Appraising the heavy metal content of a man-made lake in Benin City, Nigeria in relation to its current uses

Man-made lakes are constructed for water storage, irrigation, drinking water, recreation, flood control and energy production. Inland man-made lakes are usually fresh; providing immense ecosystem services to man. Heavy metal content of a man-made lake meant for flood control was assessed in two stations and seasons. The aim is to determine the suitability of the water for its current uses - fishing, recreation and watering of cattle. Eight (8) heavy metals were evaluated and compared with standards for aquatic life, recreation and livestock production while Water pollution index (WPI) was used to determine the suitability. The values of the metals were: iron (1.08-2.88 mg/L), manganese (0.54-1.35 mg/L), zinc (0.78-1.88 mg/L), copper (0.33-1.11 mg/L), chromium (0.21-0.74 mg/L), cadmium (0.11-0.31 mg/L), nickel (0.08-0.22 mg/L), and lead (0.15-0.46 mg/L). All the metals exceeded limits for aquatic life, recreation and livestock production except for zinc and copper (recreation) and zinc, chromium and nickel (livestock production). The water pollution index (WPI) was: aquatic life (161.0-195.8), recreation (13.3-16.2) and livestock production (3.3-4.1). All the WPI values were >1; indicating highly polluted water. The order of magnitude was WPIaquatic life > WPIrecreation > WPIlivestock production. Higher values were generally recorded in station 2 and dry season though not significant. The heavy metal content was influenced by the diffused sources of stormwater channelled into the lake and season. It can be concluded that the water is not suitable for its current uses.