Impact of Aquaculture on Water Quality in Lake Kariba, Zimbabwe

Abstract

This study investigated the water quality at the aquaculture effluent discharge points in Lake Kariba. Water samples were collected at three sites designated Site 1 (Crocodile Farm effluent discharge point), Site 2 (Fish Farm effluent discharge point) and Site 3 (Control point) from the month of September 2011 to January, 2012. Physico-chemical variables (temperature, total dissolved solids, turbidity, pH, conductivity, nitrates, ammonia, and ortho-phosphate) were measured. Turbidity, total dissolved solids, pH and conductivity were found to be significantly (ANOVA, p<0.05) high at aquaculture effluentdischarge points compared to the control point. Relative to the World Health Organisation (WHO) and Environmental Management Authority of Zimbabwe (EMA-SI) guidelines for aquatic waters, turbidity, nitrates and ammonia at site 1 and site 2 were found to exceed the maximum allowable limit (5NTU), 10 mg/L and 0.05 mg/L respectively while dissolved oxygen was below the minimum allowable limit of 5 mg/L. All other physico-chemical parameters were within the accepted range at all stations. While the physico-chemical results indicated deteriorating water quality at the discharge point due to the effluent inflow, the large water volume in Lake Kariba plays an important factor in diluting aquaculture effluent.