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CONCLUSIONS
Microbial degradation appears to have played a very important role
in the weathering of oil spilled from the AMOCO CADIZ. Microbial
hydrocarbon degradation potentials are in general agreement with the
observed changes in the composition
of oil stranded within the littoral
zone. The chemical evolution of the hydrocarbon mixture within
intertidal sediments led to a relative enrichment in isoprenoid alkanes,
a transient complex unresolved mixture, and a relative enrichment of
dibenzothiophenes and alkylated phenanthrenes.
There was a general, but variable decline in concentrations of
hydrocarbons over the three year period following the AMOCO CADIZ spill
within Aber Wrac'h. The concentrations of hydrocarbons also declined at
sites that were regularly covered by tides. At the one site in lie
Grande, which is not subject to daily tidal washing, the concentrations
of hydrocarbons remained high even three years following the spill. At
nearby sites within the lie Grande salt marsh, which were physically
cleansed of AMOCO CADIZ oil, there was little chemical or microbial
evidence of any impact from the AMOCO CADIZ spill at any of the sampling
times. The incurrence of oil from the TANIO wreck was apparent even at
sites that had been oiled as a result of the AMOCO CADIZ spill.
The microbial population levels generally reflected the relative
degrees of persistence of petroleum hydrocarbons. The microbial
community at all of the sites studied had essentially the same potential
capability for degrading hydrocarbons and as such the differences in the
hydrocarbon concentrations and composition recovered from the field
samples probably reflect the initial rates of oiling and environmental
influences. The indigenous microbial community retained the capability
of responding to a second incursion of oil resulting from the TANIO
spill.
Both the field experiments and the i_n vitro studies suggest that
mixing energy, related to nutrient and oxygen availability, was
extremely important in permitting the high rates of observed oil
weathering. The occurrence of both saturated and unsaturated acids in
the sediments studied in vitro suggest that several biochemical pathways
were active in the biodegradation of the aliphatic hydrocarbon fraction.
The hydrocarbon biodegradation potential suggested that relatively high
concentrations of oxygenated aromatic hydrocarbons should accumulate,
but for unexplained reasons the analyses of the polar fraction generally
failed to show such accumulations.
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