Assessment of the Relationship Between Stream Velocity and Physicochemical Parameters of Surface Water: a Case Study of Opa Drainage Basin, Osun State, Southwestern Nigeria

This study determined the physicochemical properties of surface water in the Opa Drainage Basin, established statistical relationships between stream velocity and the physicochemical properties of the surface water, and evaluated the ecological impact of the observed relationships on water aesthetics, agricultural use, aquatic life and ecosystem health. These were carried out with a view to assess the impact of stream velocity on the physicochemical properties of surface water within the Opa Drainage Basin, Osun State, Nigeria. Twenty (20) surface water samples were collected for both wet and dry seasons using standard procedure. The concentration of the ions and heavy metals in the surface water samples were determined using atomic absorption spectrometer, while stream velocity, temperature, pH, conductivity and total dissolved solids were determined in situ. Pearson correlation coefficients (r) were calculated to assess the relationship between stream velocities and each physicochemical parameter with scatter plot to visually confirm the trends in the correlation. For the wet season, positive correlations were observed with parameters such as pH, temperature, Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), Mg2+, Cd, Co, Pb, HCO3- , SO42- , and PO42-; while for the dry season, positive correlations were observed with Electrical Conductivity (EC), Total Dissolved Solid (TDS), Temperature, DO, Mg2+, Cu, Mn2+, Pb, SO42-, and PO42-. For the wet season, negative correlations were found with turbidity, Na+, K+, Ca2+, Fe, Cu, Mn2+ and NO3-; while for the dry season, negative correlations were identified with turbidity, pH, BOD, Na+, K+, Ca, Fe, Cd, Cr, Zn, HCO3, Cl-, and NO3-. Ni, As and CO32- show no correlation with stream velocity. DO and turbidity levels in the water affects the water aesthetics, recreational value, crop health, survival of aquatic organisms and general aquatic habitat suitability. Conclusively, the study established that there is variation in the physicochemical parameters of the surface water of the Opa Drainage Basin, resulting from the variation in the stream velocity. These changes in physicochemical parameters impact the water aesthetics, agricultural use, aquatic life and the general ecosystem health within the Opa Drainage Basin.