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3.2 Surface Sediments (Atlas, University of Louisville)
The frequency of sampling for surface sediment (0-3 cm) is shown
in Table 5. Ten primary locations were sampled repeatedly (Fig. 3.7).
Results of total hydrocarbon determinations for the ten stations, as
these concentrations varied with time, are presented in Figures 3.8
through 3.12. Also included in these figures are source evaluations
for each sample hydrocarbon assemblage, based on GC information. The
biogenic (B) category indicates that terrigenous odd chain n-alkanes
dominate the f^ GC trace. The pyrogenic (P) category signifies an
important abundance of combustion-related polynuclear aromatic hydrocarbons
(PAH) in the f2 fraction as well as the presence of some
unresolved material (UCM) in both the f^ and f2» In those samples
labeled B or B/P the primary sources of hydrocarbons are as indicated
although a small fraction of the hydrocarbons may consist of petroleum.
Figure 3.13 summarizes these source criteria. Only GC/MS analysis of
each sample would definitely eliminate the small chance of a false
negative (i.e. not finding AMOCO oil where there were traces).
The error bars in the figures indicate that two determinations
were made for the December 1978 samples (Table 6) . All other determinations
were based on one replicate. Note that the coefficient of
variation ranges from .01 (1%) to .94 (94%). The higher variability is
observed in samples with the lowest and highest (^1000 ppm) absolute
concentration levels, the former due to natural patchiness, the latter
owing to "pooling" of oil in heavily impacted stations.
GC/MS results are available for stations 3, 5 and 7 throughout the
study period and are presented graphically in Figures 3.14 through
3.33. These semi-log plots illustrate quantitatively the aromatic
composition of all samples normalized to C3 dibenzothiophene or where
C3DBT is absent to pyrene. C3DBT was used to normalize the data as it
is assumed that these compounds are the slowest to weather of all of
the aromatic hydrocarbons.
All AMOCO CADIZ-impacted stations illustrate a normal weathering
sequence (i.e. see Fig. 3.1). However, fresh inputs of petroleum were
observed to impact the region of stations 7 and 8 in the form of tar
chips during November 1979 and stations 2, 11 and 12 in the form of oil
from the TANIO spill in August of 1980 (Fig. 3.34).
Although a wide range of residual oil concentrations appear in the
various samples, several trends in the data seem apparent. Stations 1,
9, and 10 remain unimpacted by the spill throughout the study. Station
2 remains unimpacted until a secondary petroleum input influences its
hydrocarbon chemistry in November of 1979 (the timing of the secondary
tar impact at stations 7 and 8 also is probably related to leakage from
the sunken tanker) and again in August of 1980, the latter relating to
the TANIO spill, also readily detected at Stations 11 and 12 at this
time. Through March of 1980 weathered AMOCO CADIZ oil is readily
detected at Stations 3, 4, 5, 6, 7 and 8. However, the results of the
August 1980 samplings indicate that inputs of non-AMOCO CADIZ hydrocarbons
(i.e. background) at Stations 6 and 8 become dominant. At
stations 3 and 7 where GC/MS data exists, the main AMOCO CADIZ aromatic
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