Multidisciplinary Study (Geochemical and Foraminiferal Assemblages) to Characterize and Assess Anthropic Activities at the Ara á Bay, S o Sebasti o Channel, Brazil

The goal of this study was to assess possible human-induced changes in the environment due to the discharge of domesticsewage into the Ara á Bay, S o Sebasti o Channel, S o Sebasti o, Brazil. In order to achieve this goal, in April 2006, weconducted grain size and geochemical (Toc, N, S, and P) analysis and determined the assemblage composition and distributionof live benthic foraminifera from shallow marine sediments collected around diffusers of the domestic sewage submarineoutfall at the Ara á Bay. Results showed that the area studied is a lithoclastic shallow environment with predominance ofsandy sediments. However, in the northeastern area of the sampling grid, it was observed high concentrations of fine sediments(silt plus clay), with significant Toc (> 1%), N (> 0.2%) and S (0.3%) contents. The organic enrichment is inferred based onthe phosphorus and sulphur contents, as well as on the oxidation-reduction potential, which was inferred using the Eh valuesand C/S ratios. In relation to the benthic foraminiferal assemblages, low richness was observed and the association is mainlycomposed of infaunal and detritivore species. There is a high abundance of Epifaunal species, which are bioindicators ofwell-oxygenated environments, in stations with no impact of the sewage discharged by submarine outfall. The occurrence ofmedium and small-sized foraminifera shells is qualitatively associated with low oxygen concentrations at the sediment-waterinterface. The dominance of a few species, especially Ammonia tepida, may indicate environmental stress.