Diurnal variation and evaluation of physico-chemical properties of the Ikpoba River, Southern Nigeria

Abstract

This study was carried out to evaluate the magnitude of diurnal variation of physicochemical parameters and potability of the Ikpoba River. Water samples were taken from stations 1 and 2 within the Reservoir and station 3 downstream. Water quality parameters showed significant diurnal, seasonal and spatial variations. In the dry season, transparency was lowest at 12 midnight, while turbidity peaked at 6 p.m. The pH was more alkaline towards mid-night, and more acidic during rainy season. Alkalinity was highest at 12 noon, while chloride peaked at 12 mid-night. NO₃, SO₄, DO, BOD₅, Na, K, Ca and Mg had higher mean values in the dry season. The heavy metals, Fe, Zn, Cu, Mn and Cr showed significant (P<0.05) diurnal variation in the dry season, while Cu, Mn, Cd and Cr were not detected in the rainy season. Zn, Fe and Pb had higher mean concentrations in the rainy season. Spatially, TDS showed significant variation (P<0.05), being highest in station 1 and lowest in station 3 during the dry season. NO₃, PO₄, DO, Ca and Mg showed significant spatial differences during the dry season. The DO was significantly higher (P<0.05) in station 3 than in stations 1 and 2 in both seasons. Ca was significantly higher (P<0.01) within the Reservoir than in station 3. Zn and Cu were significantly higher within the Reservoir, while Pb had the highest concentration in station 3. pH, BOD, Fe, Pb and Cd did not meet the Federal Ministry of Environment regulatory standards for drinking water. Diurnally, the worse case scenario for noncompliance occurred at 6 p.m., and spatially at station 3. Surveillance of drinking-water quality is therefore recommended for the Ikpoba River and other sources of community potable water supplies to avert possible health hazards. An understanding of diurnal and seasonal variability in environmental sensitivities is imperative in water quality control and assurance during data acquisition.

Key words: Diurnal, seasonal variation; water quality, regulatory standards, Ikpoba River, southern Nigeria