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effects of additional heavy oiling. This may be a result of an adaptation
of microorganisms to the presence of oil, or to a selection of oil
resistant populations.
It is not surprising that hydrocarbons did not directly inhibit
sulfate reduction since this process appears to be active in oil formation
waters (Bailey, et al., 1973; ZoBell, 1958). However, it was surprising
that compounds which inhibited acetate oxidation did not directly
inhibit sulfate reduction, as other investigations have pointed
to the importance of acetate as a substrate for sulfate reduction (Winfrey
and Ward, submitted; Srensen et al, 1981; Banat and Nedwell, personal
communication).
The chemistry of hydrocarbons present in the various sediments one
year after the spill indicated the presence of oil highly altered by
evaporation and biodegradation. The levels observed in the environment
were also lower (0.1-1 mg/g) than the levels added in our experiments
to simulate heavy oiling (50-250 mg/g). It is possible that a temporary
inhibition of acetate oxidation could have resulted from very heavy
oiling of relatively fresh oil. Such conditions could have existed at
all polluted sites immediately following the AMOCO CADIZ spill, although
rapid loss of volatile compounds probably occurred between
spillage and beaching of oil (Dowty, et al, 1981; Ward, et al, 1980).
Any inhibitory effect would then have been reduced as cleanup or transport
of hydrocarbons out of the sediments decreased hydrocarbon amount,
and as evaporation, dissolution and biodegradation altered the remaining
sediment hydrocarbons. By the time site comparison experiments
could be performed, recovery from any negative effects which might have
occurred had apparently taken place. The inhibitory effects on acetate
oxidation we observed may be significant in extremely cold regions
where slow rates of evaporation would occur.
ACKNOWLEDGEMENTS
We are indebted to the Centre Oceanologique de Bretagne at Brest
and the Station Biologique at Roscoff for providing laboratory space
and assistance. We also thank Bob Clark of the NOAA National Analytical
Facility for supplying AMOCO CADIZ mousse, George Ward of Exxon
Corp. for supplying the light Arabian crude oil, and Dale Meland and
Melinda Tussler for technical assistance.
This study was part of a joint effort undertaken by the Centre National
pour 1' Exploitation des Oceans (CNEXO) of the French Ministry of
Industry and the NOAA of the U.S. Department of Commerce to study the
ecological consequences of the AMOCO CADIZ oil spill. It was financed
by funds given to NOAA (contract NA 79RAC00013) by the Amoco Transport
Company and by the NOAA Outer Continental Shelf Environmental Assessment
Program, through an interagency agreement with the Bureau of Land
Management.
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