ASSESSMENT OF PHYTOPLANKTON COMPOSITION AND ABUNDANCE OF THE UPPER NIGER RIVER BASIN RESERVOIR

Abstract

The study evaluated the composition, abundance, and spatial distribution of phytoplankton in the Upper Niger River Basin Reservoir, Nigeria, to assess ecological status and anthropogenic impacts. Samples were collected monthly from February to July 2022 at four sites (landing site, vegetated area, open water and dam site) representing different environmental conditions. Phytoplankton were sampled using a 75 mm plankton net, preserved in 4% formalin and analyzed microscopically for identification and enumeration. Four major phytoplankton classes were identified: Bacillariophyceae, Euglenophyceae, Dinophyceae, and Chlorophyceae. Bacillariophyceae (diatoms) showed the highest diversity across all stations, with the genus Nitzschia dominating at the landing site, indicating eutrophic to hypereutrophic conditions linked to organic pollution. Data analysis revealed significant spatial variation (p<0.05) among phytoplankton groups. Euglenophyceae recorded the highest mean abundance at the landing site (151.50±2.12), further suggesting nutrient enrichment. The dominance of pollution tolerant and eutrophic indicator species, especially at the landing site, reflects substantial nutrient input from human activities. This indicates advanced eutrophication, which can threaten ecological integrity through oxygen depletion, biodiversity loss, and declining water quality. These findings provide baseline data essential for developing management strategies to control nutrient pollution and sustain the reservoir’s ecological health. Therefore, based on these findings, it is recommended that a continuous phytoplankton water quality program be establish and also implement watershed nutrient control actions to reduced nitrogen and phosphorus loading.