Evaluation of urban pollution in a tropical lacustrine ecosystem by using n-alkanes and sterols as biomarkers.

The Jacarepaguá Lagoon System (JLS) receives industrial and domestic waste in an urban area with high population density and intense economic activity. The hydrography of the lagoons favours the sedimentation of particulate material transferred from the drainage basin. Water engineering, such as channel dredging and subsea outfall, did not satisfactorily mitigate pollution effects. Therefore, the environment is highly eutrophic, presents frequent blooms of algae and generates high emissions of greenhouse gases. There is no record in the literature on the analysis of organic compounds in the water compartment. The present work applies sterols as biomarkers to quantify the degree of pollution caused by biogenic compounds in riverine and lacustrine water of the JLS. n-Alkanes were applied to estimate the fractions of petrogenic contaminants. The sums of n-alkanes and sterols analysed had average concentrations of 21 ± 20 µg L-1 and 10 ± 8 µg L-1, respectively, in the river samples and 235 ± 156 µg L-1 and 30 ± 28 µg L-1, respectively, in the lagoon samples. The work also showed that the organic compounds inside the lagoons are evenly distributed, and approximately 7% of them are transferred to the marine ecosystem. Biogenic biomarkers and the absolute concentrations of sterols showed that sewage contaminants transferred by the rivers are partially decomposed in the lagoons. The correlations between indices and physicochemical parameters indicated that the degradation of organic compounds in the lagoons occurs mainly in the sediment compartment under anoxic conditions. The indices for sewage indicate that the ecosystem has exceeded its carrying capacity. The indices based on n-alkanes reported strong contamination at all sampling stations and inferred that 75-100% of these compounds were derived from petrogenic sources. These indices did not show any difference between rivers and the lagoon, which demonstrates the resilience of these compounds in the ecosystem.

Assessment of the trophic status of four coastal lagoons and one estuarine delta, eastern Brazil.

Anthropogenic eutrophication of aquatic ecosystems continues to be one of the major environmental issues worldwide and also of Brazil. Over the last five decades, several approaches have been proposed to discern the trophic state and the natural and cultural processes involved in eutrophication, including the multi-parameter Assessment of Estuarine Trophic Status (ASSETS) index model. This study applies ASSETS to four Brazilian lagoons (Mundaú, Manguaba, Guarapina, and Piratininga) and one estuarine delta (Paraíba do Sul River), set along the eastern Brazilian coast. The model combines three indices based on the pressure-state-response (PSR) approach to rank the trophic status and forecast the potential eutrophication of a system, to which a final ASSETS grade is established. The lagoons were classified as being eutrophic and highly susceptible to eutrophication, due primarily to their longer residence times but also their high nutrient input index. ASSETS classified the estuary of the Paraíba do Sul river with a low to moderate trophic state (e.g., largely mesotrophic) and low susceptibility to eutrophication. Its nutrient input index was high, but the natural high dilution and flushing potential driven by river flow mitigated the susceptibility to eutrophication. Eutrophication forecasting provided more favorable trends for the Mundaú and Manguaba lagoons and the Paraíba do Sul estuary, in view of the larger investments in wastewater treatment and remediation plans. The final ASSETS ranking system established the lagoons of Mundaú as "moderate," Manguaba as "bad," Guarapina as "poor," and Piratininga as "bad," whereas the Paraíba do Sul River Estuary was "good."