 40 45 50 55 Year 60 65 70 75 T % Figure 2-8. Volume of water pumped from different sand strata in the Lake Charies area from 1935-65 (Harder etal. 1967). 22 2.5.2 EFFECTS OF WITHDRAWALS Large-scale and unregulated ground-water pump- ing results in hydrologic problems such as declining water levels, stream flow depletion, saltwater intrusion, and land surface subsidence. When pumping is started in a well, the water table is drawn down around the well to form a cone of de- pression. The cone expands and the water table is pro- gressively lowered until a balance is achieved between the rate of flow of water to the well and the amount pumped. If pumping rates continue to increase, the size of the cone also increases. The creation of this depression around a well or group of wells has led to at least two documented effects in the Chenier Plain and vicinity; saltwater intrusion and land subsidence. In the 210 m (689 ft) sands of the Chicot Aqui- fer in Calcasieu Parish most of the ground water moved gulfward prior to large-scale pumping opera- tions. Because of the large freshwater head, saltwater was flushed from the landward portions of the aqui- fers. Because ground-water levels have declined in the last few decades, the direction of the hydraulic gradient has been reversed, the density balance has been dis- turbed, and recharge with saltwater from the Gulf has begun. The 210 m (689 ft) sands in central Cal- casieu Parish now contain salty water as far north as Lake Charles, and saltwater intrusion has caused many industries to discontinue pumping operations from this aquifer (Zack 1973). Decline in ground water in the Gulf Coast Aquifer near Houston has also occurred (fig. 2-9). The removal of water from the pore space of the sands creates a void. Water from adjacent clay layers moves into the interbedded sands. The dewatered clays are highly compressible and become compacted. In turn, the compaction is translated to the land sur- face as subsidence. Ground-water and mineral extrac- tion has led to a maximum of 2.5 m (8.2 ft) of subsi- dence in northern Galveston Bay (Kreitler 1977). 20 30 40 SO 80 90 .C100 120 . i I I I M I I I I I I I I I I I I I I I L M I I I I I M 40 44 48 52 56 60 64 68 Figure 2-9. Depth to the water table in the Gulf Coast Aquifer at Houston, Texas, 1939-72 (Kreitler 1977). 23 3.0 Chenier Plain Basins 3.1 INTRODUCTION-GENERALIZED BASIN DESCRIPTION A basin, the result of long-tenn geologic pro- cesses, can be described as a set of interacting habitats constrained by climate and physiography, and inte- grated by the flow of water througli it. Each habitat type has characteristic species and productivities. Man is a major factor in a basin; his activities influ- ence nearly all natural processes. The objectives of the basin-level analysis are to describe the natural functions of Chenier Plain basins and the modifica- tions caused by human activities. A conceptual model of basin-level processes and interactions places in perspective the detailed analysis that follows. The model (fig. 3-1) includes only the most critical components and processes, and shows interactions of water, wetlands, up- lands, wildlife and fish, and man. At this level of analysis, hydrological and land-modifying processes are emphasized because they determine the capacity of a basin to support renewable resources such as waterfowl and fishes. Thus, the basin-level discussion of living resources emphasizes factors tliat change habitat area rather tlian habitat quality. The latter is discussed in part 4. Differences among basins result from differences in the relative areas of habitats, the degree of interaction among them, and in basin inputs and outputs. A drainage basin can be envisioned as four linked submodels driven by a set of forces external to the basin (fig. 3-1). Each submodel represents a different group of processes interacting within the basin. They are: (A) basin hydrologic processes, which represent water storage and flow through a basin; (B) land- modifying processes, which result in the exchange of area among different habitats and especially in the loss of natural wetland; (C) the renewable resource productivity of a basin, or its capacity to sup- port wildhfe and fish species, to purify water, and to perfomi other services for men; and (D) basin-level socioeconomic processes, those human activities and management decisions that impinge directly on natural processes in a basin. 3.1.1 HYDROLOGIC PROCESSES IN A BASIN Hydrology (part 2.4) has already been identified as a major factor in the development of the entire Chenier Plain region and is largely responsible for the unique characteristics of each basin. Further, the hydrologic regime at any specific site within a basin determines the kijid of habitat that develops at the site (Bahret al. 1977). Basin hydrology results from; the interactions among water stored and flowing in a basin (Aj); upstream riverine and rainfall inputs of water, sediment, and nutrients (Aj); and downstream tidal water with accompanying salts, sediments, and nutrients (A3) (fig. 3-1). Hydrology detennines habitat type by water levels, flows, and salinity gradients. Water levels are controlled by the pressure head between water level at a given site and upstream and downstream water levels; consequently they are modified by rainfall, tidal stage, and wind direction and intensity. The pressure differentials and resultant water flows con- tribute to the potential natural resource productivity of a basin by facilitating the movement of organisms, nutrients, organic matter, and wastes from one part of the basin to another. For instance, the export of organic detritus and the flushing of wastes and toxins are important to the maintenance of biological production in open water areas. In this context, man- made impoundments or canals modify water flow, thus changing these hydrologic processes. Mean salinity and sahnity range at any given site in the basin are detennined by the relative volume, timing, and duration of upstream (fresh) and down- stream (saline) inputs. Sediments and nutrients are distributed among various basin habitats by fresh- water inflows and by currents produced by density gradients (salinity). In summary, the hydrologic submodel symbolizes the physiograpltic configuration of a basin that, together with upstream and downstream water sources, determines the water level and water flow regimes and the salinity and turbidity regimes at any point in the basin. These parameters in turn control the type of habitat that can develop at that site and directly influence the productivity of those habitats. 3.1.2 LAND-MODIFYING PROCESSES Over the past several thousand years^ the domi- nant trend in the Chenier Plain has been an increase in wetlands, concurrent with the fonnation of new chenier ridges, at the expense of aquatic habitats. In contrast, during the past 50 years, the major change has been loss of wetlands (fig. 3-1). Subsi- dence and erosion that lead to wetland degradation and its conversion to open water are natural geo- logic processes. But these natural processes have been accelerated by modifications, such as canals and con- trol structures, which have changed basin hydrology. Also, impoundment of weflands for waterfowl, or drainage for agriculture, industry, and urban use result in wetland degradation. These changes may result from activities outside the basin. For example, maintenance of the present Mississippi River course on the eastern side of^ the Mississippi Delta during the 20th century has meant that, until the recent growth of the Atchafalaya River, very little new sediment reached the Chenier Plain. Modification of ridge and upland areas is not depicted in figure 3-1 , but changes in these habitats have also occurred through residen- tial and urban development. 25 C3 — 0. c 4= 1) •J O cj 'ob o "o o a; I- O r- C o o •a N u D a CO 26 3.1.3 BASIN RENEWABLE RESOURCE PRO- DUCTIVITY (RRP) A basin's RRP is determined by the kinds of habitats it contains, their areal extent, and their juxtaposition (since many species require access to two or more habitats during their Ufe cycle). The RRP submodel (fig. 3-1) consists of four main com- ponents: producers (Cj), consumers (C,), refugia (C3), and storage (C4). Components C, (producers) and C2 (consumers) reflect the "quality of the basin," which is related to the kinds of renewable resources that a basin can support. For example, the inland open water habitat can be in a balanced state with respect to nutrient input and use, and support many species, or it can be degraded by excessive nutrient loading into a dangerous eutrophic state and support few species. If environmental changes (such as modi- fied flooding regimes or eutrophication) occur, the quaUty of a given habitat will be modified. Changed quality leads to such changes in community struc- ture as the increase of undesirable fish species in waters of a dangerous eutrophic state. As some habitat types decrease in size, it is important to preserve natural areas. These serve as refugia (C3) that are important in maintaining a diverse gene pool. Freshwater wetlands and water bodies (C4) are especially valuable for storing surface water, which is used by man for many purposes. For example, much of the irrigation water for rice in Louisiana and Texas is stored in fresh marshes. In the Chenier Plain this freshwater supply is in contact with ground- water aquifers. Ground-water aquifers often extend beyond basin boundaries, thereby becoming a re- gional resource. As water flows over wetlands, many chemical transformations occur. Inorganic nutrients, that could cause dangerous eutrophic states, undergo important changes. The nutrients may be taken up during plant growth or by bacteria. Some of these nutrients may be exported later as organic detritus. Phosphorus may physically bind with sediments, and nitrogen com- pounds may be denitrified. These processes are im- portant in determining the load of nutrients a basin can assimilate and the resulting quaUty of water within the basin (Hutchinson 1969). 3.1.4 SOCIOECONOMIC PROCESSES Basin-level socioeconomic processes (fig. 3-1) have been organized into seven components: (D,) fish and wildlife resources harvested by man both commercially and for sport; (Dj) agricultural activities; (D3) mineral extraction, primarily pe- troleum and natural gas; (D4) the total human population, its energy and material requirements, and its waste production; (Dj) all commerce and industry such as manufacturing, refining, and retail sales, along with the concomitant waste release; (Dg) transportation activities that facilitate mineral extraction and other industries but also may disrupt natural ecosystems by such alterations as dredging and leveeing; and (D^) government services, including government subsidies for transportation, flood control projects, refuge acquisition, and sewage treatment plants. In general, all these socioeconomic processes require large quantities of freshwater for irrigation, human consumption, and industrial processing. Human activities are a major influence on basin level processes. For this reason, the socioeconomic sectors are described in part 3.2, and the effects of their activities are identified and quanfified where possible. In part 3.3 through 3.5, basin level pro- cesses are elaborated and the influence of human activities on these processes is considered. The dynamics of individual basins of the Chenier Plain are summarized in part 3.6. 3.2 SOCIOECONOMICS 3.2.1 INTRODUCTION Techniques. Analysis of the ^economics of the Chenier Plain region has required extensive modifi- cafion of existing data. The boundaries of the Chenier Plain region and basins were drawn along lines dic- tated by the natural physiography of the region. Socioeconomic data, on the other hand, are collected by political unit. Therefore, the primary data are usually from the parishes (counties) of the region (volume 2, appends 6.2). In the text, socioeco- nomic data are displayed by basin. The assumptions made in converting parish-based to basin figures are stated either in the figure legends or in the accom- panying appendixes. The second problem, inherent in studies of this kind, is that of comparing diverse materials in com- mon temis. A comparison of shrimp and Gulf men- haden is a good example, because they are harvested for different purposes. The annual harvest of men- haden in pounds far exceeds the harvest of shrimp, but the dollar value of the shrimp fishery exceeds that of menhaden. Menhaden are processed into fish meal or oil, while shrimp are processed for human consumption. The immense harvest of menliaden could have much more severe environmental reper- cussions than the harvest of shrimp; yet from an economic viewpoint, shrimp is the more important commodity. This problem pervades the analysis of the socioeconomic sectors. We have, in general, relied on dollar values as an index of the magnitude of different man-related activities in the Chenier Plain, but it should be remembered that this does not necessarily signify the relative environmental impact of those activities. The various socioeconomic sectors, e.g., trans- portation and mineral extraction, can influence natural basin processes through activities they gen- erate. Since several different sectors may generate the same kind of activity, the environmental impact of one sector may be difficult to distinguish. Because canal dredging and spoil is an impact that results from eight different economic sectors (table 3.1), it is difficult to establish each sector's relative impact on the environment. 27 Table 3.1. Socioeconomic components and ecologically sensitive activities generated by thenL The matrix identifies major activities associated with each sector of the economy. Ecologically sensitive activities Economic sectors Waste generation Habita t mod ificati on c w (M (M M e .2 S e _C O E = ■3 oint source griculture ru e s M e 2 ■<3 ■a 60 NTS ■o E > < 11 be T3 V ft. ■< S te. U ii 3 =s 0^ Natural resource exploitation 3 ■a e 3 o 60 .3 Commercial fishing & trapping Recreational fishing & hunting Agriculture Mineral extraction Resident population Commerce & industry Port & navigation Highways, rails, airports Government services • • The primary ways in which socioeconomic sectors interact with natural processes are in (1) waste gen- eration, when industrial or domestic pollutants are discharged into the basin; (2) habitat modification, when spoil banks arc created, wetlands impounded, or upland forests cleared for agriculture; and (3) na- tural resource exploitation, including water use and refuge creation. Overview. The Chenier Plain region is predomi- natly a rural and agrarian area, and tlie population density is low because the extensive wetlands are un- suitable for urban development (table 3.2). The west- ern edge of Sabine Lake in the Sabine Basin is, in con- trast, heavily industrialized. In addition, major urban areas occur just north of the Chenier Plain boundaries, and these have a major impact on the Chenier Plain. North of the Vermilion Basin lies the city of Lafayette. Several farming communities-Crowley, Rayne, and Jennings-are lorth of the Mermentau and Chenier basins. Lake ' harles is the major industrial metropol- itan area th lies along the northern border of the Calcasieu P n ; the entire Texas coast north and west of the Sa' i and East Bay basins is heavily indus- trialized Given the population distribution, it is to be expected tliat the impact of human, industrial, and urban development on all basins of the Chenier Plain except Sabine Basin woidd come from adjacent inland areas, whereas commercial exploitation of the natural renewable resources through agriculture, trapping, and fishing is by the resident population. However, the major pressure on noncommercial sportfish and wildlife is from individuals who live outside the Chenier Plain boundary. The four sectors that directly harvest the region's resources are (1) mineral extraction, (2) agriculture, (3) commercial trapping and fishing, and (4) recrea- tional fishing and hunting. This section will discuss the ecological impacts of these sectors; of the resident population; of transportation development, particu- larly for navigation; and of the local, State, and Federal governments. 28 Table 3.2. Human population distribution in the Chenier Plain basins and adjacent northern parishes (counties). Chenier Plain Chenier Plain plus adjacent northern parishes (counties) Basin Population'' (number) Land area (ha) Density (persons per ha) Population (number) Density (persons per ha) Vermilion 804 56,335 0.014 112,547 2.00 Mermentau 7,974 206,567 0.039 90,857'= 0.31 Chenier 1,220 89,151 0.014 Calcasieu 9,790 94,428 0.104 127,483 1.35 Sabine 130,636 244,543 0.534 337,730 1.38 East Bay 4,824 54,821 0.088 250,000*^ 4.56 Calculated from 1970 Census (U.S. Department of Commerce 1973), by summing the population of all cities with population 1000, then prorating the rural population of individual wards (divisions in Texas) by the areal proportion within a basin boundary. Inland area exclusive of open water. Includes population north of the Chenier Plain boundary. East Bay plus about one- fifth of Harris County, Texas. Approach. Typically, each sector has an eco- nomical and ecological impact on the Chenier Plain region. Each important activity is identified and its magnitude in relationship to die economic sector is discussed. The sectors and resulting activities are summarized in matrix form in table 3.1. The effect of each activity on the ecosystem is discussed in sections dealing with hydrology, land-modifying processes, and natural resource productivity. 3.2.2 MINERALS Production. Mineral extraction particularly oil and gas, is the major industry on the Chenier Plain. The dol- lar value of minerals extracted in 1974 was six times greater than the total value of the renewable resources (table 3.3). On a statewide basis, more than 96% of the mineral production value is derived from the mineral fuels, natural gas and crude oil (Jones and Hough 1974). Although the doUar value is stOl increasing, the volume of production peaked in 1970 and has been decUning since 1971 (fig. 3-2). A second trend is the depletion of inland (coastal) production and the development of new weUs farther and farther off- shore in Federal waters of the Gulf of Mexico. Within the Chenier Plain, the total value of minerals extracted in 1974 was $438 million. Most of this production was within the "intermediate" zone defined by the Louisiana Department of Conservation (Melancon 1977). This zone includes most of the coastal marshland. Production in the nearshore Gulf is, with the exception of the Vermihon Basin, a rather small proportion of total production. (Details of 1974 production and cumulative production by field in the Chenier Plain are in appendix 6.2). Table 3.3. Annual value of major resources of the Chenier Plain. Value Resource Millions of Dollars Oil and gas* 438 Agriculture 28 Commercial fishing and trapping'^ 12 Recreational fishing and hunting 21 1974 production (Melancon 1977). 1974 production (U.S. Department of Agriculture 1975). '^Based on 1963-1973 commercial production (U.S. Depart- ment of Commerce 1976), see table 3.29. Based on calculations shown in tables 3.32 and 3.33. The oil and gas production and value in 1974 was highest in the Mermentau Basin (60x10^^ kcal, $114 million), followed by the Chenier and East Bay basins (table 3.4). The Chenier and Mer- mentau basins sustain the most intense mineral extraction per unit of area. Human Activities that Affect the Environment. Pollutants : Mineral extracfion results in discharges of brine into coastal and estuarine waters, and also in oil spills. The latter include chronic low level spills, and major spills. Brine water is discharged into wells, pits, and nonpotable water bodies in the Louisiana portion of the Chenier Plain (table 3.5 and appendix 6.2). For areas close to the coast, disposal into saline waters is the most economical practice. The environmental 29 effects of surface disposal are much more adverse in freshwater areas. Because of tlie lack of saline waters, the large volume of brine generated in the Mermentau Basin is returned to disposal wells. Part 3.5.3 discusses the environmental effects of brine. In addition, large amounts of drill fluids containing biocides are disposed of into reserve pits (inland) or discharged into the Gulf. Little is knovm about the environmental effects of these fluids. Large volumes of freshwater are an additional requirement for well leaching. As an example, the freshwater demand for the LOOP storage facility in the Clovelly salt dome (in Barataria Bay, east of the Chenier Plain) is estimated at up to 8.8 x lO"* m^ (3.1 X 10^ ft^) per day. The maximum 12-month withdrawal has been estimated at 30.56 x 10^ m^ (1.08 X 10^ ft^). The impact of this withdrawal rate would depend on the size of the watershed area and Table 3.4. The 1974 production of oil and gas in the Chenier Plain (Melancon 1977). Kcal equivalent^ (kcalx lO'^) Crude Natural Basin oU (bbls) gas (mcf) Vermilion 2,833,930 112,943,923 Mermentau 8,543,329 189,940,493 Chenier 2,485,233 193,579,634 Calcasieu 6,003,821 43,191,467 Sabine (La.) 3,832,609 39,269,853 (Tex.) 1,900,025 6,105,777 Sabine total 5,732,634 45,285,630 East Bay 8,163,375 123,346,093 Total 33,762.322 708,287,240 Value*" $1,000 32.6 60.4 52.4 19.7 15.5 4.3 19.8 43.0 227.9 53,151 114,011 75,633 52,405 37,045 14,235 51,280 91,092 437,572 ^Assuming one million Btu/mcf natural gas and 5.8 million Btu/bbl crude oil. Calculated at the rate of $0.307/mcf for natural gas, and $6.52/bbl for crude oil. Table 3.5. Louisiana brine disposal by basin, in mbbi (Louisiana Department of Conservation 1977). Basin To disposal wells To pits To nonpotable water bodies Vermilion 1,648.7 3,601.8 Mermentau 32,415.2 34.1 1,388.9 Chenier 2,657.8 42.1 4,461.7 Calcasieu 3,308.6 50.0 4,134.6 Sabine (La.) 675.2 10.3 6,446.3 Two potential developments related to energy production on the northern Gulf coast may increase the impact of brine. Both the Department of Energy (DOE) and private corporations [e.g., Louisiana Offshore Oil Port, Inc. (LOOP)] are leaching salt from salt domes to create chambers for crude oil storage. One such site is the Hackberry salt dome in the Calcasieu Basin. Other sites are east of the Chenier Plain in the Weeks' Island and Choctaw dome areas. In addition, development of geothennal/geopressure energy sources would require disposal of enormous quantities of brine. Many potential brine disposal locations are within the Chenier Plain (fig. 3-3; see appendix 6.2 for well description). The possibility of significant environmental modification by discharge of this brine into the Gulf is currently under investi- gation by the Division of Geothemial Energy (DGE). the flow of water through it. In Barataria Bay with an upstream watershed area of 3,400 km^ (1,313 mi^) and a mean annual rain surplus of 42 cm (16.5 in), this withdrawal rate would be 1.7 to 3.4% of the freshwater input (Gosselink et al. 1976). The impacts of brine disposal are discussed in part 3.5.3. The probability of major oil spDls from transpor- tation has been evaluated by Bryant (1974) from U.S. Coast Guard data. He estimated a probability of 6.7 tons (6.1 tonnes) of crude oil spillage per vessel- year of operation in the superport region east of the Chenier Plain (table 3.6). This type of spill would be expected only in the navigation channels and approaches of the Calcasieu and Sabine waterways. The probability of pipeline spillage is extremely small (table 3.7). Nearly all incidents are associated with structural failure, ruptures, or leaks. Bryant (1974) used an estimate of 320,000 km (198,839 mi) of pipeHne in existence during 1971 and 1972 to cal- culate an expected spillage of 16.3 l/km/yr(6.9 gal/ mi/yr) or 0.008 incidents/km/yr (0.013 /mi/yr). Extrapolating for the estimated 7,549 km (4,691 mi) of pipelines in the Chenier Plain, an average annual spillage of about 770 bbl/yr of crude oil is predicted. Although this is small, the possibility of single large accidents exists. 30 c o 1- in o BJ : 3 ^ J ON uiiiaa uoiiiia 3 c < 3 eo s:. on c/l 3 M n OD K T3 •a C c rt ra Natural Gas/ trillion cubic feet/year « •» 1 « " '• ' > ? = • i / I 2^ nj c3 r-f 'Z- r- r ^^ y^ X) [-;- » / / < u^ lA i / ^ *• ns 196 74). / - = (millio aisiana ugh 19 5; Si '\ 1 _ o n o o O-JX z ■ S 1 • 1 1 oducti oil in esand \ 2 I s fll \ \ « v,^ '% \ 3 rt J— \ ^ \ • 5 '*- On 1 Vi 1 < O — \ 8 w 1 ro § 1 ' ' § % I 8 S > 4^ 3 op leaA/siaJJBq UOJII Ul £ /IjO puespmbj-j seg |BiniE|\| r-- ON, c IS K C m 't« '3 O -J 3 O n _o +-» O u a. o l-H O w 60 o D 60 •a (U kH (U X) E 3 z I 3 60 31 Table 3.6. Expected oil spillage due to non-catastrophic incidents (vessel not sunk) involving seagoing vessels in superport region (Bryant 1974). Probability of polluting incident per vessel-year in region 0.000615 Average spillage per polluting incident, in tons Expected spillage ( tons) Type of incident Per vessel-year Per vessel-day Breakdown 25 0.015 0.000042 Capsizing 0.00030-' 213 0.065 0.000178 Collision 0.0177 225 3.98 0.0109 Explosion 0.00153 72 0.11 0.0003 Fire 0.00397 360 1.43 0.00392 Ramming 0.00641 158 1.01 0.00277 Structural failure 0.00244 40 0.098 0.0002" Total 6.708 0.018380 Table 3.7. Pipeline spillage incidents and volume for the United States and its territories during 1971 and 1972 (Bryant 1974). Number Spillage per of Spillage incident Incidents incidents (bbl) (bbl) Casualty 12 211.9 17.7 Rupture, leak or structural failure 2,266 63,367.2 28.0 Equipment failure 223 902.5 4.0 Personnel failure 40 290.4 7.3 Deliberate discharges 4 48.1 12.0 Natural phenomena 11 611.7 55.6 Unknown 26 319.9 12.3 Total 2,582 65,751.7 Overall Averag e 25.5 Perhaps a more serious long-term hazard of mineral production within the inland wetlands is the chronic spilling of small quantities of oil over a period of many years. Some of this oil finds its way into the sediments of the surrounding wetlands, as shown by hydrocarbon analyses (Bishop et al. 1976). The sedi- ments appear to act as a sink for the liydrocarbons, releasing them slowly to the bottom waters in oil field canals (Milan and Wlielan 1978). Impoundment s: Leveed pits are created for confinement of brine associated with mineral ex- traction. The volume of brine disposed of in this fashion in the Chenier Plain is small relative to other disposal means (table 3.5). The number of these leveed pits is small and total area is insignificant, although the local impact may be important. Probably a more important activity is the in- advertent creation of impoundments as a result of canal dredging. Spoil banks from crisscrossing canals or from canals along natural ridges may effec- fively cut off an area from nomial water flow. The number and area of impoundments due to mineral extraction activities alone are difficult to quantify. Impoundments are discussed further in parts 3.3 and 3.4. The effect of impoundments on biota is discussed in part 4.0. Water Based Construction : The Chenier Plain has an overall density of about 0.33 well/km^ (0.85 well/mi^) (Louisiana Department of Conservation 1977); the Calcasieu Basin has the highest density- 0.72 well/km^ (1.86 wells/mi^). Probably the major impacts of well construction are disturbances of the site. Construction of pipeUnes is another activity associated with mineral extraction. The direct con- struction effects are small compared to the major impact of the resulting canals. Canal Dredge and Spoil. The major long-term iinpact of mineral production on basins is tlie con- struction of canals and their associated spoil banks through shallow water bodies and wetlands. Table 3.8 shows the length and area of these canals (plates 5A and 5B). The majority of canals provide access for navigation, although road embankment canals become increasingly important toward the west end of the Chenier Plain. Most pipeline canals are back-filled, but many later become shallow-water hnear features because of compaction and erosion. (See part 3.3 for a discussion of impacts of canals.) Oil field activity canals cover about 6.700 ha (6,556 a) of tlic Chenier Plain. Associated spoil banks cover anywhere from two to three times as mucii area as the canals (Craig etal. 1979). Using a conservative factor of twice the canal area for spoil banks, the total land permanently impacted by canals and spoil banks is about 20,000 ha (49,421 a). This type of modification is discussed in part 3.4. 32 Table 3.8. Lengths and areas of oil production related canals for each basin and the total for the Chenier Plain. Navigation canals Canals for road embankments Length Area (km) (ha) Open pipeline canals Total Basin Length (km) Area (ha) Length (km) Area (ha) Length (km) Area (ha) Vermilion 137.3 824 15.5 11 25.3 13 178.1 848 Mermen tau 310.4 1,863 56.5 40 84.7 42 451.7 1,945 Chenier 150.3 902 109.3 76 75.1 38 334.7 1,016 Calcasieu 122.7 736 115.2 81 41.3 31 279.2 848 Sabin, La. 120.2 721 76.2 53 13.3 7 209.7 781 Sabine, Tex. 41.3 248 1.7 1 0.6 1 43.6 250 Sabine Total 161.5 969 77.9 54 13.9 8 253.3 1,031 East Bay 5.5 887.7 33 5,327 1 263 240.3 132 5.5 1,499.5 33 Total 374.5 5,721 3.2.3 AGRICULTURE Production. The magnitude of the agricultural industry in the Chenier Plain is indicated by the total farm acreage, the acreage of rice and other cul- tivated crops, and the total number of famis (fig. 3-4). About 147,000 ha (363,492 a) were being fanned in 1975. Forty percent of this was cropland; the rest was pasture. Of the cropland, 87% was rice. In 1974, rice area was 48,600 ha (120,093 a) and the average yield was 3.9 t/ha (1.75 tons/a) (Fielder and Guy 1975). The Mermentau and Sabine basins are the major agri- cultural producing areas (plate 3B). The total market value of the region's agricultural products in 1974 was about $28 million. About $20 miUion of this was derived from crop production, chiefly rice (table 3.9). These figures are estimates for individual basins, calculated from parish (county) pro- duction figures. An average value per hectare of fann- land was calculated from the parish (county) infor- mation. This value was used with the fann area (de- tennined from 1975 U.S. Geological Survey ortho- photoquads) to estimate the total value of agricul- tural products. The data (U.S. Department of Agricul- ture 1975) indicate there is a wide discrepancy across the Chenier Plain in the market value of agricultural products per hectare of farmland. This value varied in 1974 from a low of about $126/ha ($51 /a) in the Sabine Basin to a higli of $370/ha ($150/a) in Ver- milion Basin. The reason for variation is unclear but is probably related to the proportion of the total farm area in rice production and the proportion which was fallow in 1974. For instance, Cameron Parish, Orange, and Galveston counties, all had low ratios of harvested cropland to total cropland [0.35, 0.32, and 0.42 re- spectively, (U.S. Department of Agriculture)], and low ratios were associated with low market values per hectare. The Mermentau and Sabine basins produce the highest total values of farm products because of the large areas involved, in spite of the relatively low Table 3.9. Estimated farm area and value of all agricultural products and of crops by basin in 1974. Market* value Farm of all agricu Itural products Total Estimated value of crops Crop Value/ha'' Total area Value/ha value area value Basin (ha) w ($x 1,000) (ha) (S) ($ X 1,000) Vermilion 5,374 370 1,988 2,056 448 917 Chenier 3,421 193 660 670 314 210 Mermentau 59,435 240 14,264 36,366 348 12,655 Calcasieu 13,238 168 2,224 7,268 326 2,369 Sabine, La. 5,944 126 6,242 1,221 282 2,222 Sabine, Tex. 43,590 126 8,941 210 East Bay 19,420 136 2,641 3,765 322 1,212 Total 150,422 $28,107 60,282 $19,586 *U.S. Department Agriculture 1975. See appendix 6.2 for details of data conversion from parish-based (county-based) basin. Calculated as in a) using parish values for value per acre of total cropland (Orange $61; Galveston $79.7; Jefferson $205,1; Chambers $181.6; Calcasieu $145.6; Cameron $90.8; Jefferson Davis $201.4; Vermilion $180.4). 33 L o o (fl a o ^ O T3 4) ra > •«-' 0) 3 k. O 3 w 0) (0 a. O 0) u 15?^ O o CO O O CM sujjej io jaquinr^ O O O O Q. O (O O o o 6 o o o o" - .'^y^ ^^^ 6^^ .v<^"' C*' tf^' 0^*= ,0^*= A^" ^" ..^^'^ vie' «^' ;vv°^ (A (0 CQ e .^■^ ^*^ 6*^ C^' vVC-' xe^'= Jc^' .<^-^ A*^ \t« .<<^*= >ie' A<^^ .V" in 60 < Q c ^ o :3 X) X3 1/ < i 6Ij ieg| eajv 34 values per unit area in the Sabine Basin. In contrast to the total agricultural value, the crop value per hectare of cropland in 1974 varied much less [from about $ :50/ha ($101 /a) in Sabine Basin to $445/ha ($ 1 80/a) in Vemiilion Basin] . Since the early 1900s, the total area of cropland on the Louisiana coast has been declining slowly (fig. 3-5), although the production per hectare for rice has increased in a spectacular manner (Fielder and Guy 1975). In the Chenicr Plain, agricultural habitat has increased 4% since 1952 (table 3.10), This small increase generally reflects a substantial (9 to 45%) increase in the eastern part of the Chenier Plain with a net loss in Sabine and East Bay basins. Agricultural Activities that Affect the Environ- ment. Loss of natural habitats to agriculture : Agri- cultural activities take place in areas that were for- merly wetland, ridge, or upland forest. Over 80% (7,285 ha) (1,800 a) of the increased agricultural area since 1952 has resulted from draining natural and im- pounded wetlands. Another 1.500 ha (3,707 a) have been "reclaimed" from natural ridges and forested land. As figure 3-5 shows, most of the land currently in agriculture was being fanned many years before 1952. These old sites developed first on the fertile prairies of the Chenier Plain and later on cleared upland forests of the region. The normal sequence is to use high, well-drained grasslands first, then to clear upland forests, and finally to drain wetlands. At the same time, urban expansion takes over agricultural land, as shown for the Sabine Basin in table 3.11. Between 1952 and 1974 there was no reversal of this process in the Chenier Plain. That is, no agricultural land reverted to natural wetlands or uplands, although in the Sabine Basin, 204 ha (504 a) of pasture were converted to open water habitat. , Table 3.10. Areal changes in agriculture habitats from 1952 through 1974. (ha) +551 Areal changes" in land usage Total (ha) Basin Rice (%) +30.8 Non- (ha) +451 rice crops (%) Pasture (ha) (%) (%) Vermilion +51.5 +676 +25.6 +1,678 +45.4 Mermentau +2,238 + 7.3 +877 +34.9 + 1,893 + 8.9 +5,008 + 9.2 Chenier +29 +76 +196 +48.2 + 120 + 4.6 + 345 + 11.3 Calcasieu + 1,300 +30 +214 +16.0 -352 - 5.6 +1,162 + 9.6 Sabine -945 - 9.4 +20 + 1.9 -1,277 - 3.1 -2,202 - 4.3 East Bay*^ -386 - 9.8 +68 +51.9 +121 + 0.8 Total - 197 +5,794 - 1.0 + 4.0 ^Increase (+) or decrease (-) from 1952 area. ''For East Bay from 1954 to 1974. Table 3.11. Hectares of natural habitat converted to agriculture, and agricultural habitat converted to urban use in the Chenier Plain from 1952 to 1974. Basin Habitat converted to agriculture Vermilion Mermentau Chenier Calcasieu Sabine East Bay Total* Natural marsh 619 2,466 none 1,049 321 none 4,455 Impounded marsh 800 2,030 none none none none 2,830 Natural ridge 104 145 376 62 20 none 707 Spoil none none none 140 none none 140 Upland forest 177 289 ... b 199 none ... 665 Swamp forest none 1,700 118 5,048 — none 1,450 none 341 none 118 Total 376 8,915 Agricultural habitats con- verted to urban use 22 40 31 272 2,339 197 2,901 T"he totals do not agree with the total habitat changes in table 3.10 because some minor conversions are not shown. Broken line indicates that habitat does not exist in the basin. 35 400 300 (0 o 200 w TJ C CO (0 3 o 100 (0 o Area of harvested cropland Yield of rice X"- 5000 .4000 3000 £ Q. 2000 1000 .w . 1929 1939 1949 Year 1959 1969 Figure 3-5. Change in area of harvested cropland and yield of rice in coastal Louisiana (Corty 1972, Fielder and Guy 1975). Agricultural Drainage Canals. About 3,450 km (2,144 mi) of agricultural canals (40% of the total length of all canals in the Chenier Plain) were dredged primarily for agricultural drainage or access (table 3.12). Canal density in individual basins varies from 0.37 to 0.56 km/km^ (average of 0.46 km/km^). About half of these canals drain upland areas. The rest flow through wetlands adjacent to the uplands (plates 5A and 5B). The agricultural drainage canals form a gridlike network along the northern parts of the Chenier Plain. The impacts of these canals on the natural system are discussed in parts 3.3, 3.4, and 3.5. Agricultural Runoff. Canals are dredged in the low-lying agricultural lands of the Chenier Plain primarily to drain the land and not for irrigation, since much of the water for flooding rice land comes from wells (see the following section about Surface- and Ground-water Use). The accelerated runoff increases erosion and the leaching of fertilizers and manure from the soil. The U.S. Department of Agriculture (1975) reports that an average of 0.38 ± 0.04 tonnes fertilizer is used on each fertilized acre in the Chenier Plain parishes. This amount and the Table 3.12. Length and density of agricultural drainage and access canals in the Cheneir Plain basins^. Basin Upland (km) Wetland (km) Total (km) Density" (km/km^) Vermilion 66.2 Mermentau 668.2 Chenier Calcasieu 217.5 Sabine, La. 58.5 Sabine, Tex. 553.5 Sabine Total 612.0 East Bay 197.2 Total 1,761.1 167.4 488.3 329.2 300.0 83.9 212.2 296.1 108.1 1,689.1 233.6 1,156.5 329.2 517.5 142.4 765.7 908.1 305.3 3,450.2 0.41 0.56 0.37 0.55 0.37 0.56 0.46 Wetland drainage plus canals associated with access roads. b 2 Total canal length (km) -rarea (km ) of wetlands and uplands in basin. 