Metals in sediments of São Paulo State reservoirs: subsidy to decision making through geostatistical and ecotoxicological approaches

Abstract

The monitoring and management of aquatic organisms are fundamental to ensure the sustainability of freshwater bodies, especially in reservoirs. In Brazil there are some normative related to the obligatory of cyanobacteria and coliforms monitoring, but not of macrophytes, for example. A monitoring plan has to monitor changes in water and sediment quality, and a management program has to plan practical actions necessary to ensure the quality for current and future uses of a reservoir as well as to maintain its ecosystem services. The aims of this project is to evaluate the horizontal spatial heterogeneity of metals concentrations in surface sediments of some São Paulo State reservoirs, especially copper, as well as their total stock in the sediment, under the premises of geostatistics. In this way, the bathymetric map and the morphometric magnitudes of the studied reservoirs (Guarapiranga, Rio Grande arm - Billings complex, Itupararanga, Broa and Paiva Castro) will be obtained. Subsequently, working in a GIS, based on the determined metal concentrations, now supported by ecotoxicology, criteria will be developed that will allow to pass from quantitative to qualitative aspect and spatially define zones of different sediment qualities, based on different toxicity potentials to biota. Differences are expected between the reservoirs and their biota (phytoplankton and zooplankton also studied), due to the significant amounts of copper sulphate and hydrogen peroxide applied in Rio Grande and Guarapiranga reservoirs, in comparison with others reservoirs. The data collected will also support discussions about water quality management program, in particular the use of algicides, now endorsed by Conama Resolution 467, published in 2015, which regulates the use of physical, chemical and biological processes, such as algicides, to control the disordered or undesirable growth of organisms of the flora and fauna giving also other measures. (AU)