remain for long periods of time and (2) alter the water regime of a given 

 area of land by increasing or decreasing the frequency of submergence/ 

 emergence, average depth, and duration of submergence. Areas dominated 

 by maiden cane may be replaced by stands of rushes, sedges, canes, or 

 other emergent species when the frequency and/or duration of submergence 

 increases. The converse may occur when frequency and/or duration of 

 submergence decreases. Although these vegetative groups may shift in 

 relative importance because of changes in submergence, no significant 

 changes in fauna would be expected since the vegetation types support the 

 same consumers. 



The depressions might allow a faster runoff of surface and standing water 

 in localized areas, but this drying effect on adjacent regions is usually 

 small. The long-term effects on suspended sediments and nutrients are 

 slight. 



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. 

 Waterfowl and wading bird use would be expected to increase in these new 

 depressions retaining standing water. At the ecosystem level, however, 

 this increase is insignificant. 



Increases in suspended sediments associated with excavation are transient 

 and are confined to a relatively small area, especially 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 pro- 

 portional 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 years or less, depen- 

 ding upon the edaphic conditions and sources of seed stock. Increases in 

 suspended sediments associated with marsh vehicle traffic also have short- 

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

 than effects associated with canal erosion. 



The canal creates a large continuous route for increased inundation by 

 adjacent waters, either fresh or brackish. The pattern and height of spoil 

 placement are the most important factors that determine if this new standing- 

 water body is isolated from the contiguous marsh, or whether its waters 

 may inundate extensive marsh areas. In addition, the spoil deposits par- 

 alleling the canal and wellsite interrupt existing water flows. This 

 blockage may result in localized changes in runoff and standing water. 

 Thus, the total area affected is site specific and may range from the 

 construction site alone to much larger marsh areas if important drainages 

 are altered. 



Replacement of stands of fresh marsh vegetation by bodies of standing 

 water (canals, wellsites, and bugg tracks) results in increases in 



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