Hydrochemistry and quality assessment of surface water in Oba Dam, Ogbomoso, Southwestern Nigeria

Abstract

Hydrochemistry of the surface water in Oba Dam, Ogbomoso was investigated to determine the chemical characteristic and evaluate the water quality for drinking, domestic and agricultural usage. Twenty selected water samples collected at different points within the reservoir were analysed for pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Hardness (TH) and major ions (Na⁺, K⁺, Mg²+, Ca²+, Cl^-, NO₃^-, SO₄^2-, HCO₃). The pH values (6.5-7.9) of the samples suggest circumneutral to weakly alkaline nature of the water in Oba Dam. The cations are dominantly Na⁺ and K⁺, while the anions are mainly NO₃^-, Cl^- and SO₄^2-. The plot of the chemical data in Piper diagram revealed the water samples as Na-K-Cl water facie suggesting that the water chemistry is being controlled mainly by anthropogenic inputs. Comparing the analysed water samples with WHO and Nigerian water quality standards shows that all the chemical parameters were within the desirable limits for drinking purpose. Similarly, the computed water quality index (WQI) values (15-21) for the studied water samples suggest excellent quality for drinking and domestic purposes. Calculated parameters like sodium adsorption ratio (SAR), percent sodium (%Na) and Keller index (K1) reveal that most of the analysed water samples are suitable for irrigation usage. However, higher Na⁺ content of few samples restrict the suitability for irrigation purposes. Therefore, this calls for regular monitoring of sodium contents to ascertain suitability for agricultural irrigation.