36 proportion of acres fertilized were used to estimate the total fertilizer use in the Chenier Plain (table 3.13). Probably tire major use is in rice cultivation where the fertilizer blend of 18-18-9 (percent N-PjOj-KjO) is commonly applied at planting time. The resultant nutrient load (expressed as phosphorus) to basin waters and its contribution to eutrophication are discussed later. Use of agricultural areas by wildlife: Although the creation of agricultural land destroys natural habitat (for instance, the loss of the grassland habitat of the Attwater prairie chicken), it also provides an important concentrated food source that is available to some wildbfe, particularly migratory birds. The use of rice fields and pastures by waterfowl is discussed in part 5.0. The agricultural areas appear to be especially valuable when conditions are unfavorable in adjacent wetlands. Surface- and Ground-water Use. Rice irrigation puts severe seasonal demands on the freshwater supply in the Chenier Plain. Since over 95% of the water used for agriculture (fig. 3-6) in Louisiana is for rice production (98% in the southwest por- tion of tlie state, including tlie Louisiana portion of the Chenier Plain (Louisiana Department Public Works 1971), other agricultural uses will be ignored. Considering the rice area in the Chenier Plain basins, the freshwater usage for rice ranges from 0.7 niilUon m^ (24.7 million ft-') in the Chenier Basin to 320 million m^ (1 1,301 million ft^) in the Mermentau Basin (fig. 3-7) for an estimated total of 571 million m^ (20,165 ft-') (based on 3.11 acre-feet per acre, Louisiana Department Public Works 1970). The timing of this withdrawal is ecologically important since it corresponds with the hottest months of the year when water demand by natural vegetation is also at its peak (fig. 3-8). In the southwestern part of Louisiana (including Vernon, Beauregard, Allen, Evangeline, St. Landry, and Acadia parishes as well as the Chenier Plain parishes), 38% of the required water is purchased from commercial suppliers, 28% is self-suppUed from surface water, and the rest is pumped from ground- water by the rice growers (table 3.14). Overall, about 66% of the water is drawn from the surface, the rest from wells. The Vermilion River and the Gulf Intercoastal Waterway (GIWW) supply about 26% of the total irrigation surface water used in southwestem Louisiana. Other principal water sources for surface water in the Chenier Plain region are tabulated by the Louisiana Department of Public Works (1970). The use of surface and ground water for agri- cultural irrigation is only one demand on this re- newable resource. The total demand and environ- mental impUcations are discussed in part 3.5.3. Table 3.13. .'Vrea of agricultural lands, fertilized lands, and tons of fertilizer used for each Chenier Plain basin. Agricultural land (ha) Fertilized land'' Quantity used*" Basin Percent of agricultural land Area (ha) (t) Vermilion 5,374 0.45 2,418 917 Mermentau 59,435 0.24 14,264 5,411 Chenier 3,421 0.29 992 376 Calcasieu 13,238 0.25 3,310 1,256 Sabine, Total 49,534 0.15 7,430 2,818 East Bay 19,420 0.14 2,719 1,030 Total 150,422 31,133 11,809 ^Fertilizer ratio not stated in U.S. Department of Agriculture (1975), but the common ratio for rice is 18-18-9 (N-P2OJ-K2O). Calculated from the parish percentage of fertilized land (U.S. Department of Agriculture 1975) converted to basin values using agriculture factors developed from the rural population figures (appendix 6.2). ''At a rate of 0.173 + .019 short tons/a (0.379 metric tonnes/ha) (U.S. Department of Agriculture 1975). 37 too 90 80 70 60 50 40 30 20 Other Commefcial Commercial Liirestock Poultry Crops Catfish Craylish Category Figure 3-6. Water usage for agriculture in Louisiana in 1967 (Louisiana Department Public Works 1970). n n Figure 3-7. Volume of water used for agriculture in each basin (Louisiana Department of Pub- lic Works 1970). 60„ 50 40^ 30_ 20 10 3S^ 14% JS% 15% 12t J-F-M * S-O-N-D Figure 3-8. Percentage distribution of monthly water usage in southwestern Louisiana in 1967 (Louisiana Department of Pubhc Works 1970). Table 3.14. Source and volume (millions of cubic meters) of water for irrigation in south- west Louisiana (Louisiana Department of Public Works 1970). Source Surface water Ground- water Total Purchased Self- supplied 787 584 718 718 (34%) 787 1,302 Total 1,371 (66%) 2,089(100%) 3.2.4. COMMERCIAL TRAPPING AND FISHING Production. The commercial harvest of wildlife resources on the Chenier Plain includes furbearers and commercial fishes. The fur and commercial fishery in- dustries are basically noncompetitive since they re- quire different equipment and harvest from different habitats; however, both industries involve organisms which depend on wetlands for at least a portion of their life cycles. Furbearers : The trapping of mammals (primarily muskrat and nutria) for fur is more closely controlled, since trapping occurs primarily on private lands or refuges for which permits or leases are required. Musk- rats, which represent a significant proportion of the total fur catch, are fairly easy to quantify. The 1973 harvest of nutria and muskrat in southwest Louisiana amounted to 749,670 and 86,087 pelts, respectively (table 3.15). During the same period, the combined estimated harvest of both species from the Texas por- tion of the Chenier Plain was about 35,000 pelts (Bill Brownlee, pers. comm., Texas Parks and Wildlife De- partment). In tlie western part of Louisiana, muskrat and nutria harvest totaled about 1,600,000 pelts in 1975 (fig. 3-9). The number of pelts harvested in eastern Louisiana has also fluctuated, but appears to be in- creasing after a low during the 1970 to 1974 period. The annual harvest density of muskrat and nutria on the Chenier Plain was estimated at 147,000 and 429,000 pelts, respectively, by Palmisano (1972a and 1972b) (tabic 3.16). These estimates were in line with the actual pelt harvest statistics for western Louisiana and for eastern Texas (appendix 6.2). In addition, the expected harvest of nutria and muskrat by basin indi- cated that Sabine and Calcasieu basins should yield the most muskrat and the Memientau Basin should be optimum for nutria (figs. 3-10 and 3-1 1). The values of the pelts to the trappers was around $3.2 million. 38 Western Louisiana Eastern Louisiana Years Figure 3-9. Annua] muskrat and nutria pelt production for coastal Louisiana 1968-76 (Louisiana Department of Wildlife and Fisheries). 160, 60 50 40 Z 30 20 10 Muskrat Basin Q % % \ \ 140 1 120 Nutria t 1 1 (A 100 > ra I 80 60 - Z 40 - 20 - t Basin \ \ % %. % \ \ \ \ Figure 3-10. Estimated number of muskrat pelts pro- duced from the Chenier Plain basins, based on 1975 habitat areas and on har- vest densities determined by Palmisano (1972a). Figure 3-11. Estimated number of nutria pelts pro- duced from the Chenier Plain basins, based on 1975 habitat areas and harvest densities determined by Palmisano (1972b). 39 Table 3.15. Harvest and value of fur animak in Louisiana in 1973 (Louisiana Department of Wildlife and Fisheries). Species Nutria (eastern La.) Nutria (western La.) Muskrat (eastern La.) Muskrat (western La.) Mink Raccoon (coastal) Raccoon (upland) Opossum Otter Skunk Fox Bobcat Beaver Coyote Total pelts and value Nutria Muskrat Raccoon Opossum Total meat and value Number of pelts 1,000,000 749,670 200,000 86,087 38,940 45,000 139,688 33,676 5,989 747 3,312 953 472 382 2,304,916 Pounds of meats 11,000,000 250,000 1,000,000 300,000 12,550,000 Average price per pelt ($) (1973 price) 4.50 6.00 3.25 4.50 7.00 6.00 7.50 1.50 30.00 1.25 15.00 20.00 6.00 12.00 Average price per pound 0.09 0.09 0.30 0.25 Value (S) Total 4,500,000 4,498,020 650,000 387,392 272,580 270,000 1,047,660 50,514 179,670 934 49,680 19,060 2,360 4,584 11,932,454 990,000 22,500 300,000 25,000 1,387,500 13,319,954 Table 3.16. F^stimated Chenier Plain harvest of muskrat and nutria, based on habitat area and yield per unit area (Palmisano 1972a, b) Area Pelt harvest/ 1,000 ha Muskrat Nutria Estimated har\'est Muskrat Nutria Habitat (1,000 ha) No. of pelts Fresh marsh ic impounded 278 52 1,236 14,460 343,600 Intermediate marsh 85 346 741 29,400 63,000 Brackish marsh 101 971 222 98,100 22,400 Salt marsh 17 297 Total 5,050 147,010 429.000 Actual 1975 pelt harvest* 150,000 400,000 *For western Louisiana sec figure 3-9. 40 using pelt values of $4.50/muskrat and $6.00/nutria. The highest returns of nearly $ 1 million each per basin for muskrat and nutria pelts came from Mermentau and Sabine (table 3.17). Alligator : Closely controlled aOigator harvests have been conducted in the Louisiana portion of the Chenier Plain since 1972. In 1976, the total revenue from this industry was about $0.5 milHon (table 3.18). Commercial estuarine-dependent fishery : The commercial fishery includes the estuarine-dependent marine and brackish water fishery, shellfishery, and the freshwater fishery. Commercial catches of estuarine-dependent spe- cies for the northern Gulf coast are recorded by major inshore estuarine lake or bay or by offshore grid zone [National Marine Fisheries Service (NMFS) 1976]. Many locally knowledgeable fishery biologists beheve that only a fraction of the landings for species other than Gulf menhaden are actually recorded by NMFS statistics. However, these statistics are the only con- sistent landing records available. The bulk of the har- vest occurs offshore, but part of the life of the com- mercially important species is spent in the inland marshes and estuaries. That is, each species must be able to enter marshes, estuaries, and offshore waters at appropriate stages of its life cycle (part 4.0). Fur- thermore, the commercial species move alongshore, Table 3.17. Estimated value^ of the muskrat and nutria fur industry for each basin. Harvested pelts ' Valu? Total Basin Muskrat Nutria Muskrat'' Nutria*^ value $ Vermilion 19,500 31,324 87,750 187,944 275,694 Chenier 20,874 69,519 93,933 417,114 511,047 Mermentau 8,280 155,800 37,260 934,800 972,060 Calcasieu 34,050 40,320 153,225 241,920 395,145 Sabine 52,625 116,780 236,812 700,680 937,492 East Bay 11,402 14,895 51,309 89,370 140,679 Total 146,731 a and estimated ha 428,638 660,290 2,571,828 3,232,117 Calculated from are rvest per unit area as in table 3.20. ''At $4.50/pe!t. '^At $6.00/pelt. Table 3.18. Value of alligators harvested from the Louisiana portion of the Chenier Plain for 1972 through 1976. Average price Total Number of animals Average per linear foot revenue harvested and sold size ($) ($) 1972^ 1,350 (1,337 sold) 6'ir' 8.10 74,773.00 1973'' 2,821 (2,916 sold)<^ 71" 13.13 268,542.45 1975'^ 8.00 251,876.00 1976'^ 4,300 (4,360 sold)'' 7'0" 16.50 509,060.00 Palmisano et al. 1973. Joanen et al. 1974. Included farm-raised animals. Louisiana Wildlife Fish Commission News Release, New Orleans, La., 19 October 1976. 41 probably westward with the prevailing currents so that the catch in a grid zone offshore of a particular basin may have little relationship to the ability of that basin to provide for the needs of a species throughout its en- tire Lfe history. An excellent example is the Sabine Basin. The shrimp fishery offshore of Sabine is a thriv- ing one, but in recent years the Sabine estuary has pro- duced no commercial landings of shrimp (National Marine Fisheries Service 1976). Therefore, most of the shrimp caught offshore of the Sabine Basin use other inshore areas as nurseries. The approach used in analyzing fishery data for this report was that of Lindall et al. (1972). The total offsliore yield in Louisiana was attributed to various basins based on the relative densities of juveniles caught inshore and the estuarine habitat area of each basin (National Marine Fisheries Service 1976). Relative in- shore juvenile densities were based on trawl catches reported in the Cooperative Gulf of Mexico Estuarine Inventory and Study, Louisiana (Perret et al. 1971). This approach recognizes the value of the inland nur- sery ground even though it is not the immediate site of the fishery catch. A total of 244,511 t (539 inilhon lb) of fishery products were harvested from the Chenier Plain in 1975 (table 3.19). (Appendbc 6.2 shows figures for 1970 through 1975.) Gulf menhaden accounted for about 95% of the tonnage landed in the Chenier Plain. Shrimp were a distant second with 2.9%. The only other species of significant commercial value were blue crab and American oyster. There are also small land- ings of other finfishes, such as sea trout and red drum (redfish). The catch of the estuarine-related freshwater species is also recorded. Of these, members of the cat- fish family are the only species currently reported. Apparently no commercial harvest of wild crayfish presently exists in the Chenier Plain, although landings were reported as recently as 1972. In terms of dockside value, menhaden (49%) and shrimp (44%) produce most of the income, followed by oyster and blue crab. The total dockside value of the industry in the Chenier plain was about $31 mil- lion in 1975. Table 3.19. Weight and value of commercial landings of fish in western Louisiana and the Galveston area in 1975 (U.S. Department Commerce 1976). Weight Value Fishery (kg X 1,000) (Perc ent of total) (Sx 1,000) (Percent of total) Estuarine-dependent marine fisheries Menhaden 233,872 95.6 15,423 49.2 Shrimp 7.024 2.9 13,777 44.0 Blue crab 2,257 0.01 763.3 2.4 Oyster 561.0 0.002 957.3 3.1 Sea trout 216.3 0.001 183.3 0.01 Redfish 49.3 trace 38.1 0.001 Flounder 23.0 trace 18.2 0.0006 Subtotal 244,002.6 31.160.2 Estuarine-related freshwater fishery Catfish ic bullhead Other species Subtotal Total 124.6 384.0 508.6 244.511.2 trace • 0.002 0.002 93.9 65.0 158.9 31,319.1 0.003 0.002 0.005 42 The calculated total harvest (offshore and inland) of estuarine-dependent fishes and shellfishes per hect- are of inland water (salinity > 5°/oo) in the Chenier Plain showed that the Chenier Basin had the highest production (table 3.20). Vermihon Basin values were derived from Hydrologic Unit VII; Chenier Basin values, from Hydrologic Unit VIII; and Calcasieu and Sabine basins values from Hydrologic Unit IX as de- scribed in LindaU et al. (1972). East Bay Basin values were determined from Texas landings for grid zone 18, inshore and offshore. The mean 1970 through 1975 reported catch for each species was divided by the Galveston Bay inshore estuarine area (mean salin- ities > 5°/oo). Exceptions were blue crab and Gulf menhaden values. Blue crab production for Sabine Lake was calculated directly from landing data because of the high local production (appendix 6.2). No com- mercial menhaden landings occur in Texas although menhaden is a dominant juvenile fish in Galveston Bay and Sabine Lake (Reid 1955). The menhaden in- dustry is based in Louisiana and Mississippi; catches in east Texas waters are reported in Louisiana today. The menhaden value determined for Hydrologic Unit IX (Lindall et al. 1972) was used for all three western basins. The total production of each basin was calculated on the basis of unit area values (table 3.21). Calcasieu, Sabine, and East Bay basins had high menhaden pro- duction. Calcasieu and East Bay basins also support important shrimp fisheries. The Sabine Basin shrimp production (as contrasted to the Sabine offshore har- vest) is probably insignificant; the last inshore com- mercial harvests occurred in 1972 (appendix 6.2). Some shrimp are occasionally caught in Sabine Lake, so the basin may make some contribution to the offshore fishery. Similarly, Atlantic croaker and sea trout harvests have fallen to nothing, and the oyster beds are permanently closed because of contamination (part 3.6.6). It should be noted that there is relatively large production of blue crab in Sabine Basin and large production of oysters in East Bay Basin. In effect, the Me rmentau Basin is fresh- water, having Uttle exchange with the nearshore zone. It had been assumed to support no marine fishery, but recent water management practices may have changed this (part 3.6.3). Table 3.20. Estimated commercial catch per hectare of inshore area in 1963 - 1973 for estuarine-dependent fishes and shellfishes. Basin Species Vermilion Chenier Mermentau Calcasieu 439 Sabine 439 East Bay' Menhaden 183 1,391 439 Shrimp 9.8 47 27 (27)'^ 27 Blue crab 4.0 4.6 3.9 17.1 6.6 Oyster (meat) 0.1 1.2 8.1 Croaker 8.4 29.4 20.2 0.07 Sea trout 1.7 8.1 4.1 0.54 Spot 2.0 10.3 4.8 Red drum 0.01 0.2 0.2 0.12 Total 209.01 1,490.4 500.4 483.3 481.43 ^Based on 1963-1973 average Louisiana production and inshore juvenile density. From table 31, Fish and Wildlife Study (Lindall et al. 1972). The densities were reported by hydrologic unit for Louisiana. The value used for Vermilion was that of Unit VII; Cheniar and Mermentau, Unit VIII; and Calcasieu and Sabine, Unit IX. Mermentau Basin has no salinity greater than 5%o. "^Mean inshore and offshore Grid 18 yield 1970-1976 divided by estuarine water area of Galveston Bay. "^This value is based on the 1963-73 production mean and 1967 trawl data. Since that time, commercial production has ceased in Sabine Lake and trawl catches showed low densities of shrimp. 43 Table 3.21. Estimated contribution^ of each Chenier Plain basin to the commercial harvest of fishes and shellfishes (kg x 1000). Vermilion Chenier Mermentau Calcasieu Sabine East Bay Menhaden 2,835 5,488 13 ,136 12,459 11,047 Shrimp 151 186 803 763= 679 Blue crab 62.6 18.2 117 85 166 Oyster 1.6 36.9 204 Croaker 13.1 116.1 603 1.7 Sea trout 26.1 31.9 124 13.5 Spot 31.3 40.8 144 137 Red drum 0.2 trace 6.7 6.4 3.0 Calculated from inland cstuarine area and production per unit area of table 3.20. Mermentau basin has no salinity greater than 5 °/oo. Sabine probably no longer contributes significantly to the offshore catch. The commercial fishery harvest is largely dependent on the three westernmost basins (table 3.22). These basins appear to have near optimal conditions for estuarine-dependent species (part 4.0). Large expanses of wetlands connect to inland brackish bays and lakes. The Vermilion Basin appears to be less productive, perhaps because of excessive freshwater and silt discharged from the Atchafalaya River. The Chenier Basin is highly productive on a per unit area basis, but it is too small to support a higli total production. Table 3.22. Estimated landed value ($ x 1,000) of estuarine-related fishes and shellfishes, by basin. Value per kg* (S) Value ($x UDOO) Vermilion Chenier Mermentau Calcasieu Sabine East Bay Gulf menhaden 0.093 262.5 508.2 1,216.3 1,153.6 1,027.3 Shrimp 2.15 325.3 400.3 1,724.0 1,638.?^ 1,459.9 Blue crab 0.26 16.6 4.8 31.1 126.1 3.2 Oyster 1.37 2.1 50.4 279.5 Atlantic croaker 0.073 0.9 8.4 43.9 0.1 Sea trout 1.10 28.8 35.2 136.5 14.9 Spot 0.055 1.7 2.2 8.0 7.5 Red drum 0.46 0.1 trace 3.1 2.9 1.4 Total 638.0 959.1 3,213.3 2,928.3 2,826.3 Calculated from table 3.21 and the 1973 dockside value (Lindall et al. 1972). Mermentau Basin has no salinity greater than 5%o. No commercial shrimp production currently exists in Sabine Lake, which suggests that the offshore catch is not dependent on Sabine Lake. 44 I Estuarine-related freshwater fishes and shellfishes : calculated by basin the same way as for the estuarine- The commercial value of the freshwater fishery on dependent species (tables 3.23, 3.24, and 3.25). The the Chenier Plain is negligible compared to the largest calculated value ofS100,000in the Mermentau estuarine-dependent fishery (table 3.19). Production Basin would support only a few fishermen full time, per unit area, total production, and dollar value were Table 3.23. Commercial production (kg) per unit of area (ha) of freshwater fishes for each basin (Lindall et al. 1972). Basin Species Vermilion Chenier Mermentau Calcasieu Sabine East Bay Catfish and bullhead 3.69 1.91 1.91 0.08 0.08 Crayfish 0.61 0.30 0.30 Buffalo 0.98 0.37 0.37 Gar 3.25 0.40 0.40 0.47 0.42 Carp 0.01 0.07 0.07 East Bay has no commercial freshwater fishery. Table 3.24. Estimated total commercial production of freshwater fishes by basin^ (number of hectares of freshwater area in parentheses). Basin Vermilion Chenier Mermentau Calcasieu Sabine East Bay'' Species (3,450) (1,678) (104,545) (11,000) (17,503) (1,388) Catfish ic bullhead 12,760 3,197 117,177 863 1,373 Crayfish 2,088 508 18,610 Buffalo 3,364 620 22,745 Gar 11,214 677 24,814 5,178 8,239 Carp 39 113 4,136 ^Calculated from the unit area production and the area of water with mean salinity greater than 5 /oo as shown in table 3.23. East Bay has no commercial freshwater fishery. Table 3.25. Estimated value ($) of the freshwater fishery in the Chenier Plain, by basin* Value^ per kg Vermilion Chenier Mermentau Calcasieu Sabine Catfish and bullhead 0.68 8,271 2,185 80,082 590 939 Crayfish 0.44 920 224 8,206 Buffalo 0.31 1,038 191 7,020 Gar 0.24 2,719 164 6,018 1,256 1,998 Carp 0.09 trace 13,398 trace 2,764 365 101,691 Total 1,846 2,937 East Bay Basin has no commercial freshwater fishery. Calculated from table 3.24 and the dockside value in 1973. 45 Summary : Table 3.26 summarizes, by basin, the estimated 1973 value of the commercial fish and fur industry in the Chenier Plain. The value of the com- bined industries is approximately $12 million. About 73% of this is the estuarine-dependent fishery, most of the remainder is the fur industry. Because of its exten- sive estuarine-dependent fishery, the Calcasieu Basin supports the largest combined industry. Despite their size, the Sabine and Mermentau basins have industries that are not as valuable. The Mermentau Basin has no significant estuarine-dependent offshore fishery, and in the Sabine Basin, man's activities have resulted in serious fishery decline. Trapping and Commercial Fisheries Activities that Affect the Environment. The major ecological impact of trapping and commercial fisheries is the direct har- vest pressure on the resource. In addition to the har- vest of fish and mammals, there is the immense loss of the small fishes and shellfishes trapped in the trawls along with the harvested shrimp. It has been estimated that shrimp comprise only 5 to 32% of most trawl catches on a weight basis (Klima 1976). The non- commercial species are usually returned to the water, but few survive, and most become part of the detritus food base of the estuarine system prematurely. Ap- parently there have been no investigations into the ef- fect of this loss of small fishes and shellfishes on estu- arine ecosystem dynamics. In areas of intensive shrimp fishing, trawling could influence the trophic structure because it would tend to favor omnivorous feeders over top carnivores. Trawls also re-suspend bottom sediments and nutrients, increasing water turbidity. This increased turbidity of estuarine and nearshorc Gulf waters is evident during periods of intensive trawl- ing. Seafood processing plants produce detrimental discharges, but with a few exceptions these seem to be minor. Discharges from menhaden processing plants south of Calcasieu lake near Cameron, Louisiana, con- tributed significantly to the high colifonn counts that caused closure of the oyster beds in the lake late each summer. Construction of docks and other facilities for the industry produces local ecological impacts. Canals significantly influence the inshore hydrologic flow. The large, deep channels in the Chenier Plain were constnicted primarily for ocean-going freigliters and tankers, but many of the smaller navigation channels are used extensively by the commercial fishing fleet. Pirogue ditches constructed by trappers can, in hy- drologically critical places, erode rapidly into major waterways (Davis 1973). There are about 3,400 km (2,100 mi) of navigation channels in the Chenier Plain (table 3.27). Table 3.26. Estimated value (S x 1000) of commercial fishes, shellfishes, and the fur industry in the Chenier Plain (1973)*. Commercial harvest Estuarine-dependent Freshwater Basin Fur industry fishery fishery Total Vermilion 275.7 638 13.3 927 Chenier 511.0 959.1 2.8 1,472.9 Mermentau 972.1 101.7 1,073.8 Calcasieu 395.1 3,213.3 1.8 3,610.2 Sabine 937.5 1,290.1 2.9 2,012.8 East Bay 140.7 3,232.1 2,826.3 8,926.8 2,945.0 Total 122.5 12,281.4 Summarized from tables 3.17, 3.22. and 3.25. 46 Table 3.27. Length (km) and area (km ) of navigation canals in the Chenier Plain. Basin Vermilion Chenier Mermentau Calcasieu Sabine East Bay Total First order canals 53.28 592.2 Second order canals 19.95 2,850.1 Total Area (km^) Length (km) Area (km^) Length (km) Area (km') Length (km) 5.10 56.7 2.28 325.5 7.38 382.2 1.53 17.0 3.77 538.3 5.30 555.3 13.44 149.4 6.92 987.9 20.36 1,137.3 11.25 125.1 2.40 342.9 13.65 468.0 15.84 175.9 4.10 586.4 19.94 762.3 6.12 68.1 0.48 69.1 6.60 137.2 73.23 3,442.3 ^Major canals dredged and maintained to facilitate both interstate and intrastate navigation. Canals for small craft, or short, deep spurs to allow access from first order canals to industrial sites. 3.2.5 SPORT HUNTING AND FISHING Magnitude of the Activity . The magnitude and value of sport fishing and hunting have traditionally been difficult to assess because reliable samples are difficult to obtain, and a large sampling effort is re- quired. Three approaches have been used: license sales analysis, creel censuses, and telephone surveys. All have been used within the Chenier Plain, but none of them was designed for the study area specifically. This report presents the available data from studies in southwestern Louisiana and eastern Texas. To evalu- ate the sport hunting and fishing effort in the Chenier Plain itself, average man-days/man/yr spent in hunt- ing or observing wildhfe were calculated from these studies and applied to population figures for the Chenier Plain basins. The value of each activity was then calculated by applying appropriate dollar values/ man-day. Thus, the results (the number of man-days, demand for, and dollar value of hunting and fishing) are directly proportional to the population size. The human population within the study area is so small (with the exception of the industrial area along Sabine Lake) that its sport fishing and hunting impact is al- most negligible. The dense populations just north of tlie study area boundaries, however, use the Chenier Plain extensively for saltwater fishing and for hunting, particularly for waterfowl. It is known from the Fish and Wildhfe Study (U.S. Army Engineers unpublished) telephone survey that 70% of the saltwater fishermen in the coastal parishes travel less than 80 km (50 mi) to fish, and that 84% of waterfowl hunters hunt with- in 80 km (50 mi) of their homes. Therefore, to esti- mate the present demand for sport hunting and fish- ing within the Chenier Plain, the basin population was augmented by the population of the parishes (counties) immediately adjacent on the north. In the case of East Bay Basin, the applicable population was arbitrarily placed at 250,000, about one-fifth the population of tlie adjacent Galveston County area. [This figure may be somewhat high since Heffeman et al. (1977) report from a creel census of the whole Galveston Bay, a total fishing effort of 909,000 man-days/yr. Using their estimate of 16.2 man-days/fishennen/yr, this is the equivalent of 56,000 fishennen. If 20% of the population fishes (table 3.28), the East Bay Basin area is only drawing from a population of about 280,000.] These population estimates should be reasonable for waterfowl hunting and saltwater angling for which the coastal areas must be used; the estimates may be less satisfactory for fresliwater fishing and for small and big game hunting, since appropriate habitat exists north as well as south of the population centers. Table 3.29 shows hunting and fishing license sales in the three-parish area of southwestern Louisiana for 1967 through 1975. These sales represent about 12.5% of the State total of resident fishing licenses, 7% of the resident hunting licenses, and 4.4% of the big game licenses. The influx of hunters to the Chenier Plain is shown by the large number of nonresident licenses issued (26% of the State total). Table 3.28 summarizes estimates of participation rates for sport fishing and hunting. The best surveys for Louisiana were the 1974 State Comprehensive Outdoor Recreation Plan (SCORP) Survey (Louisiana State Parks and Recreation Commission 1974) and the Fish and Wildlife Study (U.S. Army Engineers unpub- lished). The latter agrees reasonably well with the 1970 national survey U.S. Fish and Wildlife Service (1972) in estimating that 20 to 27% of the Louisiana popula- tion engages in sport fishing, although the percentage is much lower for urban residents. The percent of li- cense sales to the total population, when adjusted for hunters and fishermen younger than 16 and older than 59 years, coincides with a telephone survey conducted by SCORP. These survey estimates for all categories, of hunters and fishermen are considerably higher than those reported in the Fish and Wildlife Study. The more conservative figures from the latter study were used in this report because the design of the survey and the statistical analysis of the results were consid- ered the best available, even though the survey was conducted in 1968. 47 Table 3.28. Estimated percent of population that engages in sportfishing and hunting according to various studies in the United States and Louisiana. Activity United States Urban Rural West-south central Statewide Louisiana Coastal parishes Calcasieu Cameron &: Vermilion parishes Sportfishing Freshwater SjJtwater 12.3^ 25.5" 27.4" 26° 55^ 30^^ 23' 19.4" Hunting (overall) Small game Big game Waterfowl 13. r 11.3^ 35^ 23'' 21'^ 15.7° *Fish and Wildlife Service 1972 b U.S. Army Corps Engineers unpublished. ''Louisiana State Parks and Recreation Commission 1974. '^Based on Louisiana fishing and hunting license sales (1970); increased by 21% to adjust for hunters and fishermen younger than 16 years, and older than 59 years. Table 3.29. Total fishing and hunting license sales for Calcasieu, Cameron, and Vermilion parishes, 1967 through 1975^. Year Fishing Resident Non- resident Hunting Resident Non- resident 1967-68 1968-69'' 1969-70 1970-71 1971-72 1972-73 1973-74 1974-75 29,502 12,124 34,577 31,040 30,091 29,733 35,231 38,726 492 454 526 458 425 398 576 809 23,535 23,508 24,189 25,652 23,277 23,837 23,020 23,086 2,095 1,741 2,162 2,849 2,882 3,162 2,799 2,792 ^his three-parish area had 187,126 residents 5 years of age or older, State Comprehensive Outdoor Recreation Plan (SCORP) 1974. This represents 5.4% of the State population. The second year of a two-year licensing experiment was dropped at the end of this period. Hunting : Table 3.30 summarizes the man-days of use related to wildlife in the Louisiana coastal zone, from the Fish and Wildlife Study (U.S. Amiy Engineers unpublished) telephone survey conducted in 1968. The table shows that the per capita usage rate in the Chenier Plain was higlier tlian the usage rate for the entire Louisiana coast. The study indicated a relatively high frequency of "nonconsumptive" wild life -oriented recreation (bird watching and recreational boating). The total estimated wildlife-oriented recreational use for the southwestern part of the State was 2.75 man- days/individual/year. 48 Table 3.30. Man-days of hunting and recreation per year for coastal Louisiana. Southwestern Louisiana 26 coastal parishes (Hydrologic units VII-IX) Man-days/yr^ Man-days/man/yr" Man-days/yr*" Man-days/man /yr' X 1,000 X 1,000 Wildlife-oriented recreation'^ 888.5 0.42 202.6 0.42 Hunting Small game 1,083.9 0.51 576.5 1.21 Squirrels 256.3 0.12 129.0 0.27 Rabbits 538.7 0.26 207.9 0.44 Quail and dove 266.7 0.13 220.5 0.46 Other small game 22.2 0.01 19.1 0.03 Big game Deer and turkey 148.9 0.07 67.7 0.14 Waterfowl 764.9 0.36 466.4 0.98 Duck 603.4 0.29 358.7 0.75 Geese 123.6 0.06 101.4 0.21 Other marsh birds 37.9 0.02 1.36 6.3 0.01 Total 2,886.2 1,313.2 2.75 ^Table 25, app. D, Fish and Wildlife Study (U.S. Army Engineers unpublished). 1968 population of 26 Louisiana coastal parishes = 2,104,800. ''Table 42, app. D, Fish and Wildlife Study (U.S. Army Engineers unpublished). Seven southwest parishes and one-half the population of St. Mary Parish = 477,861. Birdwatching, photography, etc. The wildlife-oriented recreational use has an esti- mated value of over $13 million in the Chenier Plain basins (table 3.31). The man-days were calculated by multiplying the population by the man-days/man/yr value for southwestern Louisiana. The dollar values were calculated from values for different kinds of wildlife recreation prepared by the U.S. Water Re- sources Council (1973). The values range from $2 to $9/man-day, which appear to be conservative. The figures for each basin represent the expected use-level based on the resident population and on the adjacent parish (county) populations, and they have no relation to the relative availability of suitable habitat for wild- Ufe within each basin. Therefore, one might expect considerable lateral movement of hunters across basin lines to locate optimum habitats. Thus, the total esti- mate of 2.5 million man-days of hunting/yr for the entire Chenier Plain may have more significance than the figures for individual basins. Sportfishing and SheUfishing: The expected sport- fishing demand amounted to 10.8 million man-days for the entire Louisiana coastal zone and 2.0 million man-days for the southwestern portion of the State (table 3.32). Sportfishing demand was about 4 man- days/man/yr for southwestern Louisiana, compared to an annual demand of 5 man-days/man/yr for the entire State. The saltwater sportfishing demand can be compared to the 305,600 man-days of fishing esti- mated from a recent saltwater creel census in Sabine Lake (Breuer et al. 1978). Ninety-five percent of the fishing parties using Sabine Lake came from Jefferson and Orange counties, which had a 1970 population of 315,943. The estimated 0.96 man-days/man/yr for tliese counties agrees closely with the 1.0 value for southwestern Louisiana (table 3.32). The sportfishing demand in the Chenier Plain basins was calculated by using the sportfishing demand values for southwestern Louisiana. The method was the same as that used to calculate hunting demand. There was an estimated total annual demand of 3.8 milhon man-days for all types of sportfishing (table 3.33). Nearly one -half of this is for fresliwater fishing; most of the rest is for saltwater angling. The total value of this demand is conservatively estimated at about $7.7 million. The combined demand value for fishing and hunting is estimated to be about 6.4 mil- lion man-days and $21 million. 49 e ■a e n u be e •3 •e c Id O U O _s o "3 "' > X "i -o o ^ T O t, 3 •3 - s > X 1; 2- n. 2ro u ■0 n c ii o sis CO CO u H s § o X 4( -B g e c "3 a o BU u 00 CO d d -H O 00 00 oi CO r^ CO ;o CM d '^' 'H rt< csi d ■* in O IN d >n O <£> CO O CO 00 o CO o CO CO CO irj csi CO lO •* CM O CO o 00 ^ CM t^ in ^o in to 00 rt ^ Co' ^ CM '^' <— » CM CO CM ^ in en ^-* CO r-^ 00 CM -rf 00 oi in c^j d CM d d d o in ■* CM in CO CM CM CO r^ '^ CO (^i ^ r- dm cmci CMm CTi 000 oocM inr~ ^O a-, 00 ~^ ^^ cr> ID CM •"* ^ CO CM CO CO 00 CM in 01 00 CO lO CO CO in CM I— 1 00 in CM CO Ol (O y5 in cm" CM ci in 00 ^H ■^ in CM CM CO ^ rt -H CO CM co_ d in CO CO r^ o — . o 00 in CM CO CM 00 -H rt in CTl 00 CO 00 CO ■* CO in 'J- in <*< CM in CM r^ Tf r^ CO CO Tf ■>t (Jl in ai 00 00 CO CM no in 00 r^ f 'f r^ 00 CM cn en r^ r^ r~ •* ^H 01 CM CM CO >n — '-■ f-H CO CM r. 3 u c 0^ c y CJ ^ fe U n tfi > s •ii (/2 o H S :=- « — 3 •S £ O J m J3 E 3 c -3 c c o c '-J «% .2 ^ ■a 3 u O U 1/3 C U 5 S U >- 5| -3 t, c 1^ X c o ■o ^c= . 3 a. d " o c4 -O 50 Table 3.32. Estimated sportfishing demand in the Louisiana coastal zone*. 26 Coastal Parishes'' Man-days/man/yr Man-days per year (x IJOOO) Southwestern Louisiana*- (Hydrologic Units VII, VIII, and IX) Man-days/man/yr Man-days per year (x IPOO) Saltwater sportfishing Freshwater sportfishing Sport shrimping Sport crabbing Sport crayfishing Total 1.92 1.66 0.18 1.07 0.29 5.12 4,045 3,491 373 2,250 610 10,769 1.00 1.90 0.23 0.79 0.26 4.18 479 908 112 378 125 2,002 U.S. Army Corps Engineers unpublished, Lindall et al. 1972. The 1968 population of the 26 Louisiana coastal parishes = 2,104,800. The 1970 population of seven western parishes (Acadia, Calcasieu, Cameron, Iberia, Jefferson Davis, Lafayette, Vermilion, and one half of St. Mary ) = 477,861. Based on 1968 telephone survey. Table 3.33. Demand for and value of sportfishing in the Chenier Plain. Fishing activity, man-days/yr X 1 ,000* Basin Population Saltwater Freshwater Shrimping Crabbing Crayfishing Total Value Vermilion 802^ 0.8 1.5 0.2 0.6 0.2 3.3 6.6 112,547 112.5 213.8 25.9 88.9 29.2 470.3 940.6 Mermentau 9,194 9.1 17.5 2.1 7.3 2.4 38.4 76.8 &: Chenier 90,857 90.9 172.6 20.9 71.8 23.6 379.8 759.6 Calcasieu 9,790 10.0 18.6 2.3 7.7 2.5 41.1 82.2 127,483 127.5 242.2 29.3 100.7 33.1 532.8 1,068.6 Sabine 130,636 130.6 248.2 30.0 103.2 33.9 545.9 1,091.8 337,730 337.8 641.7 77.1 266.8 87.8 1,411.2 2,822.4 East Bay 4,824 4.8 9.2 1.1 3.8 1.3 20.2 40.4 250,000 250.0 475.0 57.5 197.5 65 1,045.0 2,090.0 Total annual demand*^ 648.9 1,297.8 3,839.1 7,678.2 Calculated from the indicated population and the man-days per man per year shown in table 3.32. Calculated at $2 per man-day (U.S. Water Resources Council 1973). The first population number for each basin is for the Chenier Plain boundaries. The second number includes the adjacent urban parishes (counties) to the north. 51 Sportfishing and Hunting Activities that Affect the Environment. The most important ecological ef- fect of sportfishing and hunting is the direct harvest of fish and wildlife (part 3.5.2). Other impacts may be significant locally. Construction of recreation cen- ters, boat launching ramps, picnic grounds, parks, camping spots, and private camps, may cause localized pollution and environmental disruption. The location and identity of such centers in the Chenier Plain are shown in plates lA and IB. The use of lead shot may modify the impact of hunting,but it has not been fully evaluated. Wildlife Refuge Establishment. The factors that lead to the isolation of natural areas for refuges are varied. The concern of wildlife enthusiasts was un- doubtedly one iniDortant factor. In the Chenier Plain 135,559 ha (334,974 a), including the 57,000 ha (140,850 a) Sabine National Wildlife Refuge have been set aside as refuges by Federal, State, and private or- ganizations (table 3.34). The eight refuges comprise over 11% of the area of the Chenier Plain, exclusive of the nearshore Gulf habitat. They are discussed in some detail in part 4. Most of the refuges were estab- lished primarily for waterfowl management but con- trolled access, controlled development, and manage- ment practices make them important refuges for many other species. 