Trophic descriptors of the reservoirs in the Cantareira System (São Paulo, SP)

Abstract

Comparative studies of environments with different trophic status is a form to identify patterns and general rules that explain, at least partially, phytoplankton associations along certain trophic conditions. Due to the impact that phytoplankton species composition can cause on functioning of aquatic ecosystems, it is important to understand the factors that govern the associations and the structure of the phytoplankton community. Several studies showed that the new tool to classify the structure of phytoplankton according to functional groups (FGs) is more efficient in ecological studies as compared to the traditional classification by taxonomic groups and conclude that different systems share similar functional groups according to their trophic status. The phytoplankton FGs may play an important role in making decisions during the implementation of measures to restore degraded environments. The study will be developed at Cantareira's System reservoirs, which form the most important water supply system for the Metropolitan Region of São Paulo (MRSP) and accounts with 58% of the flows offered to 17.2 million people, 9 million just in São Paulo city. The system consists of five reservoirs connected by canals and tunnels. The waters of the Alto Piracicaba are transported by gravity through 48 km of tunnels and canals from Jaguari-Jacareí reservoir interconnection, passing through Cachoeira, Atibainha and finally Paiva Castro's reservoir, at Juqueri river. From this point, the water is also driven by gravity to the Pumping Station of St. Inês, and after a discharge of 120 m, the waters reach Águas Claras reservoir, being conducted by gravity to the water treatment station Guaraú and finally distributed in the MRSP. Watersheds forming System Cantareira have been¬¬ suffering severe impacts by anthropogenic uses. All basins forming this System have over half of its territories altered by human activities. Sewage services situation in Cantareira system is very worrying because in 2003 although many municipalities have a coverage of 100% in the sewage collection, mostly are released untreated directly into rivers. This data set defined by high percentages of use and occupation of the spaces and the incipient sanitation coverage, in particular collection and treatment of wastewater in Cantareira System municipalities, causing a worrying future scenario, as already known in the MRSP, in Billings and Guarapiranga basins. At Cantareira System algaecide applications (copper sulphate) have been occuring in water outflow from Atibainha reservoir, just before the encounter with Juqueri river, particularly in the warmer months of the year, in summer, in order to control the cyanobacterial bloom. The continuation of the same policies applied in Billings and Guarapiranga basins now applied at Cantareira System basins, with probable negative effect on water quality of its reservoirs is a worring fact. These measures are palliative and directly reflect changes in the structure of phytoplankton along a gradient of resource availability, ie according to its trophic status. Thus, this project aims to characterize and compare the masses of water according to their trophic status in five Cantareira System reservoirs (Jaguari Jacareí, Cachoeira, Atibaia and Paiva Castro) and contribute by identifying the dominant phytoplankton FGs in reservoirs with information aimed at expanding the knowledge of this system for better management of their water and watersheds, in order of realization of an efficient monitoring process and in decision making during the implementation of restoration measures. (AU)