Efeitos de diferentes intervenções no processo de eutrofização do lago Paranoá (Brasília - DF)

Abstract

Long-term environmental monitoring of aquatic ecosystems is essential to understand their dynamics and to the proposition of management practices. Paranoá Reservoir was created in 1959 and was subject to a long period of eutrophication. In this paper, data obtained by the monitoring program carried out by the “Companhia de Abastecimento e Saneamento de Brasília”, between 1976 and 2001, were evaluated to measure the effects of three direct interventions on water quality (as measured by water transparency, P-total and chlorophyll-a concentrations): the activation of two water treatment plants (01/1993); the proper operation of these plants (01/1996), and a major flushing event (sudden release of water in 11/1999). The following results were obtained: i) the first intervention had no effect on the mean values of the variables analyzed; ii) the chlorophyll-a and total phosphorus concentrations signifi cantly declined after the second intervention; iii) water transparency increased after the third intervention. An apparent mechanism of phosphorus feedback supported by phytoplankton was interrupted by the flushing and, after that intervention, the primary production of Paranoá Reservoir declined to a new level. The dataset obtained by the monitoring program was essential to understand this process and, therefore, the continuity (and even amplifi cation) of this program was fully justified.