ABSTRACT
Rivers play a major role in the development and social wellbeing of people living around them. The Okhuaihe River is one of the numerous inland freshwater bodies in Nigeria and serves as a major source of freshwater to several rural communities in Edo State. This study was carried out to determine the water quality status of the River using its physicochemical and biotic components - zooplankton distribution and diversity. Water samples were collected from four designated stations from the river stretch between the months of October 2016 to June 2017. Physicochemical parameters were analyzed using standard methods while zooplankton samples were sorted and identified using standard identification keys. Data analysis using Statistical Package for Social Sciences and Excel ToolPak were carried out to ascertain the effects of spatial and seasonal variations of water quality and zooplankton. The water quality index (WQI) was also computed. The results obtained showed that chemical oxygen demand, sodium, magnesium, nitrogen dioxide, ammonium, biochemical oxygen demand and turbidity showed significant variations (p < 0.05) across the stations. Higher mean values were recorded in the dry season except for total dissolved solid (61.02 mg/L), electrical conductivity (123.61), magnesium (0.70 mg/L), chlorine (37.35 mg/L), calcium (2.39 mg/L), potassium (0.20 mg/L), bicarbonate (26.74 mg/L) and chemical oxygen demand (17.21 mg/L) which recorded higher mean values in the wet season. Iron, zinc and cadmium showed significant variations (p < 0.05) across the stations; while manganese, copper, chromium, lead, and nickel were not significantly different. Water quality index (WQI) revealed that the water quality of Okhuaihe River suitable for consumption. A total of thirty-three (33) zooplankton species shared within 2 phyla, 3 classes, 3 orders and 8 families, with a total number of 323 individuals were recorded for fauna abundance. The most abundant species were Alonella excise and Echinisca triseralis. Order Cladocera accounted for 26.0% while Copepoda and Rotifera accounted for 67.0% and 7.00% respectively. Zooplankton abundance was higher in the upper reaches of the river, showing no significant difference (p > 0.05) in abundance and spatial distribution across the four sampling stations. Diversity indices revealed that stations 1 and 2 were the highest in taxa richness, followed by stations 3 and 4. The zooplankton community was characterized by species which indicated good water quality and most physicochemical parameters determined did not exceed permissible limits.
