Watershed land use, surface water vulnerability and public health risks of two urban rivers, Ado-Ekiti, South-West Nigeria

Abstract

The disruption of watersheds due to indiscriminate land use and urban development increases the vulnerability of adjacent surface water to contaminants of anthropogenic origin. This study assessed the relationship between disrupted watershed, drinking water quality and health risks of two urban rivers: Ureje and Awedele, Ado-Ekiti (Nigeria). Monthly samples of surface water (n = 60, per river) collected across seasons for 6 months (January–June, 2017) were analyzed for twenty-nine drinking water parameters including metals, nutrients (phosphates and nitrates) and pathogens using standard methods. The difference in the mean concentration of parameters between rivers was determined using t test, while the association between change in seasons and water quality parameters of both rivers was highlighted using principal component analysis (PCA). The risk was assessed based on on-site inspection studies and water sample analysis using WHO semiquantitative risk matrix approach. Inferences on surface water vulnerability were made from percentage built-up areas, riparian cover and stream order within each watershed. Mean concentrations of Pb, Cd, Fe, Mn, nitrates and coliform presence in samples from Awedele river (0.02 ± 0.00; 0.005 ± 0.001; 5.44 ± 1.33; 0.81 ± 0.03; 58.03 ± 0.10 mg/L; 1.2 × 106 MPN/100 ml, respectively) and Cd, Fe, Mn, nitrates and coliform in samples from Ureje river (0.004 ± 0.0001; 4.96 ± 0.12; 0.54 ± 0.01; 62.08 ± 0.02 mg/L; 1.6 × 103 MPN/100 ml, respectively) were above the permissible limits of WHO drinking guidelines. Risk assessment revealed urban runoff and unsanitary practices within the watershed as possible hazardous events which may compromise water quality of both rivers, while the PCA associated greater likelihood of surface water deterioration with areas of a higher percentage built-up area and lesser riparian density and width. We infer that disrupted watersheds and greater riparian depletion due to urbanization increased chances of metals and pathogens incidence that negatively impacts water. A twofold strategy of policy protection of watersheds and public health education on sourcing polluted surface water is recommended.