Effects of urbanization on water quality in a watershed in northeastern Brazil

Changes to land use generate imbalances in the natural dynamics of aquatic ecosystems. These changes can vary according to the specific characteristics of each environment and due to seasonal factors, reinforcing the importance of studies in this area in different regions of the globe. Thus, the aim of this study was to analyze the effects of land use change on the rivers and streams of the Cachoeira River Basin in the Northeast of Brazil. Samples were collected bi-monthly at 16 points along the basin over 1 year and analyzed for physical and chemical parameters (temperature, pH, conductivity, and percentage saturation of dissolved oxygen), inorganic nutrients (NO₃^-, NO₂^-, NH₄⁺/NH₃, PO₄^3-, SiO₄) and dissolved major ions (Ca²⁺, K⁺, Mg²⁺, Na⁺, HCO₃^-). The highest concentrations of NO₃^-, NO₂^-, NH₄⁺/NH₃, and PO₄^3- occurred at the points with the highest percentage of urban areas and population density. The major ions Ca²⁺, K⁺, Mg²⁺, Na⁺, and HCO₃^- were positively correlated with the percentage of pasture coverage; however, the high concentrations of these ions and the strong correlation between them revealed that other factors besides land use, such as soil cover, geological formation, and water deficit, may be jointly contributing to increases in their concentrations. Thus, the results show that urbanization represents the type of land use with the greatest negative effect on water quality since it alters the concentrations of inorganic nutrients dissolved in the Cachoeira River Basin.