2. Primary ecological alterations 



2.1 Creation of depressions in land surface by marsh vehicles 



2.2 Loss of vegetation and consumers along canal route and within 

 wellsite due to excavation and covering 



2.3 Creation of a body of standing water about 3 m (8-10 ft) deep for 

 both the length of the canal and at the wellsite (approximately 50 

 by 115 m, or 150 by 350 ft) 



2.4 Increases in concentrations of suspended sediments and dissolved 

 nutrients 



2.5- Blockage and/or diversion of normal waterflow path 



Attribute alterations 



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 a 23-m 

 (70-ft) wide canal and a 0.58-ha (1.2-acre) wellsite and burial of bor- 

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

 type of spoil disposal technique. Along the canal route, up to 10 ha per 

 km (40 acres per mi) may be modified by spoil placement. This direct 

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

 in the area. 



This loss could be significant if it occurs during periods of high river 

 discharge, when the total area of food and cover is reduced because of 

 submergence. In cases where the existing vegetation is a pest species, 

 floral destruction may be considered beneficial since (1) it reduces the 

 reproductive potential of the pest species, (2) it opens dense stands of 

 vegetation and increases the "edge effect," and (3) it might allow the 

 zone to be invaded by a more desirable species. For single wellsites, 

 the total area affected is usually small in comparison to the remaining 

 area of undisturbed marsh, and the effects on transpiration, evapora- 

 tion, sediment trapping, available nutrients, and peat accumulation are 

 insignificant. However, as each new canal and wellsite is excavated, the 

 carrying-capacity burden of the intact marsh is increased. Cumulative 

 effects are unknown, and the threshold point (where one additional well 

 will significantly affect the marsh) is obscure. 



273 



