The amount of detritus exported to the adjacent estuarine system is 

 directly proportional to the standing crop of smooth cordgrass. If 

 the affected area is close to the estuary, the frequency of inunda- 

 tion and detritus export may remain unchanged. However, the depres- 

 sions allow faster movement of water in both directions. This 

 results in an increase of turbidity and a decrease in the efficiency 

 of the detritus-filtering mechanism of the salt marsh. Thus, a net 

 increase of exported detritus could result. Net amounts of nutrients 

 and sediment probably would not change significantly. 



If the affected area is further removed from the estuary where 

 isolated ponds may 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 with standing 

 water. At the ecosystem level, however, this increase is slight. A 

 relatively small amount of dredging may be required when small lines 

 cross existing watercourses. The increased concentrations of nutri- 

 ents and sediments are of short duration and involve small areas. 



The immediate alterations resulting from dredging pipeline canals 

 are similar to those associated with dredging access canals or con- 

 structing access roads. The long-term effects may differ, however, 

 because of backfilling and plugging practices. During the staking 

 of pipeline canal routes, surveyors and their equipment trample and 

 crush vegetation outside the zone to be excavated, but the area 

 involved is small. Furthermore, much of this trampled area may be 

 covered by spoil as the dredging proceeds. A more significant 

 vegetation loss occurs during excavation of the canal and burial of 

 bordering marsh by spoil. The area of the latter zone is dependent 

 upon the type of spoil disposal technique. This direct loss results 

 in an immediate decrease in food and cover for the consumers in the 

 area. The total area affected is usually small in comparison to the 

 remaining productive vegetation, and impacts on animals, nitrogen 

 fixation, and detritus export are minor. However, as each new canal 

 is excavated, the carrying capacity of the intact salt marsh is 

 decreased. Cumulative effects are unknown, and the threshold point 

 (where one additional canal will significantly affect the marsh) is 

 obscure. 



Increases in suspended sediments associated with excavation are 

 transient and affect a relatively small area, especially if 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 latter 

 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 auxiliary marsh buggy traffic 

 also have short-term and long-term components. 



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