3.2.6 COMMERCE, INDUSTRY, AND THE RESIDENT POPULATION (county) data were multiplied by the proportion of that parish's population living within a basin's borders. This assumes that each parish is homogeneous. How- ever, most of the industrial and commercial activity is concentrated just north of the Chenier Plain borders. As a result, the influence of the industrial-commercial sector is probably somewhat exaggerated. Also, em- ployment figures (U.S. Department of Commerce 1975) record only employees covered under the Federal Insurance Compensation Act. Because of the provisions of the act, fishery and agricultural em- ployees are underestimated, and self-employed indivi- duals are not included in the U.S. Department of Commerce figures. Population. The Chenier Plain is predominantly a rural area and with the exception of the Texas portion of the Sabine Basin, the population density is often less than one individuaI/5 ha (12 a). In comparison, the overall Louisiana population density is one person/ 3 ha (7 a) and the density of the adjoining industrial- ized Harris County, Texas, is about 4 persons/ha (3 a). The population of the Chenier Plain changed Uttle from 1960 to 1970 (table 3.35). There has been modest growth, but the urban areas of Calcasieu Parish and Jefferson County have not grown. Bolivar Peninsula in the East Bay Basin is a rural appendage of Galveston County, separated from it by Galveston Bay, so that the Galveston County figures are not representative of East Bay. This section provides a general view of the magni- tude and character of the local economy as a source of activities having an impact on the Chenier Plain ecosystem. The Chenier Plain basin boundaries, as described, do not correspond with political boundaries. Hence, extrapolations have been necessary to estimate economic indices for the basins. To do this, parish Table 3.34. Refuges, parks, and management areas in the Chenier Plain. Refuge Basin Size (ha) Management objectives Preserve and improve habitat Preserve and improve habitat Preserve and improve habitat Habitat improvement for waterfowl; hunting Habitat improvement for waterfowl; hunting Habitat improvement for waterfowl Habitat improvement for waterfowl, preservation of estuarine marshes; recreation Habitat improvement for waterfowl; hunting Paul S. Rainey Wildlife Refuge Louisiana State Wildlife Refuge Rockefeller Wildlife Refuge Sabine National Wildlife Refuge Lacassine National Wildlife Refuge Anahuac National Wildlife Refuge Sea Rim State Park J. D. Murphree Wildlife Manage- ment Area Vermilion 10,522 Vermilion 6,070 Chenier 34,800 Calcasieu and 57,809 Sabine Mermentau 12,856 East Bay 3,981 Sabine 6,117 Sabine 3,404 52 Table 3.35. Population of parishes (counties) over- lapping the Chenier Plain region (U.S. Department Commerce, Bureau of Census 1973). ty) Year Parish (Cour 1960 1970 Change (%) Louisiana Cameron 6,909 8,194 18.6 Calcasieu 145,475 145,415 Jefferson Davis 29,825 29,554 -0.9 Vermilion 38,855 43,071 10.9 Texas Chambers 10,379 12,187 17.4 Galveston 140,364 169,812 20.1 Jefferson 245,659 245,659 -0.4 Orange 60,357 71,170 17.9 Total 677,823 725,062 7.0 Employment. Manufacturing and mining are the major areas of employment in the Chenier Plain re^on (fig. 3-12). The $32 million payroll for the Sabine Basin is indicative of its industrial character. Manu- facturers are the major employers in this basin, pri- marily those engaged in refining and petrochemical- related manufacturing. This is true also in the Calcasieu and East Bay basins although the total payroll is smaller. The large petrochemical complex at Lake Charles, Louisiana, lies outside of the Chenier Plain and will be treated as an outside influence on the re- gion. Oil and gas industries are the major employers in the eastern basins and account for about 40% of the total payroll value. As indicated, the agricultural, fish- ing, and trapping sectors are under-represented in these employment data. Industrial and Urban Activities that Affect the Environment. Major environmental impacts of indus- trial and urban areas are effluent discharges (both domestic and industrial), habitat loss, and surface and groundwater use. In addition, construction activities increase runoff of sediments and nutrients into wet- lands and streams, and this runoff is accelerated by drainage canals constructed in low areas (Gael and Hopkinson 1978). Habitat loss : In the Chenier Plain, the major urban-industrial land occupied 26,137 ha (64,586 a) or 3.5% of the total land area in 1974 (table 3.36). This is an increase of 5 ,446 ha ( 1 3 ,45 7 a), or 26%, since 1952. The urbanized land is concentrated in the west- ern half of the Chenier Plain, primarily in Texas. How- ever, the Calcasieu Basin has shown the most rapid conversion of land to industrial and urban use between 1952 and 1974;most of this urbanization has occurred at the expense of weflands (1,233 ha) (3,047 a) and agriculture (2,901 ha) (7,168 a) (table 3.37). Five hundred forty-six hectares of upland forest habitat were also cleared between 1952 and 1974 for urban use. Urban and industrial discharges : The per capita water and energy requirements and effluent produc- tion from typical urban situations have been sum- marized in a number of studies (table 3.38). Because of the low population density in the Chenier Plain, domestic sewage loading rates within the basin must be low, but the total watershed includes several densely populated areas. In the rural areas, septic tanks or no treatment at all are the rule, and no records of dis- charge rates are available. Table 3.39 contains esti- mates of discharge (stated as phosphorus) for the Chenier Plain basins. Estimates were detennined from discharge data from treatment plants, and industrial point sources (appendix 6.4) and urban runoff. Much of the total load of phosphorus entering the Chenier Plain is from the heavily populated areas of the Sabine Basin and the Lake Charles area just north of the Cal- casieu Basin. Industrial discharges vary greatly and may be much more toxic than domestic sewage. Particularly damaging to the ecosystem are heavy metal bypro- ducts of manufacturing, and synthetic organic toxins that the natural biota can rarely degrade. Plates 5 A and 5B show the location of these discharges within the Chenier Plain. The effects are often localized, e.g., in the Calcasieu ship channel, sediments have accumu- lated high concentrations of certain heavy ipetals. The effects of these discharges are discussed in part 3.5.3. Table 3.36. Area and changes in urban-industrialized land in the Chenier Plain. Increase in Increase Area (1974) Percentage c if total area 1954 to 1974 1952 to 1974 Basin (ha) 199 land area ( 1974) (ha) (%) Vermilion 0.4 87 78 Chenier 401 0.4 152 61 Mermentau 1,595 0.8 52 3 Calcasieu 2,277 2.4 1,428 168 Sabine 19,088 7.8 3,449 22 East Bay 2,577 4.7 278 12 Total 26,137 3.5 5,446 26.3 53 CO o c o 0) a 60^ 40 20 60 40 20 60 40 20 Vermilion Total $242,000 H n n Chenier Tofa/ $584,643 n XHL Calcasieu rofa/ $5,868,600 m m Mermentau Total $3,459,900 K JM. Sabine Total $32,523,700 Ml _E3_ East Bay Tofa/ $3,074,100 :■:■: 3 S: 3 U 0) Q> 0) c o ■o (D (0 3 »t k: o 0) •^. 5 > X 0) c ■D > C > T3 C T3 C (0 ^ <» 5 $ IDBI ■o 0) ^ » $ E 0) Fresh Mars J Impounded ■a 0) T3 C 3 o a p W 3 3 < cc O z CO 03 ^ c«( rt (O K 00 O) o! T- 4^ n cd Xi C •a a 43 •a c CO c o •5b O DC m 3 63 Salinity 29, 1963 Figure 3-16. Average surface salinity (°/oo) contours along the Louisiana coast during (A) high river stage, April 21-29, 1963 and (B) low river stage, December 1 1-16, 1963 (Murray 1976). 64 Figure 3-17. Tidal phases at several locations along the Louisiana and east Texas coasts. 65 water regime displays two highs, in spring and in late fall (fig. 3-18). The spring high may be associated with river stages and abundant local rainfall. The fall peak seems to be a result of the predominant southerly summer winds that gradually build up the water level along the northern Gulf coast. This seasonal cycle means that wetland inundation does not occur equally throughout the year. Table 3.46. Mean coastal tidal fluctuations for Chenier Plain basins. Tidal fluctuations Mean Standard deviation Basin (cm) (cm) Vermilion 3 7.5 ±15 Mermentau* 0.0 0.0 Chenier 24-42 ±19 Calcasieu 75 ±41 Sabine 40 ±47 East Bay 30 Has no tide. Figure 3-18. Monthly water-level fluctuations for 1963-66, and montlily mean and stan- dard deviation, 1963-74, in the Calcasieu Basin (U.S. Army Corps of Engineers). The importance of tides varies widely in the dif- ferent Chenier Plain basins. Vermilion and East Bay are open estuarine systems with significant tidal action. Although the pass to the Gulf in the Chenier Basin is small, the basin lies parallel to the coast, and the wet- lands that are not impounded are strongly influenced by tidal action. Both the Calcasieu and Sabine basins were fonnerly much fresher bodies of water than they are now, but they currently sustain significant tidal action because of the deep ship channels con- necting the Gulf to inland waters. The Sabine ship channel has resulted in strong tides and salt intrusion directly into tlie northern end of Sabine Lake (part 3.6.6). In contrast, the Mermentau Basin is effectively cut off from any tidal action by control structures that impound the entire basin (part 3.6.3). For the past 40 years, the water level has been in- creasing along the northern Gulf coast (Hicks and Crosby 1974). Tide gage records for most of the United States show the same phenomenon because of a combination of sea level rise and land subsidence. In the past 10 years, the rate of sea level rise seems to have accelerated. Rates on the Gulf coast are among the highest in the nation (Hicks and Crosby 1974). On the Chenier Plain, tide gages in all basins agree qualitatively. The average rate of apparent sea level rise (i.e., change in gage readings) is about 1 .7 cm (0.7 in)/yr (table 3.47). Therefore, inter tidal zone wetlands must aggrade at a rate equal to their subsidence; changes in the rate of net subsidence (due to all causes) signal major shifts in marsh formation or erosion. Table 3.47. Mean annual rise in water level by basin. ^ Basin Annual rise (cm/year) Vermilion Mermentau Chenier Calcasieu Sabine East Bay Average 0.94 2.13 2.10 2.00 No record 1.50 1.73 Mean of one to five gages per basin. See part 3.6. 3.3.4 SUBUNITS INFLUENCED BY FRESHWATER Both local rainfall and river discharge into the Chenier Plain significantly infiuence the hydrology of the basins. The region influenced by river runoff de- pends on the discharge volume of the river. If the volume of discharge is small in comparison to the tidal prism, then the river influence is secondary to tides. This is the case for most shallow embayments along the southeastern Atlantic coast and the northern Gulf of Mexico. However, the ridges that give the Chenier Plain its name are effective barriers to the Gulf, and 66 tidal action in the estuaries is generally restricted. River runoff varies widely from year to year, and in liigh discharge periods the fresh water of the estuary expands but contracts again as discharge slows. Upstream discharge. The upstream watersheds of all the rivers are less than 24,000 km^ (9,266 mi^). Only the Sabine watershed drains an area greater than 10,000 km^ (3,861 mi^). Rain surplus is similar throughout these watersheds, so discharge is propor- tional to watershed area (fig. 3-19). The Chenier Plain watersheds are small in comparison to that of the Mis- sissippi River, which drains about 5 million km (1.9 million mi^ ) of upland surface. Since these watersheds are small, their seasonal discharge patterns conform closely to the local rainfall pattern, with only small lag times. A typical seasonal discharge pattern for Chenier Plain rivers is shown in figure 3-20. Here the surface water input into the Calcasieu Basin at Kinder, Louisiana, corresponds closely to the rain surplus in the upstream watershed. The upstream discharge is important as a source of sediments and nutrients and as a moderator of salinity. Many organisms and processes are keyed to the annual cycle of fresh water input. 300 O 2.0^ o J? to A, "» River Flow »' » 1.0 * 4 1 1 1 1 1 1 1 1 1 1 1 1 JFMAMJJ ASOND Month Figure 3-20. Mean monthly rain surplus or deficit estimated from rainfall, temperature, and evapotranspiration (Borengasser 1977) for the Upper Calcasieu River drainage basin, and the surface water flow into the Calcasieu River at Kinder, Louisiana (U.S. Geological Survey 1977). Upstream inflow to coastal basins has, historically, been modified by cultural activities. Modifications range from indirect activities, such as clearing of for- ests, which dramatically increases runoff (Likens and Bomiann 1974), to control structures and dams that directly modify flows. Within the Chenier Plain, the watershed most seriously affected by discharge modi- fication is the Sabine. The creation of the Toledo Bend resevoir on the Sabine River (which carries most of the water discharge into Sabine Lake) has resulted in a large reduction in sediment load and total discharge, and in a change of the seasonal timing of discharge. This, in tum, has influenced salinity and biological changes in the estuary (part 3.6.6). 67 Renewal time. It is instructive to evaluate how much each basin depends on runoff to supply fresh- water and to estimate roughly how often the waters in each basin are replaced or renewed. Renewal time is an important concept in water quality management, and has been modified by management practices in the Chenier Plain basins (table 3.48). First, the annual rain surplus decreases from east to west across the Chenier Plain, from 60 cm (23.6 in) in the Vermilion Basin to only 20 cm (7.9 in) in the East Bay Basin. This surplus multiplied by the surface area of each basin gives the total volume of freshwater generated within that basin and available for runoff or ground- water recharge. The large surplus from local runoff explains why the Chenier Plain region is so fresh in spite of its proximity to the coast. The volume of water entering each basin from upstream is shown for comparison. The freshwater budgets for the Calcasieu and Sabine basins are dominated by riverine input; the other basins depend primarily on local rainfall. Estimates of the renewal time of water for each basin listed in table 3.48 are based on the assumption that the freshwater surplus is the sole agent of water re- newal. Since the tidal prism is a significant percentage of the mean water depth of these shallow estuaries, the renewal time would be different than indicated in table 3.48. However, the Gulf tidal waters tend to move in on flood tides and then recede again on ebb tides, with mixing only where they interface with estuarine waters, so that the net exchange is probably quite small (Happ et al. 1977). Wind-generated cur- rents can also increase renewal time as discussed in part 3.3.5. In table 3.48, another calculation is made for the large inland lakes only, with the assumption that all runoff in a basin empties into these lakes. Calculations for the Vermilion and East Bay basins are misleading because they are parts of larger basin systems outside the Chenier Plain boundaries. How- ever, the relatively long renewal time for East Bay is probably correct in a qualitative sense, and the sys- tem as a whole would be expected to have more ma- rine influence than other basins. Vermilion Basin is probably fresher than indicated by the renewal time because the Atchafalaya River to the east depresses salinity throughout the Atchafalaya/Vermilion Bay systems. The rapid renewal times for Calcasieu and Sabine basins result from the large riverine input. This rapid flushing of basin waters suggests a capacity to sustain higher nutrient loadings than poorly flushed systems. An increase in the depth and width of tidal inlets should result in a faster renewal time. Small canals in the interior basin act the same way. They offer less resistance to water than natural, shallow, sinuous channels allowing water to move in and out more rap- idly. They also change circulation patterns and de- crease sheetflow across wetlands. Excessive diversion of water from upstream for agriculture and industry increases the renewal time (days) of the basin. Since the renewal time is related to the total nutrient load a body of water can assimilate, its modification can in- fluence the eutrophic state of the water body. 3.3.5 SUBUNITS DOMINATED BY WIND-DRIVEN CURRENTS The large, shallow lakes of the Chenier Plain are affected by tides, but wind is often the dominant mechanism controlling currents, water height, and flushing rates. Dominant winds along the coast are either from a southerly direction (usually in sununer) or from the north (in winter), as previously indicated in figure 2-6. In large lakes, especially ones which are oriented north to south, such as Calcasieu and Sabine, these winds, acting over a long fetch, generate currents that can reach up to 3% of the wind velocity (Murray 1975). The effect of wind on water levels is often dra- matic, and waterflows generated by the buildup of a hydrauUc pressure gradient across small inlets and narrow channels connecting lakes can be large. The initial response of the water surface to a wind change is rather rapid, usually occurring in less than 24 hr. Sustained winds blowing across a water surface tend to push the water in the direction of the wind, piling it up against the shore, until an equilibrium is reached between the wind stress in one direction and the op- posing water slope created by the water buildup. This wind setup reaches a maximum value rather rapidly, depending on windspeed and the open water fetch (table 3.49). When tide is phased with winds, their combined action can change water levels several meters in a matter of hours. After the initial, predictable and rapid response, sustained winds have unpredictable ef- fects (Wax 1977). For instance, the response to dif- ferent weather types is shown at Hackberry about halfway up the western shore of Calcasieu Lake near the ship channel (fig. 3-21). Synoptic Weather Type 1 represents initiation of a typical cold front with northerly winds. It always results in a lowering of the water level, whether surplus water is available or not. However, Weather Type 3, typically weather following a cold front and representing northerly air flow sus- tained over several days, showed variable effects on water level. To explain the unpredictable results in Calcasieu Lake , Wax (1977) suggests that river runoff into the upper basin generated by the same weather conditions might arrive at the lake several days after cold front passage, or a long-term setup could occur as winds pile water at the outlet at the southern end of the lake causing a bottleneck in the flow and raising water levels at the Hackberry gage. As shown in figure 3-2 1 , Weather Types 1 , 2, and 3 associated with northerly winds all tend to depress water levels, whereas easterly winds (Types 4 and 5) and south- southeastedy winds (Types 6 and 7) tend to increase water levels by forcing water into the in- shore estuaries against the slight surface slope. These weather events influence flushing times, turbidity, and wefland flooding. When turbulence and currents increase and water levels are abruptly changed by combinations of tide and winds, mixing of tidal and estuarine waters is increased. This mixing and the magnified flows through tidal inlets significantly in- crease the rate of flushing of the estuary. In shallow bays and lakes, wind-driven waters stir up bottom sediments and increase turbidity. 68 « .a >- .a u B '^-» E ^ (S i« V ^ b V t« G a u 3 •a e n 3 a c o H CO* H s .E OS « ii X -J fl o X HVi 3 O a rt D !« rt O "-.Sox ^H eo 00 r^ ^ o in <£> 00 in m CM CM i-H q l-H r-. q t- CM <£> - 3 C w :<^ f-^ d in d on d s S to in ^ ■* CM w c .a .9 e X t^ e ti CO t^ w ^ Os '"' o jn ii "O >. •ti D. o w 5 («- JZ t V) o 3 1- c rt 3 >s rt S: O S J3 ■& c -o _0 iL» « U a. o V rt u — 3 C vi u D c ^* 6 c i_ o a c :3 t*- Xi 1- 2 o ft; c rt Q H ■o VM ^ W rt u M c "^ (A "rt c 3 cr u u o c 73 ■g 73 C ^ rt u 5 £ tM c o c u i- 3 t a. E* c c o O '^ >. « "O rt ■g X -H O = V i = 2 1^ C rt 03 o o E 4-1 rt u o ^ J^ x: rt x: !A u t-i o_ b O •D V 69 Table 3.49. Minimum fetch and duration required for full development of set-up associated with various wind speeds. Wind speed Fetch Duration (kn) (km) (hr) 10 18.5 2.4 20 140 10 30 520 23 ''Wax 1977, modified from Bascom 1964. SYNOPTIC We*TMEB TYPES -e;. ^/ /\ no wslvr aurplut [1 1 wa1«r turplul Figure 3-21. Relationship between water levels and different weather types for Calcasieu Lake near Hackberry, Louisiana (Wax 1977); text describes synoptic weather types. 3.3.6 SUBUNITS OF EXCHANGE BETWEEN WATER BODIES AND WETLANDS Wetlands are built by the deposition of sediments carried by flooding waters. The growth of vegetation, the use of wetlands by aquatic organisms, the export and import of organic matter, and the cycling of nu- trients are dependent on periodic flooding. It is dif- ficult, therefore, to overemphasize the importance of the exchange of water between wetlands and adjacent water bodies. Wetland processes tend to stabilize marsh eleva- tion somewhere around mean sea level (MSL) (Sasser 1977). If elevations become too low, the vegetation is flooded for longer periods than it can survive and the marsh erodes. At the other extreme, as wetlands ag- grade they are flooded less and less often until they no longer receive the sediment supply necessary for continued growth. Sasser (1977) found Uttle differ- ence in elevation within different marsh vegetation types in eastern Louisiana. There, marshes varied in elevation between about -9 cm and +9 cm (± 3.5 in) relative to local MSL. Saline marshes receive regular flooding from tidal waters. As tides attenuate upstream meteorological forces affecting water levels become more dominant. If marsh elevation is assumed to be at local MHW, at Calcasieu Pass water exceeds this elevation 243 times per year and remains over the marsh for an average of 6.9 h/inundation. Upstream at Hackberry where freshwater runoff primarily controls water levels, the same elevation (e.g., local MHW) was exceeded only 200 times but the mean inundation was of longer duration. In Barataria Bay, Louisiana, where gage sta- tions span the distance from the Gulf pass at Bayou Rigaud to the intermediate marshes upstream at Bara- taria, the same relationship holds but is even more dramatic. The frequency of inundation decreases up- stream but the duration, both in terms of total hours per year and hours per event, increases (table 3.50). Table 3.50. Duration of water above local MWH, frequency of inundation, and mean inundation duration in 1971 in the Calcasieu Basin and in Barataria Bay (data from U.S. Army Corps of Engineers). Hydrologic Time above Frequency Mean duration unit MHW (inunda- of inundations (% of yr) tions/yr) (hrj^ Calcasieu Basin Cameron Pass 19.2 243 6.9 Hackberry 29.1 200 12.7 Barataria Bay Bayou Rigaud 12.1 128 8.3 Lafitte 23.7 79 26.3 Barataria 41.3 75 48.2 The seasonal inundation regime of the marshes near Hackberry in Calcasieu Basin, which is fairly typ- ical for the entire Chenier Plain, shows that marshes are inundated most often during the fall and winter months (fig. 3-22). This does not correspond with the months of highest mean water, May through Septem- ber (fig. 3-18). However, it does correspond with the months when tlie variation in water level is high, as indicated by the standard deviation curve. During the summer, water levels are high but are below marsh elevation; they are less variable than water levels dur- ing winter montlis so they usually do not exceed marsh elevation. In the early winter and to a lesser degree in the spring, althougli the mean water level is lower, the range of fluctuation is much greater and marshes are flooded more often. The increased variability in win- ter is probably associated with storms and illustrates the importance of rain and wind for marsh flooding. 70 g400 z i 300 X 2 < I 200 100- M J J Month Figure 3-22. The hours per month that the water levels are above mean high water in marshes at Hackberry, Louisiana (U.S. Army Corps of Engineers). The pattern of inundation is important for an- other reason (fig. 3-22). During the months of June, July, and August, salinities are highest in the estuaries because of a combination of high sea stage (fig. 3-18) and low rain surplus (fig. 3-20). During this period, marshes are infrequently flooded with water more sa- line than normal. Wlien such floods occur during a pe- riod without rain and with high evapotranspiration rates, salts accumulate in marsh sediments. This may have serous consequences in fresh, intermediate, brackish, and salt marshes. For instance, there is some indication that periodic salt accumulation has killed stands of saltmeadow cordgrass in brackish marshes along Calcasieu Lake. The salt accumulation is a re- sult of the overall salinity increase accompanying dredging of the Calcasieu Ship Channel (J. Valentine, Pers. Comm., U.S. Fish andWildlife Service, Lafayette, La.). In the Chenier Plain, the amount of wetland that is freely flooded by estuarine waters has been dras- tically reduced by human activities. Much of the wet- land (162,000 ha, 400,311 a) is impounded, e.g., over one-half of the wetlands in the Chenier Basin are behind some type of levee. In addition, many marshes are semi-impounded by canal spoU banks and other levees that restrict or redirect water flows. The entire Memientau Basin can be considered an impoundment in which water levels are controUed by structures in all the major channels draining the basin. Only the Calcasieu and Sabine basins have large areas of unim- pounded wetlands. In both of these basins, hydrologic modifications have changed water flow and saUnity patterns, which have resulted in high marsh loss rates (part 3.4). 3.3.7 SUBUNITS WITH LITTLE OR NO WATER EXCHANGE-UPLANDS AND IMPOUND- MENTS Uplands are important to the hydrologic processes of a basin as a source of local runoff water and as na- tural barriers to water flow. Since much of the upland area in the Chenier Plain is impounded for rice, the quantity of free runoff is probably not as important as the quality of this water since it carries sUt, nu- trients, and toxic chemicals into the estuary . The drain- ing of rice fields is controOed, so runoff from them does not correspond with heavy rainfalls. Impounded wetlands normally have very Utile exchange with sur- rounding waters, although undoubtedly there is seep- age through levees, and overflows during high water conditions. Water-level management practices also re- sult in some water exchange. However, in terms of the estuarine system, these impoundments are effec- tively cut off and no longer contribute to the normal hydrology of the basin. Also, sheet flow across wet- lands is disrupted by impoundments, and continuous canals associated with leveee construction act as con- duits that speed drainage and allow water to bypass marshes altogether. 3.3.8 HUMAN IMPACTS ON THE HYDROLOGIC REGIME Man has modified the hydrologic regime of the Chenier Plain basins to such an extent that there are now no basins on the plain untouched by human in- tervention. These modifications can be classed as those that affect (1) the upstream water flow into the basins, (2) the circulation within the basin, or (3) the near- shore Gulf circulation (table 3.51). The direct effects can be measured in terms of a number of attributes of the hydrologic regime: freshwater supply, salinity, sediment input, sediment deposition and erosion, water levels, overland flow, and circulation. Table 3.51 indicates the sections of this report that discuss those effects. The primary hydrologic changes give rise to a series of secondary effects. The concern at the basin level is primarily for the secondary effects to habitat type, area, and interactions. However, the functional characteristics and the biota of habitats also respond to the changes (part 3.4.3) and are discussed in parts 4.0 and 5.0. The quantitative evaluation of the effects of modi- fication in the hydrologic regime of Chenier Plain basins is severly hampered by the absence of good hydrodynamic models. Good models should be a pri- ority item for management because water flows are the key to the productivity of the Chenier Plain. Ex- isting models have demonstrated their usefulness. Tracor, Inc. (1971) modeled water quahty parameters in a two-dimensional model of Galvestion Bay that in- cluded East Bay. The U.S. Army Corps Engineers (1950) predicted saltwater intrusion from a model of the Calcasieu River and connecting waterways. More comprehensive hydrodynamic models have been de- veloped for estuarine areas (Lauff 1967), but they have not been applied to the Chenier Plain basins nor have they been apphed in any systematic way to pre- dict the hydrological modifications associated with canals in general. However, certain large-scale water 71 modifications lend themselves to evaluation. In the Chenier Plain, the management of water in the entire Mermentau Basin, the navigation channel in the Cal- casieu Basin, the upstream reservoir and major ship channel in the Sabine Basin, and the Gulf Intracoastal Waterway (GIWW) are examples. All except the GIWW example are discussed in part 3.6. The GIWW runs from east to west across all of the basins except the Chenier Basin. In spite of its length and importance, there appears to be no comprehensive quantitative study of the hydrologic impact of the GIWW. It is known to facOitate the flow of water laterally across basin boundaries; an average flow of 110 m^/sec (3,885 ft^/sec) occurs westward from the Sabine Basin to the East Bay Basin. The quality of this water de- pends on its proximity to channels interconnecting with the Gulf; the GIWW can carry saline waters into formerly freshwater areas. In addition to facilitating east to west water flow, spoil banks of the GIWW are significant barriers to overland sheet flow and may also disrupt local animal movement patterns. North and south portions of the basins are, in effect, hy- drologically cut off from each other by the GIWW. As a result, sahnity and vegetation gradients across the GIWW can be much sharper than elsewhere in the basins. The GIWW and other major pubhc works are superimposed on a history of many smaller activities that have modified hydrology during the past 100 years or more. Their cumulative impact has been ex- tremely difficult to evaluate because the effects have occurred over a long period of time. There is at least minimal infomiation on freshwater flows from up- stream gaging stations as well as some data on saUnity. However, data on sediment inputs are extremely scarce. Net sediment deposition and erosion rates can be deduced from maps and aerial imagery. However, without a large major modehng effort, the ability to detect and/or predict modifications of water levels, circulation patterns, and wetland flooding regimes is limited, and only large-scale effects can be documented with any confidence. The hydrologic effects of canals and their associ- ated spoil banks are difficult to document quantita- tively. Canals are a major measureable feature of hu- man occupancy of the Chenier Plain, and there are 8,714 km (5,415 mi) of canals of various types (table 3.52). Plates 5 A and 5B display the distribution of these canals. About one-third of the total are agricul- tural drainage canals; additional canals were con- structed for other purposes and only incidentally Table 3.5 1. Flow model of primary' and secondary effects of cultural modifications of the hydrologic regime on the Chenier Plain ecosystem. Natural hvHrolofHr Cultural Parameters Discussion regime modification Primarily 'effected and examples -* Upstream water inflow Nearshore Gulf circulation Basin circulation water and wetlands Land use changes Control structures Freshwater supply Salinity Sediment input Sediment deposition/erosion Water levels Overland flow Circulation Part 3.3.4; Sabine 3.6.6 Part 3.3.3; Calcasieu 3.6.5 Part 2.2; Sabine 3.6.6 Part 2.2; 3.3.6: 3.4.3 Calcasieu 3.6.5 Part 3.3.8; Calcasieu 3.6.5 Part 3.3.6; Chenier 3.6.4 Part 3.3.8; Calcasieu 3.6.5 ^ Groins Jenies Canals spoil banks * ^ levees Secondary effects on I habitat type and area Part 3.4.3 Ueposition/erosion/subsidcncc Salinity shifts Impoundments Spoil areas Drained areas Habitat interaction-interface effects Eutrophication (part 3.5.3) Secondary effects on habitat function Part 4.0 Community structure Productivity Community distribution Flux of organic materials Flux of inorganic nutrients Secondary effects on biota Part 5.0 Migrations-routes and timing Salinity tolerance Food availability Substrate suitability Production Access 72 o H s '3 e CM in H >, GQ o •* a 00 -H Id 00 Cji to be r-^ 00 o M z B o lf> „M Oi r^ cd CO to rt "^. 9 .« ^ "*' s oo" ID '5 CM o H lO r^ Tt" ^ a '^ O CM O oi lo in 00 CM o t^ •* CM o r^ CM ^ ■*' ■* •* a> ^ r^ CO lO 00 CTl lO .- q 00 >n c^i CM •* !^ CO u 3 ■w r^ rt C CO a; oi r^' Nf 00 — ' Ol s 00 CO CM CO C O ID VO oo' 00 —I in CO in ID 1— ( co' CO in CM CM 00 in rt CM oo' oi 00 r^ CO 00 CM r- " ^ s bo 2 •> -5 a E ■^ [^ '^ .^ ^ ^ ^ in u in q o o 3 3 o in CM O 2 o CM Ol < ^^ CT) in -^ O] O] "rt CM 00 CO 4-> o (D d d f— 1 •^ H CM in CM « a cd k. < 03 00 in 00 t^ in 00 CM CO d CM o CM in in q ^. id' d CM in CM j^ o o -; o '^'2 CM 00 I^ 00 q O q q ■* CM ID d o CO CO t-H in lo CM 00 r^ in eo 00 in r* co' d CO 2 ■»■ CO eo •* CM CO Ol q d CO tD I^ CM to in 1 °] eo q eo' ■*' IT) CM o c^i CO o 00 CO in o ID M 00 00 C r- y O a 2 -S. !: w »J TS o M ^ g. bo n E c 3 fi. 3 E J3 '^ VO 5 J ■5 < H D. O a. H V 73 modify flows. The navigation and oil field access canals together account for over one-half of the total. These were built to provide the most direct and/or cheapest route from one point to another and were constructed without regard to hydrologic effects. There is httle documentation on the hydrologic effects of these canals the relationship between the hydrologic altera- tions and wetland loss and salinity changes in the Chenier Plain are not clear. The complexity of the ecosystem has made it difficult to draw a causal con- nection. A study is needed similar to the modeling ef- fort in the upper reaches of Barataria Bay (Light 1976). Light's model suggested that dredged canals in the basin have increased peak discharge rates by nearly 100%; consequently, runoff occurs more rapidly than it would normally, and low-water stages have been lowered about 15 cm (6 in). These changes result in a higher suspended load capacity and more wetland in- undations of shorter duration. At the basin level correlations between habitat modifications (such as erosion) and human activities (such as canal density) have been made. Although the approach does not concern itself with the mechanisms of the response-that is, the way the hydrologic regime is modified and in turn modifies habitats— it has pro- duced useful insights that are discussed in part 3.4.6. A correlation has recently been drawn between canal density and eutrophication. Bedient and Gate- wood (1976) showed that in Florida, as agricultural drainage canal density increased, phosphorus concen- trations in receiving waters also increased. Gael and Hopkinson (1978) reported a similar phenomenon in the Barataria Basin, southeastern Louisiana, for oil field access canals (fig. 3-23). They found that the eutrophic state indices (high index infers a dangerous eutrophic state) for various areas in the basin (as mea- sured by an index of four water quality parameters— Cumulaliv* Orkinsg* Ocntity m/fc Figure 3-23. The relationship of the trophic state index of water to drainage density in tJie upper part of Barataria Basin, Loui- siana. The regression Hne accounts for 59% of the variation among points and is highly significant statistically (Gael and Hopkinson 1978). chlorophyll a, total nitrogen, turbidity, and total phosphorus) were directly proportional to canal den- sity. Canals speed the runoff of sediment- and nutrient- rich agricultural water, and water from cleared forests and urban lands. Instead of fiowing slowly over wet- lands, where much of the sediment and nutrient load is captured, this water flows directly through the canals into downstream lakes and bays where the nutrients stimulate the plankton growth that results from in- creased eutrophication. 3.4 HABITATS AND LAND-MODIFYING PROCESSES 3.4.1 INTRODUCTION Except for the major commercial and sports spe- cies, relatively little is known about the standing stock, life history, and ecological importance of the many species inhabiting the Chenier Plain. Normal year to year population fluctuations are wide, and a basin- level inventory at any one time (if it were possible) would yield litfle infomiation about the factors that control population size. Populations of individual species result from the interaction of many factors. A broad evaluation of living resources requires the use of describable units; the habitat is used for that purpose in this report. Re- gardless of what is not known about living organisms, it is known that they require a place to live-a habitat. (Part 4.1 considers further development of the con- cept.) Certain attributes of habitats make them useful indices of living resources. First, they are objectively defined landscape units whose areal extent can be de- temiined. Second, if the ecology of individual species is determined for small, representative habitat areas, the results can be extrapolated to similar habitats else- where. Third, tlie habitat as a unit contains an entire spectrum of species, many virtually unknown yet all functional parts of the habitat. Since our understand- ing of these non-resource species (Ehrenfeld 1976) and of their importance to ecosystems is fragmented, emphasis should be on interactions between species and their habitats. Finally, since a habitat is an irre- ducible requirement of a species, changes in extent of habitats can be expected to reflect long-term popula- tion shifts for species of interest. The habitat acts as an integrator of information about individual species. The habitats and their location in a basin result from the interaction of geomorphic, cUmatic, hydro- logic, and biotic processes on the geologic template of the Chenier Plain. Habitats are dynamic, and the interactions among habitats change constantly under the influence of these forces. The physical processes have been described in parts 2.0 and 3.3; biotic effects are dealt with in part 4.0. Documentation of the rates of change and processes responsible for major changes are provided in tlie following section. This section does not address the internal dynamics of these habi- tats (for instance, changes in productivity of existing habitats; part 4.0 deals with that topic). 