Spatio-temporal Dynamics of Physico-Chemical Parameters and Aquatic Insect Assemblages in a Western Nigerian River: An Approach to Water Quality Assessment

Purpose: This study evaluated the interconnected dynamics of water physico-chemical parameters and aquatic insects within Omi River, a perennial lotic system in Iwajowa Local Government Area of Oyo State, Western Nigeria, to assess its water quality and biological integrity. Methodology: Sampling was conducted at five stations over an annual cycle from December 2024 to September 2025 to capture seasonal variations. Physico-chemical parameters were monitored alongside aquatic insect communities. Spatial and seasonal variations were assessed, while Canonical Correspondence Analysis (CCA) was used to examine relationships between environmental variables and aquatic insect distribution. Findings: A total of 1,040 individuals belonging to six orders, 19 families, and 44 genera were recorded, with Rhagovelia sp. dominating (24.04%). Environmental conditions were highly uniform spatially, with BOD being the only parameter showing significant spatial variation (p < 0.05), reflecting mild downstream organic enrichment at Station 5. Seasonal variation was pronounced, with river width, depth, volumetric discharge, turbidity and dissolved oxygen (DO) significantly higher during the wet season (p < 0.001), whereas TDS and electrical conductivity (EC) were significantly higher during the dry season (p < 0.001). Total abundance and diversity metrics were higher during the stable dry season, whereas EPT abundance increased during wet-season aeration. Although CCA was not statistically significant, it indicated that discharge, depth, stream width and turbidity were the primary ecological variables structuring species distribution, outweighing nutrient gradients. Contribution: The study demonstrates that Omi River retained high biological integrity during the study period and provides an important baseline framework for water-quality assessment and freshwater conservation in Western Nigeria and the wider West African region.