Point-effluent Discharge and River Recovery Potential: An Assessment of Spatio-Temporal Distribution of Heavy Metals in Water and Sediment from Upper Ogun River, SouthwestNigeri

Abstract

Wastes are often discharged into surface water systems like rivers with little or no consideration for their assimilative capacities.
In this study, we have investigated the pattern of river recovery for the upper river Ogun at varied points using six sampling
stations of 250m interval i.e., upstream (ups 1, ups 2), dp (discharge point) and downstream (dst 1, dst 2 and dst 3) for 6-months
across seasons. Samples analyzed for metals (Cd, Mn, Pb, Zn, Cu, Fe and Cr), in surface water and sediment showed a
concentration gradient from the discharge point to downstream stations. All metals in sediment except Zn and Mn showed clear
temporal patterns with higher concentrations in either dry season or rainy season. Discriminant function analysis (DFA)
delineated sampling stations into least-polluted, intermediate- polluted and highest metal-polluted respectively. The classification
of dst 3 alongside ups 1 and ups 2 suggests significant recovery 750m downstream from the discharge point. In general, although
the river has experienced degradation, recovery to a condition close to its pre-disturbance state was observed.