Seasonal Variation and Pollution Assessment of Some Physicochemical Parameters of the Surface Water of Mahin Lagoon and Its Adjoining creeks, South-Western Nigeria

Abstract

Indiscriminate discharge of untreated wastes from into the aquatic ecosystem may result in deterioration of water quality, as well as poses a great threat to the balance of aquatic ecosystems and human health. This study investigated the seasonal variation in physicochemical characteristics and assessed the pollution status of Mahin Lagoon and its adjoining creeks using standard method. Results of physico-chemical parameters varied significantly (p<0.05) across seasons and stations, with the following mean values: Temperature (27.79±0.96^oC), salinity (7.65±0.99‰), conductivity (15.23±17.63µS/cm), pH (7.74±6.57), DO (7.65±0.99 mg/L), BOD (7.74±6.57mg/L), nitrate (8.00±3.67mg/L), sulphate (8.60±5.01mg/L), phosphate (3.88±1.55mg/L). Heavy metals were with the following mean values: Zn (7.15±6.31mg/L), Pb (0.04±0.21mg/L), Fe (10.63±6.02mg/L), Cu (1.16±1.72mg/L), Cr (0.02±0.00mg/L), Cd (0.01±0.08mg/L), Ni (0.28±0.45mg/L) and Co (0.26±0.44mg/L). The physic-chemical parameters were within the permissible limits recommended by International Organizations for lotic ecosystem. However, the single-factor pollution index (PI) classified pH, DO, BOD, Cu and Zn within the ‘medium pollution’ category while nitrate and phosphate indicated heavy pollution status. The PI also revealed that Cu, Fe and Ni were at serious pollution level while Co and Cr were at non-pollution level. The comprehensive pollution index revealed that the water was severely polluted (CPI < 2). The Hazard Quotients of heavy metals in the surface water were less than 1 (HQ < 1) indicating there was no risk to human health through ingestion or dermal contact. Therefore, the water from the Mahin lagoon and its adjoining creeks may still be suitable for domestic use and conducive for survival of aquatic life.