2.6 Creation of a pathway parallel to levee for more rapid upland 

 drainage and standing water from marsh 



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 fill as 

 construction proceeds. A more significant vegetation loss occurs 

 during excavation of a 5-m (15-ft) wide borrow ditch and burial of 

 marsh by fill for the roadway. The width of the latter zone is 10 

 to 13 m (30 to 40 ft). This direct loss results in an immediate 

 decrease in food and cover for the consumers in the area. For a 

 single roadway through a brackish marsh, the total area affected is 

 usually small in comparison to the remaining productive vegetation; 

 the impacts on consumers, competition (shading), rough mat formation, 

 and detritus accumulation are insignificant. However, as each new 

 road is constructed, the carrying capacity of the intact brackish 

 marsh is decreased. Cumulative effects are unknown, and the thresh- 

 old point (where one additional road will significantly affect the 

 marsh) is obscure. 



The depth and number of ruts created by marsh vehicles involved in 

 road construction 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/emergence, 

 average depth, and duration of submergence. Areas dominated by 

 marshhay cordgrass may be replaced by stands of three-square or 

 other water-tolerant species when the frequency and/or duration of 

 submergence increases. The converse may occur when frequency and/or 

 duration of submergence decreases. Although the total area affected 

 by vehicle ruts is site specific, it is usually small when compared 

 to the total area of brackish marsh. Consumers that depend upon 

 these grasses and sedges for food and/or cover may ultimately 

 increase or decrease. 



The depressions allow a faster runoff of surface and standing water 

 in localized areas. The long-term effects of 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 new depressions with 

 standing water. At the ecosystem level, however, this increase is 

 insignificant. The movement of vehicles over the marsh also crushes 



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