enhancement (canal digging). A basic characteristic of the marsh's 

 hydrologic regime, average water depth, is altered. Such changes are 

 site specific and areal magnitude is a function of the spill size. Plant 

 alterations may result if the hydrologic regime is altered such that wide 

 areas or criticial waterways are permanently affected. A site may be 

 drained or alternatively impounded. 



Disturbances associated with vehicular and boat traffic, human presence, 

 and cleanup procedures typically cause short-term displacement of 

 sensitive wildlife species from otherwise favorable habitats nearby. 

 Displacement may affect feeding waterfowl concentrations, bird rookeries, 

 and vertebrate movement patterns. Following activity completion, species 

 reenter nearby sites if the areas remain essentially unaltered. Human 

 activity and associated noises extend project effects beyond the bounda- 

 ries of the spill site. 



4. Key attribute alterations 



The primary alteration is the complete or partial removal of biotic com- 

 ponents, due to the effects of spilled oil and the cleanup procedure. 

 Consumer response varies by species, size of the area affected, site 

 characteristics, and resultant floristic changes. An oil spill has the 

 potential to kill thousands of waterfowl; contaminate shellfish; kill 

 fish, crab, and bivalve larvae; foul bottom sediments; and kill emergent 

 grasses. Cleanup methods determine site alterations that occur and 

 whether subsequent biotic changes are temporary or long-term. For 

 example, spills and cleanup procedures restricted to aquatic areas would 

 have only minimal effects on higher vegetated marsh sites. Marsh buggies 

 and other surface vehicles would not be required; operational aspects 

 could be accomplished by outboard and/or airboats. Potential alterations 

 of importance to the ecosystem pertain to changes in land elevations as 

 result of emergency earthworks required to contain or divert an extensive 

 spill. Subsequent alterations in water depth and circulation patterns 

 can result. 



Site shutdown and restoration. 



1. Activity sequence 



Completion of exploratory drilling, removal of production facilities, 

 backfilling of pipeline ditches, and spill cleanup usually signal initia- 

 tion of the shutdown and restoration phase. Permanent structures, 

 equipment, concrete foundations, pipes, surface flowlines and supply 

 lines, well casings, drilling mud, and other artifacts of oil production 

 are removed if they possess salvage or reuse value. Otherwise, only as 

 much attention is paid to restoration procedures as is required by 

 Federal and state regulations, lease stipulations, and general company 

 policy. In delta marshes restoration typically includes removal and/or 



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