AMOCO CADIZ POLLUTANTS IN ANAEROBIC SEDIMENTS: 

 FATE AND EFFECTS ON ANAEROBIC PROCESSES 



by 



1 112 



David M. Ward , Michael R. Winfrey , Eric Beck and Paul Boehm 



1) Department of Microbiology, Montana State University, Bozeman, 

 Montana 59717 



2) Energy Resources Company, Inc., Cambridge, Massachusetts 02138 



INTRODUCTION 



It was estimated that much of the oil spilled after the wreck of 

 the AMOCO CADIZ impacted intertidal and subtidal sediments (Hann, et 

 al, 1978; Gundlach and Hayes, 1978). Considerable differences exist 

 between sediment and aquatic environments which could have dramatic 

 effects on the persistence of spilled oil and its effects on the native 

 biology of coastal environments. Recent investigations have shown that 

 intertidal and subtidal sediments are anaerobic except in the initial 

 few millimeters near the surface (S^rensen, et al, 1979; Revsbech, et 

 al, 1980a, b) . Since oxygen is known to be of extreme importance in 

 the microbial biodegradation of hydrocarbons (Atlas, 1981; Hambrick, et 

 al, 1980; DeLuane, et al, 1981; Ward and Brock, 1978) it is likely that 

 the persistence of hydrocarbons would be much greater in anoxic sedi- 

 ments. This could create a source of relatively unweathered petroleum 

 for secondary pollution events. One of the major objectives of this 

 study was to investigate the extent of pollution by AMOCO CADIZ oil in 

 anaerobic coastal sediments. Evidence for weathering and potential 

 biodegradation of sediment hydrocarbons under aerobic and anaerobic 

 conditions was also obtained in chemical and microbiological studies. 



Sediments are also important sites where extensive mineralization 

 of organic matter and recycling of nutrients occurs (Fenchel and J#r- 

 gensen, 1977). The effect of oil on sediment microorganisms and pro- 

 cesses has been examined in some studies (Walker, et al, 1975; Knowles 

 and Wishart, 1977) but only a few studies have examined the effects on 

 mineralization (Griffiths, et al, 1981, 1981 (in press)). Because of 

 the extreme thinness of the oxygenated zones of coastal sediments, an- 

 aerobic processes are important in mineralization and nutrient recycl- 

 ing (S^rensen, et al, 1979). The effects of oil on anaerobic processes 

 have not been studied . Many studies on sediment chemistry and microbio- 

 logy support the model for anaerobic microbial food chains in marine 

 sediments presented in Figure 1 (see Mah, et al, 1977; Fenchel and J^r- 

 gensen, 1977; Rheeburg and Heggie, 1977; Bryant, 1976). Within anaero- 

 bic zones polymeric organic matter is fermented principally to H , CO 

 and acetic acid. Acetate and H„ are the main energy sources for spec- 

 ialized anaerobic bacteria which terminate the food chain. The activi- 

 ty of these terminal groups is thought to be important in influencing 

 fermenting bacteria to produce mainly acetate, H„ and CO (Bryant, 

 1976) . The importance of these energy sources in marine sediments has 



159 



