concentrations were extremely low (less than 5 (Jmoles/1) and relatively 

 constant with depth. Methane concentrations were significantly higher 

 at the lie Grande oiled site (p < .001). 



Sediment Hydrocarbons 



Sediments collected during December 1978 and March 1979 were ana- 

 lyzed for hydrocarbon content (Table 2) and type (Figs. 4 and 5) . Sur- 

 face sediments (0-5 cm) at all sites oiled with AMOCO CADIZ oil exhi- 

 bited a composition indicative of highly weathered oil residues. The 

 saturate fractions were comprised of a degraded hydrocarbon assemblage 

 with greater degradation in estuary and marsh mudflat samples than in 

 the beach sample as evidenced by the relative dominance of the branched 

 isoprenoid hydrocarbons (Fig. 4). Residual alkylated phenanthrenes , 

 and dibenzothiophenes in the aromatic/unsaturate fractions (Fig. 5) 

 also indicated the presence of weathered petroleum. All samples known 

 to be impacted by AMOCO CADIZ oil exhibited a characteristic unresolved 

 complex mixture (UCM) in both saturate and aromatic/unsaturate frac- 

 tions indicative of weathered petroleum (Farrington and Meyers, 1975). 



Qualitative and quantitative differences existed between oiled and 

 unoiled control sediments in the 0-5 cm depth interval. Hydrocarbon 

 content was always higher in oiled sediments (Table 2) . The control 

 estuary sediment exhibited a small UCM and hydrocarbons indicative of 

 biogenic origin in the saturate (odd chain alkanes n - C to n-C_ ) and 

 aromatic/saturate (polyolef inic material) fractions. Tne control marsh 

 sediment exhibited a mixture of hydrocarbons of biogenic (odd-chain al- 

 kanes n-C.,. to n-C„ ) and petroleum (UCM) origin, with low concentra- 

 tions of residual aromatic/unsaturate hydrocarbons. The control beach 

 sediment exhibited a n-alkane series (n-C ,. to n-C„~) and UCM in the 

 saturate fraction, and polynuclear aromatic components originating from 

 combustion of fossil fuel (eg. , nonalkylated 3-5 ringed polynuclear 

 aromatics) (Youngblood and Blumer, 1975). 



The types and amounts of hydrocarbons were consistent with the 

 known degree of impact from the AMOCO CADIZ oil spill. It is clear 

 that in control beach and marsh sediments impact by hydrocarbons of 

 petroleum or other anthropogenic sources had occurred. 



Evidence for degraded Amoco Cadiz oil at various sediment depths 

 is summarized in Table 2. At the beach station AMC-4 , AMOCO CADIZ oil 

 was evident in the hydrocarbon assemblage down to the 10-15 cm interval 

 in a sample collected in December 1978, and to the 15-20 cm interval in 

 a sample collected in March 1979. At Aber Wrac'h there was evidence of 

 AMOCO CADIZ oil to the 10-15 cm interval at both collection dates. The 

 amount of oil decreased with depth as evidenced by the total hydrocar- 

 bon concentration and the increasing contribution of native sediment 

 hydrocarbons (e.g., plant derived saturate and aromatic/saturate com- 

 pounds) which dominated in the deepest layers as in the entire Aber 

 Ildut core (see Figs. 4, 5). Similar results were found at the lie 

 Grande oiled site where AMOCO CADIZ oil was detected in the 5-10 cm 

 layer on both sampling dates and biogenic compounds dominated deeper 

 layers. 168 



