Microalgae are sensitive bioindicators of aquatic ecosystem health, yet their spatiotemporal dynamics in tropical reservoirs under combined pesticide and heavy metal stress remain poorly documented. This study evaluates microalgal diversity, water quality, and contamination levels in Oyan Reservoir, Nigeria, to assess ecological health and human risk. Water, soil, and fish samples were collected monthly (April 2021-September 2023) from eight stations. Microalgae were identified microscopically; physicochemical parameters were measured in situ. Pesticides and heavy metals were analyzed via GC-MS and ICP-OES/CV-AAS. Toxicity tests, biosorption experiments, and EMSphere-enabled GIS mapping using QGIS v3.28 were conducted. Statistical analysis was performed using IBM SPSS 28. Microalgal abundance declined by 30-50 at agricultural stations (OYR 2, OYR 5), with Microcystis aeruginosa (Kützing) Kützing dominance reaching 94.4. Key contaminants: -endosulfan (1.8 g/L), chlordane (1.4 g/L), heptachlor (1.2 g/L), Pb (0.03 mg/L), Hg (0.01 mg/L). Fish tissue revealed contamination of Cu (3.91 mg/kg) above the WHO limit. The Hazard index (HI 7.99) indicates elevated cumulative risk. Chlorella vulgaris Beijerinck demonstrated 89 biosorption of -endosulfan. Oyan Reservoir is under moderate anthropogenic stress. Pollution-sensitive diatoms (e.g., Synedra ulna (Nitzsch) Ehrenberg, Nitzschia palea (Kützing) W. Smith) declined, while pollution-tolerant cyanobacteria proliferated, confirming ecosystem degradation. Microalgae serve as effective bioindicators and biosorbents. Integrated management including organic farming, phycoremediation, and community-based monitoring via EMSphere is essential for sustainable freshwater governance.
Nkonyeasua et al. (Thu,) studied this question.