Primary ecological alterations 



2.1 Creation of depressions in land surface by narsh vehicles 



2.2 Loss of vegetation along canal route due to excavation and covering 



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



2.4 Increases in concentrations of suspended sediments and dissolved 

 nutrients 



2.5 Blockage of normal waterflow pathways 



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. Up to 0.1 km of marsh per km of channel may be 

 covered by spoil from the excavation, though 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. In cases where the existing vegetation is a pest species, 

 flora destruction may be considered beneficial for several reasons: (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 more desirable species. For single 

 canals, the total area affected is usually small in comparison to the 

 remaining area of undisturbed marsh, and the effects on transpiration, 

 evaporation, sediment trapping, fire, available nutrients, and peat 

 accumulation are limited. However, as each new canal and wellsite is 

 excavated, the carrying capacity of the intact marsh is decreased. 

 Cumulative effects are unknown, and the threshold point (where one 

 additional canal will significantly affect the marsh) is obscure. 



The depth and number of ruts created by marsh v 

 the total number of trips and the degree to whi 

 ing tracks. In areas that are submerged contin 

 depressions are less likely to significantly al 

 In such regions, confinement of marsh vehicle t 

 may be wise. However, in areas of higher eleva 

 from retraced trails will form depressions for 

 if deep enough, may result In standing bodies o 

 The orientation and depth of the depressions de 



ehicles are dependent upon 

 ch vehicles retrace exist- 

 uously (or nearly so), the 

 ter water movement patterns, 

 raffic to a narrow corridor 

 tion, deep ruts resulting 

 the movement of water and, 

 f water during wet seasons, 

 termine whether they (1) 



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