A importância de um alagado para a qualidade da água em um ecossistema urbano impactado por resíduos domésticos

Abstract

Lakes and lagoons are abundant components of the natural landscape of the state of Rio de Janeiro, Brazil. However, due to human activities, many of those are under strong ecological impact. Vigario Lake and Taquaruçu Lake are important water bodies in the city of Campos dos Goytacazes but still receive domestic sewage along their margins. The water flows from Vigario to Taquaruçu Lake, passing through a wetland, which is fully colonized by aquatic macrophytes, especially Typha domingensis and Eichhornia crassipes. In this study, water samples were collected during a monthly monitoring of 12 months in 1999 and an intensive sampling in the dry and wet periods in 2000/2001 in representative stations along the study area for determination of physico-chemical and chemical variables. In the wetland, a place of anoxic characteristics, denitrification, ammonification and release of orthophosphate from the sediment to the water column could be detected, while other important limnological processes of oxidant waters could be observed in the lakes, despite the contamination. A controlled mesocosm experiment was designed to quantify the function of the wetland on the depuration of the waters from the Vigario Lake. Such artificial system could significantly remove biochemical oxygen demand in 84%, total and thermotolerant coliforms in 94% and 87% respectively, dissolved and total nutrients from the waters coming from the Vigario Lake. For the removal of ammonium and dissolved phosphorus, the presence of aquatic macrophytes was mandatory in the system. Key words: constructed wetlands; lakes; nitrogen; nutrients; phosphorus; wetlands.