74 3.4.2 APPROACH The Chenier Plain region was divided into 14 habitats as defined in table 3.53. The habitat defini- tions are based on a combination of natural charac- teristics and land uses that are not always mutually exclusive. Overlap of natural and cultural processes occurs in every habitat. Ten of the habitats-the two aquatic habitats, the five natural wetlands habitats, and three upland habitats-are landscape units which function naturally. Three other "habitats" are clearly cuhurally modified. In these areas natural processes have been dramatically changed by cultural needs. The remaining habitat, impounded marsh, is rather diverse and contains areas where natural processes predominate as well as other areas where agricultural processes exert control. Impounded marsh is recog- nized by straight spoil bank or levee boundaries that isolate the impoundment from surrounding wetlands and water bodies. Controls on these levees range from "flap gates" which prevent the inflow of surface water but allow excess rainwater to run off, to im- poundments that are routinely drained by pumping and are used for cattle grazing. In this study these drained impoundments are distinguished from pasture habitat by the fact that they are dominated by native vegetation. These habitats were idenfified on the most recent (1974) U.S. Geological Survey 1:24,000 scale ortho- photoquads or topographic maps. Wetlands were de- lineated by updating the marsh-type map of Chabreck et al. (1968), by infonnation from the Texas Bureau of Economic Geology (Fisher et al. 1972), and photos from low altitude overflights supplemented with lim- ited ground reconnaissance. Black and white aerial coverage was used to map habitat changes over the period 1952 to 1974. This coverage did not extend to the East Bay area, for which 1954 maps were used. Present habitat area was determined using a point converting (grid sampUng) method developed by Gagliano and van Beek (1970). Canal lengths were digitized, and area was derived from average widths for different types (app. 6.4). 3.4.3 PRESENT HABITAT COMPOSITION AND DISTRIBUTION The areal extent of habitats in the Chenier Plain in 1974 is listed in table 3.54, while the distribution of habitats within individual basins and habitat area changes since 1952 are provided in appendix 6.4. By eliminating the nearshore Gulf habitat, the reader is provided with a better perspective of the relative abundance of habitats landward of the shoreline. The distribution of the five major habitat groups is shown on Plates 3A and 3B. The relative size of each habitat type does not necessarily correlate with its actual importance. The urban habitat occupies only 2.8% of the land area, but its influence extends to every other habitat of the Chenier Plain. The generalized distribution of habitats in a Chenier Plain basin, in relation to various hydrologic subunits, is shown in figure 3-15. The agricultural habitats (pasture and rice field) are lumped together in tliis schematic because of their close association with one another. These habitats dominate the upper part of a basin on the Pleistocene surface. Pasture and a limited amount of land used for truck crops are also found on the cheniers. The swamp forest habitat is typically found on river floodplains beyond "normal" tidal influence. This habitat is present in the Calcasieu, Mermentau, Sabine, and Vermilion basins. The East Bay and Chenier basins have no swamps because brackish tidal waters influence their wetland areas. In addition, since the East Bay Basin does not contain a major river sys- tem, there is no major floodplain for swamp forest to develop. Although the total area of swamp forest in the Chenier Plain is small, more extensive areas of this habitat type can be found on floodplains upstream from the study area. This is particularly true of the Calcasieu and Sabine floodplains. Historically, upland forests have not been exten- sive in the Chenier Plain (Fisk 1944) but much of this habitat has been converted to agricultural lands. Only a few isolated stands of upland forest now exist in the northern portions of the basins. The ridge habitat can be divided into two major types, natural and man-made. Natural ridges in the form of cheniers are concentrated near the coast and generally decrease in area as one moves inland. Pleisto- cene islands are topographic high areas surrounded by marsh. They are located close to the marsh-Pleistocene boundary. Natural levees of sufficient elevation to be classified as ridges are relatively rare in the Chenier Plain. The upper parts of the Calcasieu, Mermentau, Sabine, and Vermilion rivers contain small levees that support vegetation distinct from the surrounding swamp forest. Remnant levees of older river courses and shorelines appear occasionally in the Chenier Plain. Man-made ridges, largely in the form of spoil banks, are found randomly throughout the Chenier Plain. Because spoil banks are associated with canals, their distribution is reflected by that for canals (Plates 5 A and 5B). Spoil banks occupy 2% of the total area of the Chenier Plain, and this area is greater than that of the beach, swamp forest, upland forest, or salt marsh habitats. Perhaps more significant is the fact that spoil banks make up almost one-half of the total ridge habitat. Hydrologically, however, these man- made ridges function differently than natural ridges, because their orientation is random wdth respect to historic circulation patterns. Most of the urban habitat is found on higher ele- vations landward of the fresh marsh zone. However, many small communities are located closer to the coast, on ridges and along major waterways (plates lAand IB). The salt marsh habitat is generally found as a nar- row zone between the beach and the first major land- ward ridge. At the site of major passes, salt marsh may extend inland and fringe the waterA'ays. 75 Table 3.53. Definitions of the habitats of the Chenier Plain. Habitat types Aquatic 1. Nearshore Gulf — all waters between the coastline and the 9 m (30 ft) depth contour in the Gulf of Mexico. Intermittently exposed mudflats are considered part of this habitat. 2. Inland open water — all inland lakes, rivers, bayous and canals, including intermittently exposed mudflats. Emergent wetland 3. Salt marsh — saline intertidal marshes dominated by smooth cordgrass^, with saltgrass and blackrush common. 4. Brackish marsh — intertidal marshes and associated small ponds dominated by saltmeadow cordgrass and saltgrass; salinities generally less than 10 °/00. 5. Intermediate marsh — marshes and associated small ponds, periodically flooded with nearly fresh water, but occasionally by brackish water. Dominated by saltgrass, buUtongue, and seashore paspalum. 6. Fresh marsh — marshes flooded by fresh water, and with a diverse flora dominated by maidencane, bulltongue, and alligatorweed. 7. Swamp forest ~ forested freshwater wetlands with diverse flora dominated by baldcypress and tupelo. 8. Impounded marsh — marshes surrounded by dikes, spoil banks, or natural levees that modify normal flooding. These exist in saline to fresh areas. They may be permanently flooded or pumped dry, but all are dominated by native emergent wetland vegetation (as opposed to impounded agricultural land). Upland 9. Ridge (cheniers, levees, spoil banks. Pleistocene islands) — landforms elevated above normal flood levels. Linear features within the wetlands except for Pleistocene islands. Usually forested except for recent spoil banks. 10. Beach — narrow strip of land along the Gulf, composed of fine sand and shell fragments. Sparsely vegetated. 1 1. Upland forest — areas of bottomland hardwood and pine forest on the upland Pleistocene terrace. Agricultural 12. Rice field — cropland planted in rice or other crops, whether leveed or not. Often rotated with pasture. 13. Pasture — land improved for grazing by planting of improved grasses and by fertilization. Often rotated with rice field. Urban 14. Urban - land areas developed for residential and industrial use. A land use category, but not described as a habitat for native fauna. Scientific names of plants listed in Table 4.27. 76 Table 3.54. The area of Chenier Plain habiuts in 1974. Percent of Area Percent of inland Habitat (ha) total area* Aquatic Nearshore Gulf 371,257 28.2 0.0 Inland open water 200,844 15.2 21.2 Wetlands Salt marsh 17,155 1.3 1.8 Brackish marsh 100,855 7.7 10.6 Intermediate marsh 84,843 6.4 9.0 Fresh marsh 116,331 8.8 12.3 Swamp forest 6,538 0.5 0.7 Impounded marsh 161,781 12.3 17.1 Uplands Ridge (cheniers, levees. spoil banks) 59,761 4.5 6.3 Beach 6,164 0.5 0.6 Upland forest 15,864 1.2 1.7 Agriculture Rice field 60,298 4.6 6.4 Pasture 90,125 6.8 9.5 Urban 26,137 2.0 2.8 Inland area excludes the Nearshore Gulf Habitat. Fresh, intermediate, and brackish marsh habitats show similar distribution patterns. These marshes tend to run parallel with the main avenue of water exchange, almost perpendicular to the coast in zones of decreas- ing salinity (fig. 3-15). As one moves along the coast away from tlie tidal passes, the marsh zones tend to form bands which are parallel with the shoreline. Col- lectively, these marsh types represent nearly one-third of the total area landward of the nearshore Gulf habi- tat. In terms of area, impounded marsh represents the third largest habitat. It includes aO leveed and flooded wetlands, regardless of salinity, within which water level is controlled to some extent. Impounded marsh tends to become increasingly fresh, since rain- fall exceeds evapotranspiration. It comprises one-third of all marsh area and, as such, is indicative of the ef- fort to manage marsh for one purpose or another. Im- pounded marsh is found within all the other marsh types except salt marsh. The average size of an im- pounded area is rather large, almost 800 ha (1^77 a). Some impoundments, however, are only a few hect- ares in size but one on the Sabine National WildUfe Refuge is weU over 10,000 ha (24,71 1 a). The inland open water habitat is the largest in area other than nearshore Gulf. Typically, each basin contains at least one large open lake or bay. The two flanking basins, Vermilion and East Bay, contain an open bay system, whereas the remaining basins contain large lakes. These large water bodies, which account for most of this habitat type, are relatively stable in comparison to the numerous small, shallow ponds scattered throughout the Chenier Plain. Many of the latter are rapidly increasing in size. All basins except Mermentau contain beach and nearshore Gulf habitats. For area statistical analyses, the nearshore Gulf habitat is reported by basin al- though it is truly a regional habitat and has no real boundaries except for the coastline. The VermiUon Basin contains a large proportion of this habitat. The wide, shallow shelf in this area represents the western margin of Recent Mississippi River deltas (plate 2). The beach habitat is typically bounded on its sea- ward side by the nearshore Gulf habitat and by either salt or brackish marsh on its landward side. It is a highly dynamic habitat. Morphological changes usually occur with seasonal frequency. Sediments comprising the beach are variable throughout the Chenier Plain. Beach morphodynamics was discussed in part 2 (see also part 4.11). 3.4.4 HISTORICAL CHANGES IN HABITAT COMPOSITION AND DISTRIBUTION From the perspective of tens or even hundreds of years, drainage basins in the Chenier Plain are constant in area. However, habitats within these basins have gained or lost area in response to natural processes or to man-induced disturbances. This study focuses on the changes over the last 25 years, but natural processes have been at work for millennia and many culturally induced changes occurred before 1952. Habitat changes can result from normal environ- mental processes. The beach habitat, for example, can be displaced seaward or landward depending on sedi- ment supply and other factors. Beach displacement involves the loss and gain of other habitats. For in- stance, shoreline advance involves the gain of habitat landward of the beach (usually marsh) at the expense of the seaward habitat (nearshore Gulf). Many recent changes have resulted directly from cultural activities. These are easily documented if the change is direct and intentional. The dredging of a canal through a marsh Ulustrates the direct conversion of marsh to inland open water habitat and to spoil (ridge habitat). However, the indirect and cumulative impacts of such activities are not easily determined. 77 These indirect and cumulative changes are the most significant long-temi impacts of human activity in the Chenier Plain. Natural and man-induced changes, in the habitat composition of a basin can be either desirable or un- desirable depending on one's point of view. It is rare that a change is either wholly desirable or wholly un- desirable in terms of man's interest in natural resources. For example, hurricanes modify wetlands, kill many wetland aniinals, increase soil salinities, and cause ex- tensive damage to cultural features. On the positive side, the flood waters clear clogged waterways of nui- sance floating vegetation, release organic detritus from the upper marshes to open waters bodies (Craig et al. 1979), and destroy perennials in the fresher marshes which are replaced by annuals that are more desirable as food for waterfowl (Louisiana Department of WUdlife and Fisheries 1959). Cultural features, such as canals and spoil deposits, often increase the extent of saltwater intrusion, alter historic flow pat- terns and, in some instances, cause impoundment or drainage of large areas of wetland. However, spoil banks provide areas suitable for nesting aUigators and provide avenues of wetland access for deer and other mammals. Of the 14 habitats described for the Chenier Plain, all have undergone some change in their relative area over the past 25 years (table 3.55 and app. 6.4). The habitats Usted in this table do not correlate exactly with the 14 habitats previously described. The four natural marsh habitats have been combined since there was no accurate method to determine the 1952 dis- tribution of each wetland habitat individually. The ridge habitat was divided into two categories: natural and spoil. This distinction was warranted since natural ridge habitat is being lost and spoil areas are increas- ing. The agricultural habitat was divided into three subhabitats (rice field, non-rice cropland, and pasture) in order to determine whether there were any tem- poral changes in these agricultural subhabitats with respect to land use. The total change of 107,000 ha (264,290 a) dur- ing the 23-year period examined is equivalent to 8.1% of the total Chenier Plain area. A more realistic value of habitat change can be obtained by eliminating the changes within the agricultural subhabitats (e.g., rice to non-rice cropland) and by eliminating the nearshore Gulf from area calculations. This results in a total change of 93,000 ha (229,808 a) or 9.8% of the total inland area. 3.4.5 HABITAT CHANGE BY DIRECT HUMAN ACTION It is apparent (table 3.55) that culturally-modified habitats are increasing in size. As of 1975, pasture, urban and impounded marsh habitats, and spoil and agriculture areas represented 38.5% (287,434 ha, 710,265 a) of nonaquatic habitats in 1974 and only 31.2% (232,717 ha, 575,056 a) in 1952. This increase was at the expense of natural habitats. Table 3.55. Net habitat change in the Chenier Plain from 1952 to 1974^. Habitat Net area change (ha) Net percentage habitat change 1. Nearshore Gulf + 1,539 +0.4 2. Inland open vkfater +28,026 + 16.2 3. Natural marsh -81,276 -20.2 4. Impounded marsh +38,112 +30.8 5. a. Natural ridge -1,247 -3.8 6. b. Spoil a. Rice field +5,365 +2,787 +23.1 +6.7 7. b. Non-rice cropland Pasture +1,826 +1,181 +29.0 +1.3 8. Urban +5,446 +23.3 9. Beach -116 -1.8 10. Upland forest -1,247 -7.7 11. Swamp forest -396 -5.7 *1954 to 1974 for the East Bay Basin. Includes salt, brackish, intermediate, and fresh marsh. The net increase of 38,1 12 ha (94,177 a) of im- pounded marshes accounts for most of the 54,717 ha (132,209 a) increase in culturally-modified habitats. For the most part, these areas are privately owned, al- though some of the increase is the result of estabhsh- ment of wildlife refuges in the Texas portion of the Sabine Basin during the period between 1952 and 1975. The privately owned impounded areas are used for several purposes. Some may eventually be drained for agriculture. Many areas were established for com- mercial recreation purposes, largely for waterfowl hunting. Others were created to prevent land loss (which decreases the number of possible land uses). The urban habitat has increased by 5,446 ha (13,457 a) over the same period. About one-fifth of this increase was at the expense of fresh marsh. Most of the increase, however, was at the expense of up- land habitats. Thus, residential areas, and industrial and commercial complexes have expanded at the ex- pense of agricultural lands, ridge, upland forest, and (despite the threat of hurricanes) beach habitats. Con- tinued expansion of the residential component will probably occur at the expense of upland agricultural areas. However, that portion of the industrial sector that requires access to navigable waters will probably expand at the expense of wetlands or inland open water habitat because of the lack of better drained land remaining along these waterways. Althougli some agricultural land has been con- verted to other socioeconomic uses, there has been a net increase of 5,794 ha (14,317 a) between 1952 78 and 1974. A portion of the increase can be attributed to loss of upland forest and ridge habitat, but most agricultural expansion has been at the expense of wet- lands. Because little upland forest and natural ridge area remains, future expansion in agriculture will in- volve the draining of wetlands. The recent (1952 to 1974) picture is clear: as agricultural land is preempted for urban and industrial expansion, it is replaced by the increased draining of wetlands. The agricultural habitat has been divided into pasture, rice, and non-rice cropland in table 3.55. The non-rice cropland includes some sugarcane areas in the Vermilion Basin, soybeans scattered throughout the uplands, and truck crops in the uplands and along the ridges. All three categories have experienced a net gain from 1952 to 1974. The gains, however, have not been uniform. It appears that there has been a shght shift of agricultural land use within the confines of the study area, with rice expanding into wetland areas, and otlrer crops that cannot succeed on wet- land soils gaining more acreage on better drained sur- faces. 3.4.6 NATURAL HABITAT CHANGES AND INDIRECT CHANGES CAUSED BY MAN Indirect or unintentional habitat changes caused by man, and changes brought about through natural processes have been significant and are discussed by Gagliano (1973). The separation of indirect man- induced change from natural change is difficult. Some of the changes are the result of natural processes. Shoreline erosion that results in the loss of wetlands is predominantly a natural process, although man may act as a catalyst. In areas where man has con- structed jetties and groins he has certainly altered erosion and deposition rates. Hurricanes are short- term, natural stresses that affect man-altered wetlands more than natural marsh areas (Chabreck and Pal- misano 1973). Peat bums resulting from either natural or man- made fires, and local "eatouts" of marsh grasses by geese and muskrats (O'NeU 1949) have been docu- mented as factors involved in land loss. Whereas these factors may be significant on a local level, most of the land loss is goverened by other processes on a basin level. The major change in habitat types during 1952 to 1974 in the Chenier Plain was the loss of natural marsh (includes salt, brackish, intermediate, and fresh marsh) (table 3.55). Although about one-half (40,242 ha, 99,440 a) of the natural marsh has become im- pounded marsh habitat, otlier habitat types have also replaced natural marsh (table 3.56). Impounded marsh habitat continues to function as wetland habitat for some species such as waterfowl and marsh mammals, but it has less value than natural marsh when viewed as a component of the estuarine ecosystem (part 4.2). There has been some loss of natural marsh to agriculture and to spoU banks, but most (26,280 ha, 64,939 a) of the remaining loss has been to inland open water. Also, some inland open water habitat has been changed to impounded marsh to maintain ade- quate water quality and/or to control water level. The 28,662 ha (70,825 a) loss is equivalent to a 7.2% loss rate of natural marsh to open water from 1952 to 1974. This rate is the overall loss for the six basins in the Chenier Plain and a high degree of vari- ability exists between basins. A portion of the 7.2% loss rate can be attributed to the direct conversion of wetlands to open water by canal dredging. The total area of marsh lost through this activity was 2,685 ha (6,635 a), a rate of 0.7% for the period 1952 to 1974. The present distribution of canals is shown in Plates 5A and 5B. The total area occupied by canals and accompanying spoU banks is 4.3% of the Chenier Plain excluding the nearshore Gulf. From 1.0 to 2.2% of the land area is occupied by canals in each basin (table 3.57). Table 3.56. Loss of natural marsh* in the Chenier Plain in 1952 to 1974. Habitats replacing natural marsh Area (ha) of natural marsh converted Percent of 1952 natural marsh area Processes causing loss 26,280 6.4 Subsidence/erosion 1,903 0.5 Net shoreline erosion 40,242 9.9 Leveeing 2,685 0.7 Dredging 5,370 1.3 Dredging 4,5 73 1.1 Draining 1,027 0.3 Draining Inland open water Nearshore Gulf Impoundments Canals Spoil areas Agriculture Urban Total 82,080 20.2 ^Includes salt, brackish, intermediate, and fresh marsh. 79 Natural processes also erode marshes. These pro- cesses involve the relationship between the elevation of the marsh and of the sea. The northern Gulf coast is subsiding. The elevation of the marsh can never ex- ceed the highest elevation of ambient water, for water carries and deposits sediment onto the marsh surface. The deposition of waterbome sediment coupled with the fonnation of peat elevate the marsh surface. Re- gional and local subsidence, along with a rise in sea level during this century, tends to lower the elevation of the marsh with respect to the sea. The net subsid- ence rate of the land in the Chenier Plain is about 1 .7 cm (0.67 in) per year (equal to the net rise in water level, table 3.47). Unless marshes are elevated by sedi- mentation and peat deposition at a rate equivalent to the net subsidence rate, they eventually drovm and become shallow, open water. Table 3.57. Percentage of onshore area occupied by canals in each basin in the Chenier Plain, excluding spoil bank area. Basin Percentage (%) Vermilion Chenier Mermentau Calcasieu Sabine East Bay 2.2 1.9 1.7 1.8 1.2 1.0 The present distribution of habitats within indi- vidual basins and habitat area changes are provided in appendix 6.4. Over the entire Chenier Plain the unex- plained natural marsh loss rate (that is, the conversion to open water, table 3.58) is 6.4%. However, in four of the basins (excluding Calcasieu and Sabine), this unexplained loss rate is only about 2%. Since the geo- logical history of all basins is similar, and since all show about the same rates of net subsidence (or sea level Table 3.58. Percentage of land loss" Chenier Plain in the Chenier Plain Basin Calcasieu Sabine Chenier Mermentau Vermilion East Bay All basins Land loss (%) 17.2 6.5 2.2 3.3 2.0 1.9 6.4 Land loss is defined as that area of natural marsh that has transformed into open water during the specified period of time, including shoreline retreat and direct conversion to canals. From 1952 to 1954 except for East Bay, which was com- puted for 1954 to 1974 and adjusted. rise), the estimated rate of marsh loss due to natural processes of 2.3% in 23 years, or 0.1% per year, ap- pears reasonable. This suggests that the extraordinarily high rates of loss of natural marsh in the Calcasieu and Sabine basins are the result of the many indirect and cumulative stresses that locally upset the balance between aggradation and subsidence (part 3.6). This conclusion is supported by a recent study of marsh loss within the Louisiana coastal zone by Craig et al. (1979). They found that after a canal is dredged, it tends to widen at a rate of 4 to 15%/yr. The Humble Canal system and the Superior Canal, both in the Rockefeller Wildlife Refuge in the Chenier Basin, are widening at rates of 7 and 13%/yr, respectively (Nichols 1958, Craig etal. 1979). Craig et al. (1979) also found a direct relation- ship between land loss rates and canal density for the entire Louisiana coast and for sections of Barataria Bay (fig. 3-24). The regression lines for the two graphs cross the ordinate somewhere around 0.1% marsh loss per year. The 0.1% represents losses to processes other than those caused by man. Equation of best fit • y . 074 + 0. Ix '^ 0.69 Canal Aiaa Paicani ol Totat Marsh Araa j Figure 3-24. Relationsiiip between canal density and wetland loss rates (A) in coastal Louisi- ana, and (B) in the Barataria Basin, Loui- siana (Craig et al. 1979). 80 The major wetland changes in the last 25 years in the Chenier Plain have been cultural and include im- poundment of wetlands, canal dredging and spoil de- position, and draining for agricultural and urban use. The rapid loss rate to inland open water habitat can- not reasonably be attributed to natural erosion and subsidence alone. These natural processes can explain about one-third of the wetland loss. Tlie rest is pre- sumed to be due to hydrologic changes incurred by the dredging of numerous canals and especially the major ship channels through the Chenier Plain wet- lands and the removal of httoral sediments which are placed in spoil banks during channel maintenance. 3.5 RENEWABLE RESOURCE PRODUCTIVITY 3.5.1 INTRODUCTION Analysis of the quantity and quaUty of renew- able resources of the Chenier Plain is the heart of this ecological characterization. The living resources have evolved along with the major long-term geologic and climatic processes that formed the Chenier Plain. The mixture of land and water areas, which we have called habitats, continue to change slowly with time under the influence of natural processes characteristic of any coastal zone. These habitats, maintained to a large extent by the flow of water over, around, and through them, support a characteristic flora and fauna. Some plants and animals are commerciaUy important; some are prized by sportsmen; some have important functions in habitats; and others are threatened with extinction. One could consider these living organisms to be the end products of the physical and chemical processes of the Chenier Plain. The organisms interact with each other in a complex trophic web. The environ- ment limits species diversity and productivity. By modifying any of the physical and chemical processes in this long chain of events, man can alter the living resources. The human activities that affect the environment, described in part 3.2, have been shown to influence the system's hydrology (part 33) and the system's habitats (part 3.4). Habitat modifica- tion in turn is responsible for long-term changes (per- haps the most significant changes) in the potential liv- ing resource production in the Chenier Plain. Direct exploitation of living resources is also capable of changing the resourcepotential(part 3.5.2). Deteriora- tion of the quantity and quality of water can change habitats both in areal extent and in their ability to maintain their characteristic flora and fauna. Water quality on the Chenier Plain is evaluated in part 3.5.3. 3.5.2 THE POTENTIAL FOR RENEWABLE RE- SOURCE PRODUCTION IN THE CHENIER PLAIN This section discusses the importance of habitat potentials for renewable resource production in the Chenier Plain. In part 3.4, the area of habitats was considered. In this section net photosynthesis and an index of wetland-water coupling (ratio of marsh edge to marsh area) are two indices of quality that will be examined to evaluate the potential for resource pro- duction. Water quality is a third facet of basin quality and is treated separately in part 3.5.3. Renewable re- source productivity has already been defined (part 3.1.3) as representing the "quality" of a basin. This quality is partially expressed as the capacity of a basin to support organisms that are valued by man for their food, recreational and esthetic value, and/or functional value to the system; but the concept of habitats also includes refuge value for the many species whose eco- logical function is poorly recognized or whose exis- tence is still unknown. A primary requirement for a high quality ecosys- tem is an abundant source of food energy. Emergent wetland vegetation is the main energy source for fish and wildlife resources in the Chenier Plain basins. (A detailed description of the function of wetland habi- tat is presented in part 4.2.) The organic carbon pro- duced in emergent wetlands is deposited as peat, grazed or decomposed in place, or washed into the inland open water habitat. This last energy pathway, the export of organic carbon, is critical to many im- portant aquatic species that are supported by a detritus-based food web (part 4.3). Thus, the inter- play between wetlands and water bodies is important. The average annual net photosynthesis for the Chenier Plain calculated from annual production esti- mates is 1 7,628,5 19 t (19,432,1 16 tons) (table 3.59) and is discussed in part 4. The magnitude of produc- tion for each basin varies directly with the amount of wetland area. All vegetation produced is not eaten by consumers in the food web so the values listed in table 3.59 represent the potential organic energy available in each Chenier Plain basin. Average values exceed 1,300 t/km^ (3,711 tons/mi^ or 1300g/m^ or 4.26 oz/ft^) and are extremely high when compared to ecosystems worldwide. The resource potential of the Chenier Plain is probably as high as that found any- where else in the United States. Natural habitats are steadily being lost to those modified by man, and wetland habitats in particular are being lost at a rate of about 0.1%/yr(part 3.4.6). In addition, productivity of existing habitats may be decreasing because of culturally induced stress; that is, habitat quality may be degraded. In both cases, the long-term trend is a decrease in net photosynthesis and living resources in the Chenier Plain. The second index of basin quality, marsh edge: marsh area ratio, has been used less as a diagnostic tool. However, the importance of wetland-aquatic coupling in general, the evidence for high diversity and productivity along marsh-water edges (part 4.2), and the relative ease of determining this index sug- gests that it may be a useful tool for comparing productivity in coastal environments. Because tidal currents scour small channels in the marsh, the marsh edge: marsh area ratio tends to be highest in salt marsh habitat and decreases as marshes 81 become increasingly fresh (fig. 3-25). The ratios were calculated from 1:24,000 USGS maps by digitizing. The area totals are conservative because many small marsh ponds were excluded. In the Sabine and Cal- casieu basins the edge: area ratios were higher in fresh marsh than in brackish or intermediate marsh habitats, perhaps because land loss (marsh degradation) is oc- curring so rapidly in those basins. If the ratios are in- dices of marsh productivity, then data indicate that salt and brackish marsh habitats are more productive than fresh marsh for estuarine-dependent organisms. Canals in wetlands have been shown to change hydrologic patterns, thereby modifying habitats and basin quality. Canals, because they are straiglu rather than sinuous and edged with high spoil banks that do not permit overbank flooding, have low edge; area ratios. For this reason alone, one would suspect that these factors reduce habitat and basin quality. In a recent study, it was found that the area of natural sinuous channels in marshes, and the edge : area ratios were reduced as the canal density increased (R. E. Turner, Pers. Comm. Center for Wetland Resources, Table 3.59. Calculated net photosynthesis (primary production) by basin. Basin Area (km=) Average net -•photosynthesis per km^ (t/yr) ) Estimated net photosynthesis/ basin (t/yr)^ Vermilion Mermentau Chenier Calcasieu Sabine East Bay Total 1,909.10 2,680.64 1,954.47 1,756.27 3,759.79 1,119.26 13,179.53 1,047.14 1,591.92 1,222.44 1,452.11 1,369.10 1,139.15 1,999,100 4,267,374 2,389,228 2,550,299 5,147,516 1,275,002 17,628,519 Summarized from appendix 6.3. 70 60 a. >■ n 50 40 » 30 w 20 ? 10 East Bay Sabine Salt Marsh Brackish Marsh Intermediate Marsh Fiesh Marsh m 1 Calcasieu Chenier and Mermentau Vermilion Baiin and Marsh Types Figure 3-25. The ratio of marsh edge lengtli to total wetland area, by marsh type, in each basin. 82 Louisiana State University, Baton Rouge). Apparently shallow natural channels fill with sediments because man-made canals capture waterflow. This phenomenon also occurs where highway embankments cross tidal marshes and disrupt natural channels, which subse- quently fill in. The reduction in the edge: area ratio under these circumstances suggest that the quality of the natural environment has been reduced. Docu- mentation is poor, but in at least one case it has been shown that marsh macrophyte production was signif- icantly reduced (Allen 1975) when edge: area ratios were reduced. Refuges. An important component of the natural resource productivity of a basin is its capacity to serve as a refuge for animals. The term "reftige" impUes a variety of uses for a habitat in addition to use primar- ily for its food (trophic) value. "Refuge" also includes shelter provided by habitats which may lie outside of- ficially designated private. State, or Federal refuge boundaries. For threatened and endangered species and perhaps others, the value of the gene pool may far outweigh other values. A habitat, e.g., ridges, rhay provide refuge for migrating species at a critical time, which gives it a value far in excess of its normal carry- ing capacity. Species that require refuges can include animals that migrate daily over short distances (intrabasin) as well as seasonal, long-range migrants. Intrabasin migrants include roseate spoonbills and bald eagles, as well as reptiles and mammals that spend part of their lives on ridges and feed in wetlands. Seasonal long- range migrants include a wide range of organisms such as warblers, waterfowl, juvenile shrimp, and even monarch butterflies. Natural marshes (salt, brackish, intermediate and fresh) are being lost in the Chenier Plain at the rate of about 1%/yr (table 3.56). Other less abundant habi- tats are often destroyed by man because they are par- ticulariy desirable for development. Wooded cheniers are scarce in the low-lying areas of the Chenier Plain and are particularly suitable for building sites. The location and size of private. State, and Federal refuges within the Chenier Plain are identified in plates 6A and 6B and table 3.34. These refuges represent 14% of the inland area of the Chenier Plain and are comprised of wetland and aquatic habitats whose pri- mary use is for wateri'owl, alligator, and fur manage- ment. The fact that they are closely supervised, that hunting is controlled, and that development is re- stricted make them excellent refuges for threatened and endangered species. For instance several pairs of red wolf are beheved to reside on the Sabine National Wildlife Refuge. On the other hand most of the re- fuge land within the Chenier Plain has been impounded so that movement of migratory fishes and shellfishes between impounded areas and estuaries is discouraged. These refuges therefore represent tradeoffs between fish species and game species. Forested cheniers and swamps are two habitats that are rapidly being exploited and should be con- sidered "critical" in the sense of their vulnerability to complete eradication in the region. The latter are abundant elsewhere along the Louisiana coast, but local areas of undisturbed swamp within each basin cover less than 1% of the area and are being lost at a rate of about 0.25%/yr (table 3.5 5). Forested cheniers are perhaps the major unique feature of the Chenier Plain. These ridges have been extensively developed, and are in danger of being irretrievably lost. Bird rookeries and archeological sites (plates 6A and 6B) are other unique features on the Chenier Plain landscape that fall under tlie general category of re- fuges. Commercial and Sport Species. Harvest of the most commercially important species in the Chenier Plain— menhaden, shrimp, oyster, blue crab, nutria, and muskrat— was discussed in part 3.2.4. Long-term harvest trends for these species suggest that they are being exploited at their maximum, and with the pre- sent carrying capacity the possibility of significantly increased harvests is remote. Menhaden. Menliaden harvest has increased reg- ularly since 1946 (fig. 3-26). The effort expended during the 1969 to 1974 period seems to be resulting in the maximum sustainable yield (Schaafet al. 1975). Similar clupeid fisheries on the East and West coasts have suffered dramatically from over exploitation. Shrimp. Although year-to-year catch fluctuations are fairly large, the white and brown shrimp harvest (1959 to 1973) shows no consistent upward or down- ward trend (figs. 3-27 and 3-28). It is possible that en- Ughtened management can result in some increase, but this would be through control of the size of harvested shrimp, not through increased production potential. Continued wetland loss will eventually be reflected in harvest reduction. Oyster. Oyster production varies a great deal lo- cally, since oyster growth depends on suitable sub- strate, favorable salinities, and flowing waters. The trend in the Chenier Plain has been to a reduction in size or loss of oyster beds, or at least to closure be- cause of pollution. This has occurred in the Calcasieu and Sabine basins and in part of East Bay Basin. Oyster production can be increased by appropriate manage- ment as is shown by the development of oyster beds where spoil banks have washed out along the Calcasieu Ship Channel (Van Sickle 1977). However, unless pol- lutant discharge is controlled, oyster production will undoubtedly continue to decline. Blue Crab. The small size of the blue crab industry suggests that exploitation could be expanded in the Chenier Plain. Blue crabs are scavengers that seem to adapt to conditions associated with man's develop- ments. For instance, the blue crab industry in Sabine Lake is thriving despite the decline of other species. It would be surprising if the environmental degrada- tion did not adversely affect the edibUity of crabmeat. Even if fully exploited the value of this fishery would be small compared to shrimp and menhaden. Other Fishery Species. The only Other group of fish for which an unexploited potential seems to exist is the industrial bottomfishes. The industrial bottom- 83 o o o o o o o O o o o o o o o o o o o o 00 r>- (D in ^ CO OJ ^ (000' L ^ sauuoi) qoiBQ 00 n ii a> > at •a ui o N w c o o 'C o o ^ tj- o^ CJ ^" ■»-» X S M <«z Cm 0} U 1 60 c o o 2 12 CO c o vi i-> •a ^ "3 "1 « JS -^ ^ 4^ =«2 o o o -J o CM »^ dJ t^ LU menhad yield is 4 C (u r*% « z ^ CO in CO 05 ,— r 7=" 3 CO (J) in CO c£ ^ ^ ^ J. in CO i- in 3" EZ ^ CO O) in (saiej6o|!