showed steeper Eh profiles than estuarine sediments and oiled sediments 

 were more reducing and showed steeper Eh profiles than unoiled sedi- 

 ments of the same type. The large Eh change with depth (300mv over 

 1 cm (lie Grande oiled site) or 2 cm (Aber Wrac'h) suggested that sedi- 

 ments below these depths are likely anoxic. 



Chloride (data not presented) was relatively constant at all depths 

 in all sites and was near seawater chloride levels (20,000 mg/liter). 

 The concentrations of dissolved sulfate and methane with depth in each 

 site are reported in Table 1. No major differences in sulfate concen- 

 tration with depth or between cores were observed, _and levels were 

 similar to seawater values (approximately 800 mgSO, -S/l ). Methane 



TABLE 1. Sediment Chemistry 3 



SULFATE CHEMISTRY** 



DEPTH AMC 4 TREZ-HIR ABER WRAC'H ABER ILDUT ILE GRANDE ILE GRANDE 

 (cm) (oiled) (control) 



METHANE CHEMISTRY 



Sediments collected in March 1979 



Results expressed in pg SO, -S/ml porewater 



p 



Results expressed in (jmoles CH./l sediment 



167 



