Multiple biogeochemical indicators of environmental quality in tropical estuaries reveal contrasting conservation opportunities

Abstract

Estuaries are under major impacts from pollution even when managed as conservation units. Here we used multiple biogeochemical indexes of contamination and trophic status, including faecal sterols, biopolymers and trace metals, to determine and compare environmental quality of two tropical estuaries with contrasting conservation status. In the metropolitan estuary, eutrophic/hypereutrophic conditions and high concentrations (>1.0 µg g−1) of coprostanol were spatially correlated to sources of raw sewage input. Unexpected eutrophic sediments were also detected at the estuarine reserve, but with low sewage contamination indicating that high organic availability and burial predominated. The natural or polluted eutrophic sediments were determined by comparing multiple contamination indexes, which indicated sediment contamination within the metropolitan estuary. This study indicates that the long-term conservation of estuarine ecosystems on the Atlantic coast of Brazil are threatened by a typically poor sewage treatment and suggests that estuarine sediment quality need to be evaluated by multiple proxies before estuaries can be included in spatial conservation planning.