Abstract

Olayiwola, Olajumoke Abidemi, Onianwa, Percy Chucks and Olayiwola, Waliyat Bolarin

Osun River is important for domestic, recreational and other activities. It flows along a channel that may be polluted by inputs from industrial, agricultural and other anthropogenic activities. Surface water was sampled bimonthly from July 2006 to May 2008 at upstream and downstream points of the main river course and 31 tributaries. Water samples were analyzed for pH, alkalinity, hardness, ammonia, anions and turbidity. Statistical evaluation of data was carried out. The concentrations (mg/L) of alkalinity, hardness, ammonia, nitrate, phosphate and chloride were 93±130, 116±120, 4.2±6.6, 1.8±1.5, 0.15±0.23 and 54±110 and turbidity, 34±43 FTU. Spatial classification revealed tributary at Adeti (Ilesha) to be strongly polluted compared to other tributaries. All the tributaries met requirements for irrigation, recreation and livestock rearing, but they need pretreatment for other categories of industrial usage. Fifty-three locations were acceptable (Class 2), and four excellent (Class 1). Time series modelling, using Number Cruncher Statistical System fitted well for nitrate (R2= 0.79) and phosphate (R2= 0.84) data and gave their 2018 predicted values of 19.2 and 18.1 mg/L