Key attribute alterations 



Restoration of the hydrologic regime is the pivotal aspect of site 

 rehabilitation, which controls or combines with other less critical 

 regulatory parameters to ultimately determine the health and pro- 

 ductivity of the brackish marsh environment. The water regime 

 determines how much water covers the marsh, how long it is sub- 

 merged, how frequently the substrate is exposed above the water 

 table, and what the salinity range may be. Standing water also 

 provides cover for numerous aquatic and semiaquatic consumer species, 

 and also provides a mechanism for transporting detritus and dissolved 

 nutrients. Second-order effects include regulation of gaseous 

 exchanges between substrate and plants and the regulation of nutri- 

 ent availability. Reestablishing prior drainage pathways, surface 

 contours, and unblocking former sources of water inflow by filling 

 in or plugging canals, removing or breaching continuous elevated 

 levees and spoil banks, and revegetating barren sites facilitates 

 hydrologic restoration. 



Fresh Marsh 



Seismic preexploration. 



1. Activity sequence 



Surveyors enter the marsh by truck, marsh buggy, vessel, 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, buggy, or vessel and one or two 

 support vehicles enter next; holes are drilled, charges and 

 recording equipment 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 



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