3. Attribute alterations 



The movement of work crews and marsh vehicles tramples and crushes 

 vegetation in a zone wider than that cleared for shot placement. 

 Vegetation may be completely uprooted and destroyed in some cases; 

 the extent and degree of destruction are dependent on the hydro- 

 logical conditions of the area. Because meadow and emergent 

 vegetation types are located on higher elevations, they are more 

 susceptible to such destruction; submergent and floating vegetation 

 types are less likely to be completely removed from production by 

 vehicles. Additional vegetation destruction occurs during placement 

 of navigation equipment and temporary docking facilities. Any 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, 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 a 

 more desirable species. The total area affected is usually small in 

 comparison to the remaining area of undisturbed marsh, and the 

 effects on transpiration, evaporation, sediment trapping, available 

 nutrients, and peat accumulation are insignificant. 



The depth and number of ruts created by marsh vehicles are dependent 

 upon the total number of trips and the degree to which vehicles 

 retrace existing tracks. In areas that are submerged continuously 

 (or nearly so), the depressions are less likely to significantly 

 alter water-movement patterns. In such regions, confinement of 

 marsh vehicle traffic to a narrow corridor may be wise. However, in 

 areas of higher elevation, deep ruts resulting from retraced trails 

 will form depressions for the movement of water. 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 average depth of of water. 

 Areas dominated by maiden cane or other shallow-water species may be 

 replaced by stands of rushes, sedges, canes, or other deepwater 

 emergent species when the average depth increases. The converse may 

 occur when the average depth decreases. Although the total area 

 affected is site specific, it is usually small when compared to the 

 total area of undisturbed marsh. Because both of these vegetation 

 types support the same consumers, no significant faunal changes 

 would be expected. 



The depressions allow a faster runoff of surface and standing water 

 in small, localized areas. The long-term effects on suspended sedi- 

 ments and nutrients are insignificant in this turbid and nutrient- 

 rich system. 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 these new depressions with standing water. 

 At the ecosystem level, however, this increase is insignificant. 



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