Effect of rainfall seasonality and land use on the water quality of the paraíba do sul river

Monitoring water quality is important for the suitable management of water resources. Therefore, this study aims to assess the main water quality parameters and the National Sanitation Foundation-Water Quality Index (WQINSF) of four locations on the Paraíba do Sul River basin, in the state of Rio de Janeiro, influenced by different land use and land cover, and in the dry and rainy seasons. The following quality parameters were evaluated: total phosphorus (TP), nitrate (NO3-), dissolved oxygen (DO), potential of hydrogen (pH), turbidity (Turb), thermotolerant coliforms (Col), total dissolved solids (TDS), biochemical oxygen demand (BOD), water temperature (Twater) and air temperature (Tair). Statistical differences (p < 0.05) were observed between the dry and rainy seasons for the parameters: TP, Col, Turb, TDS, Twater, Tair, NO3-, DO, and WQINSF. The concentration of rainfall was effective in water quality parameters behavior. WQINSF was lower in the rainy season and possibly the runoff was the major cause of water quality degradation. Land use and land cover influenced the concentration of DO and Col and, consequently, WQINSF. Despite statistical differences, in most cases, the Paraíba do Sul River basin lies in medium water quality index according to the classification of the National Water and Sanitation Agency (ANA).