Assessment of Aquatic Macroinvertebrate Diversity as Bioindicators of Water Quality in Ogun River, South West Nigeria

This study assesses the diversity of aquatic macroinvertebrates as biological indicators of water quality in the Ogun River, Ogun State, located in Nigeria's South West geopolitical zone. Aquatic macroinvertebrates are widely used as bioindicators because their community composition reflects cumulative environmental conditions over time rather than point-in-time chemical measurements. A descriptive survey was conducted at six stations along a gradient from relatively pristine upper reaches to the more impacted lower sections near Abeokuta. Macroinvertebrates were collected using Surber samplers and kick nets, identified to family level, and quantified. The BMWP score and Average Score Per Taxon (ASPT) were calculated for each station. Physicochemical parameters were measured concurrently. A total of 39 macroinvertebrate families were recorded. Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness was highest at upstream stations (ASPT 5.6) and lowest at stations near urban inputs (ASPT 2.8). Diptera larvae, particularly Chironomidae, dominated polluted downstream stations, confirming organic enrichment. Canonical correspondence analysis revealed dissolved oxygen and biochemical oxygen demand as the strongest determinants of community structure. The study demonstrates the effectiveness of macroinvertebrate bioassessment as a cost-effective water quality monitoring tool for the Ogun River basin and recommends its adoption into routine monitoring programmes by the Ogun-Osun River Basin Development Authority. Keywords: macroinvertebrates, bioindicators, water quality, Ogun River, BMWP score.