Abstract

Seasonal variations in physicochemical properties of the surface water of River Osun in Osogbo, Nigeria, were investigated from May to August 2012 and November to February, 2012/2013. The water body of the mentioned river received water and wastes from the other effluences. Physicochemical parameters were determined in triplicate at three different points of the river, across the two seasons of the year. The points were named AR, BR and CR, for the rainy season and AD, BD and CD for the dry season. Samples taken from May to August represents the rainy season in the year 2012, while that of November to February 2012/2013 represents the dry season analysis. Standard methods were used in carrying out the experiments. Parameters values were gotten by the mean calculated from the triplicate determination of each sampling point. The average result determined revealed pH level of 5.87 and 6.63 for rainy and dry seasons, respectively; 137.00 and 101.33 µscm^-1 for conductivity, 90.50 and 21.06 mg/L for total alkalinity, 2.53 and 1.77 mg/L for biochemical oxygen demand (BOD), dissolve oxygen (DO) of 3.17 and 3.97 mg/L, chloride of 10.47 and 8.20 mg/L, total hardness of 4.13 and 2.73 mg/L, chemical oxygen demand (COD) of 3.58 and 2.81, mg/L, total dissolved solids (TDS) of 62.53 and 35.43 mg/L, total suspended solid (TSS) of 25.40 and 9.30 mg/L, nitrate-nitrogen of 1.72 and 3.87 mg/L, nitrite-nitrogen of 0.23 and 0.23 mg/L and ammonia nitrogen 0.35 and 0.31 mg/L, respectively for the months of May and August 2012 and November and February 2012/2013. Heavy metal concentration were also analyzed for iron (Fe) which gave the value of 0.001 and 0.0027 mg/L, copper (Cu) 0.0010 and 0.0013. mg/L, 0.0020 mg/L and 0.002mg/L for zinc (zn) and 0.0023 and 0.0013 mg/L for nickel, all represents the two seasons, respectively. The parameters determined revealed that in most point of the river, rainy season exhibit higher values than the dry season. This could be as a result of the effluence flowing into the river body with more loads during the rainy season as compared to the dry season.

Key word: Seasonal variations, River Osun, water, physico-chemical.