Multiple benthic indicators suggest low sewage impact from an ocean outfall in a high-energy sandy shore (South Brazil)

摘要

Increasing urbanization in coastal areas has not paralleled with adequate sewage treatment, and the overload of organic matter compromise important economic, ecological and social values supported by these ecosystems. Ocean outfalls may be an effective alternative to the destination of wastewater in coastal regions, provided they are properly installed and monitored. In this study, we investigated the effects of a small outfall on a high-energy sandy shore, southern Brazil, using sedimentary steroids, biochemical composition and nutritional quality of organic matter and free-living nematode biodiversity as indicators. The results showed that physical disturbances prevail near the outfall, affecting the densities of the fauna and phytopigments. The higher concentrations of sedimentary sterols detected at 1000 m NE from the outfall indicated the influence of the local hydrodynamic conditions in the transport and dispersion process of the sewage. In this area, the sewage contamination changed the benthic trophic state from oligotrophic to eutrophic, and lead to a strong decrease in the trophic diversity and increase of opportunistic nematode genera. Overall the results showed a relatively low and limited spatial impact from the outfall. The integrated use of fecal sterols, benthic trophic state and nematodes biodiversity were highly effective in detecting sewage contamination of low input of wastewater in a highenergy sandy shore.