>| ^o suojnjiu) }S3AJe|-| ajoqsuj (SLuej6o|!>{ ^o suo!||!UJ) jsaAJBH ajoqs^io S o U Q c 3 o o g •c aa ■3 c 2 u g g o o ■a o c t^ m as u ^* 2 '-> £ g I u 3 85 O) 00 CO 0) c 3 o ■o J CO J ^O SUOIIIJUJ) }S8Aje|-| ajoqsui (>^ ' "hL ^ t""" CO in ^iH ^ CO CO 1^ d 1 .■.■.■.■■■.■.■.■.■.■...■.■.■.;i 1 — ...J ^ , Jt H frr0m r-^ Hi t_ rf;« in CO in CO O) in CO CO CNJ J in (sujejBo|j>| |o suofiijiu) E o U a Q D 3 00 o •a >. X) C 3 O -J O X) o ac c •3 c CO '5 E E o o (U I. o ™ 0^ 2 o x: u, £ E 00 I rn l-c 3 86 fish industry, which depends primarily on the Atlantic croaicer, is just beginning to develop in the Chenier Plain (fig. 3-29). Since 1953 the harvest in the near- shore Gulf has increased from 14 to 43 million kg (31 to 95 miUion lb) (Gutherz et al. 1975). Nutria and Muskrat. As indicated in part 3.2.4, muskrat and nutria harvests have been dechning in the Chenier Plain since 1971 in spite of sustained har- vests in the southeastern part of the State (fig. 3-9) and in spite of increased Ucense sales (part 3.2.4). Reasons for the declining harvests in the Chenier Plain are not obvious. Habitat area loss is occurring at a much slower rate than harvest decline. There is some evidence for competition between nutria and muskrat where their habitats overlap, but long-term trends of muskrat production are difficult to assess because of extreme variability. The most conservative assump- tion is that production cannot be expected to increase because the resource is fuUy exploited and that care- ful management is required to maintain present levels of production. Sportfishing and Hunting Potential. The sporttlsh- ing potential on the Chenier Plain was evaluated on the basis of available area of aquatic habitat and esti- mated potential yield, using the method described in the Fish and Wildhfe Study (U.S. Army Corps of Engi- neers, unpublished). These estimates are based on the best avaUable information from fishery biologists familiar with the Chenier Plain. The desired sportfish catch is estimated at 4.5 kg (10 lb) of saltwater sport fish and 0.9 kg (2 lb) of freshwater sport fish per man- day (table 3.60). The saltwater estimate is somewhat conservative because it does not include the nearshore Gulf. Wildlife hunting potential was calculated by esti- mating the area required each year to support various types of hunting for different habitats in the Chenier Plain (table 3.61). The numbers for each species are in terms of man-days of hunting per unit area to al- low comparison with demand figures generated in part 3.2.5. Data are based on estimates from wildlife biologists of productivity and standing stock as well as the sustained harvest potential for each habitat. The estimates indicate that 1 ha (2.47 a) of fresh, in- termediate, or brackish marsh will sustain about two man-days of hunting per year. Saline marshes are less useful for hunting purposes. Peak populations of waterfowl reach 3.8 million and the estimated annual harvest is 561,013 (table 3.62). The total supply of saltwater fishing and sport- hunting is estimated [app. 6.3 (10)] by multiplying area times man-days of potential use for each habitat. In figure 3-30, this supply is compared to the demand estimated in part 3.2.4. Freshwater sportfishing is ex- cluded from this analysis. Freshwater fishing is avail- able north of the Chenier Plain as well as in the Chenier Plain, so it is difficult to estimate the demand for this type of recreation. In contrast, saltwater fishing is confined to the coast. Similarly, for hunting the sup- ply represented in the figure is generated by waterfowl and other wedand species unavailable outside the Chenier Plain. 84° 50' Figure 3-29. Fishing areas for industrial bottom fish along the northern Gulf coast (Gutherz 1975). 87 Table 3.60. Estimated annual sportfish catch and the effort this catch will support by basin, in the Chenier Plain" Basin Type of activity Estimated obtainable yield (kg/ha) Water'' area (ha) Potential sport fish catch (x 1000 kg) Potential'^ effort (man-days X 1000) Vermilion Saltwater finfishing Freshwater finfishing 22.4 33.6 15,532 3,451 348 116 77 128 Chenier Saltwater finfishing Freshwater finfishing 22.4 56.0 3,962 1,679 88 94 20 104 Mermentau Saltwater finfishing Freshwater finfishing 56.0 61,522 3,446 3,799 Calcasieu Saltwater finfishing Freshwater finfishing 22.4 22.4 29,910 11,004 670 247 148 272 Sabine Saltwater finfishing Freshwater finfishing 22.4 22.4 28,368 17,570 635 392 140 433 East Bay Saltwater finfishing Freshwater finfishing 22.4 25,175 22.4 1,389 Total Saltwater finfishing Total Freshwater finfishing 564 31 124 34 - 2,305 4,326 509 4,770 Data from tables 3 and 7, Appendix D, Fish and Wildlife Study (U.S. Army Corps of Engineers unpublished). Saltwater area greater than 5 *'/oo salinity includes salt and brackish marshes. Freshwater area less than 5 /oo salinity includes fresh and intermediate marshes. Calculated at 10 Ib/man-day for saltwater fishing and 2 Ib/man-day for freshwater fishing. Mermentau has no saltwater fishery. Table 3.61. The area (ha) of various habitat types requured to support one man-day of hunting for various wildlife species. Hectares per man-day of hunting" Dove Habitat type Deer Turkey & quail Rabbits Squirrels Ducks Geese Other marsh birds Salt marsh 16.24 33.67 13.48 Brackish marsh 8.00 33.39 3.33 Intermediate marsh 5.27 33.02 2.93 Fresh and impounded marsh 2.29 15.42 2.67 Pasture 3.64 4.50 Rice 3.87 6.73 Forest 0.95 3.37 33.77 2.70 1.35 134.68 26.95 1.62 2.67 1.60 1.47 1.05 7.89 2.14 4.45 8.01 1.24 27.03 26.91 4.05 22.50 9.00 Calculated from Fish and Wildlife Study tables 29 and 33 (U.S. Army Corps of Engineers unpublished). 88 Table 3.62. Average peak populations and harvest of waterfowl species in the Chenier Plain. Percentage Peak Percentage of total Species populations* of total peak population Annual harvest annual harvest*^ Mottled duck 49,414 1.3 36,361 6.8 Mallard 236,972 6.1 78,632 14.8 Gadwall 611,451 15.8 52,296 9.8 Baldpate 383,895 9.9 33,607 6.3 Green-winged teal 586,400 15.1 76,601 14.4 Blue-winged teal 327,941 8.5 43,257 8.1 Northern shoveler 159,896 4.1 21,503 4.0 Northern pintail 474,210 12.2 63,131 11.9 Wood duck N.A. N.A. 4,608 0.9 Ring-neck duck 40,720 1.0 2,117 0.4 Scaup 47,021 1.2 8,001 1.5 Redhead 1,319 0.03 787 0.14 Canvasback 2,400 0.06 827 0.15 Hooded merganser 2.012 0.05 1,302 0.3 Fulvous tree-duck N.A. N.A. 0.0 Lesser snow goose 448,727 11.6 72,965 13.7 White-fronted goose 49,826 1.3 20,260 3.8 Canada goose 3,272 0.08 16,030 3.0 Coot 455,553 11.7 43 .01 Total 3,881,029 100.02 532,328 100.00 Hugh A. Bateman; Louisiana Wildlife and Fisheries Commission, Waterfowl Inventory Field Sheet 1969-1977; Texas Parks and Wildlife Dep., 1955-1957, 1974-1975; aerial waterfowl survey results. Federal Aid Projects W-106-R-2. U.S. Fish and Wildlife Service, 1975. Distribution in parishes (counties) of waterfowl species harvested during 1961-1970) hunting seasons. This figure represents the percentage of the total harvest of all species. 89 A heavy demand exists for sporthunting, and saltwater sportfishing in the Chenier Plain, since the demand projected from telephone surveys far exceeded the available supply (figure 3-30). In addition, the hunting supply may be overstated, since some of the refuge land and some privately owned land is closed to hunting. The saltwater sportfishing supply-demand rela- tionship survey determined that an average Louisiana fisherman felt he needed to catch 4.5 kg (10 lb) of fish a day [0.9 kg (2 lb)/hr based on 5-hr day] to sat- isfy his requirements (U.S. Army Corps of Engineers, unpublished). The demand figures are based on this estimate. However, in recent censuses in Sabine Lake and Galveston Bay, Texas (Heffeman et al. 1976, Breuer et al. 1978), it was found that fishermen were landing only about 0.22 kg (0.50 lb)/hr in Sabine Lake and 0.3 kg (0.66 lb)/hr in Galveston Bay. Saltwater Sportllstiing Sporthunting o 300 Figure 3-30. Supply of and demand for saltwater fish- ing and sporthunting by basin, in the Chenier Plain, excluding the Nearshore Gulf Habitat (U.S. Army Corps of Engi- neers, unpublished). 3.5.3 SURFACE WATER Surface water and ground water aquifers extend- ing beyond the Chenier Plain boundaries have been discussed earlier in general tenns (parts 2.4 and 3.3). This section evaluates the adequacy of surface water supplies. Surface Water Quantity. The sources of fresh sur- face water are rain and upstream runoff into each basin. The largest amount of this freshwater is absorbed and evaporated by natural vegetation. One important rea- son for the high productivity of Chenier Plain vegeta- tion is the normally abundant water supply. Fresh surface water is also required by wildUfe species. After the requirements of the natural biota, agriculture is the largest user of freshwater in the Chenier Plain, fol- lowed by industrial and residential use. Table 3.63 summarizes an approximate annual budget for water sources and uses and assumes that all water was evenly spread over the total basin surface. Rainfall amounts to II 3 to 1 46 cm (44 to 5 7 in)/y r and is supplemented by riverine inflows that significantly affect the water budgets. East Bay has the least rainfall and no signifi- cant river inputs. As a result, its total surface fresh- water supply is only 113 cm (44 in)/yr. In contrast, because of their large river systems, the Sabine and Calcasieu basins have nearly 400 cm ( 1 57 in) of fresh water each year. Eighty-four to 97 cm (33 to 38 in) of this water is evaporated, mostly by plants. How- ever, this water reenters the basin in various forms of precipitation. In comparison, total use by agriculture and industry is less than 21 cm (8 in), excluding the Sabine Basin where 70 cm (28 in) is used per year. The use figures are somewhat inflated since much of the industrial water is returned to the stream from which it was pumped, and about 407c of the agricul- tural water is returned. Ignoring these return flows, all basins but East Bay, Texas have net annual sur- pluses of more than 76 cm (30 in). East Bay has al- most nosurplus(17cm, 6.7 in), and estimated deficits [periods when soil moisture was insufficient to sup- ply maximum evapotranspiration as calculated by the method of Borengasser (1977)] accumulated over an average year are 24.5 cm (9.6 in). Thus, fresh surface water is a critical factor in the East Bay Basin. Other basins have sufficient supplies on an annual basis, pri- marily because of riverine inputs. However, the sum- mer agricultural demands in the Mermentau Basin ex- ceed the summer surplus. During this period, surface water levels fall and salt intrusion would occur if con- trol structures were not present (part 3.6.3). Surface water surpluses help to maintain the freshwater head necessary to prevent serious saltwater intrusion, and to flush the lower estuaries. Hence the term "surplus" is a misnomer. Without this water moving through the basins and offshore, the estuaries and wetlands would be significantly more saline and the entire character of the coastal region would be different. Surface Water Quality. The chemical composi- tion of a water body reflects local and basin-wide chemical inputs. A disturbance in the chemical com- position of an aquatic system, either through the in- troduction of a foreign substance or through an in- crease in concentration of a natural component, may be followed by a change in the biotic community. Thus, the biotic composition of an aquatic system re- flects the water quality of that system. Eutrophication. A complete evaluation of water quality in Chenier Plain basins would require the con- sideration of phosphorus and nitrogen; ion balance (the relative abundance of sodium and potassium to magnesium and calcium); trace metals-mercury, co- balt, zinc, cadium, iron, manganese, chromium, cop- per, and lead (at a minimum); numerous organic pes- ticides and petrochemical compounds; the dissolved gases (oxygen and ammonia); and bacterial concen- trations. The available data are too fragmentary for a 90 Table 3.63. Annual water balance for Chenier Plain basins. Mermentau &: Source Vermilion Chenier Calcasieu Sabine East Bay River input (cm/yr) 89 27 253 258 Rain (cm/yr) 114 146 138 140 113 Total 303 173 391 398 113 Use Evapotranspiration 83.6 90.8 96.7 97.3 91.4 Agriculture 0.03 5.9 3.0 6.1 2.5 Industry 0.05 4.3 64 2.3 Accumulated surplus (cm/yr) 139 76 287 231 17 Accumulated deficits (cm/yr) 17.5 17 15.5 19 24.5 Rainfall 30 year average from U.S. Weather Bureau records; Riverine input long term average USGS 1977; evapotranspira- tion calculated from Borengasser 1977; agriculture and industry use from table 3.41 and figure 3-7 assuming all industrial water and 2/3 agricultural water from surface. It is assumed all water was evenly layered over each basin. broad evaluation. Therefore, eutrophication is evalu- ated by using phosphorus as a general index of water quality. "EutropWcation" refers to the natural or artificial addition of nutrients to bodies of water, and the effects of these additional nutrients on the biota (National Academy of Sciences 1969). The ecological consequences of nutrient additions, beneficial and/or deleterious to the aquatic habitat, are discussed in part 4.8. Generally, excess nutrient addition results in aquatic community changes that may be detrimental to sport and commercial fisheries. Phosphorus (P) is the critical limiting nutrient in freshwater ecosystems (Likens 1972). It is a conve- nient indicator of eutrophication because it is not lost as a gas through biological decomposition or chemical change. Furthermore, it is a common constituent in most of the common sources of materials that cause eutrophication: municipal sewage, urban runoff, drainage from agricultural land, and natural sources (detritus, waterfowl wastes, eroded minerals). It is a poor index of industrial wastes which can contain a wide variety of toxins. Because P is a normal compo- nent ofmost pollutants, its analysis within the Chenier Plain waters allows a useful evaluation of water qual- ity. This general analysis will be supplemented by in- formation about other pollutants that appear to be important in individual basins. Because of the rapid transformations of P (and other nutrient elements) in the water column, the concentration of inorganic P alone is a poor index of eutrophication (Hutchinson 1969). A more significant indicator is the total amount of P contained in inor- ganic and organic dissolved forms. Phosphorus drains into the major water bodies of each basin. This input load, expressed in grams per cubic meter (g/m^), pro- vides anindexof theeutropliic state of different water bodies. The "input load" retained in the water, the biota, and the underlying sediments of a basin, con- stitute the "storage" compartment of an aquatic eco- system. In this analysis the nutrients are assumed to be homogeneously distributed throughout the water bodies. Point sources of discharges are identified and their magnitudes are listed when available (plates 5A and 5B). Concentrations generaUy decrease as a func- tion of distance from the source and of the volume of the receiving waters because of mixing and dilution. Circulation patterns determine how well these nu- trients become mixed throughout the system. As a re- sult, localized areas of high biotic production (ad- vanced stages of eutrophication) can occur even though the entire water body may not exhibit over- enrichment. If nutrient inputs continue to exceed the capacity of the system to assimilate them over time, advanced stages of eutrophication proceed from point sources and affect more extensive areas. Thus, the average input load provides an indication of nutrient enrichment of a water body even though the eutrophic state may vary from place to place (Craig et al. 1979). It is assumed in this report that processes occurring in saline waters are similar to those in freshwater sys- tems and that it is valid to average quantities over an entire basin, regardless of the fact that differences oc- cur in salinity. For instance, salt water flocculates col- loidally suspended nutrients so that they sink. The re- lationship between the loading rate and P retention in the sediments was worked out for freshwater lakes and may not apply equally in brackish areas. Finally, nitrogen (N) is more often limiting as a nutrient than P in coastal marine systems (Ryther and Dunstan 1971). This, however, does not invalidate the use of P as a tracer of eutrophication, since N and P appear to- gether in equal amounts in most pollutants. Input loading rate. Critical P levels were taken as indicators of eutrophication from previous studies (table 3.64). The values of Shannon and Brezonik (1971) stated on a volumetric basis are used in this re- port. They considered P loads less than 0.12 g/m^ (1.2 X 10''' oz/ ft"' )/yr as permissible, and loads greater than 0.22 g/m' (2.2 x lO"'* oz/ft^)/yr as dangerous. 91 Table 3.64. Permissible, and excessive loading rates for phosphorus as an index of eutrophication. Reference Rate Permissible Excessive Shannon and Brezonik (1971) Shannon and Brezonik (1971) VoUenweider (1968) for lakes < 5m Craig and Day (1979) Volumetric (g/m'/yr) Areal (g/m^/yr) Areal (g/m^/yr) .^eral (g/m^/yr) 0.12 0.28 0.07 0.4 0.22 0.49 0.13 0.40 These levels are useful indices for many different kinds of water bodies. The stage of eutrophication in an en- tire water body is influenced, however, by the flush- ing or replacement rate of the water body, retention of nutrients in bottom sediments, the previous his- tory of eutrophication, the water depth, and the total water volume. These factors should be considered in site-specific analyses. Output and storage (retention). A portion of the nutrients discharged into a lake is later discharged from the lake in the stream outflow. Inorganic P can be transformed to organic forms within minutes and subsequent chemical changes depend on cycling rates of the biota and on sedimentation rates. Eventually some of the P entering the water body leaves down- stream, although it may not be in the same form. The losses of P increase as the areal water load increases. The areal water load of a body of water (m/yr) is de- fined as the ratio of the outflow volume[(m /yr to its surface area (m^)]as shown by the empirical relation- ship developed by Kirchner and Dillion (1975) in fig- ure 3-31. Retention and outflow are influenced by the pre- vious history of the water body (Craig et al. 1979). In fresh waters with a previous history of low P loading rates, the sediment acts as a sink and traps P efficiently . But if excess nutrients are introduced, the sediments gradually become saturated with P and are able to store new P only at slow rates related to the net rate of sedimentation. Estuarine sediments naturally trap P (Pomeroy 1970). In shallow water areas such as those in the Chenier Plain, where wind, dredging activities, or other factors stir up these enriched sedi- ments, P is released into the water column. Thus, the concentration in the water is buffered by the under- lying sediments. Tidal flux is an additional factor that influences the export of P from estuarine waters. In tidal areas, the areal water load, based on freshwater flow througli the lake, underestimates the dilution of a pollutant. This was demonstrated by Ketchum (1969) for the Hudson River estuary. His findings suggest that (1) retention values from Kirchner and Dillion (1975) are probably overestimated in estuaries with significant tidal action and (2) pollutant dis- charge into tidal waters can be expected to influence upstream as well as downstream areas. An example of the latter is the discharge from menhaden plants in the lower Calcasieu River that resulted in closure of the oyster beds upstream in Calcasieu Lake. P loading rates in Chenier Plain estuaries were de- termined from the total water discharging into a basin and the P concentration in runoff entering each basin from its drainage area. The analysis was perfonned for the entire watershed area of each basin, not just the area within the Chenier Plain boundaries. The P loading rates were determined by multiplying the Shannon and Brezonik (1971) coefficients of P run- off from different land types (urban, industrial, agri- culture, forests, wetlands, etc.), by the area of each A'*si Wal^rload q^ m yr Figure 3-3 1 . The relationship between the areal water- load (qs) and phosphorus retention (Rp) in fifteen southern Ontario lakes, from Kirchner and Dillion (1975) as shown in Craig etal. (1979). type. The total loading rate was them compared with P loading rates from eariier studies to determine the sensitivity of the basin to eutrophication. Details of the methodology are given in appendix 6.4. The values obtained across the Chenier Plain are shown in table 3.65. In all cases the heaviest contributor to P runoff 92 Table 3.65. Summary of discharge, loading rate, and eutrophic state of surface waters of Chenier Plain Basins. Item Vermilion Mermentau and Chenier Calcasieu Sabine East Bay Total discharge into major water body (m^/yearx 10^) 15.89 53.42 49.75 149.58 5.22 Total phosphorus (g/yearx 10 ) 3.86 10.72 12.96 4.90 0.42 Loading rate (g/m^/year) 0.24 0.20 0.26 0.03 0.08 Eutrophication sensitivity Excessive See Appendix 6.4 for sources and details. Borderline Excessive Permissible Permissible was the agricultural land. Not only does each water- shed have a large proportion of its land tied up in agri- culture, but the P coefficients are high because of soil erosion and excess fertilizer runoff. Vermilion and Calcasieu basins have high loading rates and danger- ous stages of eutrophication could develop. Memientau Basin is borderiine; P loads in Sabine and East Bay basins appear to be in the permissible range. The Vermilion Basin has a high rate because of the Ver- milion River discharge volume. The loading rate of the river suggests that dangerous eutrophic states could develop, but when emptied into Vermilion Bay and exchanged with West and East Cote Blanche bays, the volume is probably diluted to the permissible range. Measurements of P indicate a decreasing concentra- tion as one progresses eastward. The Calcasieu Basin, on the other hand, has a high loading rate (0.26) and is probably very prone to eutrophication problems. The P loading is high because of the high proportion of agricultural land in the up- stream watershed. The low P load in the Sabine Basin results from the relatively high discharge rate that ef- fectively dilutes P. Brine. Salt is a naturally occurring material, but in high concentrations it may become a toxin, rather than a nutrient. Marine organisms are adapted to con- centrations of about 36 %o, and estuarine organisms are usually able to tolerate wide fluctuations in salt concentration. However, sudden severe changes or ex- treme concentrations can kill flora and fauna. Small changes in the mean concentration result in shifts in the dominant plant species. The greatest damage oc- curs in fresh waters and fresh marshes where endemic species usually have a low salt tolerance. The Gulf of Mexico provides the largest source of salt on the Chenier Plain. Intrusion of this salt into freshwater estuaries was discussed in part 3.3.8. In ad- dition, release of large quantities of highly concen- trated brines from industrial sites has severe local ef- fects and perhaps long-term general effects. Major sources of brine are oil wells and leachate from salt domes (particularly in the Calcasieu Basin). A 1956 survey conducted by the Louisiana Department of Conservation reported that salt water composed al- most 70% of the total liquids produced by oil and gas wells. Brines which are separated and released at well- sites, contained concentrations of dissolved constitu- ents (table 3.66) that range from 20 %o to more than 300 %o (Collins 1970). The average concentra- tion is 110 °/oo (Lisa Levins, Pers. Comm., Energy Resources Co., Cambridge, Massachusetts). As an oil field becomes older, its saltwater pro- duction tends to increase. Not only is there a higher concentration of salt in the water, but the ratio of salts differs from that of sea water. Because of the differences in major ions, brines are often far more toxic than sea water. Whether an oil field brine will damage the marsh environment depends in part upon the method of dis- posal. The return of brine through injection into suit- able subsurface formations below the lowest known freshwater aquifer is the most satisfactory method of disposal. In addition to subsurface injection, brine is sometimes retained in pits. Large voumes are then re- leased into surface waters. This is the most deleterious disposal technique. Another significant source of brine is leachate from salt domes. Some of the salt domes are leached to create caverns for storing wastes and oU. For oil storage, a large surface reservoir of brine must be kept to pressurize the well (Gosselink et al. 1976), but most of the leachate is disposed of permanently. Dis- posal offshore in Gulf waters is projected for the ex- tremely large volumes of brine anticipated for the proposed Louisiana Offshore Oil Port storage caverns (Gosselink et al. 1976) and the Hackberry dome Stra- tegic Petroleum Reserves Program (NOAA 1977). In the latter case, it was predicted that under normal conditions, a brine diffuser located about 9.6 km (6 mi) off the Calcasieu Basin coast (at the basin/Gulf boundary) would produce a salinity change at the bottom of the water column greater than 1 °/oo over 93 Table 3.66. Comparison of constituents of brine water from some southwestern Louisiana oil fields vWth constituents found in sea water (Collins 1970). Brine Sea water Constituent 0/00 0/00 Li 1 -4 0.2 Na 11,791 -46,789 11,000 K 45-328 350 Ca 867 - 3,026 400 Mg 375- 1,283 1,300 Sr 15- 188 7 Ba 5-95 0.03 B 3-31 5 CI 20,548- 78,136 19,000 Br 18-97 65 1 8-42 0.05 HCO3 83-334 160 SO, 0-466 3,900 an area of 730 ha (1804 a). Under stagnant conditions the area involved would be 1,215 ha (3002 a). Disposal of smaller amounts of brine into inland water bodies would have more serious consequences because of the shallow depths and surrounding wet- lands. There is indication that brine discharge has been a contributing factor in the rapid marsh degrada- tion north and west of the Hackberry salt dome in Calcasieu Basin. The uncontrolled dilution and disposal of brines into streams and surface waters has been permitted in some areas during periods of high stream flow or sur- face water runoff. There is a danger of creating unde- sirable concentrations of dissolved salt during periods of low flow. Concentrations that are dangerous to aquatic flora and fauna and can also cause water to be unfit for irrigation or other human use during the pe- riods of greatest need (Louisiana Geological Survey 1960). Additional information on the effects of brines may be found in Chipman (1959), Simmons (1957), Renfro (I960), Bernstein (1967), Gunter (1967b), Waisel (1972), Mosely and Copeland (1974). Industrial toxins. Waters in several areas of the Chenier Plain have been subjected to significant toxin loads. The toxins can take many fomis, but in general (in addition to brines), they include heavy metals, organic toxins (pesticides, etc.), oxidizable organic compounds that reduce available oxygen, thermal ef- fluents, and bacterial contaminants. There is qualita- tive summary information on the severity of the water quality problems in each Chenier Plain basin (table 3.67). Industrial pollution in the Chenier Plain occurs in the Sabine Lake and Sabine River, the Calcasieu River and its tributaries, the lower reaches of the Vermilion River, and in some stretches of the GIWW. Most of the pollution is localized. The enormous amounts of organic materials, indicated by the total biological and chemical oxygen demand load, must be considered against a background of a naturally high level of organics and sediments in the region. This load de- pletes dissolved oxygen locally to create anoxic con- ditions; such conditions, however, can also occur na- turally in waterways. Most of the discharged organic toxins are alipha- tic hydrocarbons that are discharged in fairly large amounts in both the Sabine and Calcasieu basins. In addition, at least one industry in the Calcasieu Basin discharges chlorinated hydrocarbons that are ex- tremely toxic to aquatic organisms and are readily de- graded. Thennal pollution is widespread in both the Sabine and Calcasieu industrial areas. Local effects must be fairly severe since temperatures over40°C have been recorded in receiving streams (Environmen- tal Protection Agency 1972), but no studies have been made of the consequences in the Chenier Plain. The Calcasieu River is contaminated with heavy metals. In the late 1960's, high concentrations of mercury were found in many fishes and shellfishes from the area. The major source of the mercury was apparently one industry (Pittsburgh Plate Glass, Inc.) in the Lake Charles area. In 1971, the plant installed treatment facilities that reduced the discharge to about 0.25 kg/day (0.55 lb/day). Since that time, rather high concentrations of mercury have still been found in fishes, but a 1972 investigation failed to turn up any significant mercury sources (Environmen- tal Protection Agency 1972). Chromium is a highly toxic contaminant released in large amounts in the petroleum refining process (309 kg/day, 681 lb/day in the Calcasieu Basin). Lead is released (primarily by one industry) at over 4,000 kg/day (8,818 lb/day). Analyses of water samples taken any distance downstream from discharge sources generally fail to show elevated concentrations of these heavy metals 94 I Table 3.67. Water quality of Chenier Plain basins. Status or water Basin quality problem Vermilion Mermentau/Chenier Calcasieu Sabine East Bay EPA water quality . » a,b status Industrial BOD^ and COD discharge kg/day Organic toxins discharged Thermal Heavy metals' WQ'^ EL 6341^''' 4650^ WQ° 249,700^ Chlorinated hydrocarbons + Lead (4000 kg/day) Copper (100 kg/day) Zinc (23 kg/day) Chromin (309 kg/day) Mercury (1 kg/day) Cadmium (1.8 kg/day) WQ= 61.000" LAS (detergent)'' EL O vVQ- does not meet water quality standards even after application of effluent limitations required by the Federal Water Pollution Control Act Amendments of 1972 (FWQA). EL - water quality is meeting water quality standards of the FWQA. ''Weston 1974. Vermilion River from Interstate 10 Bridge to GIWW. Calcasieu River from Oakdale above Lake Charles to Gulf; West Fork Calcasieu River from Houston River downstream, Bayou D'Inde. Sabine River and Sabine Lake. BOD = Biological oxygen demand; COD = chemical oxygen demand. ^Domingue et al. 1974. ''Diener 1975. + Indicates heating causes significant local effects. ^Environmental Protection Agency (1972). Nearly all discharges occur above the Vermilion Basin Boundaries. because they bind readily to suspended clays and are rapidly sequestered in the sediments. The importance of benthic organisms in the trophic structure of es- tuaries (part 4) makes this behavior of heavy metal pollutants particularly critical. Dredging of contaminated sediments suspends and disperses heavy metals. When these sediments are piled on spoil areas, the heavy metals are absorbed by plants and thereby enter the food web, or they may be carried into water bodies by runoff. The most heavily populated and industrialized basins, Sabine and Calcasieu, are experienceing serious contamination problems from heavy metals and or- ganic pesticides. Although these heavy metals are, for the most part, confined locally they move into the food chain through benthic and nektonic feeders that spread the toxins throughout the estuarine system. 3.6 ECOLOGY OF INDIVIDUAL BASINS 3.6.1 INTRODUCTION Previous chapters of this report have dealt with the major processes that control basin systems on the Chenier Plain. In each basin all of these processes are at work, but because physiography, hydrology, and socioeconomics differ, the basins are dissimilar. This chapter describes the major features of each basin and identifies the dominant forces shaping each one and the critical problems. 3.6.2 VERMILION BASIN General features. The Vermilion Basin lies on the eastern edge of the Chenier Plain. The boundaries, as drawn for this study, (plate IB) do not describe a complete drainage unit. The basin is part of the Ver- milion Bay system. Vermihon Bay is open to the east and strongly influenced by westward flowing waters of the Atchafalaya River (fig. 3-32). As circumscribed for this study, the Vermilion Basin is a small unit, 1,909 km" (741 m?). Sixty per- cent of this area is a large, shallow shelf in the near- 95 X) c U •o c C c o > C/3 c o •sb . ac I l-H a 5 » □ OHE^Bm 96 Table 3.68. Summary of natural and cultural features of Vermilion Basin. A. Hydrology of the Vermilion Basin B. Primary production, potential yield and harvest of living resources of Vermilion Basin. Riverine Processes Freshwater flow volume (into basin) (fig. 3-33) Vermilion River 15.9 x 10*m^/yr Atchafalaya River dilution of Vermilion Bay from the east Annual rainfall 144 cm (Lafayette) Annual rain surplus (fig. 3-33) 60.6 cm/yr Minimum freshwater renewal time: 61 days Surface water slope: Vermilion River 1.25 cm/km Freshwater B/Schooner B-0.28 cm/km Tides: Range: Vermilion River at Vermilion Lock 37.5 cm ± 15 cm (standard deviation) Period: Diurnal (predominantly) Water level variation Seasonal: Spring-Summer peaks, winter minimum (fig. 3-34) Long term: 0.94 cm/yr rise (1945-1974) (fig. 3-34) Salinity: Seasonal: (fig. 3-35) Long-term: (fig. 3-36) Control structures and modifications At Schooner Bayou, Vermilion Lock Per km^ Net primary production (t/yr) Appendix 6.3 Sport hunting and fishing use estimated potential yield Big game (man-days x 1000/yr) Small game (man-days x 1000/yr) Waterfowl (man-days x 1000/yr) Saltwater finfishing (man-days x 1000/yr) Freshwater finfishing (man-days x 1000/yr) Total Agriculture Commercial species harvest Shrimp (kg x 1000/yr) Menhaden (kg x 1000/yr) Blue crab (kg x 1000/yr) Oyster (kg meat x 1000/yr) Other saltwater finfishes (kgx 1000/yr) Freshwater finfishes (kgx 1000/yr) Nutria (pelts /yr) Muskrat (pelts /yr) Per basin 1,047 1,999,100 14.2 23.7 63.0 76.7 127.0 304.6 380 2,839 0.98 151 18.3 2,835 0.4 62.6 0.01 1.6 70.7 32.9 31,324 19,500 Method explained in part 3.5.2 Present harvest attributed to basin (part 3.2.4) continued 97 Table 3.68. Summary of natural and cultural features of Vermilion Basin (continued). C. Habitats of Vermilion Basin CI. Habitat area in 1974 and net changes since 1952 Habitat Area 1974 Percent of Change in area 1952 to 1974 (ha)^ total area (ha) (%) Nearshore Gulf 115,599 — 200 0.5 Inland open water 18,977 25.2 1,485 8.5 Natural marsh 36,031 47.9 -6,800 -15.9 Impounded marsh 7,962 10.6 2,673 50.5 Swamp forest 464 0.6 -91 -16.4 Natural ridge 1,062 1.4 -154 -12.7 Spoil 1,593 2.1 1,099 222.5 Rice field 730 1.0 551 307.8 Non-rice cropland 1,326 1.7 451 51.5 Pasture 3,318 4.4 676 25.6 Urban 199 0.3 87 77.7 Beach 396 0.5 Upland forest 3,253 4.3 -177 -5.2 Total 190,910 1 hectare (ha) = 2.47 acres (a) Calculation excludes area of nearshore Gulf habitat C2. Habitat modification from 1952 to 1974 due to identifiable human activities Change in 1974 as 1952 Changed to (by- 1974) Area percent of Area original Cause of change Habitat (ha) Habitat (ha) 1952 habitat Filling and draining Natural marsh 42,831 Agricultural 619 1.4 Urban 15 0.04 Impounded marsh 5.289 Agricultural 800 15.1 Impounding Natural marsh 42,831 Impounded mzu-sh 3,473 8.1 Canal dredge and spoil Natural marsh 42,831 Spoil 1,099 2.6 Natural marsh 42,831 Canal 550* 1.3 Upland construction Upland forest 3,430 Agricultural 117 5.2 Natural ridge 1,216 Agricultural 104 8.6 Ridge 1,216 Urban 50 4.1 Agricultural 4,989 Urban 22 0.4 Calculated as 1/2 spoil area continued 98 Table 3.68. Summary of natural and cultural features of Vermilion Basin (continued). C3. Natural wetland loss (1952-1974)-summary Area To Process (ha) Canals Dredging 550 Inland open water Subsidence 844 Nearshore Gulf Shoreline erosion/deposition 200 Impounded marsh Leveeing 3,473 Spoil Dredging 1,099 Agriculture Draining 619 Urban Draining 15 Percent of 1952 area Total 6,800 1.3 2.0 0.5 8.1 2.6 1.4 0.04 16.04 P. Cultural Features of the Vermilion Basin Dl. Socioeconomics Population: 804 Employment: (Figure 3-12) Commercial harvest Value (Sx 1000) Production (1974) Value ($x 1000) Fishing Shrimp Menhaden Blue Crab 325.3 262.5 16.6 Minerals Gas (mcf) 112,943,923 34.674 Oyster Other estuarine- 2.1 Crude oil (bbls) 2,833,930 18,477 dependent species 31.5 Total 53,151 Freshwater finfish 13.4 Agriculture Subtotal 651.4 Crops 917 Trapping Other 1,071 Nutria 187.9 Total 1,988 Muskrat 87.8 Sport hunting/fishing Saltwater sportfishing 454.6 Subtotal Total 275.7 927.1 Freshwater sportfishing 486.0 Navigation Small game hunting 408.6 Total traffic: 998,284 tons 1976; Big game hunting 141.3 declining from peak 1.9 Waterfowl hunting 992.7 million tons. 1967 Total 2,483.2 Imports: non-fuel mined products Exports: Oil and petrochemicals continued 99 Table 3.68. Summar>' of natural and cultural features of Vermilion Basin (concluded). D2. Total 1974 canal area D4. Estimated sport Hshing and hunting supply and demand (man-days x 1000) Har\xst as percent of estimated Supply Demand sustained yield 110 574 175 147 Area Length (ha) (km) Navigation 73S 382 Agricultural drainage 72 234 Oil activity 848 178 Transportation embankment canals 5 8 Other 1 O Total 1,664 804 Big game 14.2 15.7 Small game 23.7 136.2 Water- fowl 63.0 110.3 Saltwater fishing 76.7 112.5 D3. Water use Annual volume (m x 10 ) Agriculture Municipal Industrial Total 7.1 0.1 0.0 T7 D5. Nutrient and toxin discharges Phosphorus (P) loading rates to entire Vermilion Basin drainage area Cultural P input (g/yrxio") Natural P input (g/yrxlO^) Total P input Urban Industrial Rice Non-rice agriculture 12.00 0.03 65.00 265.00 ive Forest Lake Barren land Oil well brine To wells 1.648.7 disposal (n To pi 34.1 1.10 51.80 0.05 Total Surface water discharge (m x Pload(g/m^/yr) Eutrophic state 333.03 10* /yr) 15.9 0.24 Excess 52.95 385.98 nbbls) ts To surface waters 3,601.8 Vermilion River is heavily polluted with industrial wastes 100 shore Gulf habitat, a remnant of an early delta lobe built when the Mississippi River flowed in its most westward course. Because of sediment discharge by the Atchafalaya River, mudflats are again rapidly forming off the Vermilion coast, and the coastline is accreting at Chenier Au Tigre. Within Vermihon Basin most of the inland open water is that part of Vennihon Bay within the basin boundaries. The bay is protected from the Gulf by Marsh Island, and exchanges water with the Gulf through the narrow, deep Southwest Pass. The bay is also open to the east, connecting with the West Cote Blanche Bay. Westward-flowing freshwater from the Atchafalaya River and the Wax Lake Outlet keeps the whole basin rather fresh. Although the wetlands of the basin exchange water freely with Vermilion Bay, the area of salt marsh habitat is very small and most of the marshes are brackish or intermediate (table 3.68). Most freshwater flow from the north is through the VermOion River (fig. 3-33). Bayou Teche water is also diverted to the Vermihon River through Bayou Fusilier and Ruth Canal. This fresh water is confined by the high banks of the lower Vermilion River so that overbank flooding does not occur normally ex- cept near the mouth. Drainage is complicated by the complex network of dredged canals that include the Gulf Intracoastal Waterway (GIWW), that intersects the Vermilion River about 5 km (3 mi) above its mouth, the Vermilion River cutoff that bypasses Lit- tle Vermilion Bay and Little White Lake, and the Schooner Bayou cutoff that connects the GIWW with Schooner Bayou (plate IB). On the west and northwest, drainage into the Vermilion Basin is restricted by the embankment of Louisiana Highway 82, by spoil banks along the Schooner Bayou/Freshwater Bayou system, and by control structures at Vermilion Lock, Freshwater Bayou , and Schooner Bayou designed to preserve fresh supphes in the Mermentau Basin (part 3.6.3). Docks on Freshwater Bayou restrict direct exchange of water with the Gulf and probably reduce the use of wedands by estuarine-dependent organisms in the area north of the locks. North of Vermihon Bay some high land exists with a small forested area, agriculture, and a few villages. The lower part of the basin has poor access, except by boat, and no permanent settlements are found there. Diurnal tides are pronounced as far north as Abbeville . They average 3 7.5 cm ( 1 4.8 in) at Vermilion Lock (fig. 3-33). Seasonal water levels peak in spring and early fall (fig. 3-34), but do not show the distinct low level during the summer found elsewhere on the coast, perhaps because of Atchafalaya River water. Since 1945, mean armual water levels have shown an annual increase of 0.94 cm (0.37 in) per year at Vennilion Lock (fig. 3-34). This is comparable to, or slightly lower than, rates elsewhere along the Chenier Plain. At the Lock, water is nearly fresh (fig. 3-35). The long-term trends at this location show a decrease in salinity since 1947 (fig. 3-36), due probably to a combination of wet years and freshwater discharges from the Mermentau Basin. Vermilion Bay and its adjacent wetlands support large populations of shrimp, Gulf menhaden, blue crab and other estuarine-dependent organisms. Nutria and muskrat are harvested from the wetlands, and waterfowl are abundant. The potential for fresh and saltwater finfishing is also high (table 3.68). Socioeconomics. The Vermihon Basin has an ex- tremely small human population— 804 individuals. The work force is employed primarily in mining and mineral fuel-related jobs (fig. 3-12). Only in Intra- coastal City is there industrial development in the basin. The annual values of commodities produced by the basin are: oil and gas S53.2 million; agricultural products, S2 million; fish and fur animals, $913,000; and sport fish and game, 52. 