Further away from tidal influence, conditions in the canal may be 

 quite variable, and at times anoxic (Smith, 1970; Adkins and Bowman, 

 1976; Darnell, 1976). There may be a buildup of organic matter 

 because of the high proportion of organic sediment, limited aeration 

 of the water column, and poor flushing similar to residential dead- 

 end canal problems (Adkins and Bowman, 1976). Darnell (1976) noted 

 possible buildups of sulfates in these canals, but the work of 

 Adkins and Bowman (1976) showed no systematic increase in canal 

 sulfates compared to control areas. The canals, however, may have 

 more variable conditions than do control areas. 



If the result of the canal construction is more marsh flooding, the 

 salinity of the soil and water will increase. This nay lead to 

 changes in plant composition and increased nutrients over a long 

 time period. 



The net export of detritus to the open waters of the bay system 

 would likely decrease for two reasons: (1) excavation of the chan- 

 nel has removed vegetation and (2) the continuous spoil banks inter- 

 rupt existing small tidal streams that carry detritus out of the 

 marsh. 



Increases in suspended sediments associated with excavation or 

 maintenance are transient and affect a relatively small area, espe- 

 cially if temporary plugs are placed at the mouth of the canal. 

 Long-term effects are results of erosion of canal banks and spoil 

 deposits; erosion of the former is proportional to the speed and 

 amount of boat traffic. Erosion of spoil deposits will proceed 

 until they become vegetated by pioneering plant groups. This ecesis 

 will usually occur within two yr or less, depending upon the 

 edaphic conditions and sources of seed stock. Increases in suspended 

 sediment associated with marsh buggy traffic also have short-tern; 

 and long-term components; effects of both components are usually 

 less than effects associated with canal erosion. 



Replacement of stands of marsh vegetation by bodies of open water 

 (canals) results in conversion from salt marsh or tidal channel to a 

 deeper aquatic system, with attendant changes in the community. 

 Marsh grass and epiphytes decrease while algae become the prevalent 

 producers. Corliss and Trent (1971), comparing phytoplankton produc- 

 tion in natural and altered areas, found that net primary production 

 of algae in canals was higher than in bay and marsh channels. Other 

 studies (Darnell, 1976) have noted decreased net production or 

 organic material when all primary producers are considered. 



There may be decreases or increases in numbers of consumers in 

 canals (Bourn and Cottam, 1950; Willingham et al., 1975; Adkins and 

 Bowman, 1976), though measures of standing biomass have generally 

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



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