Attribute alterations 



Any movement of vehicles and workers over the marsh surface crushes 

 vegetation. The vegetation may be completely uprooted and destroyed in 

 some areas, depending upon the soil moisture conditions and the type of 

 transportation that is utilized. The vegetation loss results in an 

 immediate decrease in food and cover for the consumers in the area. The 

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

 area of productive vegetation because (1) the gravity meter is quite 

 portable, (2) data stations are not located along predetermined straight 

 lines, and (3) the stations are not regularly spaced. Stations may 

 frequently be reached by boat or on foot; a maximum of one lightweight 

 surface vehicle is necessary for the entire operation. Furthermore, this 

 vehicle need not travel straight-line paths across the marsh surface; it 

 can make maximum use of existing roads or canals. Therefore, the effects 

 on transpiration, evaporation, sediment trapping, available nutrients, 

 and peat accumulation are negligible. 



The above discussion indicates that total vehicular traffic associated 

 with gravity surveys is less than that associated with seismic surveys. 

 Nevertheless, any marsh-surface vehicle may potentially alter local land 

 elevations. Ruts resulting from their use may form depressions for the 

 movement of water. The orientation and depth of the depressions deter- 

 mine 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 water (storage 6). 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 fauna! 

 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 sediments 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. 



The degree and significance of wildlife displacement resulting from 

 gravity-meter surveys are slight. This is because of the small number of 

 people and short period of time required to complete a survey, as well as 

 the lack of noise. 



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