Assessment of Anthropogenic Influences on the Benthic Invertebrate Community of Oghan River in Edo State, Nigeria

The influence of anthropogenic activities on a freshwater ecosystem was investigated by sampling for physicochemical parameters, heavy metals and benthic invertebrates of Oghan River in Ora Community, Ovia South-West Local Government Area of Edo State, Nigeria. Samples were collected monthly for a ten months period across three stations between 09:00 and 12:00 hrs on each sampling day for laboratory analysis following standard procedure. No significant variation (P > 0.05) was observed between the parameters, although heavy metals in sediments were above the WHO recommended limit for freshwater ecosystems. For benthic organisms, about 386 individuals belonging to 23 taxa, 11 families and 6 orders were recorded. Among the orders, the most dominant were Diptera (44.94%), Odonata (28.31%), Ephemeroptera (13.77%) while the least was Diplogasterida (0.26%). The families were dominated by Chironomidae (32.47%), Baetidae (13.77%) and Libellulidae (12.73%). Species diversity (2.677) and richness (4.002) were highest in station 1 and lowest in stations 2  (2.357) and 3 (2.745) while species evenness was highest in station 3 (0.791) and lowest in station 1 (0.6924). The elevated levels of heavy metals and the decrease in sensitive benthic taxa observed in the river is an indication that anthropogenic activities could be impacting the water quality and benthic invertebrate community of the river.