Table 1. Percentage of coverage of vegetation and open water in 

 a 541 -ha marsh adjacent to Black Lake, Louisiana, 1940-83. 



by erosion, subsidence, and inadequate drainage of the area that prevented recolonization by more 

 salt-tolerant species. 



Levees surrounding this management unit were constructed over a 25-year period. The east 

 levee was in place in 1940, the north levee was installed in 1965, the south levee was installed in 

 1960, and the west levee was completed in 1977. After completion of the levee system, two Fixed- 

 crest weirs were installed. Breaches in the levee system, however, prevented water management 

 until 1980, when the levee system was repaired and two 6-ft-wide guillotine-style structures were 

 installed. After 1980 the two guillotine-style structures were used for water control. 



U.S. Soil Conservation Service investigations of the area, beginning in 1984, determined the 

 average marsh elevation on this management unit to be -0.38 m MSL. Marsh elevation decreases 

 from north to south. The highest elevation occurs in the northwest corner of the marsh. The two 

 water control structures were determined to be inadequate for water management. 



METHODS 



A conservation plan was developed to revegetate the north half of area with emergent species 

 and the south half of the area with submergent species (widgeongrass). The optimal water regime 

 for the majority of emergent marsh plants ranges from a few inches above marsh level to a few 

 inches below marsh level. This condition allows gas exchange essential for plant growth in the root 

 zone when the water level is down and maintains the wetland character of the marsh. 



A pump was installed in 1986 to facilitate lowering water levels (drawdown) within the 

 management unit. Seeds germinate more readily under the drier conditions associated with 

 lowering water levels (deMond 1986). Also, drying out a marsh during the summer firms up the 

 bottom resulting in reduced turbidity from waves and gives a firm substrate for widgeongrass 

 establishment (USDA Soil Conservation Service 1977). 



The pump and structures were used to effect a drawdown of the area in the summer of 1986, 

 summer of 1987, and spring of 1988. Several soil samples were taken from the area in 1986 and 



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