nutrient, and turbidity levels. All 

 were located in the upper freshwater 

 portion of the basin, or adjacent to the 

 natural levee in the New Orleans area, 

 and all were strongly impacted by urban 

 and/or agricultural runoff. Stations 

 with a negative index were generally 

 mesotrophic; they had clear water and 

 relatively low nutrients and chlorophyll 

 levels. Most were in the lower basin 

 where there were no direct introductions 

 of upland runoff. 



Rates of Wetland Loss 



A number of studies have been con- 

 ducted on wetland loss (conversion of 

 wetland to open water or spoil banks) in 

 the Barataria basin (Adams et al. 1976; 

 Craig et al. 1979; Turner et al. (1982). 

 These studies have shown that (1) the 

 greatest wetland loss is in the saline 

 and brackish marshes (Table 15); (2) 

 wetland loss is apparently related to 

 canal density; and (3) the rate of wet- 

 land loss is accelerating. 



Adams et al. (1976) studied land 

 changes for a number of sites in the 

 Barataria basin; a positive relationship 

 was found between canal density and 

 wetland loss (Table 16). 



The same pattern is true for the 

 Louisiana coastal zone as a whole (Craig 

 et al. 1979). Turner et al. (1982) 

 recently examined the relationship be- 

 tween canals and wetland loss for each 

 basin of the MDPR using the USFWS habi- 

 tat maps (Wicker et al. 1980b). Wetland 

 loss in the Barataria basin is acceler- 

 ating, as indicated by a comparison of 

 rates from 1890-1960 and 1960-74 (Table 

 15). This trend of accelerating wetland 

 loss has recently been documented for 

 the MDPR (Gagliano et al. 1981). The 

 area occupied by canals in the Barataria 

 basin also seems to be increasing (Table 

 17). 



Impoundments 



Beginning in the late 1800* s and 

 continuing until the 1970' s, impound- 

 ments have been created for agriculture 

 or urban development in fresh and 

 brackish marshes. Impoundments include 



areas diked and pumped dry, areas diked 

 without pumping, and areas partially 

 leveed with reduced connection to nearby 

 water bodies. There are numerous wet- 

 land sites within the Barataria basin 

 that are partially or totally impounded, 

 and cut off from free movement of water, 

 dissolved and suspended matter, zoo- 

 plankton, and nekton. Many of these 

 sites were created inadvertently as a 

 result of cumulative effects of projects 

 in the wetlands (e.g., construction of 

 canals with spoil banks) . 



An example of accidental impound- 

 ment is an area of swamp west of Lac des 

 Alleraands that has been almost com- 

 pletely impounded by road embankments, 

 and by the spoil bank from dredging 

 Bayou Chevreuil (see Hopkinson and Day 

 1980b; Conner et al. 1981) Studies have 

 shown that this impounded area does not 

 dry out as natural swamp does; it has 

 much lower water turnover, and lower 

 primary and secondary productivity; and 

 its wildlife habitat value has decreased. 

 Virtually no fish were found in the 

 stagnant water in the area. 



Many of the impounded areas in the 

 Barataria basin were originally con- 

 structed as a means of floating out 

 timber. Some of these areas have been 

 enlarged, and new impoundments have 

 been created by the placement of dredged 

 spoil material from channelization, road 

 construction, and canals constructed for 

 pipelines, drainage, and petroleum 

 access . 



Former wetland areas that have been 

 diked and are maintained as dry land for 

 residential purposes or other uses are 

 near or below sea level. The elevation 

 is lowered because of the compaction of 

 soils and the oxidation of peats after 

 the land was pumped dry. Because of the 

 high costs of keeping such land dry, 

 many sites were abandoned and now are 

 open water ponds, being too deep to 

 support emergent vegetation. Other 

 areas of marsh have been diked but have 

 not been continuously pumped and are 

 impounded marshes. In addition to these 

 sites, a number of areas adjacent to the 

 natural levees of the Mississippi River 

 and Bayou Lafourche have been impounded 



114 



