artificial tidal outlets. The significance of this increase is 

 dependent upon the orientation, density, and length of buggy tracks. 



Increases in suspended sediments associated with excavation are 

 transient and affect a relatively small area. Long-term effects are 

 results of erosion of the borrow ditch and the roadway levee. 

 Erosion of the latter will proceed until it becomes 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-term and long-term components; effects 

 of both components are usually less than effects associated with 

 borrow ditches and roadway levees. 



Replacement of stands of marsh vegetation by bodies of deeper water 

 (borrow ditch and buggy tracks) 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 more prevalent. Corliss and Trent (1971) compared 

 phytoplankton production in natural and altered areas on the Texas 

 coast. They 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 of 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 

 abundance are evident along with changes in absolute numbers as the 

 area is altered in character from marsh to a deeper water body 

 (Lindall et al., 1973; Dale, 1975; Adkins and Bowman, 1976). 



With a shift in primary producer type, consumers dependent upon 

 phytoplankton may increase in the affected area. Those dependent 

 upon epiphytes and marsh grasses will decline. It is difficult to 

 predict which groups of consumers increase or decrease because many 

 of them use organic matter for food from a variety of sources in the 

 marsh. Consumers further along the food chain, such as wading 

 birds, may increase or decrease depending upon disturbance factors 

 and the sorts of consumer species available for food. The areal 

 increase of new aquatic habitat is usually less than the area 

 affected by levee construction plus marsh buggy traffic. Turbidity 

 that results from chronic erosion decreases the suitability of the 

 standing water as habitat for phytoplankton, aquatic invertebrates, 

 and fishes. 



Disturbance factors should be recognized as an important considera- 

 tion because they extend the effects of the project beyond the 

 boundaries of the immediate site. 



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