Impact of Effluents on Water Quality and Benthic Macroinvertebrate Fauna of Awba Stream and Reservoir

A study on the impact of effluent discharge on water quality and the benthic macro invertebrate fauna of the Awba stream and reservoir was carried out between April 2007 and May 2008. Benthic macro invertebrate and sediment samples were collected with a Van Veen grab, while physico-chemical parameters were sampled with Hach’s Company Fish Farmers’ Water Quality Test kit. Four stations were chosen for this study. A total of 4 taxa comprising 10 species of organisms were recorded. The abundance of these species and the physicochemical parameters at the various stations were significantly different (P<0-05). Dissolved oxygen was considerably lowest at Station 2 (1.38 ± 0.19mgl^-1); a region of intense organic pollution during the study period. This was accompanied by high values of dissolved CO₂ (20.0 ± 1.51mgl^-1), total hardness (103.0±7.87mg (CaCO₃)/l), ammonia-nitrogen (3.0±0mgl^-1) and increased pH values (8.5±0.27). Water temperature values was also highest at this station (30.7±1.15°C). The values obtained for the physico-chemical parameters and correlation values with the tested organisms indicated that changes in community structure had occurred as a result of changes in prevailing conditions in the habitat. The levels of trace metals (Zn, Mn, Cu, Pb, Ni, and Cr) were analyzed and there was no statistically significant difference in the values recorded between stations. The levels of these metals except zinc and manganese fell within the limits specified by USEPA as values recorded for zinc and manganese were higher than the acceptable limits specified by USEPA.