5 million (table 3.68). As in other basins, the mineral extraction industry dom- inates the economy. Waterbome transport into and through the basin was about 1 million tons (0.9 million tonnes) in 1976, representing a decline from the peak of 1.9 million tons (1.7 milUon tonnes) in 1967. Nonfuel mined products are imported into the basin and oil and petrochemicals are exported. Effects of Human Activities on the Environment. Hydrologic effects: The effects of modifications of the normal hydrologic regime by canals, spoil banks, and control structures in the Vermihon Basin may be masked by the overpowering influence of the Atcha- falaya River, which floods Vermilion Bay with fresh water and high nutrient sediments. Habitat effects: Unexplained wetland losses in the Vermilion Basin are occurring at a rate of about 0.09%/yr (844 ha or 2,086 a since 1952), the lowest rate along the Chenier Plain coast, inspite of the ex- tensive hydrologic alterations (table 3.68). The rela- tive stability of the marshes may result from the heavy sediment influx from the Atchafalaya River. Total wetland losses have been 15.9% (6,800 ha or 16,803 a) since 1952. Over one-half of this loss (3,473 ha or 8,582 a) has resuhed from impoundment. Canal and spoil area increases have amounted to 1 ,649 ha (4,075 a). Drainage for agriculture accounts for the majority of the remaining area. Although there is shoreline ac- cretion along the eastern coast of the basin, the re- treating shoreline on the western coast has resulted in a net loss of 200 ha (494 a) for the entire basin. Spoil area has tripled since 1952, indicating a significant increase in the rate of canal construction. In the entire Chenier Plain, about 85% of the present canal system was dredged prior to 1952. The rate of conversion of wetlands to agricultural land also has increased. As indicated in part 3.2.3, agricuhural area in the Louisiana coastal parishes has been declining slowly since the early 1930s. The Ver- milion Basin is an exception; its agricultural area in- creased 24% since 1952 and shows the highest dollar return per hectare of farmland in the Chenier Plain. 101 30_ RUTH CANAL VERMILION RIVER AT LAFAYETTE i! 40 1971 1971 1968 1969 J FMAMJ JASOND Month 15 10 _ in 1 = (A E 01 u r 5 u « O 10 B 1964-1973 — , — j r~ =4— = : == * ' ' ' ■*■.>.■■ J FMAMJ JASOND Month 10^ C (A 3 1962 a 3 5 - < * -> » 1 1 c rv -5 o E K 2 u J > < W) >• ^ > 2 03 < 1 '"J 1 u. IW) nil 1***1 '*' useui aAoqe imBish .'!l / f — ■' ••'.'' ^ ,''''k<^ CO / y'J^"^^^ 8 / yy^ W. > eg CD ^C Vf 1 !) V « 1 - \ - \ r < / / -^ * - \1 • / / o £ ^ \ / / 3 S Xn-\ 1 1 ' ^V\ V l E ^^* • ^Sii^^ > ^^^ \ \v\ 1 1 1 \ \ / 1 \ OWC") s in o n [uiol ISW OAoqv l»Aen iSjBAA -1 Q - O - v> o 2 OS U C •T3 T3 CS > (IJ >> > "~2 a; -^- Ui c 1) n -4-* E 02 C a> <1) E & o ^ Q« c u< C u c^ •4—1 CO h # 5> D ■♦-» •J flfl a c u^ o C/!! • 03 Zi c > o ^ ;= c •s « E i> >.£ •" o > 'C 3 fc 103 i n lO o> N r>. 00 00 T" in o 00 ■1 ^ w CM w >- o o c o . ;=! ^~- i '~' a, J= — ■>-' c *C 00 -8 ON S — o c E .2 « ■?^. "O -a =3 «L) << 0) n > (0 I ^ ^ ~ r f - < - I _ "-^ "x - > — < - 1 X X > - / rf- ' o z o en < < c o |oo/q] uouefAsa pjepuBjs Q o [oo/o] AjiUNOino c S <= .2> c« •2 ■" o ^- >> ■H " E c tj p • 104 The reasons for the high returns, however, are not clear (see part 3.2.3). It is hkely that continued agri- cultural expansion into marginal wetlands will acceler- ate drainage canal construction and nutrient runoff. Water quality is already a problem in the VermiUon River. Loading rates of P to the basin place it in the excessive eutrophic state, primarily because of runoff from upstream agriculture (table 3.68). Agricultural expansion, therefore, is hkely to aggravate eutrophica- tion problems in the more enclosed bays and small lakes. The Atchafalaya River undoubtedly influences tlie productivity and diversity of Vennihon Bay but its significance has not been totally considered. Effects on renewable resources: The overall trend in habitats is for a continuous, slow conversion of na- tural areas to culturally maintained systems. The con- version of relatively unique swamp forest and ridge habitats in particular, can be expected to result in permanent loss of some of the rarer animal species that hve in these habitats. Both habitats normally support a diverse flora and fauna. Because they are elevated areas in the middle of lands subject to inunda- tion, ridges have a particularly valuable function dur- ing storms and as a refuge for migratory song birds (part 4.13) The silt-laden Atchafalaya waters are probably the most important influence on the fishery resources of the Vermilion Basin. The extensive oyster reefs that once fringed the gulfward edges of the bay have been smothered by sOt or killed by the freshwater. The average salinities decreased to 3 %o in the bay (Juneau 1975). Throughout the Atchafalaya and Ver- milion bays, typical freshwater species such as white crappie, bluegill, sheepshead minnow, and blue cat- fish are found in the same waters as such marine organisms as the Atlantic midshipman. Gulf toadfish, Atlantic cutlassfish, and Atlantic stingray (Juneau 1975). As mudflats build out and become stabilized over the shallow shelf, a diverse benthic fauna should develop. This in turn should benefit demersal fishes. The Vemiilion Basin is severly impacted by activ- ities associated with oil and gas recovery, and with agriculture. These activities generally lead to acceler- ated rates of wetland loss, and eutrophication is al- ready evident. At the same time, rapid land accretion, extreme turbidity, and high nutrient loads are result- ing from the delta-buUding processes of the Atcha- falaya River. Because of both cultural and natural processes, this basin is an area of intense ecological interest and worthy of wise management practices. 3.6.3 MERMENTAU BASIN General features. The Mermentau Basin is unique in the Chenier Plain for several reasons. It was formeriy part of the Mermentau/Chenier drainage system, but the natural chenier ridges along its southern boundary and a number of water control structures have es- sentially resulted in a single, large freshwater im- poundment. Therefore, the basin has no nearshore Gulf habitat. Several large shallow lakes cover about one-quarter of the basin area (fig. 3-32). The natural and impounded wetlands (47% of the area) are all fresh. Most of the remaining land, which lies along the northern edge of the basin, is used for rice cultiva- tion and for cattle. The basin is supplied with fresh water (fig. 3-37) by the Mermentau River, which cuts diagonally across it. Water control structures at Catfish Point, Schooner Bayou and the Superior Canal, the Vermihon and Cal- casieu locks on the GIWW, and locks at Freshwater Bayou (fig. 3-32) restrict the fiow of fresh water out of the basin and of salt water into the basin. The main purpose of the control structures is to provide a large freshwater reservoir for agricultural (rice) irrigation so as to prevent tidal flooding, and to pro- vide higher water levels for navigation. The locks and control structures are manipulated to maintain mini- mum water levels within the basin at 60 to 70 cm (24 to 28 in) above Gulf MLW and to prevent salt intru- sion. They are generally closed on incoming tides and when inside stages decline below 0.66 m (2.17 ft) MLG. However, they are opened when stages exceed 0.60 to 0.67 m (1.97 to 2.20 ft) MLG and flows are adequate to prevent salt intrusion. Before 1951, surface water in the basin was pumped into rice fields and the flow in the Mermentau River was often reversed. Upstream flows of up to 56.6 m^l sec (2000 ft^/sec) were recorded. This caused saltwater intrusion into the lower basin (Army Corps of Engineers 1961). Fresh water moves laterally between the Mermentau and Calcasieu basins via the Calcasieu Lock, depending on the direction of the hy- draulic head. Because of these control structures, there is no significant diurnal tide within the basin. Wind tides dominate the circulation of Grand and White lakes. Seasonal water levels are modified from the typical dual spring and fall peaks. They are relatively high all year except during June and July (fig. 3-38). The water is neariy fresh year round, but chlorinity rises to about 1.7 %o inside the Catfish Point control structure in June and July (fig. 3-39). Since the con- trol structures were installed in 1950, salinity appears to have been declining slowly, although year-to-year variability is high. Since 1965, rainfall has generally been above normal, and it appears that of the control structure has reduced salinities (fig. 3-38) under these circumstances. Gages show a net long-term water level increase of 2.13 cm(0.83 in) per year in the basin (fig. 3-38). Historically, the Mermentau was an estuarine nursery ground, but it no longer functions in this capacity as far as fisheries are concerned (Gunter and Shell 1958, Morton 1973). Commercial freshwater fishing for catfish and other species exists in Grand Lake, White Lake, and adjacent waters. The major commercial living resource is nutria (table 3.69). The area attracts large numbers of waterfowl, both because of the extensive fresh marshes and also because of the nearby rice fields. The potential for freshwater fin- fishing is also high, although there is very httle re- corded commercial use of this resource. Socioeconomics. Most of the residents of the Mermentau Basin are members of farming families. 105 2000_ 1000. A 1965-1976 I I I I I I L I I _75 50 25 J FMAMJ J ASOND Month JFMAMJJASOND Month m ss =~^ J FMAMJJA SOND Month _3 a 3 20 15 10 r 5 Q 1973 Id I L _L J F M A M J J A S Month O N D Figure 3-37. Freshwater supply of Mermentau Basin: (A) riverine input from U.S. Geological Survey discharge data; (B) mean monthly water surplus (deficit); (C) monthly water surplus (deficit) in a dry year; and (D) monthly water surplus (deficit) in a wet year. Calculated from U.S. Weather Service data, as described by Borengasser 1977. 106 ^x uoiteiASQ pjepueis O O ItuD] |9Aen jejBM UB»H 1SW a*o / / ■^ r^ on D ^- > ^Ji 1-. ™ <- ^ en C C-- "S C ea o ^•^ )-, g I- o « u .— ■^ "S i~, C3 2 D ^s •4^ CO ^ rfac hly "3 3 C C S_^ ,,<-^ cd ..PQ ^ ^ E hJ ^< 00 ^ ro (U ii 3 60 [i. 107 standard Deviation 1 _ o ♦<• c o O 2_ J F AMJJASOND Month Figure 3-39. Monthly means and standard deviations (1947 to 1974) of chlorinity in the Mermentau Basin inside Catfish Point control structure, from U.S. Army Corps of Engineers records. The few communities along the northern boundary of the basin are agriculturally oriented. These people are not adequately represented in the employment statis- tics in figure 3-12, which report only employees cov- ered by the Federal Insurance Compensation Act. Despite the importance of farming, the largest in- dustry in the basin is mineral extraction. Minerals, the most valuable products of the basin, were worth $1 14 million in 1974. Agricultural products are worth about $14 milhon per year; commercial fishing and trapping, about $1 million;and sport fishing and hunt- ing, $2 million. The volume of waterborne commerce into and through the basin is stable at about 2 miUion tons (1.8 million tonnes) per year, most of it (1.4 million tons or 1.27 million tonnes) involves the export of crude petroleum. This volume is small compared to the 50 million tons (45 million tonnes) of traffic in the Calcasieu Basin and 100 miUion tons (91 miUion tonnes) in the Sabine area. Effects of Human Activities on the Environment. Hydrologic effects : The extensive modification of the natural hydrologic regime of the Mermentau Basin by control structureshas been described. Within the basin, circulation patterns have undoubtedly been modified by the extensive canal network 2,826 km (1,756 mi) long (plate 5B), covering 2.1% of the basin area (table 3.69). In addition, impounded wetlands within the basin cover 18% of the area and further modify the inundation and flushing patterns of the wetlands. A final factor is the withdrawal of fresh water for rice irrigation. This is calculated at 3 x 10* m'' (1.1 x 10'° ft^), about one-third of the total flow of the Mer- mentau River (table 3.69), the major stream feeding the basin, and about 10% of the total annual water surplus of the basin, including rain. This demand oc- curs almost entirely during April, May, June, and July when the basin nomially sustains rainfall deficits (fig. 3-37) and river discharge is at its minimum. About 40% of the irrigation water is returned to the basin when rice fields are drained toward the end of sum- mer (Texas Water Development Board 1977). Because about one-third of the total irrigation requirement is supplied by groundwater, the volume of water released is actually greater than the surface water withdrawn earher in the season. Thus, surface waterflows out of the basin are actually larger at present than before the control structures were installed. The net effect has been to modify the normal flow and water level pat- terns in the basin. Figure 3-40 shows how effective the control structures are in controlling water level in the basin and in preventing saltwater intrusion. At the northern station on Freshwater Bayou, the water level inside the lock in the winter is as much as 30 cm (12 in) above the level one-half mile downstream outside the lock (Freshwater Bayou, south). During the sum- mer when Gulf water levels are higher than water levels in the basin, the structures prevent intrusion of salt water. Habitat effects. WeUand loss is occurring at an annual rate of 0.88% (20,132 ha or 49,751 a from 1952 to 1974). All but 3,356 ha (8,293 a) can be ac- counted for by direct cultural modification: impound- ing of wetlands accounts for 12,797 ha (31,622 a or 63%) and draining for agriculture, another 2,584 ha (6,385 a) 13% (table 3.69). The residual wetland loss was 3.3% between 1952 and 1974, or 0.14%/yr. This rate is a little higher than the residual loss rates for the Vemiilion,'Chenier, and East Bay basins. Wild- life biologists familiar with the basin attribute this loss to erosion of lake shorehnes. This erosion results from maintenance of high water levels behind the control structures. Except for occasional dry years, abnormally high water levels over the marshes also prevent gennination of annual grasses and sedges which are valuable waterfowl food (Vaughn, R. R.,U.S. Fish and Wildlife Service, Atlanta. Ga., letter dated 1 April 1977 to District Engineer, U.S.A.C.E., New Orleans, La.). 108 Table 3.69. Summary of natural and cultural features of Mermentau Basin. A. Hydrology of the Mermentau Basin B. Primary production, potential yield and harvest of living resources of Mermentau Basin. Riverine Processes Upstreeim drainage area 9,539 km Freshwater flow volume (into basin) 53.4 X 10*m^/yr(fig. 3-37) Seasonal: Annual rainfall 146 cm (at Lake Arthur) Annual rain surplus (Chenier and Mermentau) 55.2 cm/yr (fig. 3-37) Maximum freshwater renewal time: (Chenier and Mermentau) 83 days Surface water slope: 0.011 ft/mi= 0.2 cm/yr (fig. 3-38) Tides: No significant diurnal tide Range: Period: Water level variation Seasonal: One minimum only in June-July (fig. 3-38) variability highest in May Long-term: 2.13 cm/yr rise (fig. 3-38) Salinity: negligible Seasonal: Peak in May-June (fig. 3-39) Variability highest during summer Long-term: Slight decrease but variability high Control structures and modifications At Catfish Point Control Structure Vermilion Lock Schooner Bayou Control Structure Calcasieu Lock Freshwater Bayou Control Structure Small structure on Superior Canal on Rockefeller Refuge GIWW Per km^ Net primary production (t/yr) Appendix 6.3 Sport hunitng and fishing use estimated potential yield* Agriculture Commercial species harvest Shrimp (kg x 1000/yr) Menhaden (kg x 1000/yr) Blue crab (kg x 1000/yr) Oyster (kg meat x 1000/yr) Other saltwater finfishes (kgx 1000/yr) Freshwater finfishes (kgx 1000/yr) Nutria (pelts/yr) Muskrat (pelts/yr) 380 Per basin 1,592 4,267,000 Big game (man-days x 1000/yr) 59.3 Small game (man-days x 1000/yr) 88.7 Waterfowl (man-days x 1000/yr) 141.5 Saltwater finfishing (man-days x 1000/yr) Freshwater finfishing (man-days x 1000/yr) 3,799 Total 4,088.6 128,109 187 155,800 8,280 Method explained in part 3.5.2 Present harvest attributed to basin (part 3.2.4) continued 109 Table 3.69. Summary of natural and cultural features of Mermentau Basin (continued) C. Habitats of Mermentau Basin CI. Habitat area in 1974 and net changes since 1952 Habitat Area 1974 (ha)=' Percent of total area Changes in area 1952 to 1974 (ha) (%) Nearshore Gulf Inland open water Natural marsh Impounded marsh Swamp forest Natural ridge Spoil Rice field Non-rice cropland Pasture Urban Beach Upland forest Total 61,497 79,052 49,399 1,660 3,998 8,636 32,976 3,390 23,069 1,595 2,772 268.044 22.9 29.5 18.4 0.6 1.5 3.2 12.3 1.3 8.6 0.6 1.0 3,873 6.7 20,132 -20.3 10,767 27.9 -134 -7.5 -146 -3.5 1,000 13.0 2,238 7.3 877 34.9 1,893 8.9 52 3.4 -289 -9.4 1 hectare (ha) = 2.47 acres (a) Calculation excludes area of nearshore Gulf habitat C2. Habitat modification from 1952 to 1974 due to identifiable human activities Change in 1974 as 1952 Changed to (by 1974) Area percent of Area original Cause of change Habitat (ha) Habitat (ha) 1952 habitat Filling and draining Natural marsh 99.184 Agricultural 2,466 2.5 Impounded marsh 38,632 Agricultural 2,030 5.3 Swamp forest 1.794 Agricultural 118 6.6 Impounding Natural marsh 99,184 Impounded marsh 12,797 12.9 Canal dredge and spoil Natural marsh 99,184 Spoil 1,019 Canal 510 1.0 0.5 Upland construction Natural ridge 4,143 Agricultural 145 3.5 Upland forest 3.081 Agricultural 289 9.4 Agriculture 54.427 continued Urban 40 0.1 110 Table 3.69. Summary of natural and cultural features of Mermentau Basin (continued). C3. Natural wetland loss (1952-1974)— summary To Process Area (ha) Percent of 1952 area Canals Dredging 510 Inland open water Subsidence 3,340 Nearshore Gulf Shoreline erosion/deposition Impounded marsh Leveeing 12,797 Spoil Dredging 1,019 Agriculture Draining 2,466 Urban Draining Total 20,132 0.5 3.4 12.9 1.0 2.5 20.3 D. Cultural Features of the Mermentau Basin Dl. Socioeconomics Population: 7,974 Employment: See figure 3-12 Production Value (1974) ($ X 1000) Minerals Gas (mcf) 189,940,493 58,312 Crude oil (bbls) 8,543,329 55,702 Total Agriculture Crops Other Total Sport hunting/fishing Saltwater sportfishing Freshwater sportfishing Small game hunting Big game hunting Waterfowl hunting Total 114,014 12,655 1,609 14,264 367.2 392.4 330.0 114.3 801 2,005 Commercial harvest Fishing Shrimp Menhaden Blue crab Oyster Other estuarine- dependent species Freshwater finfish Subtotal Trapping Nutria Muskrat Subtotal Total Value ($ X 1000) 115.1 70 101.7 286.8 934.8 37.3 972.1 1,358.9 Navigation Total traffic: 2,086,473 tons, 1976 fairly stable last 10 years Exports: chiefly crude petroleum (1.4 million tons) continued 111 Table 3.69. Summary of natural and cultural features of Mermentau Basin (concluded) D2. Total 1-974 canal area D4. Estimated sport fishing and hunting supply and Area Length demand (man days x 1000) (ha) (km) Harvest as percent of Navigation Agricultural drainage 2,036 350 1,137 1,156 Supply Mermentau Chenier Demand estimated sustained yield Oil activity Transportation canals Other 1,945 452 embankm ent 228 40 40 41 Big game 59.3 24.9 Small game 88.7 31.1 2.7 110.0 15 92 Total 4,399 2,826 Water- fowl 141.5 97.2 89.0 37 D3. Water use Saltwater fishing 147.8 379.8 257 Annual volume (m^ xlO'^) Agriculture 319.6 Municipal 1.1 Industrial 1.8 Total 322.5 D5. Nutrient and toxin discharges Phosphorus (P) loading rates to entire Mermentau and Chenier basins drainage area Cultural P input (g/yrxlO*) Natural P input (g/yrxlO^) Total P input Urban 213.60 Forest 7.87 Industrial 0.11 Lake 112.60 Rice 737.10 Barren land 0.07 Non-rice agriculture 193.10 Total 1,143.91 120.54 Surface water discharge (m x 10* /yr) 53.4 Oil well brine disposal (mbbls) Pload(g/m^/yr) 0.2 To wells To pits 34.12 Eutrophic state Borderline 32,415.24 1,264.4 To surface waters t 1,388.9 112 30_ E u g a a ■o c o m 15 E u CO < 45 30 a ^ 15_ o Inside North Control Gate, _L ± M M J J Month N Figure 3-40. Monthly mean water levels above mean sea level (MSL) inside and outside the Freshwater Bayou control structure (1963-1974), from U.S. Army Corps of Engineers gages. In addition to loss of natural marsh, there has been a small loss of upland forest and swamp forest habitats, primarily to agricultural use. These habitats each compose less than 1% of the basin area. Swamp forest habitat, in particular, is rapidly disappearing from the Chenier Plain region. Effects on renewable resources: In a Study con- ducted from September 1951 through June 1953, immediately after installation of the locks and con- trol structures, Gunter and Shell (1958) found that marine and estuarine organisms dominated Grand Lake, and nearby Little Bay. Morton (1973) has shown that the basin now functions as a fresh-water im- poundment and 80% of the aquatic species are those typical of freshwater areas. Erosion of the shorelines of White and Grand lakes has been extensive and severe. Nutria, the most important furbearer, appears to be declining because of the high water levels, and muskrats have not occurred in the basin since installa- tion of the control structures. The results of impounding wetlands may have long-term implications for water quality management. The impoundment of wetlands within the Mermentau Basin may have different implications than elsewhere. Because of water control structures, the basin does not function effectively as an estuarine nursery. The marshes within the impounded basin do function ef- fectively as habitats for waterfowl, nutria, alligators, wading birds, and other marsh wildlife. The impound- ments may have long-term implications for water qual- ity because the basin has a relatively long freshwater flushing time (83 days, table 3.69). Heavy loads of agricultural fertilizer are drained from the rice fields, and the drainage network of canals accelerates the runoff process and bypasses normal overland flow, dumping nutrients directly into the shallow lakes. Im- poundments do not have the nutrient filtering cap- 113 Table 3.70. Summary of natural and cultural features of Chenier Basin. A. Hydrology of the Chenier Basin B. Primary production, potential yield and harvest of living resources of Chenier Basin. Riverine Processes Freshwater flow volume (into basin) no data Upstream drainage area 9,539 km drains into Mermentau Basin, which, in turn, drains partially into Chenier Basin Annujil rainfall 146 cm (at Lake Arthur) Annual rain surplus (Chenier jmd Mermentau) 55.2 cm/yr Maximum freshwater renewal time: (Chenier and Mermentau) 83 days Surface water slope: See Mermentau Basin (fig. 3-38) Tides: Range: 24 to 42 cm (monthly mean) (fig. 3-32) Period: Primarily diurnal Water level variation Seasonal: Minimum November-February, high all summer (fig. 3-41) Long term: See Mermentau Basin (fig. 3-38) Salinity: Seasonal: No data Long term: No data Control structures and modifications Flow into Chenier Basin is discharged from Mermentau Basin at Catfish Point Control Structure (CPCS). GIWW Per km^ Per basin Net primary production (t/yr) 1,222.4 2,389,228 Appendix 6.3 Sport hunting and fishing use estimated potential yield^ Big game (man-days x 1000/yr) 24.9 Small game (man-days x 1000/yr) 31.4 Waterfowl (man-days x 1000/yr) 97.2 Saltwater finfishing (man-days x 1000/yr) 147.8 Freshwater finfishing (man-days x 1000/yr) 103.7 Total 405.0 Agriculture Rice (t/yr) 69 Commercial species harvest Shrimp (kg x 1000/yr) 4.7 186 Menhaden (kg x 1000/yr) 139.1 5,488 Blue crab (kg x 1000/yr) 0.5 18.2 Oyster (kg meat x 1000/yr) Other saltwater finfishes (kg x 1000/yr) 188.8 Freshwater finfishes (kgx 1000/yr) 5.1 Nutria (pelts/yr) 69,519 Muskrat (pelts/yr) 20,874 Method explained in part 3.5.2 bp, Present harvest attributed to basin (part 3.2.4) continued 114 Table 3.70. Summary of natural and cultural features of Chenier Basin (continued). C. Habitats of Chenier Basin CI. Habitat area in 1974 and net changes since 1952 Habitat Percent of Area 1974 total area (ha)^ 100,658 _ 5,638 6.0 28,242 29.8 48,834 51.5 3,288 3.5 3,420 3.6 67 0.1 604 0.6 2,751 2.9 401 0.4 1,544 1.6 Changes in area 1952 to 1974 (ha) (%) Nearshore Gulf Inland open water Natural marsh Impounded marsh Swamp forest Natural ridge Spoil Rice field Non-rice cropland Pasture Urban Beach Upland forest Total 195,447 1 hectare (ha) = 2.47 acres (a) Calculation excludes area of nearshore Gulf habitat 927 0.9 498 9.7 3,727 -32.7 0,876 28.7 -475 -12.6 1,441 72.8 29 76.3 196 48.2 120 4.6 152 61.0 -36 -2.3 C2. Habitat modification from 1952 to 1974 due to identifiable human activities Cause of change Habitat 1952 Area (ha) Changed to (by 1974) Area Habitat (ha) Change in 1974 as percent of original 1952 habitat Filling and draining Impounding Canal dredge and spoil Upland construction Natural marsh 41,969 Natural marsh 41,969 Inland open water 5,140 Natural marsh 41,969 Inland open water 5,140 Natural ridge 3,288 Natural ridge 3,288 Agriculture 3,077 Urban 22 Impounded marsh Impounded marsh Inland open water(canal) 590 Spoil Spoil Agricultural Urban Urban 0.05 10,136 24.2 740 14.4 590 1.4 1,181 4.8 249 2.8 376 11.4 99 3.0 31 1.0 continued 115 Table 3.70. Summary of natural and cultural features of Chenier Basin (continued). C3. Natural wetland loss (1952-1974)-summary To Process Area (ha) Percent of 1952 area Canals Dredging 590 1.4 Inland open water Subsidence 912 2.2 Nearshore Gulf Shoreline erosion/deposition 927 2.2 Impounded marsh Leveeing 10,136 24.2 Spoil Dredging 1,181 2.8 Agriculture Draining Urban Draining 22 0.05 Total 13,768 32.8 D. Cultural Features of the Chenier Basin Dl. Socioeconomics Population: 1,220 Employment: (Figure 3 12) Production Value (1974) ($ X 1000) Minerals Gas (mcf) 193,579,634 59,429 Crude oil (bbls) 2,485,233 16,204 Total Agriculture Crops Other Total Sport hunting/fishing Saltwater sportfishing Freshwater sportfishing Small game hunting Big game hunting Waterfowl hunting Total 75.633 210 450 660 367.2 392.4 633.0 114 801 2,005 Commercial harvest Fishing Shrimp Menhaden Blue crab Oyster Other estuarine- dependent species Freshwater finfish Subtotal Trapping Nutria Muskrat Subtotal Total Value (S X 1000) 400.3 508.2 4.8 45.8 2.7 960.8 417.1 93.9 511.0 1,472.8 Navigation (Chenier and Mermentau combined) Total traffic: about 2,000,000 short tons (1978); declining from about 3,000,000 in 1967 Imports: non-petroleum mined products Exports : crude petroleum continued 116 Table 3.70. Summary of natural and cultural features of Chenier Basin (concluded). D2. Total 1974 canal area Area Length (ha) (km) Navigation 530 555 Agricultural drainage 114 329 Oil activity 1,016 335 Transportation embankment canals 19 27 Other 75 1.754 75 Total 1,321 D3. Water use Annual volume (m^ X 10^) Agriculture 0.7 Municipal 0.2 Industrial Total 0.9 D4. Estimated sport fishing and hunting supply and demand (man-days x 1000) Harvest as percent of estimated Supply sustained Mermentau Chenier Demand yield Big game 59.3 24.9 12.7 15 Small game 88.7 31.4 110.0 92 Water- fowl 141.5 97.2 89.0 37 Saltwater fishing 147.8 379.8 257 D5. Nutrient and toxin discharges Phosphorus — See Mermentau Basin Oil well brine disposal (mbbis) To wells To pits To surface waters 2,657.8 42.1 4,461.7 117 abilities of wetlands, but data are not available to de- termine the quantitative effects on water quality of converting natural wetlands to impounded wetlands. Judging by phosphorus loading, water-quality is mar- ginal in the basin (table 3.69). There may be considerable potential for increased commercial production of freshwater finfish species and crayfish in the Mennentau Basin, since they do not appear to be exploited to any great extent. The supply of waterfowl for hunting exceeds the demand in the mermentau Basin. The decline in wetland area can be expected to lead to a decline of wildlife and water resources. Fur- ther^ expansion of agriculture in the basin can occur only at the expense ofnatural or impounded wetlands. As agriculture expands, problems of advanced stages of eutrophication will be compounded by increased nutrients from fertilizer runoff, increased water use for irrigation, and increased density of drainage canals. An infomial agreement among the U.S. Fish and Wildlife Service (FWS), the Louisiana Department of Wildhfe and Fisheries (LDWF), and the U.S. Army Corps of Engineers (USAGE) was implemented during the summer and fall of 1976. Under this agreement, the timing and extent of drawdowns needed to en- courage wildlife food-plant production and to partially restore the use of the Memientau Basin by estuarine organisms was attempted. Vaughn (Pers. Comm.) re- ported an estimated inshore harvest of white shrimp in excess of 160,000 kg (353,000 lb), and an offshore harvest of 53,000 kg (1 1 7,000 lb), based on sampling and surveys in White and Grand lakes. In addition 160,000 kg (353,000 lb) of blue crab were harvested. The combined dockside value was estimated at $1,321,000. A remarkable increase in annual grasses and sedges was also reported. There seemed to be no major conflict between this drawndown program and rice culture, navigation, or flood control. 3.6.4 CHENIER BASIN General features. The Chenier Basin is a long, narrow, east-to-west strip of land and water sand- wiched between the Mermentau Basin and the deep Gulf waters. Well-developed chenier ridges along the northern boundary, and control structures in opera- tion since 1950 on the Mermentau River and Fresh- water Bayou effectively cut this basin off hydrolog- ically from the Mennentau and Vermilion basins (piate IB). Beach ridges and smaller cheniers protect the in- land area from direct Gulf influence (fig. 3-32). Fresh- water input is limited to local rainfall and to the Mer- mentau River discharge in the extreme western end of the basin. The tidal action is strong and the natural wetlands of the basin are all salt-influenced. Because sediments from the Atchafalaya River drift westward, mud flats are developing along the Vermilion Basin coastline and are expected to develop westward across the Chenier Basin. However, shoreline erosion is oc- curring from Rollover Bayou to Hackberry Beach. The beach is accretingslowly west of Hackberry Beach to the Calcasieu River. Inland water bodies are few and cover only 2.9% of the land area; most of them are associated with the lower reaches of the Memientau River. Over two- thirds of what was once natural marsh has been im- pounded (25% of the total basin area). As a conse- quence, natural circulation patterns through the basin are severly modified. Nearly all hydrographic records are from the lower Memientau River at Grand Chenier and at Cat- fish Point control structure, both at the extreme western end of the basin. Tidal range at Grand Chenier is 24 to 42 cm (9.4 to 16.5 in), but at Catfish Point this tide is completely masked by the fiow through the control structure, when it is open (fig. 3-41). The sudden release of large volumes of fresh water also causes dramatic short-tenn salinity decreases in the proximity of the control structure (Perret et al. 1971). Long-temi mean water levels at Grand Chenier show peaks in April and Sep- tember, with little depression during the summer months. Over the years, mean water level has been rising (about 2.1 cm/yr or 0.83 in/yr) with respect to the gage elevation at a rate comparable to the Mer- mentau Basin (fig. 3-41). In addition to the Memientau River pass, a num- ber of other ephemeral passes connect the inland por- tion of the basin to the Gulf. These connections allow a high diversity of estuarine-dependent fishes and shellfishes in the inland water (Perret et al. 1971). Shrimp and menhaden are the primary estuarine- dependent commercial species caught in the basin. Trapping of nutria and muskrat is an important indus- try. Large populations of waterfowl and sport-fishes are also found here. Socioeconomics. The population of the Chenier Basin is scattered along the ridges. No dense popula- tion centers nor manufacturing industries exist. Min- eral extraction is virtually the only industry (table 3.70). The value of extracted oil and gas in 1974 was $75 million, $0.7 million for agriculture, $1.5 million for fishing and trapping, and an estimated $2 million for sport fishing and hunting(Chenier and Mermentau combined). Effects of Human Activities on the Environment. Hydrologic effects: Normal fiows of water in tiie Chenier Basin have been modified by control struc- tures and extensive impoundments (part 3.6.3). Man- ipulation of the Catfish Point control structure changes the volume and timing of discharge from the Mennentau Basin into the Chenier Basin. In addition, an extensive network of canals, 1,321 km (821 mi) in length, covers 2% of the land area; and spoil banks along these canals and along the lower Mennentau River further restrict and modify drainage. Habitat effects . Since 1952, 33% of the natural marshes have been lost. Four percent of the marshes has been directly changed by canals— either to water or to spoil. Over 900 ha (2,224 a) have been lost to shoreline erosion by the Gulf. 118 B 30 - 1971 p^ 15 • 1 1 1 ^0- 1 1 — 0^ 1 1 1 1 1 ""^J "\. JFMAMJJASOND Month 35 c standard Davlatlon of Wat»r Laval 2S E 2C 1S s - 1 1 1 1 1 Walar Laval N D Figure 3-41. Water levels in Chenier Basin; (A) surface water slope in the Chenier and Mermentau basins from U.S. Army Corps of Engineers data; (B) monthly variation in daily tidal range at Grand Chenier; (C) seasonal variation in water level in Grand Chenier over a year; and (D) typical tide record. By far the major impact on natural wetlands has been impounding. Over 10,000 ha (24,700 a) have been impounded since 1952. These impoundments tend to become increasingly fresh; their function as a detritus source and as a refuge for estuarine species is considerably decreased. Residual wetland loss to inland open water habitat has been only about 0.1%/ yr (912 ha or 2,254 a since 1952), comparable to the Vennilion and East Bay basins. Urban and agricultural land use has reduced the natural ridge habitat by 475 ha (1,174 a), a 12.6% loss between 1952 and 1974. This unique habitat is most fully developed in the Chenier Basin. Effects on renewable resources : The density of estuarine-dependent fishery species is high in the in- land open water habitat of the Chenier Basin (Perret et al. 1971), and free water exchange with marshes adjacent to the Mermentau River above upper Mud Lake does occur. However, access to marshes from the lower Mermentau River is restricted and over two- thirds of the Chenier Basin wetlands are now im- pounded. The dependence of estuarine organism on the linkage between marine waters and inland marshes has been well documented, so it seems inevitable that impoundments have seriously and adversely affected these living resources. Estimates of waterfowl hunting compared to waterfowl numbers in the Mermentau and Chenier basins suggest that some increase in hunting is possible without endangering these resources. These figures must be interpreted with care, however, since they are based on rather arbitrary assumptions about the population served by these basins. Estimates of water quality made for the com- bined Mermentau/Chenier basins indicated that load- ing rates are high enough so that a borderline eu- 119 trophic state exists. The problem is probably confined primarily to the Memientau Basin where runoff from rice fields is heavy. The Chenier Basin is isolated from population centers to the north by the extensive Mer- mentau wetlands. The area is sparsely populated; agriculture is not a major industry, and much of the land is public or private refuges. For these reasons, and because it is important to protect the unique na- tural cheniers, the Chenier Basin seems most appro- priate for the maintenance, futher development, and protection of its considerable recreation potential. 