swamps to the gulf (approximately 1.0 

 cm/km, or 0.4 inches/mi). These condi- 

 tions create sluggish bayous and promote 

 overland sheet flow of water through the 

 wetlands. Although Mississippi River 

 water no longer flows directly into the 

 Barataria basin, southeasterly winds, 

 when they occur, blow river water from 

 the Southwest Pass of the modern delta 

 back into the lower basin via the tidal 

 passes. (Day et al. 1973). 



Wetland vegetation varies from salt 

 marsh along the coast to freshwater 

 swamp at the upper end of the basin. 

 Slightly more elevated areas of the 

 upper basin support a bottomland hard- 

 wood forest community. Seaward from the 

 swamp forest, maidencane and cattails 

 predominate in the freshwater marshes. 

 Further south, intermediate and brackish 

 marshes also support a wide variety of 

 plant species, but this variety declines 

 closer to the gulf. Descriptions of each 

 of these plant communities are included 

 in this report. Additional information 

 can be found in Day et al. (1973), 

 Conner and Day (1976), Bahr and Hebrard 

 (1976), Day et al. (1977), and Hopkinson 

 and Day (1979). 



The areal extent of each habitat in 

 the Barataria hydrologic unit is listed 

 in Table 12. The boundary of the MDPR 

 does not coincide with the natural 

 boundary of the total Barataria drainage 

 basin (Figure 47). Much of the forested 

 wetland and adjacent uplands, a small 

 area of fresh marsh, and some fresh 

 aquatic areas were not included in the 

 study area that was the source of the 

 measurements in Table 12. The total 

 area of the Barataria basin in 1975, by 

 five major habitats, was estimated by 

 Hopkinson (1978) and is shown in Table 

 13. The following description includes 

 the entire basin, which is 207,000 ha 

 (511,300 acres) greater than the area of 

 the Barataria hydrologic unit given in 

 Table 12. 



Dominant Forcing Functions 



The Barataria basin was formed 

 during the past thousand years by sedi- 

 mentation from the Mississippi River 

 through Bayou Lafourche. The basin 

 received fresh water and sediment during 



annual overbank flooding, but since the 

 leveeing of the river in the 1930' s, the 

 only direct freshwater input has been 

 rain, and riverine sediments and nutri- 

 ents are no longer available to nourish 

 wetlands. The only deposition of sedi- 

 ment comes from sediments eroded from 

 adjacent waterbottoms , which are insuf- 

 ficient to maintain an elevated marsh 

 surface. The Mississippi River affects 

 the basin via the Gulf of Mexico, by 

 decreasing nearshore salinity and stimu- 

 lating nearshore primary productivity. 



The Barataria basin has well- 

 developed barrier islands compared with 

 areas such as Chandeleur Sound, Terre- 

 bonne Bay, and Atchafalaya Bay. The 

 barrier islands provide some protection 

 from wave energy. Hurricanes and lesser 

 storms still exert a powerful influence 

 on the basin, however, in the form of 

 storm surges. The marine environment 

 also provides the characteristic salin- 

 ity gradient of the estuary, and the 

 nearshore gulf is the habitat for the 

 many migratory organisms that use the 

 basin. 



Biological processes mediate the 

 physical forces that impinge on the 

 basin, e.g., wetland plants colonize 

 mudflats and slow the rate of erosion; 

 organic matter from plants contribute a 

 large portion of the soil throughout the 

 basin; benthic organisms such as oysters 

 and clams produce carbonate shells that 

 help to stabilize water bottoms and 

 beaches. 



Human activity has also become a 

 major force in the Barataria hydrologic 

 unit. The leveeing of the river during 

 the 1930' s deprived the basin of annual 

 inputs of sediments, water and nutri- 

 ents. The subsequent sediment starva- 

 tion of wetlands, subsidence, erosion, 

 and salinity intrusion into the lower 

 basin are undoubtedly responsible for a 

 major portion of the observed wetland 

 loss (Craig et al 1979). Salt water 

 intrusion causes wetland loss when it 

 results in the rapid dieback of fresh- 

 water wetland plants, and erosion occurs 

 before salt tolerant plants can recolo- 

 nize the area. Canal construction, up- 

 land runoff, and impoundments have also 

 affected the rate of wetland loss, water 



107 



