Assessment of the water quality and trophic state of the Ribeirão Guaraçau Watershed, Guarulhos (SP): a comparative analysis between rural and urban areas

Abstract The urbanization process through which large urban centers have been passing has affected drastically the availability and especially the quality of water. The Ribeirão Guaraçau Watershed, located in the northern part of the Guarulhos municipality, includes rural and urban areas of different land-use classes. The goal of this study is to assess the water quality and to diagnose the eutrophication stage of the surface waters of the Ribeirão Guaraçau, the main water course of the Ribeirão Guaraçau Watershed. To assess environmental quality, physical-chemical analyses (temperature, pH, turbidity, conductivity, and total phosphorus) and microbiological analyses (E. coli) were carried out during a period of 12 months. The Trophic State Index (TSI) was used to ascertain the environmental degradation conditions of lotic and lentic environments. The surface waters of the Ribeirão Guaraçau in the rural area are already compromised, with worsening of the water quality upstream indicated by high total phosphorus and E. coli caused by fecal contamination due to lack of basic sanitation in the region. Characteristic sites of the rural areas already present signs of degradation with trophic levels varying from oligotrophic to hypereutrophic. The need to provide sewage collectors and sewage treatment systems at the Bonsucesso Sewage Treatment Station, inaugurated in 2011, and the control of the occupation in areas that produce good quality water is paramount.