become increasingly fresh (fig. 3-25). The ratios were 

 calculated from 1:24,000 USGS maps by digitizing. 

 The area totals are conservative because many small 

 marsh ponds were excluded. In the Sabine and Cal- 

 casieu basins the edge: area ratios were higher in fresh 

 marsh than in brackish or intermediate marsh habitats, 

 perhaps because land loss (marsh degradation) is oc- 

 curring so rapidly in those basins. If the ratios are in- 

 dices of marsh productivity, then data indicate that 

 salt and brackish marsh habitats are more productive 

 than fresh marsh for estuarine-dependent organisms. 



Canals in wetlands have been shown to change 

 hydrologic patterns, thereby modifying habitats and 

 basin quality. Canals, because they are straiglu rather 

 than sinuous and edged with high spoil banks that do 

 not permit overbank flooding, have low edge; area 

 ratios. For this reason alone, one would suspect that 

 these factors reduce habitat and basin quality. In a 

 recent study, it was found that the area of natural 

 sinuous channels in marshes, and the edge : area ratios 

 were reduced as the canal density increased (R. E. 

 Turner, Pers. Comm. Center for Wetland Resources, 



Table 3.59. Calculated net photosynthesis (primary production) by basin. 



Basin 



Area 

 (km=) 



Average net 

 -•photosynthesis 

 per km^ (t/yr) ) 



Estimated net 

 photosynthesis/ 

 basin (t/yr)^ 



Vermilion 



Mermentau 



Chenier 



Calcasieu 



Sabine 



East Bay 



Total 



1,909.10 

 2,680.64 

 1,954.47 

 1,756.27 

 3,759.79 

 1,119.26 



13,179.53 



1,047.14 

 1,591.92 

 1,222.44 

 1,452.11 

 1,369.10 

 1,139.15 



1,999,100 

 4,267,374 

 2,389,228 

 2,550,299 

 5,147,516 

 1,275,002 



17,628,519 



Summarized from appendix 6.3. 



70 



60 



a. 

 >■ 



n 50 



40 



» 30 



w 20 



? 10 



East Bay 



Sabine 



Salt Marsh 



Brackish Marsh 



Intermediate Marsh 



Fiesh Marsh 



m 



1 



Calcasieu 



Chenier and 

 Mermentau 



Vermilion 



Baiin and Marsh Types 



Figure 3-25. The ratio of marsh edge lengtli to total wetland area, by marsh type, in each basin. 



82 