3.6.5 CALCASIEU BASIN General features. The Calcasieu Basin is a shallow wetland/aquatic system with a single major freshwater input at the north end and a generally north to south circulation pattern through a large central lake (plates IB and 3B and fig. 342). Some east-to-west water movement through the GIWW also occurs. The chenier ridges are well developed and effectively protect the inland marshes from the marine environment. A single major pass allows circulation with the Gulf of Mexico. In addition, Creole Canal allows freshwater drainage to the Gulf througli a one way flapgate control struc- ture at Oak Grove. Brackish and intennediate marsh habitats predominate in the basin (table 3.71; plate 33). Along the upper edge of the basin much of the land is in agriculture, cliiefly rice. The Hackberry salt dome protrudes to an elevation of about 10 m (33 ft) midway up the basin. Hydrologically the basin is fed by a fairly modest upstream water flow (table 3.71) which, combined with an annual rain surplus of 49 cm (19 in), gives a maximum freshwater renewal time of about 37 days. Therefore, the basin is well-flushed. Salinities in the upper basin adjust with the discharge of fresh water into the basin (fig. 3-43). Of all the Chenier Plain coast, tides are the most well-developed along this area. They are primarily semidiurnal and are strong as far north as the Calcasieu Lock. Mean water level shows typical seasonal peaks in April and September (fig. 3-44). Water level is rising at an ap- parent rate of 2 to 3 cni/yr (0.8 to 1 .2 in/yr), a rate characteristic of the rest of the Chenier Plain. Major living resources of the basin are shrimp. Gulf menhaden, nutria, muskrat. and waterfowl. There are two major menhaden processing plants in Cameron. Socioeconomics. The basin itself is rural, with a few small villages. However, the large industrial cen- ters of Lake Charles, Westlake, and Sulphur lie just outside the basin to the north. As with other basins, the main industry is mineral extraction, but petro- chemical manufacturing plants outside the basin are the major employers. In temis of production of crude products, minerals bring in about $52 million an- nually. Commercial fishing and trapping are a distant second with $3.6 million. Sport hunting and fishing are conservatively estimated at $2.8 million and agri- culture at $2.2 million. Thus, as elsewhere in the Chenier Plain, the renewable resources are overshad- owed by the mineral extraction industry. Waterborne commerce is also important econom- ically and volume has been fairly stable for the past 10 years. In recent years, imported crude oil and ex- ported petrochemical products have been the primary commodities. Effects of Human Activities on the Environment. Hydrologic effects'. In the mid-1800"s a natural chan- nel with a maximum depth of 4 m (13 ft) ran through the central part of Calcasieu Lake and exited via the natural sinuous portion of the lower Calcasieu River. The shallowest depth of the system was 1 m (3 ft) at the bar at the mouth of Calcasieu Pass. This bar con- trolled intrusion of salt water into the basin to the ex- tent that every spring during the freshet, the lake and pass were flushed with fresh water for periods pro- longed enough to result in oyster mortality near St. John's Island (Van Sickle 1977). From 1871, Calcasieu Pass was dredged continuously to various depths to allow ship traffic entry into the channel to Lake Charles. During these dredgings the depth did not ex- ceed 4m (13 ft) at the mouth, but increasing salinities allowed the oyster population to move progressively up the lower Calcasieu River (Van Sickle 1977). Navigation into Lake Charles from Sabine Lake was first made possible by deepening and widening the GIWW between Lake Charles and Sabine Lake. In 1937, a land-cut channel was dredged to a depth of 10 m (33 ft) along the western edge of Calcasieu Lake and was separated from the lake by spoil banks. The lower sinuous shallow pass to the Gulf was bypassed by a 10 m (33 ft) bar channel that extended some distance offshore. Although supportive data are lack- ing, later studies (U.S. Army Corps of Engineers 1950, Van Sickle 1977) suggest that saltwater intrusion up the ship channel did occur at this time. In 1946 the existing ship channel was deepened to 12 m (39 ft). In the mid-1960"s the ship channel width was doubled and the channel was dredged to a depth of 1 5 m (49 ft). Van Sickle (1977) demonstrated a resultant increase of surface salinity at Lake Charles from 5.5 to7.7%o for the 8-year period before (1955 to 1963) and after the channel dredging from 1963 to 1971 (fig. 3-45). The dredged material from the channel was used to levee off the ship channel from the lake to the cast so that Calcasieu River water that once circulated througli Calcasieu Lake now was confined to the Cal- casieu Ship Channel. At the same time (1968), the U.S. Aniiy Corps of Engineers constructed a saltwater barrier above Lake Charles to keep the saltwater wedge from moving upstream. The levee system designed to isolate the ship channel from Calcasieu Lake has subsequently been breached at both the northern and southern ends. Oyster populations have subsequently become estab- lished in the washout fans and there is a hand-tong fishery in the basin. There is some suggestion that the Creole Canal can act as a saltwater pump. Salt water coming in through Calcasieu Pass flows east into Lake Calcasieu to Grand Bayou. It pushes fresher water over the marsh along the southeastern shore of the lake and into Creole Canal. This fresh water flows to the Gulf and is replaced by saline water through Cal- casieu Pass. 120 fej^ Impounded or upland, no circulation I I Weired, controlled circulation I- -] Marsh circulati Wind driven circulation I ! Tidal c I / I Riverl Calcasieu River at Goosport Calcasieu River at Lake Charles Figure 3-42. Hydrologic regions of Calcasieu Basin. 121 Table 3.71. Summary of natural anil cultural features of Calcasieu Basin. A. Hydrology of the Calcasieu Basin B. Primary production, potential yield and harvest of living resources of Calcasieu Basin. Riverine Processes Freshwater flow volume (flow upstream) 49.8 X lO^m^/yr Seasonal: (see fig. 3-43) Upstream drainage area 13,723 km^ Annual rainfall— 138 cm (at Lake Charles) .Annual rain surplus 49.3 cm/yr Seasonal: (see fig. 3-43) Minimum freshwater renewal time: 37 days Surface water slope: Cameron Pass to Hackberry 0.76 cm/km Hackberry to Lake Chailes 0.19 cm/km (see fig. 3-44) Tides: Range: 500 cm (average of 1961-71 annual mean) (see app. 6.4) Period: Semi-diurnal with large diurnal inequality (see fig. 3-44) Water level variation Seasonal: Peaks in April and September (see fig. 3-44) Long-term: 2.0 to 3.1 cm/yr raise (sec fig. 3-44) Salinity: Seasonal: (see fig. 3-43) Long-term: (see fig. 3-45) Control structures and modifications Salt water barrier above Lake Chailes Major ship channel from Gulf to Lake Charles GIWW Per km^ Net primary production (t/yr) Appendix 6.3 Sport hunting and fishing use estimated potential yield^ Big game (man-days x 1000/yr) Small game (man-days x 1000/yr) Waterfowl (man-days x 1000/yr) Saltwater finfishing (man-days x 1000/yr) Freshwater finfishing (man-days x 1000/yr) Total Agriculture Rice (t/yr) Commercial species harvest Per basin 1,452 2,550,299 Method explained in part 3.5.2 Present harvest attributed to basin (part 3.2.4) 16.3 46.8 98.2 147.8 272.0 581.1 5,839 Shrimp (kg x 1000/yr) 2.7 803 Menhaden (kg x 1000/yr) 43.9 13,136 Blue crab (kg x 1000/yr) 0.4 117 Oyster (kg meat x 1000/yr) 0.1 36.9 Other saltwater finfishes (kgx 1000/yr) 878 Freshwater finfishes (kgx 1000/yr) 6.0 Nutria (pelts/yr) 40,320 Muskrat (pelts/yr) 34,050 continued 122 Table 3.71. Summary of natural and cultural features of Calcasieu Basin (continued). C. Habitats of Calcasieu Basin CI. Habitat area in 1974 and net changes since 1952 Habitat Percent of Area 1974 total area (ha)^ 40.243 40,956 30.3 54,803 40.5 9,751 7.2 715 0.5 8,060 6.0 3,310 2.4 5,713 4.2 1,555 1.1 5,970 4.4 2,277 1.7 844 0.6 1,430 1.1 Changes in area 1952 to 1974 (ha) (%) Nearshore Gulf Inland open water Natural marsh Impounded marsh Swamp forest Natural ridge Spoil Rice field Non-rice cropland Pasture Urban Beach Upland forest Total -161 -0.4 13,107 47.1 18,832 -25.6 3,559 57.5 -171 -19.3 -345 -4.1 848 34.4 1,300 29.5 214 16.0 -352 -5.6 1,428 168.0 -65 -7.2 -530 -27.0 175,627 1 hectare • i h \ r 1 h - 1 A Si 1 \ / ■^ •MMM •J 1 ' 1 \ \ s £ \ s s ; V ' \X- \ 1 r 1 — - \ 5 s .* \ 1 1/ - Jl 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 56 65 Y«ar Figure 3-45. Mean annual salinities at Lake Charles, Louisiana (1956-1975) from U.S. Army Corps of Engineers data. 24O0L 2200. 2000 _ iaoo_ E 1800- S 1200 _ Figure 3-46. Commercial landings of brown and white shrimp in the Calcasieu Basin in 1963-1975 (U.S. Dep. Commerce 1976a). 128 On the west edge of the basin, canals in the Sabine National Wildlife Refuge allow water flow across basin boundaries and connect the Calcasieu and Sabine basins. Because water follows the deeper, straighter dredged canals the natural streams, such as North Bayou, become filled with sediments. In addition to the ship channel, construction of other canals has been extensive. Canals 1,271 km (790 mi) in length now cover 2.6% of the land area of the basin (table 3.71). Most of these canals were con- structed either for navigation or for access to oU and gas sites. These navigation projects have resulted in signifi- cant modifications to the natural hydrologic patterns: north-to-south circulation now largely bypasses the Calcasieu Lake. The river presumably drops much of its sediment load in the ship channel rather than in the lake and adjacent wetlands. The channel permits saltwater intrusion which increases the salinity. Higher salinities have resulted in oyster beds becoming estab- lished further upstream nearer to Lake Charles (Van Sickle 1977). The many interconnecting channels of the GIWW, Alkah Ditch, and oil well access canals al- low the salt to penetrate far into wetlands. Further modifications have occurred because levees and spoil bank construction has purposefully or inadvertently impounded large wetland areas, re- ducing flushing and overland flow. Habitat effects: These hydrologic modifications have profoundly influenced wetland and aquatic hab- itats. Since 1952, 19.029 ha (47,022 a) of natural wetlands in Calcasieu Basin have been lost. Only 6,361 ha (15,718 a or 9%) can be accounted for by direct cultural changes such as impounding, draining, etc. (table 3.71). The remaining 12,668 ha (31,303 a or 17%) are lost to open water, a loss rate 0.75%/yr. By contrast, although the rates of natural processes such as sea level rise are similar in other basins, the unex- plained residual wetland loss rate is only about 0.13%/ yr (except Sabine Basin). The high wetland loss rate in the Calcasieu Basin is almost certainly caused by the changed hydrology coupled with saltwater intru- sion, and the possible effects of discharges of toxic materials and brine into the basin. Aside from the loss of wetlands to inland open water habitat, agricultural area has increased by 1 ,162 ha (2,871 a) mostly by draining wetlands; urban ex- pansion has claimed 1 ,428 ha (3,529 a) from wetland, agriculture, and upland forest habitat (table 3.71). Net shorehne erosion is very small, but erosion at Holly Beach (a vacation town) is a critical problem. There is some evidence of the development of off- sliore mudflats also, but this is poorly documented. Effects on renewable resources: The loss of na- tural habitats, particularly wetlands, signals a long- term gradual decline in the living resources of the basin. As discussed in part 3.5, these resources appear to be exploited at their maximum potential. In the Calcasieu Basin there appears to have been an increase in the harvest of certain estuarine-dependent species such as shrimp (fig. 3^6) since the widening and deepening of the ship channel. This may result from two factors. First, the increase in salinity in the estuary and se- cond, the temporary increase in the marsh to water interface associated with the wetland degradation. The potential fishery increase is balanced by other factors; the probable inland migration of the marsh zones with increasing salt and brackish marshes ac- companied by loss of intermediate and fresh marshes as degradation continues. The increase in brackish marsh at the expense of fresh and inteiTnediate marsh can be expected to be deterimental to the nutria har- vest and to most waterfowl. Waterfowl hunters in the basin already complain of the effects of salt encroach- ment on habitat changes. 3.6.6 SABINE BASIN General Features. The Sabine is the largest basin on the Chenier Plain (plates lA, 3A, and 4A, and fig. 347). Because it straddles the Louisiana-Texas border, there may be political problems in managing it as a single hydrologic unit. The land surface slope is slight and about one-half of the inland area is wet- land (table 3.72 and figs. 348 and 3-49). Sabine Lake is approximately 32 km (20 mi) long and 13 km (8 mi) wide and has an average depth of about 2 m (6.6 ft). Sabine River empties into Sabine Lake from the northeast; it has a drainage area of 24,152 km (9,325 mi^). Most of the river is impounded by the Toledo Bend Dam. The Neches River, emptying into the Sabine Lake from the northwest, has a drainage area of 20,584 km^ (7,948 mi^). Much of this river is impounded by the Sam Raybum Reservoir. A deep draft ship channel enters the basin through Sabine Pass from the Gulf and follows the western edge of Sabine Lake to the mouth of the Neches River. Here the dredged channel divides into two segments. One segment goes up the Neches River to Beaumont and the other goes up the Sabine River to Orange (fig. 347). The channel is separated from the Sabine Lake proper by a narrow strip of land, predominantly a man-made spoil island. The Gulf Intracoastal Water- way (GIWW) enters Texas from Louisiana about 4.8 km (3 mi) below Orange and continues south- westward along the deep draft ship channel on the west side of Sabine Lake. At the mouth of Taylor Bayou near Port Arthur, the GIWW leaves the lake and proceeds toward East Bay in a channel that is almost completely man-made (fig. 3-47). An outcrop- ping of high land along the ship channel on the western side of Sabine Lake has provided a site for the city of Port Arthur and intense industrial develop- ment. Likewise, the cities of Beaumont and Orange located on the Neches and Sabine rivers, respectively, are industrial centers. This is the most industrialized basin in the region and the only basin within which high population densities occur. Even so only 5% of the total basin area is urbanized (table 3.72), but activities in this area have a strong influence on the whole basin, and particularly on Sabine Lake. Thirteen percent of the inland area of the basin is in agricul- tural production, chiefly for rice and qattle. Most of the farm land is located along the northern bound- ary of the basin. On the Louisiana side of the basin the large Sabine National Wildlife Refuge encompasses 129 M |UID| i*«*-| !•)•/« 1 - TO /J ^^ J: c ■« Sb c 5 > rA I 2 §■" I o < S S' ■ iT ^ c pa I- .3 2 ^ *^ Ol - 13 -S 3 u o T3 C •o o o • c 3 o a £ « k. (A tg c 5 • > $ 2 i H a. OS c o •a O 1/1 I CO 3 141 Table 3.74. Texas landings of blue crab for Sabine Lake, and Galveston and Trinity bays, showing amount and value of landing, 1962 to 1975. Sabine Lake Galveston and Trinity Bays Year (kg) (8) (kg) (8) 1962 107,639 16,611 141,206 15,569 1965 230,973 38,044 824,599 147,345 1969 374,492 76,502 773,706 157,538 1970 310,716 63,998 1,189,339 244,798 1971 870,005 188,008 980,139 213,240 1972 584,554 127,369 848,277 191,649 1973 616,079 158,433 925,344 254,376 1974 254,379 77,090 899,489 273,301 1975 281,640 96,740 845,284 287,019 by Bolivar Roads, an improved natural pass between the Gulf and Galveston Bay which is flanked by jetties several miles in length projecting into the Gulf. Water depths in East Bay range from about 1.5 to 2 m (0.9 to 1.2 ft) at its western end to about 1 m (0.62 ft) at the eastern end. The eastern arm of the bay, called Rollover Bay, contains about 255 ha (556a) and is about 0.5 m (1.6 ft) deep. It opens to the Gulf through an old natural pass. Rollover Pass, which was reopened by dredging in 1955. East Bay Bayou, Oyster Bayou, and Onion Bayou constitute the natural drainage system (approximately 660 km^ or 255 mi") of East Bay. The Gulflntra- coastal Waterway extending from Sabine Lake enters the East Bay Basin through East Bay Bayou, crosses the northern end of Rollover Bay and extends along the bay side of Bolivar Peninsula to deep water in Bolivar Roads. Geologically the East Bay Basin has attributes of the Barrier Strand Plain of Texas as well as the Chenier Plain. Most of East Bay Basin consists of Recent de- posits of sand which fomi dune ridges on Bolivar Peninsula. Behind the beach ridge is coastal marsh. Farther inland appears the Beaumont clay surface, a coastal Pleistocene terrace that dips seaward under the Recent marsh and beach deposits (Houston Geological Society 1959). Most of the area is nearly level coastal plain comprised of the Harris-Vest on Soil Association with poor internal and surface drainage (U.S. Department Agriculture 1976). The average ground surface slope is about 0.2 m/km (1.06 ft/mi). Marsh elevations are somewhat higher than those fur- ther east toward Sabine Lake. The bay shoreline generally lacks sand beaches and in many places is associated with low-lying marshes, particularly on the back side of Bolivar Peninsula (plates 3A and 4A). On the north shore of East Bay low bluffs exist where wave-action has eroded the Pleistocene terrace deposits. Mean rainfall surplus is 20.6 cm/yr or 8.1 in/yr (table 3.75 and fig. 3-52). Most of the small bayous are weired, have low flow rates, and drain southward and southeastward into East Bay. The average annual flow of freshwater from Oyster, Onion, and East Bay bayous into East Bay is only about 2.1 x lO^m (7.4x 10''ft^) (Rice Center 1974). The primary drainage into the whole Galveston Bay system, how- ever, is via the San Jacinto and Trinity rivers, and these discharges indirectly modify salinities in East Bay through mixing with Galveston Bay waters. The Trinity River Basin is outside of the study area and its influence on East Bay will only be briefly described. Based on local freshwater drainage the maximum freshwater renewal time for East Bay is calculated to be about 577 days. This estimate is undoubtedly high because of three factors; freshwater input via die GIWW from the Sabine Basin, indirect input of fresh- water from the San Jacinto and Trinity rivers, and tidal mixing. Fresliwater from the Sabine Basin draining into the GIWW is considerable. Maximum flow rates of 113m^/sec 3,991 ft'^/sec) have been measured in the GIWW with maximum current velocities of 0.396 m/sec or 1.3 ft/sec (Jarnes et al. 1977). This results from a difference in water eleva- tion between ends of the GIWW, brought about by tlie difference in tidal ranges and lag times between Sabine Lake and East Bay, the small tidal range in the GIWW, wind set-up and/or excess freshwater inflow into Sabine Lake (James et al. 1977). Water renewal times in East Bay are also strongly influenced by tides, which are well-developed at both ends of the bay (fig. 3-53). The tides in the Gulf near Rollover Pass lag behind those at Bolivar Roads by 3.2 hr at high tide and 4.3 hr at low tide. However, since the tide gage trace at Hanna's Reef does not con- sistently lead or lag the one at Marsh Point, the tidal waters apparently enter and exit the adjacent passes without much interaction. This conclusion is sup- ported by Prather and Sorenscn (1972) who predicted that only 1% of the flow througli Bolivar Roads will be exchanged at Rollover Pass, and that the area in East Bay affected by water exchange through Rollover Pass is only about 205 ha (507a). Tides from both passes are probably attenuated somewhere in mid-bay. Wind- driven circulation is also apparently poor, probably because the bay is oriented east-to-west, whereas pre- dominant winds are north to south. Figure 3-54 shows patterns of mean, extreme higli, and extreme low salinities that document the poor circulation in mid East Bay because salinity changes occur most slowly there. The presence of live oysters in the bay is some- what contradictory to those conclusions, and further studies of East Bay circulation are needed. Seasonal peaks in mean water level occur in spring and late summer, as elsewhere in the Chenier Plain (fig. 3-53). Since 1964 the mean annual water level has risen at tlie rate of about 1.5 cm/yr(0.6 in/yr), approximating changes elsewhere on the Chenier Plain. The rather saline estuary provides excellent habi- tat for estuarinc-dependent fishes and shellfishes. Coupled with West Bay and Galveston Bay, this is the most productive estuary on the Texas Coast, particu- larly for shrimp, trout, redfish. Gulf menhaden, and oysters. Texas catch data for these species, as tabulated 142 Table 3.75. Summary of natural and cultural features of East Bay Basin. A. Hydrology of the East Bay Basin B. Primary production, potential yield an d harvest of living resources of East Bay Basin. Riverine Processes Freshwater flow volume (into basin) 0.4 m^ X 10* /yr Net primary production (t/yr) Per km^ Per basin Annual rainfall 113 cm (at Galveston) 1,139 1,275,001 Seasonal: Figure 3-52 Appendix 6.3 Maximum freshwater renewal time: 577 days Sport hunting and fishing use estimated potential yield* Surface water slope: Not computed— large open bay Big game (man-days x 1000/yr) 5.2 system. Transient slope due to Small game (man-days x 1000/yr) 18.0 tide. Waterfowl (man-days x 1000/yr) 35.2 Saltwater finfishing Tides (man-days x 1000/yr) 124.4 Range: 30 cm (fig. 3-53) Period: Diurnal Freshwater finfishing (man-days x 1000/yr) Total 34.3 217.5 Water level variation Seasonal: Low January- April; peaks in May and September (fig. 3-53) Agriculture Rice (t/yr) 3,646 Long term: 1.5 cm/yr (fig. 3-53) Commercial species harvest Salinity: 1965-1967 Mean: 14-24°/oo (fig. 3-54) Seasonal: Extreme low salinity: 2-10%o Extreme high salinity: 24-30°/oo Shrimp (kg x 1000/yr) Menhaden (kg x 1000/yr) Blue crab (kg x 1000/yr) Oyster (kg meat x 1000/yr) 2.7 43.9 0.7 0.7 685 11,057 188 181 Long term: No data Other saltwater finfishes (kgx 1000/yr) 20 Control structures and modifications Freshwater finfishes Rollover Pass constructed 1955 Weirs on most streams GIWW (kgx 1000/yr) Nutria (pelts/yr) Muskrat (pelts/yr) 14.895 11,402 ^Method explained in part 3.5,2 Present harvest attributed to basin (part 3.2.4) continued 143 Table 3.75. Summary of natural and cultural features of East Bay Basin (continued). C. Habitats of East Bay Basin CI. Habitat area in 1974 and net changes since 1954 Habitat Percent of Area 1974 total area (ha)^ 30,540 _ 26.553 32.6 19,674 24.2 4,623 5.7 4,725 5.8 2,278 2.8 3,567 4.4 199 0.2 15,654 19.2 2,577 3.2 1,256 1.5 264 0.3 111,910 Changes in area 1954 to 1974 (ha) (%) Nearshore Gulf Inland open water Natural marsh Impounded marsh Swamp forest Natural ridge Spoil Rice field Non-rice cropland Pasture Urban Beach Upland forest Total 25 0.1 444 1.7 ,380 -6.6 874 23.3 -70 -1.5 40 1.8 -386 -9.8 68 51.9 121 0.8 278 12.1 -14 -1.1 1 hectare (ha) = 2.47 acres (a) Calculation excludes area of nearshore Gulf habitat C2. Habitat modification from 1954 to 1974 due to identifiable human activities Change in 1974 as 1954 Changed to (by 1974) Area percent of Area original Cause of change Habitat (ha) Habitat (ha) 1954 habitat Filling and draining Impounding Natural marsh 21,064 Impounded marsh 874 4.1 Canal dredge and spoil Natural marsh 21,064 Spoil 58 0.3 Natural marsh 21,064 Canal 29 0.1 Inland open water 26,109 Spoil 25 0.1 Upland construction Natural ridge 4,741 Urban 70 1.5 Beach 1,270 Urban 24 1.1 ■Agriculture 19,617 Urban 197 1.0 continued 144 Table 3.75. Summary of natural and cultural features of East Bay Basin (continued). C3. Natural wetland loss (1954-1974) summary Area To Process (ha) Percent of 1952 area Canals Dredging 29 0.1 Inland open water Subsidence 397 1.9 Nearshore Gulf Shoreline erosion/deposition 65 0.3 Impounded marsh Leveeing 874 4.1 Spoil Dredging 58 0.3 Agriculture Draining Urban Draining Total 1,423 6.7 D. Cultural Features of the East Bay Basin Dl. Socioeconomics Value Population: 4,824 (Sx 1000) Employment: $3,074,100 (fig. 3-12) Commercial harvest Production Value Fishing (1974) ($ X 1000) Shrimp Menhaden 1,471.7 1,023.8 Minerals Blue crab 44.0 Gas (mcf) 123,346,093 Oyster 246.8 Crude oil (bbls) 8,163,375 Other estuarine- dependent species Total 91,092 19.0 Agriculture Crops 1,212 Freshwater finfish Subtotal 0.0 2,804.3 Other 1,429 Trapping Total 2,641 Nutria 89.4 Sport hunting/fishing Saltwater sportfishing 1,010 Muskrat Subtotal 51.3 140.7 Freshwater sportfishing 1,080 Total 2,945.0 Small game hunting 900 Navigation Big game hunting 315 Total traffic: 1,200,000 short tons/yr Waterfowl hunting 2,205 Imports: non-fuel mined products Total 5,510 Exports: non-fuel mined products continued 145 Table 3.75. Summary of natural and cultural features of East Bay Basin (concluded). D2. Total 1974 canal area t)4. Estimated sport fishing and hunting supply and demand (man-days x 1000) Area (ha) Length (km) Supply Demand Harvest as percent Navigation kment 660 91 34 26 137 305 8 38 sustained yield Agricultural drainage Oil activity Transportation embar canals Other Big game Small game Water- fowl Saltwater fishing 5,357 194 696 200 300.0 35.0 245.0 250.0 5.6 18.0 35.2 124.4 Total D3. Water use 811 488 Annua volume (m' X 10^) Agriculture Municipal Industrial Total 34.6 0.7 18.9 54.2 U5. Nutrient and toxin discharges Phosphorus loading rates to entire Sabine Basin drainage area (appendix 6.4). Cultural P input (g/yrxlO^) Natural P input (g/yrxlO^) Total P input Urban Industrial Rice Non-rice agriculture Total Surface water discharge (m x 10 /yr) 0.13 0.0 0.0 29.0 29.13 r) 5.2 0.08 Permissable Forest Lake Barren land 0.02 10.3 0.44 10.76 39.89 Pload(g/m^/yr) Eutrophic state Other important pollutants: industrial toxins and coliform bacteria East end of East Bay closed to shellfishing because of high coliform levels (plates 5A, 6.-\; Diener 1975). 146 (0 E o 10_ 5_ ■z 101 1964-1973 Mean 5_ I I I I JFMAMJJASOND Month Surplus UI o B 1962 a 1 1 — E ^ 5 10 5 5 • a 20 ^ ' t '::■ 1 1 1 1 J FMAMJ J ASON D Montti 25, 20 _ 15 _ 5 10 a (/> 5 E 5_ 10 15 1973 O-b ± I I I I I I I I JFMAMJJASOND Montti Figure 3-52. Freshwater supply of East Bay: (A) mean (1964 to 1974) monthly rainfall surpluses (deficits); (B) monthly rainfall surplus (deficit) for a dry year; and (C) monthly rainfall surplus (deficit) for a wet year. 147 IE e m X IIMil |»ABT j«iaw ""h |ui3| l*Aa-| i*)aM u»»|i( 1- D 4> 00 ti cd 5 M ^ t« c S c^ D Ji C £'5b c = •-tu C t— .2 ° *-*-< C/5 rt a 'C !r « o >o 13 >. S E O u ^< * (0 c o o J: ^ * CQ 31 ^ .-g-o '■^ vs ^^ •— o ca .« •O D. .s- §§ '^^ •gi > • ' >>! x: - o ^ S 5 ^ ^ < c ^ ca . . (D .5 E (/) i2 13 CQ 3 ^5 03 IIMII (Buau apij. uaam liaaii laAai leoM uaan UJ I i O — « - s — < c w» — c I/) o r^ _,—i^ o ^ii 2i rr, ly-i i> u, 3 00 u- |ui3| laAai laiaM uaan 148 "o O S o c o o a 3 M (L> U< 3 QQ X o o e l-H +-• X u t3 C o u n 4) I en 149 for the Galveston Bay System, are strongly influenced by the significant amount of nursery area in East Bay (appendix 6.2). Parker (1970) documented the signifi- cance of East Bay as a nursery and migratory route for juvenile brown shrimp, Atlantic croaker, and spot in the Galveston Bay System. The oyster harvest of Gal- veston Bay is greatly dependent on reefs in East Bay, particularly Hanna's Reef, Elm Grove Reef, Moody's Reef and Frenchy's Reef. These reefs have been in ap- proved oystering areas since the mid 1950's (Hofstet- ter 1977). Records of the Texas Parks and Wildlife Department (see appendix 6.3) indicate that muskrat and nutria densities are comparable to the Louisiana portion of the Chenier Plain but the habitat for these species is less extensive in Texas. Waterfowl are also valuable resources of the basin. Some 20 species of ducks and geese winter in this area around the Anahuac National WUdlife Refuge. Other marslies on the north shore of East Bay centering around Robinson Lake, Wallis Lake, Lake Surprise, and East Bay Bayou support large populations of the lesser snow goose, Canada goose, white-fronted goose, mottled duck and the fulvous tree-duck. This area also provides habitat for marsh and shorebirds and includes such species as roseate spoonbill; common, snowy, and cattle egrets; yellow-and-b lack-crowned night herons; least and American bitterns; eared and pied-bill grebes; long-billed curlew; whimbrel; common snipe and a variety of smaller shore birds and gulls. Less common species include: white-faced, and white ibises; oliva- ceous, and double-crested cormorants; anhingas; and white pelicans. All six species of North American rails reside here. Mourning doves and bob-white quail are found in the area. Five species of sea turtles are indig- enous to the area and include the Atlantic ridley, hawksbill, leatherback, green, and loggerhead. The peregrine falcon, Southern bald eagle, brown pelican and the red wolf have been sighted in the area (Lard 1978). Socioeconomics. Mineral extraction, manufactur- ing, and agricuhure (fig. 3-12) provide the main sources of employment in East Bay Basin. Oil and gas are by far the most valuable product of the basin, worth $91 million per year. Commercial fish and fur- bearers produce an annual income of about $2.9 mil- lion, agriculture $2.6 million, and sportfishing and hunting an estimated $5.5 million. These figures sug- gest tliat because of the basin's proximity to large urban centers the game sportfish, and waterfowl are the most important renewable resources of the basin. Effects of Human Activities on the Environment. Hydrologic effects : The hydrology of East Bay Basin has been modified by several cultural activities and is influenced seasonally by others. River discharge, tidal currents, and circulation patterns have been modified by human activity. The predominant factors appear to be the opening of Rollover Pass and the GIWW. The opening of Rollover Pass has improved circulation, particularly in the upper end of East Bay. Oyster reefs in most of East Bay are healthy, showing that water quality and circulation is ade- quate. Upland agriculture, particularly rice farming. uses weirs on streams to control drainage and salinity. This restricts water exchange between the marshes and the bay. However, Uttle information is available about the flushing frequencies for these wetlands. The banks of East Bay Bayou are actively eroding because of agricultural development, and creating sedimentation problems downstream (U.S. Department of Agricul- ture 1976). Water that is rich in nutrients, particularly nitrogen and phosphoms, enters East Bay via the GIWW from the Sabine Basin, suggesting the chemical pollutants could be transported to East Bay from the Beaumont-Port Arthur-Orange area (James et al. 1977). Canal density in East Bay basin is the lowest of the entire Chenier Plain (1.5% of the land area). Oil and gas development has resulted in the impoundment of weflands through road construction (appendix 6.2). Beach and shoreUne erosion and the effects of Rollover Pass and Bolivar Roads on sedimentation and erosion have been well documented (U.S. Army Corps of Engineers 1951, Jaworski 1971,Prather and Soren- sen 1972, Seelig and Sorensen 1973, McGowen et al. 1977, and Morton 1977). Rollover Bay appears to be filling with sediment derived from the Gulf beaches as well as from upstream drainage areas. Approximately 200 ha (494a) of this bay are now less than 0.5 m (1.6 ft) deep. Likewise, beach erosion and sediment movement out of Rollover Pass appears to have con- tributed to progradation of beaches on Bolivar Peninsula north of the north jetty. H abitat effects : Habitat distribution in the East Bay Basin is shown in plates 3A and 4A, and table 3.75. The rate of wetland loss to open water that cannot be explained by cultural activities is 0.08%/yr, a figure comparable to the low rate in the Vemiilion Basin. This low rate is attributed to the natural firm- ness of the substrate in East Bay Basin. The overall wetland loss for East Bay Basin was 6.9% during the period from 1954 to 1974 (table 3.75). The largest loss resulted from fill placed on wetlands for im- poundment levees. Since 1954, 87 ha (215a) have been used for the construction of canals and for the disposal of dredged material from the GIWW and from canals for housing developments on Bolivar Peninsula. Other habitat changes since 1954 are rather small. Urban growth has altered natural ridge and agricul- tural habitat and is expected to continue, particu- lariy on Bolivar Peninsula. Effects on renewable resources : The opening of Rollover Pass seems to have been beneficial to estu- arinc organisms. Reid(1955, 1956) conducted an eco- logical study of East Bay before and after the opening of the pass. His data revealed a nearly two-fold in- crease in salinity in the upper end of the bay and an accompanying increase in salt-tolerant organisms. The oyster fishery has continued to thrive in East Bay although the salinity levels have increased. Shell dredg- ing activities during the 1960's removed large quanti- ties of oyster shell from East Bay and surrounding areas. Sedimentarion from these dredging activities smothered many adjacent hve oysters and covered 150 valuable shallow water habitat (Benefield 1976). Viable finfish, shrimp, and oyster fisheries depend on thisestuarine area. The marsh areas in East Bay Basin have been used for cattle grazing since the turn of the century (U.S. Army Corps of Engineers 1900). However, the eco- logical effects of cattle grazing in marshes need more study. The most critical resource of the basin is water. Rainfall deficits always occur in summer, even in wet years, and can be severe in dry years, (fig. 3-52). Sur- face water quality appears to be adequate, judging from tlie phosphorus loading rates, even though the renewal time of the bay is long, approximately 577 days. Ground water supply, i.e., safe annual yield, in tlie Neches-Trinity coastal basin which includes the East Bay area is about 13 x lO^m^ (4.6 x lO^ft^). In 1974 about 5.3 x lO^m^ (1.9 x 10^ ft^) was pumped within the Trinity-Neches basin. Another 5.1 x 10 m^ (1.8 X 10* ft^) was pumped from outside that basin but was used in it (Texas Water Development Board 1977). Most of the latter was for manufacturing and industrial use north of the East Bay Basin. Artesian well pressures are decUning and saltwater intrusion is occurring near the Gulf (Wessebnan 1971). In the Texas City area just west of East Bay, 1 to 1.5 m(3.3 to 4.9 ft) of land subsidence has occurred as a result of ground-water withdrawal and oil and gas extrac- tion (Fisher et al. 1972). Similar subsidence can be expected in the East Bay Basin, particularly with con- tinued ground-water withdrawal. 151 ■I ff i •. 