BIOLOGICAL CONSIDERATIONS RELATED TO FRESHWATER 

 INTRODUCTION IN COASTAL LOUISIANA 



Dennis L. Chew and Frank J. Cali 



U.S. Army Corps of Engineers 

 New Orleans, LA 70160 



ABSTRACT 



Louisiana has experienced a 

 rapid loss of coastal wetlands due 

 to natural processes such as subsid- 

 ence and erosion, as well as man's 

 engineering activities including 

 leveeing, channelization and pe- 

 troleum exploration. These activi- 

 ties have led to a reduction in 

 overbank flooding and natural dis- 

 tributary flow which historically 

 provided fresh water, sediments and 

 nutrients to estuarine areas. In 

 addition, construction of large 

 navigation channels has caused pro- 

 gressive intrusion of saline waters. 

 This has resulted in conversion of 

 fresh, intermediate and brackish 

 marshes to intermediate, brackish 

 and saline marshes, respectively, as 

 well as loss of some areas of wooded 

 swamp. Saltwater intrusion and loss 

 of wetlands have adversely affected 

 productivity of wildlife and fishery 

 resources and have led to declines 

 in populations of waterfowl, fur- 

 bearers and important shellfish and 

 finfish species. Influx of saline 

 waters is particularly harmful to 

 the American oyster, due to in- 

 creased predation. Juvenile stages 

 of shrimp, menhaden and blue crabs 

 are estuarine-dependent and utilize 

 nearshore estuaries and adjacent wet- 

 lands as nursery areas. One way to 

 ameliorate loss of wetland nursery 

 areas and rate of saltwater intru- 



sion is timely introduction of fresh 

 water to provide sediments and 

 nutrients vital to coastal wetlands. 

 Major constraints to freshwater in- 

 troduction in Louisiana are poor 

 water quality and lower temperatures 

 in the Mississippi River as compared 

 to adjacent estuaries. 



INTRODUCTION 



Louisiana is experiencing a 

 rapid loss of wetlands, including 

 bottomland hardwood forests, wooded 

 swamps and coastal marshes. Gagliano 

 and van Beek (1970) reported that 

 coastal Louisiana is experiencing a 

 net land loss in excess of 16.5 

 square miles per year. These land 

 losses have occurred as a result of 

 natural processes, as well as man's 

 engineering activities. Natural 

 processes of subsidence, compaction 

 and erosion have converted large 

 areas of coastal marshes to open 

 water (Morgan 1973). 



Construction of major naviga- 

 tion channels and oil exploration 

 canals have also been responsible 

 for loss of large areas of wetland 

 habitat. An example is the 

 Mississippi River-Gulf Outlet, a 

 78-mile-long channel which runs from 

 New Orleans to the Gulf of Mexico. 

 Channel excavation, dredged material 



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