2. Primary ecological alterations 



2.1 Creation of depressions in land surface by marsh vehicles 



2.2 Loss of vegetation along canal route due to excavation, cov- 

 ering, and spreading of spoil 



2.3 Creation of a pathway about 3 m (8-10 ft) deep and 23 m 

 (70 ft) wide for increased saltwater inundation 



2.4 Increases in concentrations of suspended sediments and dis- 

 solved nutrients 



2.5 Blockage of normal runoff pathways 

 3. Attribute alterations 



Surveyors and their equipment trample and crush vegetation outside 

 the zone to be excavated, but the area involved is small. Further- 

 more, 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 bordering marsh by spoil. The area of the 

 latter zone is dependent upon the type of spoil disposal technique, 

 but it may be as much as five times the width of the canal itself. 

 This direct loss results in an immediate decrease in food and cover 

 for the consumers in the area. The total area affected for a single 

 canal may be small in comparison to the remaining productive vegeta- 

 tion, and the impacts on consumers, competition, rough mat formation, 

 and detritus accumulation can be minor. However, as each new canal 

 and wellsite is excavated, the carrying capacity of the intact 

 brackish 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 vehicles involved in 

 canal excavation are dependent upon the total number of trips and 

 the degree to which vehicles retrace existing tracks. Deep ruts 

 resulting from retraced trails will form surface depressions for the 

 movement of water and, if deep enough, may result in standing bodies 

 of water during wet seasons. The orientation and depth of the 

 depressions determine whether they (1) 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/emregence, 

 average depth, and duration of submergence. Ruts parallel to the 

 tidal flux may increase the frequency of submergence/emergence; 



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