CRITICAL ANALYSIS OF ENVIRONMENTAL FLOW ASSESSMENTS OF SELECTED RIVERS IN THE STATE OF OSUN

The fate and effects of selected metals were seasonally examined in the water and sediment of Osun, Ooni and Otin rivers. Results showed that the concentration of the metal contents were generally higher in the harmattan than the rainy season. The metal contents of the water and sediment were determined using the nitric acid digestion method. All the metals analyzed except Na and K was determined using Atomic Absorption Spectroscopy (flame emission spectroscopic method). Variations in concentrations were found for the heavy metals ranging between (0.02 and 1.42mg/l) in water and (1.1 and
1.66mg/kg) in the sediments. Sodium and potassium were found in concentrations ranging between 8.55±0.3 and 11.32±9.0mg/l in water and between 48.99±17.00mg/l and 146.10±13.01mg/kg in the sediments respectively. The statistical comparison of the values between the rainy and harmattan season in water as well as those in sediment shows no significant difference at P>0.05. All the metals were found to be within the permissible limits as recommended by WHO/NOAA for quality water and sediments except for the levels of iron (Fe) in water which was found to be above the acceptable limits. The sediments contained higher concentration of heavy metal than the water. This may be attributed to the fact that sediments usually serves as repositories in an aqueous environment.