2.6 Alteration of water flows in localized areas 



2.7 Displacement of sensitive wildlife species from adjacent areas due 

 to cleanup activities 



Attribute alterations 



Plant assemblages are removed or altered by either (1) the toxic effects 

 of spilled petrochemicals or brine or (2) the cleanup processes which 

 follow. 



Toxicity of oil pollutants varies with the petroleum fractions involved. 

 In a decreasing order of toxicity are gasoline, diesel, bunker C, and 

 crude. The most toxic oil products have the largest percentage of vola- 

 tiles, therefore, they become less toxic wery rapidly as the volatiles 

 evaporate. Ironically, the detergents used to disperse oil spills are 

 often more toxic than the spilled material. 



Natural decomposition of an oil spill begins immediately and proceeds via 

 several mechanisms. The volatile fraction evaporates at a rate which 

 depends on the temperature and wind velocity. Within 12 hr of a crude 

 oil spill, roughly 40 percent of evaporated or in the water column while 

 60 percent remains as a tarry slick. The oil can be consumed by browsing 

 invertebrates. Oil coats suspended particulate matter and sinks to the 

 bottom, thus becoming an energy source for certain bacterial that are 

 capable of oxidizing the oil. Thin layers of crude oil can be completely 

 decomposed within two or three months. 



The effect of an oil spill on the marsh depends on the size of the spill, 

 the duration of exposure, and the type of oil spilled. Prediction of a 

 spill's severity is difficult because of many compounding factors. The 

 fate of a spill depends on prevailing winds, water currents, and tempera- 

 ture. Toxicity to the biota depends on the temperature, salinity, and 

 the life form and life stage exposed. Spill coverage of the marsh is a 

 function of the currents, wind direction, and wind velocity at that 

 particular time. 



A crude oil spill causes a die-back of marsh vegetation above the oil line 

 within two or three days. Emergent grasses, sedges, and rushes are life 

 forms most likely to be affected. Cleanup efforts effect similar results 

 because of either burning or hand-cutting contaminated stems. Plant 

 species with intact root systems and large food reserves recover within 

 one year; less tolerant species require more time. If large quantities 

 of toxic materials are not rapidly dispersed over wide areas, mobile con- 

 sumers capable of avoiding contaminating substances leave the areas. 

 Less mobile consumers may be coated with oil or other noxious fractions 

 and die. Food and shelter resources become so degraded as to provided 



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