saturated substrates are excavated. It is generally agreed among 

 investigators that chemical oil spill emulsifiers, dispersants, removers, 

 etc. are very toxic to aquatic life. Not only are the chemical agents 

 toxic to aquatic invertebrates and vertebrates, but synergistic reactions 

 occur which make a crude-oil/oil-spill-remover mixture much more toxic 

 than either component separately. 



Although cleanup activities may trample and crush extensive amounts of 

 uncontaminated vegetation, the most significant alterations of the 

 cleanup sequence are concerned with changes of the waterflow regime. 

 Movement of marsh buggies and earthwork equipment associated with 

 constructing emergency containment levees or drainage channels changes 

 local land topographic features. Intramarsh circulation patterns may be 

 altered as a result of drainage blockage (establishment of levees) or 

 drainage enhancement (canal digging). Basic characteristics of the 

 marsh's hydrologic regime are altered - average water depth, duration of 

 site submergence, and frequency of site inundation. The nature of such 

 changes are site specific and the area covered is a function of the spill 

 size. Changes in plant composition may result if the hydrologic regime 

 is altered such that wide areas or critical waterways are permanently 

 affected. A site may be drained or, alternatively, impounded. 



Disturbance factors should be recognized as an important consideration 

 because they extend the project impacts beyond the boundaries of the 

 immediate site. 



4. Key attribute alterations 



The primary alteration is the complete or partial removal of biotic 

 components resulting from the effects of spilled oil and from several 

 aspects of 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 which 

 site alterations occur and whether subsequent biotic changes are tempo- 

 rary 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 a result of emergency earthworks con- 

 structed to contain or divert an extensive spill. Subsequent alterations 

 in water circulation patterns can result. 



264 



