Canals that are adequately plugged and/or backfilled may have local- 

 ized effects on drainage patterns, but they will not result in long 

 continuous pathways for increased saltwater inundation or increased 

 drainage. Open canals with accompanying levees will block or divert 

 water flows. Incompletely backfilled canals can result in long 

 straight depressions due to shrinkage and subsequent subsidence of 

 excavated spoil. The depression may enhance the export of detritus 

 and may allow increased saltwater inundation. The total area affected 

 and the significance of changes effected by blockage and enhancement 

 of water flows is site specific; these aspects were discussed in 

 preceding paragraphs concerning depressions resulting from marsh 

 buggy traffic. 



Replacement of stands of marsh vegetation by bodies of standing 

 water (open pipeline canals and buggy tracks) results in increases 

 of phytoplankton. The area is converted from a salt marsh or tidal 

 channel to a deeper aquatic system. Smooth cordgrass and epiphytes 

 are removed and phytoplankton increase in the deeper water areas. 

 Corliss and Trent (1971) compared phytoplankton production in natural 

 and altered areas and found increased net algal primary production. 

 However when all producers are considered, net production of organic 

 material decreases in altered areas compared to the marsh (Darnell, 

 1976). 



There may be decreases or increases in numbers of consumers in 

 canals (Adkins and Bowman, 1976; Bourn and Cottam, 1950; Willingham 

 et al., 1975), though measures of standing biomass have generally 

 shown a decrease (Trent et al., 1972). Shifts in relative species 

 abundance are evident along with changes in absolute numbers with 

 the creation of a deeper water body (Lindall et al., 1973; Dale, 

 1975; Adkins and Bowman, 1976). 



Since phytoplankton become the prevalent primary producers, consumers 

 dependent on phytoplankton in the affected area may increase relative 

 to other consumers. It is difficult, however, to predict which 

 groups of consumers increase or decrease because many of them use 

 organic material for food from a variety of sources in the marsh. 

 The kinds and numbers of organisms existing in the isolated, some- 

 times nonf lowing, water bodies is dependent upon the frequency, 

 timing, and amount of tidal inundation in the pipeline canal. 

 Adkins and Bowman (1976) measured abundance of nekton and zooplankton 

 in marsh control areas (one meter deep), canals open at both ends, 

 canals open at one end, and canals closed at both ends. Taken as a 

 whole, control areas and open canals were more favorable habitat for 

 nekton; semiclosed and closed canals had fewer organisms. However, 

 closed canals generally contained the largest organisms. There were 

 individual exceptions, particularly regarding shrimp. Willingham 

 et al. (1975) found a similar pattern regarding consumer species. 

 It is difficult to form conclusions regarding zooplankton due to 

 sampling problems and flooding. It is apparent that zooplankton 

 populations are quite variable in all canal types. 



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