Phytoplankton as indicators of ecological changes in Afrotropical reservoirs.

Reservoirs constitute critical freshwater ecosystems that influence regional hydrology and energy production in Nigeria; however, they are susceptible to anthropogenic impacts that alter water quality and aquatic biota. This study investigated the spatial-temporal dynamics of phytoplankton assemblages and corresponding limnological variables in ten reservoirs across Niger State, Nigeria, over two consecutive hydrological seasons (wet and dry) spanning June 2019 to March 2021. Multivariate statistical analyses, including two-way ANOVA, demonstrated significant spatial and seasonal variability in physical and chemical water parameters (p < 0.05). Canonical correspondence analysis (CCA) elucidated key environmental drivers shaping phytoplankton community structure, revealing strong correlations with nutrient concentrations and organic loading indicators. Application of the Palmer Algal Index (PAI) facilitated quantitative assessment of organic pollution gradients, corroborating phytoplankton as sensitive bioindicators of trophic status and ecosystem integrity. The results underscore the imperative for integrative monitoring and management frameworks to mitigate eutrophication and preserve aquatic biodiversity within these reservoirs, contributing to sustainable water resource management in Nigeria.