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pristane and n-C18/phytane which were 3.3 and 2.8 in the reference
mousse, were 0.07-0.58 and 0.024-0.36, respectively. Becase of the
relative persistence of aromatic hydrocarbons (Atlas, et al, 1981; Ward
et al, 1980), alkylated naphthalenes, phenanthrenes and dibenzothiophenes
remained in Brittany sediments at levels sufficient to study
weathering patterns in a long term time/depth series. The loss of
these compounds relative to the more persistant C„-alkylated derivatives
of dibenzothiophene (CL-DBT) is thought to be an index of weath-
ering (Grahl-Nielsen, et al, 1978). There is no published evidence
that changes in aromatic compounds relative to C„-DBT are due to biodegradation,
but these compounds are subject to microbial attack (Atlas,
1981).
The ratios of aromatic compounds to CL-DBT showed different
changes with time depending on type of sediment and sediment depth
(Table 3). In the AMC-4 0-5 cm interval there was a systematic decrease
in nearly all ratios from December 1978 to March 1979 to November
1979. In muddy sediments decreases were less rapid and extensive.
By March 1979, C - and C,- naphthalenes, C„- and C,- phenanthrenes
and C-DBT showed: relative decreases in the Aber Wrac'h 0-5 cm
interval. An Aber Wrac'h core collected in November 1979 was subdivided
at one centimeter intervals at the depths of greatest change in
Eh. In the 1-2, 2-3, and 3-4 cm intervals naphthalenes were "almost
entirely depleted. Relative decreases in all except C - and C,- phenanthrenes
were noted compared to earlier samples, with no great differences
among these depth intervals. Phenanthrenes were enriched relative
to C-DBT by May 1980 in the 0-3 cm interval. Ratios of aromatic
hydrocarbons to C.-DBT were generally greater in deeper layers (5-10,
10-15 cm) than in surface layers on any given date. Nevertheless, the
data suggest that decreases in naphthalenes and DBT's occurred in the
5-10 cm interval in the one year between December 1978 and November
1979, despite the relative constancy of C,-DBT over the time Results for lie Grande were similar to those for Aber Wrac'h
period.
but the
relative amounts of most components were 1978 and March 1979, there was a relative
greater. Between December
enrichment of all components
except C, -naphthalene. In March 1979, ratios
than at 0-5 cm. Finer resolution around the
were higher at 5-10
depths
cm
of greatest Eh
change was attempted on samples collected in May 1980. There was evidence
of decreases in naphthalenes compared to earlier samples at all
depths, even though the concentration of C.-DBT was very high in all
samples. Relative decreases in C -phenanthrenes and DBT's were noted
in the 0-2 mm and 2-10 mm intervals. Except for C, -phenanthrenes , ratios
were always higher in the 3-4 cm interval.
Hydrocarbon Biodegradation
14
In initial experiments, various C-labelled aliphatic or aromatic
hydrocarbons were incubated with surface sediments under aerobic conditions,
or with subsurface sediments under conditions designed to prevent
the exposure of obligately anaerobic bacteria to oxygen. The juccess
of anaerobic methods was evidenced by the reduction of SO, to
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