southern Mississippi, and south- 

 western Alabama. The 4,700-square 

 mile area extends from Dauphin 

 Island, Alabama, on the eastern end 

 of Mississippi Sound, to the east 

 bank of the Mississippi River be- 

 tween Bayous Manchac and Terre Aux 

 Boeufs in southeastern Louisiana. 

 The LCA study area encompasses that 

 part of the Mississippi River 

 Deltaic Plain located in southern 

 Louisiana, exclusive of the active 

 Mississippi Delta, extending from 

 the Atchafalaya River on the west 

 to Breton Sound on the east. A map 

 of the two study areas may be seen 

 in Figure 1. 



STUDY OBJECTIVES AND IMPACTS OF 

 FRESHWATER DIVERSION MEASURES 



Planning objectives to be 

 satisfied by freshwater diversion 

 measures include creation and resto- 

 ration of coastal wetlands, enhance- 

 ment of vegetative growth, creation 

 of favorable salinity gradients (5-15 

 ppt) and increases in productivity of 

 fish and wildlife resources. 



BENEFICIAL IMPACTS 



FISHERY RESOURCES 



Fishery resources will be bene- 

 fitted by reduction in saltwater in- 

 trusion which will increase availa- 

 bility of nursery habitat with 

 favorable salinity regimes. Sediment 

 and nutrient input resulting from 

 freshwater diversion will serve to 

 decrease marsh loss and enhance 

 vegetation growth. Increases in 

 nutrient input will also increase 

 production of phytoplankton and zoo- 

 plankton populations, which are 

 highly important in the estuarine 



food web. Increases in acreage of 

 marsh and vegetative biomass will 

 benefit fisheries production by in- 

 creasing production of organic detri- 

 tus. The majority of finfish and 

 shellfish species of commercial and 

 recreational importance are estu- 

 arine-dependent , utilizing inshore 

 estuaries as nursery areas. Juve- 

 niles of estuarine-dependent species 

 move into estuarine nursery areas, 

 and taking advantage of low salini- 

 ties, elevated water temperatures and 

 abundant food, grow very rapidly dur- 

 ing the warm spring and summer 

 months. The value of shallow marsh 

 nursery areas for estuarine-dependent 

 species has been well documented. 

 Studies by Rogers (1979) and Simo- 

 neaux (1979) in the Upper Barataria 

 Basin have shown such areas to be of 

 value to juvenile Atlantic croaker 

 and menhaden, respectively. White 

 and Boudreaux (1977) conducted stud- 

 ies which demonstrate the importance 

 of shallow marsh areas in Louisiana 

 for brown shrimp (Penaeus aztecus ) 

 and white shrimp ( Penaeus setiferus ) . 

 Turner (1979) reported that inshore 

 shrimp catches in Louisiana are di- 

 rectly proportional to the area of 

 intertidal wetlands and not related 

 to mere areal extent of estuarine 

 waters. More (1969) documented the 

 value of marsh habitat for blue 

 crabs. Studies in Texas have shown 

 the value of shallow marsh waters as 

 habitat for immature sand seatrout 

 ( Cynoscion arenarius ) and southern 

 flounder ( Paralichthys lethostigma ) 

 (Conner and Truesdale 1973). 



The value of freshwater inflow 

 has been historically demonstrated. 

 Viosca (1938) reported the 1937 open- 

 ing of the Bonnet Carre' Spillway re- 

 sulted in beneficial effects on 

 oysters, saltwater finfishes and 

 penaeid shrimp. Gunter (1950) re- 

 ported the 1945 and 1950 openings 



378 



