Disturbance factors should be recognized as an important considera- 

 tion because they extend the effects of the project beyond the 

 boundaries of the immediate site. 



Key attribute alterations 



Creation (by marsh buggies and other vehicles) and elimination (by 

 filling) of depressions in the land surface are the alterations 

 which lead to the most significant impacts on the ecosystem. 

 Induced changes in waterflow regimes allow effects which are large 

 in areal extent and long lasting. The total area affected (and thus 

 the kinds and amounts of vegetation and consumers) is site specific. 



Brackish Marsh 



Seismic preexploration. 

 1. Activity Sequence 



Surveyors enter the marsh by truck, marsh buggy, or foot, stake the 

 lines, and mark the areas where shot holes and geophones will be 

 placed. Vegetation may be cleared along a path 3 to 4 m (10 to 

 15 ft) wide. A drilling truck or buggy and one or two support 

 vehicles enter next; holes are drilled, charges and recording equip- 

 ment are placed, and shots are fired. Geophones are retrieved and 

 placed for the next series of shots. After completion of an entire 

 shot line, the holes are plugged and the crew exits. 



2. Primary ecological alterations 



2.1 Creation of ruts or depressions in the land surface 



2.2 Trampling and crushing of vegetation along shot line path 



2.3 Localized change in direction of water flow 



2.4 Creation of pathway for increased rate of flow of runoff 



2.5 Possible creation of pathway for increased saltwater inundation 



206 



