14, 



groups makes [2- C] -acetate metabolism a useful means of differentiat- 

 ing the importance of bacterial processes which accomplish its oxida- 

 tion to C0„ (sulfate reduction) or its conversion to CH, (methane 

 production, see Fig. 1). [2- C]-acetate was metabolized only to C0„ 

 at all sites except in the surface layer of the oiled lie Grande site 



where small amounts of 





CH, were detected on one occasion (March, 

 1979). This observation, however, was not repeated at later sampling 

 dates. Rates of sulfate reduction were highest in the surface layer 

 and decreased with depth in all sites (Fig. 8). Rates in the 0-3 cm 

 intervals were higher in oiled compared to control Aber mudflat sedi- 

 ments (p = .004). In the beach and salt marsh mudflat sediments , rates 

 were higher in control sites than in oiled sites (p < .001). It is not 

 possible, however, to attribute differences to the presence of AMOCO 

 CADIZ oil since other differences between sites (e.g., amount of or- 

 ganic loading) could also explain differences in sulfate reduction. 



ABER ILDUT 



ILE GRANDE 



SULFATE REDUCTION RATE (pmoles S0 4 = ' mf'-day" 1 * 



Figure 8. Depth profiles for rates of sulfate reduction in oiled and 

 control sediments. Bars indicate one standard deviation. 



To more directly observe the effect of oiling on microbial activi- 

 ties in sediments, AMOCO CADIZ mousse was added to lie Grande sedi- 

 ments, and activities compared between mousse- treated and untreated 

 sediments. Gas chromatograms of the saturate and aromatic fractions of 

 this mousse are shown in Figures 9 and 10, respectively. These tracings 

 can be compared to fresh light Arabian Crude in Figures 9 and 10. In 

 the saturate fraction of the mousse, no hydrocarbons below C-12 were 

 detected. In the aromatic fraction all predominant compounds were gone 

 and only a UCM remained. Thus, extensive weathering of the low mole- 

 cular weight compounds in the mousse had occured before collection. 

 Extensive biodegradation of aliphatic compounds was not suggested as 

 evidenced by the dominance of normal compared to isoprenoid alkanes. 



177 



