Sobre a qualidade da água do rio Tocantins a jusante da usina hidrelétrica serra da Mesa (GO).

Abstract

The present work aimed to study the variation of the physical and chemical characteristics of Tocantins river (TO), downstream the UHE Serra da Mesa in the area defined from the confluence of Cana-Brava River to the confluence of the Parana River (83 km), along a period of 2 years. Data were obtained from a research project named: "Limnological monitoring of Tocantins river downstream of UHE Serra da Mesa", as part of an agreement between the University of Tocantins and Serra da Mesa - Energy S/A and FURNAS - Centrais Eléctricas We tried to obtain the largest volume of available information referring to parameters related with water quality. Tocantins River is of multiple use (domestic supply, animal fed, clothes washing, tourism, leisure, fishing energy generation and unrestricted irrigation). The Tocantins river basin presents drainage 757.000 mVs and medium discharge of long period of 11.800 mVs. Bimonthly samplings were accomplished in seven collection points, in the period from may/98 to mar/00 two rainy and two dry seasons for the following parameters: pH, temperature, conductivity, transparency, color, turbidity, OD, chlorophyll a, reactive phosphate, ammonium and nitrate, chloride, sodium, potassium, silica, calcium, total alkalinity and total hardness. The physical and chemical characteristics observed showed that water quality of Tocantins River is adequate for its several purposes destination considering the parameters for water quality stated by CON AM A Resolution 020/86. The concentrations of nutrients evidenced that the area doesn't receive contributions that can become immediate agents of degradation of water quality. In fact, the rater of N and P corresponded to the level of oligotrophic waters. We intend to continue the monthly monitoring, in order to obtain longer temporal series that would allow a deeper study of the tendencies for eutrophication and of the possible impacts of UHE Serra da Mesa in the water quality of Tocantins River.