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14,
groups makes [2- C] -acetate metabolism a useful means of differentiating
the importance of bacterial processes which accomplish its oxidation
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 sediments
(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 organic
loading) could also explain differences in sulfate reduction.
ABER ILDUT ILE GRANDE
= 1
'
*
SULFATE REDUCTION RATE (pmoles S04 mf'-day"
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 activities
in sediments, AMOCO CADIZ mousse was added to lie Grande sediments,
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 molecular
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.
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