4.0 c:hknii:r plain habitats 4.1 INTRODUCTION Habitats are the key components of the Chenier Plain ecological hierarchy. As used in this report, they are components of basins and are also coimnunities where individual species live and reproduce. The tenn "habitat" refers to the place occupied by an entire community of organisms (Odum 1971). A habitat can be described in terms of a range of physical or abiotic parameters such as salinity and temperature, water avaUabihty, soil type, and geo- graphic reUef. It has geographic boundaries that can be measured and mapped. Odum (1971) defines a community as "an or- ganized unit that has characteristics additional to its individual and population components and functions as a unit through coupled metabolic transformations." The terni "habitat," as used in this report, defines the boundary of this community; it is not applied to indi- vidual species, except to the extent that they belong to defined communities. Any classification system is to some extent arbi- trary. In this study, basins were subdivided into geo- graphic units called habitats (table 3.53, and plates 3A and 3B). Because man is a significant influence on the Chenier Plain, some of these habitats were also land-use categories (e.g., rice field habitat). But they, like the naturally occurring habitats, could also be treated as functionally identifiable units. Fourteen habitats were defined; nearshore Gulf, inland open water, salt marsli, brackish marsh, intermediate marsh, fresh marsh, swamp forest, impounded marsh, ridge, beach, upland forest, rice field, pasture, and urban. Most of the land in the Chenier Plain basins is wetland. Wetland habitats include the swamp forest, impounded marsh, and four natural marsh types identified by vegetation and salinity differences; salt marsh, brackish marsh, intermediate marsh, and fresh marsh (Penfound and Hathaway 1938, O'Neil 1949, Chabreck et al. 1968, Chabreck 1972). The plant community in a wetland area depends upon the range of physical and chemical parameters in that area. Generally speaking, as one moves inland from the coast and salinities decrease, coastal salt marshes grade into brackish, intermediate, and fresh marshes. Figure 4-1 shows the vegetational trend in southeastern Louisiana along an 80 km (50 mi) south to north transect. The salt marsh habitat is in the southernmost zone, where smooth cordgrass is domi- nant (table 4.27 lists common and scientific names of most vascular plants identified in this study). A fairly distinct change occurs inland where saltmeadow cordgrass and saltgrass become dominant in the brackish marsh habitat. A third change in plant com- position and diversity is observed in the Lntennediate marsh habitat. This occurs with the appearance of such plants as alligatorweed, maidencane, and Walter's millet. Halfway along the transect, the fresh marsh habitat is distinguished by the presence of species such as water hyssop, water hyacinth, and cattail. Vegetational transitions in the Chenier Plain are generally similar to tliose shown in figure 4-1. How- ever, they are less distinct, because ridge plants are mixed with wetland species where cheniers modify the natural salinity gradient. Figure 4-2 shows an example of plant distribution in the region on a south to north transect through the Calcasieu Basin. Salt marsh species do not show up on this transect, but three discernible groups of plants are evident. With the exception of aster and seashore paspalum, the southern group of brackish marsh species (salt- meadow cordgrass, smooth cordgrass, and saltgrass) are identical to those found in figure 4-1. The inter- mediate marsh zone contains a variable group of common freshwater species that can tolerate low salt concentrations (alligatorweed, bulltongue,01ney's three-comer grass). At the north end of the transect, this group is augmented by strictly freshwater species such as stonewort and yellow lotus. Even though the zones are not distinct, the distribution of plant species provides a plausible criterion for distinguishing the four natural marsh habitat types. Vegetation differences also correlate with dif- ferences in soil chemistry. Chabreck (1972) and Brupbacher et al. (1973) reported that vegetation in Louisiana marshes varied with the chemical charac- teristics of soil sediments. As an example, figure 4-3 compares soil calcium and total salt concentrations within four marsh types (Palmisano and Chabreck 1972). 4.1.1 RELATION OF HABITATS TO POPULATIONS Populations exist, grow, and interact within the constraints of habitats. A habitat limits and molds a population through external forces. In turn, as inter- acting populations (the bio tic components of the com- munity) change, they modify the habitat. Three habi- tat characteristics are important for individual popula- tions. First, the carrying capacity of a habitat depends on the magnitude of primary production of the com- munity and on the trophic position of the population in question. Conceptually, a habitat has a carrying capacity for every species population that it supports. This carrying capacity can be managed by controlling primary production (e.g., increasing the amount of Olney's three-corner grass to aUow muskrat popula- tions to increase), by manipulating the trophic struc- ture of a habitat (e.g., reduction of predators in an area often allows prey species to increase in numbers), and by reducing limiting factors (e.g., providing nest- ing boxes for wood ducks where natural cavities are few). Since components of a community interact, increasing the carrying capacity for one species generally has repercussions for other species, and could be detrimental to the community as a whole. 153 Q.-0 ZZ05 I I I I i I .1 ■ I i o ^ ^ ai o o_, c . -^ O >- 0) E-i? >- *" o 1/51/5 < O ^ D-D 2 J 3 c oi ° 0) - ^ — :£ "D 0) -- r .o O == ^ < ^r'r o>-t.::!> o o ^— ^Q-j ^--c -_jr I" OH) ^_o V V ^ °'c-5 a. o ? 111 1. 4 T • I I Jl J -a i "o "*-• ^ o H^ ■*-» re "^ i'5 t/i "O !§ -J j= •4—* E c^ U nj •*-* T^ ^ CI3 Oi ID ^ 3 >< v> -^ c ^ '~ C3 ■5.H aj -a S.S 2.2 O o £ J? 6 g IT) U- s— ^ ■*-• E^ ^ *- 6 =p 00 = o f- — t: re Ss c o O y 2 o ^ 00 re ^ lant cent rom .^13 O „ re o « ^ buti ion bar. -^o ■■ t« -^ re Q-£S ^ 4 u k. §) E 09jy 3dX| saoadg (uoij 154 Transect 6 I I I I IIIHlHiH III Natural Marsh Non-Marsh III I I I ■ I Open Water Modified Marsh II- ■ _.UJ.- Ik !■ Il IlikA iflk &.L, (0 » o o a (0 (D CL J ■ ■ ■*-N I Mm Open Water (no plants) Aster Saltmeadow cordgrass Saltgrass Smooth cordgrass Gulf cordgrass Paspalum Cyperus Duckweed Walter's millet i ■ Alligator-weed Giant bulrush Smartweed Spider lily Bermuda grass Fimbristylis Marsti elder Rattlebox Water hyssop Salt marsh bulrush Three-corner grass Widgeon-grass Groundselbush, buckbrush b Bulltongue ■ Dwarf spikerush I I Stonewort Morning glory J Variable watermilfoil ■ Yellow lotus I Horned bladderwort Stations Figure 4-2. Distribution of plant species for four area types along a south-to-north transect in Calcasieu Basin inH w Hth f r M rj''^"/.^^^ 'r^'^S^ °'"^^'^*^ 'P^"^^ =^°"g the transect is indicated by the length and width of the black bar. (Data from Chabreck et al. 1968.) 155 800 D D A o o Fresh Marsh Inlermediale Marsh Brackish Marsh Sail Marsh 700 ^ 600 A o 500 Pn D 400 ^ c; o 300 - c 9 o o 200 - 100 1 1 1 1 1 1 8 12 2 4 6 Total salts (ppt) Figure 4-3. Comparison of soil calcium and total salt concentrations within four marsh types in coastal Louisiana (Palmisano and Cha- breck 1972). A second important aspect of a habitat is its areal extent. The habitat's area relates to the relative amount of space, food and cover available for a par- ticular species. Some species, e.g., the river otter, occur in low densities and range over large areas. For these species, a large continuous area of habitat is necessary to maintain the population and its gene pool. A third characteristic of a habitat that is impor- tant to individual populations is its interlinking with other habitats. Habitats are interlinked by populations that migrate from one to another. For instance, virtually all of the commercial and sportfish species in the Chenier Plain must use several habitats (near- shore Gulf, inland open water, and one or more wet- land habitats) to complete their life cycles. 4.1.2 RELATION OF HABITATS TO BASINS In part 3.0 habitats were discussed as components of basins and were considered as geographic units of defmed area. Habitats receive sunlight, water, sedi- ments and nutrients. With coupling among habitats they can be expected to produce a characteristic harvest of commercially important fishes, shellfishes and mammals, and sustain a given level of recrea- tional use. Water unifies the basin, acting as a vehicle for transport of materials and organisms among habi- tats. Renewable resource potential was discussed as a function of areal habitat change, not as a result of changes in habitat quality. In part 4.0 the emphasis changes to the biotic components of each habitat; the complex trophic structure, the major processes, and reactions of the habitat to external forces are presented. The dis- cussion is intended to show how processes which lead to changes in habitat area and quality at the basin level can also lead to changes in habitat structure, function, and carrying capacity. 4.1.3 ORGANIZATION OF HABIT.\T SECTION Wetlands appear to be the most important habi- tats in the Chenier Plain in terms of loss and vulnera- bility to change. They are therefore treated first, fol- lowed by aquatic habitats, beach and ridge habitats, upland forest habitat, and finally agricultural habitats. Within each of these groups, functional similarities far outweigh differences. Therefore, a general discussion of common characteristics within each group prefaces individual habitat treatments. Differences, especially in species composition, are considered in subsections on individual habitats. 4.2 WETLAND HABITATS From the air wetlands appear as watery grasslands interspersed with countless lakes, ponds, and sinuous streams, along whose borders the vegetation is par- ticularly lush. From low altitudes, different types of vegetation can be distinguished in broad bands, lying rouglily parallel to the major water bodies and to the coast. The five distinct natural wetland habitats are identified by their dominant vegetation (Penfound and Hathaway 1938; O'Neil 1949; and Chabreck 1970, 1972). These habitats function as they do, and occupy particular spatial relationships to each other, pri- marily because of tlie influence of two related hy- drologic processes. Freshwater from rainfall and from up-river discharge flows seaward across the basin. Saltwater influenced by tidal currents and density gradients from the Gulf tends to oppose this flow. Depending on the topographic features of the basin, the mixing of fresh and saltwater results in different marsh zones (fig. 4-4). Each of these zones supports a characteristic fiora. Three additional points should be made. First, wetland habitat boundaries are often not distinct. Salt concentrations vary over a continuum, not abniptly, and vegetation zones also grade diffusely into each other and overlap much as an ecotone separates a field from a forest. Second, wetland habitats usually occur as an ordered series. Fresh marsh is not expected to be contiguous to salt marsh, rather, there is a transition through intennediate and brackish zones. This follows from the mixing processes that produce a gradual change in salinity across the basin. Finally, the habitat zones change dynamically through time in response to natural and culturally induced changes in the hydrologic regime. For ex- ample, as natural subsidence occurs, seawater en- croaches over the land, and marsh habitat boundaries 156 move slowly up the basin (Chabreck 1970). As the basin's hydrologic regime changes, all of the habitats are affected. In the Calcasieu Basin dredging of a deep ship channel has accelerated saltwater intrusion (part 3.6. ."i). In the Mermentau Basin, on the other hand, control structures have prevented saltwater intrusion and the basin is becoming progressively fresher (part 3.6.3). 20 15 o 1 » ~ 10 c -i r 5 i 1 m 1 ( i Brackish n\ai"sh Fresh marsh and Figure 4-4. Water sahnities (mean ± standard devia- tion) in five natural habitats in the Louisi- ana portion of the Chenier Plain (Cha- breck 1972). 4.2.1 A FUNCTIONAL OVERVIEW OF WET- LANDS The structural and functional similarities of the natural wetland habitats far outweigh their dif- ferences. The trophic interactions in each habitat have much in common, although the animal species in- volved at each trophic level change with habitat. The flow diagram in figure 4-5 summarizes the inter- acting parameters characteristic of emergent wetlands. The many arrows crossing the system boundaries indi- cate the high degree of interaction between adjacent habitats. The whole system is shown as a net pro- ducer, since organic export to adjacent estuarine waters is characteristic of wetlands. The sun's energy is the ultimate source of all plant production, but the hydrologic regime (shown as H in the diagram), the available nutrients, and salts are the primary regulators of this production. Three groups ofplants are identified in the model. Most of the energy trapped is by the emergent vascular plants which dominate the marsh. The periodically inundated stems of these plants and the marsh fioor support a vigorous growth of diatoms and other algae which contribute up to 10% of the net primary production (Gosselink et al. 1977). Sub- merged grasses (such as widgeongrass) and phyto- plankton produce additional food. These three pro- ducer groups are distinguished by different rates of production, quality of production, and the relation- ship of production to biomass (turnover rate). In general, die algae, because of their high protein con- tent, are a more nutritious food source to grazers than emergent grasses are, and have a more rapid turnover rate. This makes their contribution to the food web more important than their biomass would seem to indicate. The food web sliown in the model (fig. 4-5) in- cludes a detritus compartment and three consumer groups. Because emergent grasses consist mostly of ceDulose and other compounds that are not digestible by most consumers, they are eaten by a diverse group of scavenging animals only after the dead tissue is enriched by bacteria and other microbes. This is the most important food pathway in marsh habitats. However, grass seeds and tubers, submerged grasses, and many algae are consumed directly by insects, crustaceans, birds, and even mammals such as the muskrat and nutria. These scavengers and grazers, in turn, are prey for such carnivorous animals as hawks, some fish, and predaceaous insects. While the simple food web in the model is con- ceptually useful, in reality trophic relationships are not nearly so clear. For instance, puddle ducks apparently eat vegetation to store carbohydrates for migration, but switch to high protein animal diets at nesting time. Other trophic relationships are dis- cussed in sections dealing with individual populations. For this overview it is sufficient to understand that several trophic levels exist, but that most food energy is processed through the detritus-scavenger pathway. Because primary production is high, wetlands support large numbers of migratory andnonmigratory animals. These include commercially important shell- fishes (shrimp, oyster, blue crab), finfishes (Gulf menhaden) and mammals (muskrat, nutria), as well as species prized by sportfishennen (spotted sea trout, redfish, fiounder) and hunters (ducks, geese). Other equally important marsh processes are not as closely related to the food web. These include (from Gosselink et al. 1974): 1 . The value of the marsh as a storm buffer and flood water reservoir; 2. The sediment filtering and trapping action of emergent grasses and filamentous algae; 3. The ability of marshes to purify flood waters by removal of wastes, nutrients, and toxins. 4.2.2 ROLE OF HYDROLOGY IN WETLAND HABITATS Wetland Habitats. The properties, distribution, and circulation of water are considered by many to be tlie most important controlling features of wet- land habitats. Water is the vehicle for movement of biota into and out of wetlands. Water also controls marsh productivity and species richness, peat for- mation, organic export, and the inorganic nutrient flux into the marsh. Water level determines the accessibihty of small marsh ponds to aquatic con- sumers and the usefulness of marshes to waterfowl. This section will document the importance of the fluctuating hydrologic regime that sustains wetland habitats. 157 u o -a c c o c O c o 'E, O S I 3 158 Production and Species Richness. Oxygen is an essential element in the metabolic processes con- trolling life. When wetland flooding (inundation) occurs, the amount of oxygen reaching the sediment surface is reduced. As the available oxygen in the sediments is depleted by benthic organisms, a com- plex series of chemical transformations take place, producing hydrogen sulfide, methane, and other toxic substances (DeLaune et al. 1976). One unique feature of the marsh biota is the ability to tolerate these anerobic conditions through the evolution of speciahzed mechanisms. For instance, most marsh grasses have anatomical structures that enable atmospheric oxygen to diffuse through leaves and stems to roots (Armstrong 1975). The relationship between plant success and the inundation regime is not known quantitatively. However, hydrological parameters (flooding fre- quency and duration, water depth, and current velocity) determine the sediment-carrying capacity and the level of nutrients flowing into a marsh. The inundation pattern in coastal wetlands varies across habitats. As the tidal influence decreases from salt to fresh marshes, the frequency of wet- land inundation also decreases and the average duration of each flooding increases. However, the total yearly inundation time remains fairly constant across all habitats (part 3.3). The high productivity of salt marshes has been attributed to the regular flushing with tidal waters that carry in nutrients and sediments, and carry out wastes (Schelske and Odum 1961). Recent studies in fresh and brackish wetlands, however, show that these irregularly flooded marshes can be as productive as salt marshes (Good et al. 1978). Fresh and brackish marsh plants appear to be adapted to long periods of root exposure to anoxic sediments, and apparently depend less on nutrients and sediments brouglit in by flooding waters and more on recycUng of avail- able nutrients than plants found in regularly flooded salt marshes. Hydrology and Sedimentation. The process of sedimentation and the proportion of organic to in- organic material in marsh sediments is largely con- trolled by the hydrologic regime. Marshes act as traps for sediments which are carried by water flowing across them. As the water in adjacent streams rises and floods over the marsh surface, velocities slow and suspended sediments drop out. Knowledge of the sediment-trapping capacity of salt marshes, in par- ticular, has been extensively used in Europe to build land in areas where high tidal energy results in large suspended loads (Zurr 1952,Dalby 1957). As early as 1888, Dunbar (Coates 1972) described how harbors of New England filled with silt when the great marshes were drained and leveed. This occurred because the marshes were no longer able to trap silt, and because water currents in tidal passes were reduced as the intertidaJ volume decreased. In addition to acting as a sink for suspended sediments (largely inorganic), marshes are also a source of organic detritus which can be incorporated into the marsh assediment. The more vigorous the flooding action, the more organic detritus is exported from the marsh (Gosselink et al. 1977). As a result, the organic- inorganic mix of wetland sediments depends largely upon the hydrologic regime. High energy marshes accumulate inorganic sediments. If current velocities are slow and inundation periods long, as in inter- mediate, brackish, and fresh marshes, little inorganic sediment is brought in, detritus is deposited, and marsh sediments are peaty. The rate of peat formation in the Chenier Plain varies greatly. A cross section of sediments across the Chenier Plain shows that the surface peat layer is seldom over 1 .5 m (5 ft) thick and is generally under- lain by silts and clays of the Pleistocene Terrace (Gould and McFarlan 1959). Radiocarbon dating of marsh peats has revealed deposition rates averaging from 0.3 to 1.2mm/yr (0.01 to 0.05 in/yr) (Gould and McFarlan 1959). Most of the Louisiana Chenier Plain coastal marshes are subsiding, yet, the marsh surface stays at the same level relative to local water levels. This suggests that the rate of deposition is as great as the rate of subsidence and that water level and circulation play a vital role in determining what proportion of detritus contributes to peat. If the deposition rate becomes slower than that of subsi- dence, the frequency and duration of inundation increases, resulting in plant death and erosion of wet- lands to open waters. Export of Detritus. Recent estimates indicate that about 10% of the litterfall in swamp forests are exported (Butler 1975) compared to 30% of salt marsh production (Hopkinson 1973). If detritus export is assumed to be proportional to the frequency of inunda- tion (a measure of the magnitude of flushing), it is possible to estimate the expected export from other marsh habitats. Figure 4-6 illustrates the hypothesized linear relationship between the frequency of flooding and organic export from wetlands. The coastal region is inundated almost daily by tides, but the more inland marshes, especially fresh marshes, are flooded by less frequent wind tides and during periods of high rain- faU (Hopkinson 1973, Butler 1975, Byrne et al. 1976). As a result, less detritus is exported from these marshes than from salt marshes (table 4.1). Severe stomis are also important in flushing wetlands, but no information is available about the magnitude of storm effects. 4.2.3 DYNAMICS OF ENERGY FLOW IN WET- LANDS Primary production, the conversion of solar to chemical energy by plants, sets an upper limit to the flow of energy through habitats. This chemical energy, fixed as plant tissue, is the energy available for the rest of the food web, so the potential for secondary production of fish, waterfowl, and furbearers is di- rectly related to the magnitude of primary produc- tion. An examination of the energy pathway through 159 the food web indicates the important components of the system and the seasonal dynamics of energy pro- duction. Table 4.1. Estimates of organic export from wetlands. the wetlands at tlie end of summer is not a indicator of the real productivity of the system. Table 4.2. Summary of annual net shoot production by six marsh plants (Gosselink et al. 1977). true Habitat Primary production (t/ha/yr) Exported % of net production Magnitude (g/m^/yr) Species Production* (t/ha) Ratio of production to peak biomass 22.7 27.6 28.3 14.1 9.8 30 13 12 8 10 680 360 340 110 100 Salt marsh Brackish marsh Intermediate marsh Fresh marsh Swamp forest Big cordgrass Saltgrass Blackrush Smooth cordgrass Saltmeadow cordgrass Bulltongue 11 29 33 22 42 23 1.4 2.9 2.7 2.9 3.0 3.6 Productivity. On the Gulf of Mexico coast, the year-round wami temperatures and the continuous nutrient subsidy from flooding waters combine to yield remarkably high production, judging from annual production of several important marsh plants in southeastern Louisiana (table 4.2). These yields far exceed those of other systems, even heavily fertilized agricultural crops such as sugarcane (fig. 4-7). Since on the Gulf coast many plants grow and die con- tinuously throughout the year, the yield, i.e., the harvestable biomass at the end of summer, is only about one third of the total net production for most marsh species. Thus the large stand of plants covering Best estimate from several methods, rounded to nearest metric ton. Control of Primary Productivity. Since primary production is the source of organic energy in an eco- system, it is appropriate to examine the major con- trols of this production. While most dry land plants "saturate" with light (reach maximum photosynthesis rates) at about one-half of full sunlight, many marsh plants are adapted to increase their rate of energy capture as long as light intensity increases (Black 1971). These higher rates of energy capture are not o a X 0) o c CO O) 30 20 Brackish marsh Salt marsh Swamp forest Impounded marsh Fresh marsh 1 20 40 60 80 100 120 Frequency of inundation (times/yr ) 140 160 Figure 4-6. Hypothetical relationship between frequency of inundation and organic export from wetlands (inundation frequencies from Byrne et al. 1976, export rates from Day et al. 1973 and 1977). 160 ■B u 3 "D O a > Dese r t Dry agriculture Moist agriculture Estuar i ne \r:<:.Mi\kliw^^ikiii Coastal Open ocean Figure 4-7. A compaiison of primaiy productivity for different kinds of ecosystems (adapted from Teal and Teal 1969). often obtained, however, since critical materials limit the maximum growth rate of the plants. The most common limiting materials are carbon dioxide, which enters the leaves directly from the air, and inorganic nitrogen and phosphorus which are taken up through the roots. Considerable research (VaUela and Tea! 1972, Broome et al. 1975) shows that in the salt marsh habitat nitrogen is most often limiting (table 4.3). However, in freshwater lakes and streams, phosphorus is usually the limiting nutrient and this may also be true in the fresh and intermediate marsh habitats. Recent evidence indicates that inorganic sedi- ments (primarily clays and fme silts) are the major "new" source of nutrients in Louisiana marshes. DeLaune et al. (1977), for example, showed a strong linear relationship between soil density, which is proportional to the inorganic sediment content in the soil, and biomass of smooth cordgrass (fig. 4-8). Since nitrogen is most often the limiting nutrient in coastal marshes, it is important to understand the normal sources and losses of this element. The dia- gram in figure 4-9 illustrates the marsh nitrogen cycle. The major source of nitrogen to plants is made avail- able from stored nitrogen in the soil. It comes from inorganic sediments which are carried into wetlands by flooding waters, and from nitrogen dissolved in the water column. Most of this nitrogen is incor- porated as an insoluble organic form in the sediments and becomes available to plants only after it is mi- crobially transformed into ammonia [minerahzation (3) on fig. 4-9] . Although the vegetation (4) absorbs significant amounts (5) for growth, the largest users of ammonia seem to be microscopic organisms (7), which transform plant detritus into a high protein bacterial biomass. The vast pool of atmospheric nitro- gen gas (8) is not available to marsh grasses; however, certain microscopic organisms change it into a usable organic form [nitrogen fixation (9)] . This is a source of "new" nitrogen for the marsh system, but it is normally small in relation to available sediment ni- trogen. In addition, other microorganisms in the £ 1,5Q0 y. -3686+ 7163x r =0 736" Soil density (g/cm^) Figure 4-8. Relationship between soil density and growth of smooth cordgrass. Table 4.3 Above ground yield of smooth cordgrass in September 1973 in a streamside loca- tion in Barataria Bay, Louisiana as affected by applications of nitrogen and phosphorus (Patrick and DeLaune 1976). Treatment Mean dry-weight yield (kg/ha) Nitrogen (200 kg/ha) Phosphorus (200 kg/ha) Control (no N or P) 19,160 16,560 16,660 alternately oxidized-reduced environment of the sedi- ment surface change ammonia to atmospheric nitro- gen [denitrification (10)], where it is lost from the marsh system. Normally, this process also produces small amounts of nitrogen in comparison to the total nitrogen cycled. However, when the marsh is enriched with culturally derived nitrogenous wastes, denitri- fication becomes an important mechanism to reduce 161 Nitrogen tj Figure 4-9. A model of the marsh nitrogen (N) cycle showing the major stores of N and interrelated processes (Hopkinson and Day 1977). the total nitrogen supply (Valiela and Teal 1972). Normally, the growth rate of marsh grasses seems to be limited by the rate at which organic nitrogen in the sediment can be oxidized into ammonia (3). As this is a relatively slow process, the addition of in- organic nitrate or ammonia to the marsh often stimu- lates growth. Aside from the nutritional value of specific in- organic elements to marsh plants, the total salt con- centration in the root zone exerts a strong influence on plant growth. All of the major salt and brackish marsh plants appear to be inhibited by high salt con- centrations. Even though they thrive in a moderately saline environment, growth is more vigorous for the same species in soils with lower salt content when competition from other species is eUminated. Thus the dominant species in the salt and brackish marsh habitats arc not there because they are stmiulated by the salt solution in which they grow, but because they tolerate moderately sahne conditions better than fresh marsh species. This has been demonstrated by a number of individuals (Phleger 1971, Seneca 1972, Parrondo et al. 1977) whose results are sliown in figure 4-10. Fresli marsh vegetation is particularly susceptible to salt intrusion since these species seem to be intolerant of even low salt levels. The role of severe storms in the control of vegeta- tion has often been ignored because of the difficulty of documentation. Hurricanes that strike the Chenier Plain are sufficiently intense to cause considerable short- and long-temi changes in wetlands. The imme- diate effects have been difficult to ascertain. Day et al. (1977) reported that Hurricane Carmen in 1974 de- foliated swamp forests in its path two months earlier than nomial leaf fall. A large amount of organic carbon, nitrogen, and phosphorus was flushed from the swamp to the lower estuary (fresh, brackish, and salt marshes) by the accompanying torrential rains. Part of tliis material undoubtedly resulted from the early defoliation, but much visual evidence points to thorougli Hushing of stored detritus from the swamp floor which would not wash out under normal weather conditions. Short-temi effects of Hurricane CamUle on species composition in fresh and brackish marshes 162 o o X o <>- 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4- 1.2- 1.0- 0.8- 0.6- 0.4- 0.2 \ Seedlings transported from field \ \ Log Y : 2.36819 - 0.24540x — Seedlings grown in laboratory from seed Log Y -- 2.86073 - 0.62326 ^. \ \ \ * 0.5 4.0 1.0 2.0 X - Salinity (%NaCI) Figure 4-10. The inhibitive effect of salt on growth of saltmeadow cordgrass (Seneca 1972). near the mouth of the Mississippi Riverwere described by Chabreck and Palmisano (1973). They found that although this area was regularly flooded by fresh river water, the increase in salinity caused by the hurricane tide was ephemeral. The major effect of the hurricane seemed to have been widespread destruction of vegeta- tion by wind and water, which uprooted and ripped apart stands of plants. Recovery of most species was rapid so that prehurricane levels of abundance were approached within a year. In the small lakes and ponds, however, the submerged and floating vegetation was slow to recover. Valentine (1977) described a long-term effect of Hurricane Audrey (1957) in saw- grass marshes of the Chenier Plain, apparently caused by increased soil salinity. Sediment salts became con- centrated first directly from hurricane tides, then secondarily from the dry summers following. Initially, 161,874 ha (400,000 a) of sawgrass marshes were killed. The following year 86% of this area was open water. During the 1960, '62, '63, and '65 drought years, annual grasses and sedges became abundant. By 1972 bulltongue occupied 74% of the area and white water-lily occupied 1 1%. Other floating and submerged aquatics were also common. Sawgrass never reestab- lished itself in any extensive areas, perhaps because seed viability was very low. Secondary effects of these vegetation changes on duck food habits were dramatic. Prior to 1959 sawgrass seeds were an im- portant component of duck diets. In the years imme- diately following the hurricane, duck stomachs con- tained primarily rice seeds, indicating heavy depen- dence on agricultural areas outside of the Chenier Plain. During succeeding drought years, when the marshes produced large quantities of annual grass seeds, large numbers of both ducks and geese were attracted to these habitats. Seasonal Dynamics of Organic Production and Loss from Wetlands. Although each plant species has its own seasonal growth pattern, smooth cordgrass has been extensively studied and data from this species is used to show a typical wetland seasonal pattern of organic production, mortality, and export (fig. 4-1 1). Smooth cordgrass maintains a year-round growth rate of about 8 g/m^/day (Hopkinson et al. 1977). Mor- tality during spring and summer is low so that the 163 E 800 600 400 200 CM E CM E O) 400 300 200 100 140 100 60 ^ CM E o CM E o o o o CM Live biomass of smooth corttgrass IHopkinson et al. 19771 1 1'^ S N 1 1 1 — — — 1-~ J M M 4 Mortality rate of smootti cordgrass H — r— M -I r- Dead biomassof smootti Cbrdgrass tHopkinson et al. 19771 N JMMJ SNJMM 400-1 Disappearance rate of smooth cordB'ass from rnarsh 300 200 100 — 1 r— N D 15 10 5^ E (Kit by 19711 J M M J S N J Aquatic macrobenthic population detislty M M — I r- N D IDay et al. 19731 J M M J S Stirimp biomass in lakes adjacent to salt marshes M M J T ^ I N D iJacobs and Loesch 19711 Figure 4-11. The seasonal flow of organic matter through the food chain (Turner 1977). 164 plant biomass increases to a maximum of about 700 g/m^ in late August and September. Flowering begins at this time and subsequently most of the plants die, reducing the biomass to about 200 g/m^ in January. As a consequence of winter senescence, the amount of dead grass increases rapidly to a peak in late winter. This material is broken down during the following spring and summer, and much of it is swept out of the marsh, as shown by the high rate of disap- pearance of detritus during AprU to July. The timing of the detritus pulse from the marsh corresponds with the arrival of migrating species from offshore such as shrimp that find a ready supply of food (Odum 1967). Thus plants produced in one year became available to consumers the following spring. Energy Budget of Wetlands. The organic energy budget of an ecosystem accounts for the amount of organic energy fixed in plants by photosynthesis and the relative energy demand by different consumers. Unfortunately, detailed energy budgets have been constructed for very few ecosystems. In wetlands, only salt marsh budgets are well documented (Teal 1962, Day et al. 1973). Nevertheless, quantitative energy budgets for wetland habitats in Louisiana (fig. 4-12) have been estimated and give some indica- tion of tlie relative importance of different wetland processes. The following generalizations are drawn from tliese diagrams: 1 . Direct grazing consumes a small proportion of plant production, ahhough that propor- tion increases from salt to fresh marsh habi- tats as the diversity of grazers increases. 2. Consumer species of commercial interest probably directly consume much less than 1% of net primary production. 3. Most of the organic matter produced by the system (something over 90%) is processed through a detrital system (part 4.2.4). 4. A major proportion of primary production is respired to carbon dioxide by benthic and epiphytic organisms, primarily microbial. 5. Export and deposition of organic materials in marsh sediment are inversely related and together account for 20 to 40% of primary production. Export predominates where flushing action is strong; deposition where it is weak. In the swamp forest habitat a major portion of production is accumulated as wood. 4.2.4 THE DETRITUS-MICROBIAL COMPLEX In wetland habitats little of the total plant pro- duction is consumed by grazers. Instead, plants die and the resulting detritus is modified by microor- ganisms before being consumed by other animals. In effect, the microorganisms are the first consumers in the detrital food web. Microorganisms feed on the lignins and cellulose of the dead plants, converting these compounds into microbial proteins, fats, and sugars (fig. 4-13). During the process of enrichment, many small consumers ingest the detrital material, skim off the nutritious microorganisms, and egest the undigestible plant remains. These are recolonized and the process repeated (fig. 4-14; Fenchel 1970). This is true whether the detritus lies on the marsh surface or is carried by flood waters into adjacent water bodies. Metabolic Rates. Part of the organic matter in- gested by microorganisms is used to fuel their meta- bolic processes and is lost as heat. Estimates of this heat loss are summarized by Payne (1970), who con- cluded tliat a minimum of 40% of food energy is converted to heat during growth of the microor- ganisms. Gosselink and Kirby (1974) reported that conversion efficiencies of smooth cordgrass detritus to microbial biomass in laboratory cultures were as high as 60%, but in actual marsh conditions it was thought that a more realistic conversion rate was about 25%. The conversion efficiency varies, depend- ing on the degree of aeration of the marsh surface, the flushing regime, the inorganic nitrogen available to the decomposers, and other factors. On the average, however, for every 4g (0.14 oz) of detrital food assimilated by a consumer, some 3 g (0.1 1 oz) are lost as heat. Although no data are available for other wetland habitats. Day et al. (1977) found that the total annual metaboUc loss (benthic respiration) in salt marshes in Louisiana was about 600 to 718 g/m^, while Teal (1962) found that the annual loss to microbial respiration was only 730 g/m^ in a Georgia salt marsh. Role of Benthic Organisms. Although microor- ganisms are the first to colonize the dead plant tissue, other benthic organisms are probably more important in breaking down this matter to fine particulate detritus. For instance, Fenchel (1970) showed that the degradation rate in marine turtlegrass beds was greatly increased when the leaves were exposed to amphipods. Detritus particles may be further reduced by grinding in digestive tracts of crustaceans (Odum et al. 1972). Crayfish are probably very important in breaking down leaf Utter in the swamp forest habitat. Summary. The deep layer of litter on the marsh surface should be recognized as an active biochemical factory (much Uke a cow's rumen), which transforms nutritionally indigestible cellulose to useful protein. The many small consumers Uving in tliis detritus are an important source of protein for animals higher in the food web. Events which impair the abihty of these small consumers to transfonn litter have repercussions throughout the food web. For instance, regular flooding and draining of the marsh stimulates me- taboUsm while continuous flooding results in oxygen depletion and slower decomposition rates (Day et al. unpubhshed). 165 c o 3 T3 O e 13 3 C C ca O c o o. o n. CO ca u tH nj 73 J3 en -4-* C4 +-» T3 C •a 3 X) u . c ^ >" 1? 1) Xi UJ u 166 50 £ 40 a> 4) $ >s ■a 30 0) « h- ^