2. Primary ecological alterations 



2.1 Possible creation of ruts or depressions in the land surface 



2.2 Trampling and crushing of vegetation at the station locations 



2.3 Possible localized change in direction of water flow 



2.4 Possible creation of pathway for increased rate of flow of runoff 



3. Attribute alterations 



The movement of vehicles and workers over the land surface crushes 

 vegetation. The vegetation may be completely destroyed in some areas, 

 depending upon the soil moisture conditions and the type of transporta- 

 tion 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 very 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 need not be precisely and 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 land surface; it 

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

 on consumers and detritus 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 surface vehicle may potentially alter local land 

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

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

 water during wet seasons. Th orientation and depth of the depressions 

 determine whether they (1) remain for long periods of time and (2) alter 

 the v/ater regime of the local area by increasing or decreasing the sur- 

 face water and macropore water. In extreme cases, the deep tracks 

 repeatedly cross the entire levee or spoil system; this breaching could 

 establish water flows between the systems on either side of the levee/ 

 spoil-bank system. Assuming that this major change does not occur, the 

 effects of the depressions are localized in nature. The vegetation in 

 the depressions may change to more water-tolerant grasses and sedges. 

 Consumers that depend upon the existing vegetation for food and/or cover 

 may ultimately increase or decrease. 



The depressions allow a faster runoff of surface water in localized areas. 

 The longterm effects on sediment and nutrients are limited. 



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