water body is isolated from the contiguous marsh or whether its waters 

 may inundate extensive marsh areas. In addition, the spoil deposits 

 paralleling the canal and wellsite interrupt existing water flows both 

 into and out of the marsh. This blockage may result in localized changes 

 in runoff and standing water. In some instances diversion of seasonal, 

 large-volume discharges away from marsh areas may accelerate natural 

 delta subsidence by diminishing the sediment supply. The total area 

 affected is extremely site specific, unpredictable, and may range from 

 insignificant to highly significant when compared to the total area of 

 the marsh. 



Replacement of stands of marsh vegetation by bodies of standing water 

 (canals and buggy tracks) results in increases of habitat for aquatic 

 invertebrates and vertebrates. However, there is usually a decrease in 

 primary production since the phytoplankton in deeper standing water do 

 not compensate for the losses in marsh plant production. Such replace- 

 ment of food sources (animal for vegetative) will have different effects 

 on alligators, waterfowl, and wading and shorebirds. The areal increase 

 of canal habitat is usually less than the areal decrease resulting from 

 indirect effects of canal construction plus marsh vehicle traffic. 

 Turbidity that results from chronic erosion decreases the suitability of 

 the standing water as habitat for aquatic vertebrates and aquatic inver- 

 tebrates. 



Wildlife displacement resulting from noise and human presence during 

 these construction activities is limited since dredging proceeds at a 

 rapid rate (up to 300 m, or 900 ft, per day). While the displacement 

 effects may extend beyond the project boundaries, they are minor compared 

 to the effects of long-term use of the canal (often for several decades) 

 and the amount of area altered through construction. 



Key attribute alterations 



Key attribute alterations induced by this phase of oil and gas operations 

 involve changes in land elevations. Substitution of vegetation and 

 habitable marsh surface for standing water habitat can be critical to 

 terrestrial organisms in delta marsh systems that are rapidly subsiding. 

 The need for food and cover is especially important during seasons of 

 high river discharge. 



Alteration of water flows can lead to additional (erosional) losses of 

 marsh surface and vegetation. Strategic placement of channels and spoil 

 could lead to net increase in land elevation. Alterations will even- 

 tually elicit long-term changes in vegetative cover, followed by 

 appropriate changes in consumers. 



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