southwest Louisiana and southeast 

 Texas (Gosselink et al. 1979). Based 

 on these studies, it was estimated 

 that approximately 5,000 acres/yr 

 (2,024 ha/yr) of natural and im- 

 pounded marsh were converted to open 

 water, spoil deposits, or agricultur- 

 al or urban uses between 1952 and 

 1974 in the Vermilion, Chenier, Mer- 

 mentau, and Calcasieu basins of 

 southwest Louisiana and the Sabine 

 Basin of southwest Louisiana and 

 southeast Texas. 



A recent study (Wicker 1980) of 

 the Mississippi Deltaic Plain Region 

 (MDPR) conducted for the Fish and 

 Wildlife Service's National Coastal 

 Ecosystems Team and the U.S. Bureau 

 of Land Mangement has produced 

 alarming statistics. Preliminary 

 analysis of data obtained from plani- 

 metering habitat maps prepared for 

 this study revealed that approxi- 

 mately 464,500 acres (187,983 ha) of 

 coastal marsh were lost in the Louis- 

 iana portion of the MDPR between 1956 

 and 1978, for an annual loss rate of 

 over 20,200 acres (8,175 ha) or (31.6 

 mi /yr) (Robert Ader 1980 personal 

 communication) . Combining this esti- 

 mate with the estimated marsh-loss 

 rate of 5>,000 acres/yr (2,024 ha/yr) 

 or 7.8 mi /yr (20.7 km /yr) for that 

 portion of the Chenier Plain found in 

 western Louisiana and extreme south- 

 east Texas, it is estimated that the 

 marshes of the entire LCR are being 

 lost at an estimated rate exceeding 

 25,000 acres/yr (10, 118 ha/yr) , or 

 over 39 mi yr (101.0 km /yr) . This 

 is more than twice 

 mi /yr (42.7 km /yr) 



the rate of 16.5 

 reported by 

 Gagliano and van Beek (1970). 



CAUSES OF WETLAND DETERIORATION 



Wetland deterioration in the LCR 

 is attributed to land loss and salt- 

 water intrusion. According to Craig 

 et al. (1979) land loss in the LCR 

 results from an interaction of nat- 



ural and man-induced impacts. Natural 

 land loss occurs through subsidence, 

 compaction, and erosion of the sub- 

 strate following cessation of active 

 deltaic deposition (Morgan 1973). 

 Barrier islands and tidal inlets buf- 

 fer coastal marshes from stormy 

 energy and regulate salinities. The 

 erosion of barrier islands and widen- 

 ing of tidal inlets have also been 

 identified as causes of land loss 

 (Craig et al. 1979). Numerous man- 

 induced alterations have accelerated 

 natural wetland loss. The construc- 

 tion of federally financed navigation 

 channels, mainline Mississippi River 

 levees, and upstream diversions and 

 flood control reservoirs have vir- 

 tually eliminated overbank flooding 

 along the Lower Mississippi River. 

 Consequently, most of the riverborne 

 sediments are being transported past 

 formerly active deltas and into the 

 deeper Gulf of Mexico (Gagliano and 

 van Beek 1970). This loss of sedi- 

 ment input has, except in Atchafalaya 

 Bay, prevented large-scale delta 

 building and has accelerated subsi- 

 dence and erosion of existing 

 marshes. Other human causes of wet- 

 land loss include canal dredging and 

 associated spoil disposal and drain- 

 age of wetlands for agricultural pur- 

 poses (Gagliano 1973) . Gagliano at- 

 tributed approximately 25 percent of 

 the total land loss in coastal Louis- 

 iana during the past 30 years to oil 

 and gas industry dredging. 



Saltwater intrusion, another 

 major cause of wetland deterioration, 

 is occurring in many areas of the 

 LCR. This process has been docu- 

 mented at numerous locations, such as 

 Barataria Bay (Van Sickle et al. 

 1976) and along the Mississippi 

 River-Gulf Outlet in southeast 

 Louisiana (Fontenot and Rogillio 

 1970). Saltwater intrusion has wide- 

 ranging adverse effects, such as al- 

 lowing encroachment of the predaceous 



391 



