Análise de risco ecológico como ferramenta de avaliação da qualidade ambiental do rio Sergipe

Abstract

Studies of characterization of rivers and their biological communities are fundamental to understand the ecosystem and to allow the development of conservation proposals. The Brazilian semi-arid region lacks studies on its river ecosystems, and many watercourses of important river basins remain without detailed studies. In this context, the general objective of this study was to evaluate the degree of degradation and the environmental risk of the Sergipe River, an important water course partially inserted in the semi-arid region of the Brazilian Northeast, using limnological, ecotoxicological and biological data. Seven points were chosen in the nascent-mouth axis of the Sergipe river, where measurements were made in situ and samples of water, sediment and benthic organisms were collected. Two sampling campaigns were carried out, one under the influence of the drought period (April 2013) and another under the influence of rains (August 2014), allowing a spatial and temporal analysis of the system. The limnological parameters were submitted to a Principal Component Analysis (PCA) in order to evaluate how these data are organized spatially. For the ecotoxicological studies, short-term chronic toxicity tests were carried out with Poecilia reticulata, in order to analyze the mortality and changes in the biometrics of the individuals. Benthic organisms were identified and analyzed through the calculation of diversity indexes. Finally, an Ecological Risk Assessment (ERA) was developed using the triad approach, in which data from different lines of evidence (chemical, ecotoxicological and ecological) are integrated to provide the final ecological risk to the environment. The results showed that the Sergipe river is divided in three distinct sections of characterization. In the dry season, the headland region, which is more vulnerable due to the influence of the semi-arid climate and the intermittent regime, presented a moderate level of risk, while the middle Rio Sergipe stretch presented a low risk. The upper Sergipe presented moderate to high risk levels, being this region the one with the highest urban and industrial concentration in the basin. In the rainy season, risk levels were less critical, probably due to a greater dilution of the system. These results indicate the need for more monitoring studies in the region in order to establish remediation strategies in the most impacted stretches of the river.