2.1 Introduction of toxic materials into water and soil systems 



2.2 Complete above-ground removal of vegetation in spill zone 



2.3 Partial vegetation removal in adjacent areas during access and 

 cleanup phases 



2.4 Complete removal of selected consumer species in spill area 



2.5 Increased concentration of suspended sediments and dissolved nutri- 

 ents 



2.6 Alteration of water flows in localized areas 



2.7 Displacement of sensitive wildlife species from adjacent areas due 

 to cleanup activities 



3. Attribute alterations 



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

 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 

 volatiles, therefore, they become less toxic very rapidly as the 

 volatiles evaporate. Ironically, the detergents used to disperse oil 

 spills are often more toxic that the spill materials. 



Natural decomposition of an oil s 

 several means. Depending on the 

 volatile fraction evaporates rapi 

 roughly 40 percent is evaporated 

 remains as a tarry slick. The oi 

 brates. Oil coats suspended part 

 thus becoming an energy source fo 

 zing the oil. Thin layers or cru 

 within two or three months. 



pill begins immediately and proceeds via 

 temperature and wind velocity, the 

 dly. Within 12 hr of a crude oil spill, 

 or in the water column, while 60 percent 

 1 can be consumed by browsing inverte- 

 iculate matter and sinks to the bottom, 

 r bacteria that are capable of oxidi- 

 de oil can be completely decomposed 



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

 the duration of the release, and the type of oil spilled. Prediction of 

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



262 



