Evolução da qualidade da água do Reservatório Guarapiranga (SP) pormeio de longa série temporal e histórico de mortandades de peixes na Bacia do Guarapiranga: a importância do monitoramento ambiental

Abstract

The threat to aquatic ecosystems is global and will only get worse with climate change. Continuous monitoring and assessment of aquatic ecosystems is necessary. The use of indices is recommended for monitoring, as they summarize the technical complexity of the results of the variables and translate these results into quality classes. The Trophic State Index (TSI) and the Aquatic Life Protection Index (API) were applied to a long data series to monitor the Guarapiranga Reservoir, an urban reservoir in the state of São Paulo, southeastern Brazil, which suffers from urban settlement in its surroundings and the discharge of domestic wastewater. The evaluation of the time series from 1978 to 2021 with these indices showed a deterioration in the trophic status and conservation of aquatic life in the reservoir and in one of the tributaries. The results showed that the two indices are suitable for application in a baseline network in subtropical environments. They are able to indicate locations for improved monitoring and are sensitive to environmental changes. The study conducted by CETESB of fish kill ocurrences in the Guarapiranga reservoir catchment in the metropolitan region of São Paulo from 1983 to 2021 showed both spatial and temporal changes in the quality of the catchment. During the period studied, 49 cases of fish kills were reported in the Guarapiranga catchment. The loss of aquatic ecosystem quality due to unplanned colonization was reflected in the high number of fish kills in the 1980s and 1990s. The Guarapiranga Reservoir, which receives water from the basin, also concentrated the result of this expansion of the basin's catchment area and over the years exhibited severe eutrophication, cyanobacteria blooms and the effects of algaecide application. The information obtained from the monitoring of fish mortality in the Guarapiranga basin has shown that this ecological indicator can provide important information on changes in water quality and the socio-ecological environment.