1976), insects (Farlow et al . 1978), and 

 furbearers (Palmisano 1972; Fleming 

 1975; Robicheaux 1978; Linscombe as 

 reported in Sasser et al. 1981). How- 

 ever, detailed examinations of consumers 

 in the brackish marsh habitat have 

 lagged far behind studies of the salt 

 marsh. 



CANAL (5) 



Canals, dredged primarily for oil 

 and gas extraction and navigation, are 

 important man made features of the MDPR. 

 Inventories of canal area in coastal 

 Louisiana (Barrett 1970, Chabreck 1972, 

 Adams et al. 1976) report that canals 

 make up from 0.6 to 0.9% of total marsh 

 and water area. The latest estimate is 

 that canals covered 29,447 ha (72,739 

 acres) in the MDPR in 1978, or 0.85 % of 

 the total area (Table 5). 



Barrett (1970) measured 7,356 km 

 (4,572 mi) of canals and 11,709 km 

 (7,276 mi) of natural streams and rivers 

 in a 28.632 square-kilometer (11.055 

 square-mile) area of coastal Louisiana 

 south of the Intracoastal Waterway. 

 This indicates that the total area of 

 canals is approaching that of natural 

 drainage channels. 



Canals occur in fresh, brackish, 

 and saline regions of the MDPR (Figure 

 22) . Their hydrology and ecology differ 

 with the type of wetland, salinity, 

 size, and orientation to the coast 

 (parallel or perpendicular) . Canals are 

 less productive for animal life than are 

 unaltered natural channels. Canal 

 dredging disturbs benthic communities, 

 and although recolonization may occur 

 and original biomass restored, recoloni- 

 zation is usually by opportunistic 

 species of less value to the food web 

 (Allen and Hardy 1980). Changes in sub- 

 strate character, decreased oxygen sup- 

 ply, and decreased water exchange with 

 adjacent wetlands are the probable 

 factors responsible for lower amphipod 

 and demersal fish populations in dredged 

 canals over natural streams (Lindstedt 

 1978; Allen and Hardy 1980). 



Higher densities of organisms were 

 found in unaltered open water areas than 



in open and partially open canals in 

 Terrebonne Parish (Adkins and Bowman 

 1976). Closed canals had the fewest 

 numbers of organisms. Gilmore and Trent 

 (1974) found benthic microinvertebrates 

 slightly more numerous in a natural 

 Texas marsh than in an adjacent marsh 

 altered by channelization, bulkheading, 

 and filling. Organisms were more than 

 twice as abundant by volume in the natu- 

 ral marsh. 



Lindstedt (1978) measured 60% lower 

 numbers of amphipods, total crustaceans, 

 and total organisms in oil field canals 

 than in undisturbed control sites, but 

 the effects of oil contamination could 

 not be separated from those of dredging. 

 Significantly fewer motile epibenthic 

 organisms were collected in canals in 

 oil-free control areas than in natural 

 tidal streams. These differences may be 

 related to the effects of the spoil 

 banks associated with canals that pre- 

 vent water exchange between marsh and 

 water bodies. 



When canals are dredged deeper than 

 the surrounding natural streams, they 

 tend to become stagnant and anaerobic. 

 When viewed from the air the water in 

 canals sometimes appears noticeably more 

 clayey and turbid than the character- 

 istic dark but clear water in natural 

 water bodies. 



It appears that 

 tion ecologically 

 bodies in wetlands, 

 shown to double in 

 years (Craig et al 

 also evidence that 

 capture waterflow fr 

 creeks. The continu 

 canals in the MDPR 

 mental issue (see 



canals do not func- 



like natural water 



Canals have been 



width in 1 to 50 



1979). There is 



canal networks may 



om neighboring tidal 



ing proliferation of 



is a major environ- 



ECOLOGICAL ISSUES). 



CYPRESS-TUPELO SWAMP (6) 



The category of forested wetlands 

 known as cypress-tupelo swamp occupied a 

 total of about 158,000 ha (390,000 

 acres) in the MDPR in 1978, or 4.59 % of 

 the total area, shown in Figure 23. This 

 represents a net loss of about 28,000 ha 

 (69,000 acres) since 1955 (Table 5). 



47 



