those perpendicular to tidal water movement may decrease the 

 frequency. Areas dominated by marshhay cordgrass may be replaced by 

 stands of threesquare or other water-tolerant species when the 

 frequency and/or duration of submergence increases. Areas dominated 

 by threesquare may be replaced by marshhay cordgrass when frequency 

 and/or duration of submergence decreases. The total area affected 

 is site specific and usually small when compared to the total area 

 of brackish marsh or the effects of canal excavation. 



The depressions can contribute to faster runoff of surface and 

 standing water in localized areas. Thus, the duration of submer- 

 gence and the average depth of water in nearby areas are decreased 

 while the frequency of submergence/emergence is increased. If 

 vehicle tracks occur in areas of the marsh where isolated ponds 

 exist, intramarsh circulation could be affected. Depressions could 

 connect individual water bodies and increase the intermixing of 

 their contents. 



Increases in suspended sediments associated only with excavation are 

 transient and affect a relatively small area, especially if tempo- 

 rary plugs are placed at the mouth of the canal. Erosion of canal 

 banks and spoil deposits are long-term effects. Erosion of canal 

 banks 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 sediments associated with marsh vehicle 

 traffic may have short-term and long-term components. However the 

 effects are less than those effects associated with canal erosion. 



The canal also creates a large route for increased saltwater inunda- 

 tion (Bourn and Cottam, 1950; Gagliano, 1973; Copeland and Dickens, 

 1974; Darnell, 1976). The pattern and height of spoil placement are 

 the most important factors that determine if the salt water is 

 contained within a localized zone or inundates extensive areas. 

 Waterflow in the canal depends upon canal location and orientation 

 in the marsh, the influence of tidal waters, and the portion of the 

 canal in question. Long, straight sections of the canal, especially 

 with tidal influence, may show an increase in the volume of water 

 exchange compared to the preconstruction conditions (Gagliano, 

 1973). 



Further away from tidal action, especially in dead-end canals, 

 circulation may be poor and conditions may be quite variable (Smith, 

 1970; Adkins and Bowman, 1976; Darnell, 1976). There may be a 

 buildup of organic matter, limited aeration, and poor flushing. 

 Darnell (1976) noted possible concentrations of sulfates in these 



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