Analysis of Phytoplankton Composition as Indicators of Water Quality in Jebba Lake, Kwara State

This study analysed the composition and abundance of phytoplankton communities in Jebba Lake, Kwara State, North Central Nigeria, as biological indicators of water quality and trophic status. Phytoplankton serve as sensitive indicators of eutrophication, pollution, and seasonal hydrological changes in lake ecosystems that support productive inland fisheries. Water samples were collected from eight stations distributed across the lake at monthly intervals over a five-month period coinciding with both dry and wet seasons. Phytoplankton were identified and enumerated using inverted microscopy following Utermöhl sedimentation procedures. Concurrently, physicochemical parameters including pH, temperature, transparency, nitrate, phosphate, and dissolved oxygen were measured. A total of 46 phytoplankton taxa from six divisions were identified, with Chlorophyta (green algae) and Cyanobacteria being the most dominant. Cyanobacterial blooms occurred at three nearshore stations during the dry season, coinciding with elevated phosphate concentrations and reduced water column mixing. Shannon diversity index values ranged from 1.22 to 2.84, indicating varying trophic conditions across the lake. Stations near agricultural drainage outlets recorded the highest nutrient levels and lowest diversity values, while midlake stations showed healthier phytoplankton assemblages. The Palmer's pollution index confirmed moderate organic pollution at two southern stations. Findings suggest progressive eutrophication in parts of Jebba Lake that may compromise fish habitat quality. Regular phytoplankton monitoring is recommended as a component of the Jebba Lake fisheries management programme. Keywords: phytoplankton, water quality, Jebba Lake, eutrophication, biological indicators