The Spatio- Temporal Changes in Water Quality and Influences on the Phytoplankton, Zooplankton and Fish Species in Four Large Riverine Ecosystems in Lake Victoria Basin, Kenya

Rivers and streams in the Lake Victoria Basin (Kenya) (LVBK) are vital for aquaculture, irrigation, hydropower, domestic use, and biodiversity conservation. However, increasing population, urbanization and pollution, and changes in landuse/landcover are factors that contribute to the modification of the riverine habitats which also serve as fish breeding areas. There are increasing concerns on the potential loss of biodiversity juxtaposition the expanding anthropogenic pressures but gaps exists on information available. This study was conducted during the persistent heavy short rains (November 2019) and dry conditions (March 2020), and was used to assess the environmental conditions of rivers Nzoia, Yala, Awach and Nyando using indices of physico-chemical parameters, nutrient levels, plankton, aquatic macro-invertebrate assemblages and fish species composition and abundance. Structural and abiotic differences were found in selected site habitats due to the high gradient variation from the lake shore areas. River drainage basins are extensive and under heavy agricultural and human activities with reduced soil cover which contributes to increasing loading of eroded soils and materials which impact the quality of surface water. We identified significant spatio-temporal variations in nutrient levels, biodiversity, and water quality indices across four major rivers, highlighting hotspots of eutrophication and biodiversity vulnerability. Sampled rivers exhibit high turbidity with variable concentrations of nutrient elements downstream. Results show seasonal and anthropogenic influences on the water quality in all the river channels, which is likely to impact resident species. The high abundance of diatoms and chlorophytes as dominant phytoplankton families, is an indication of cultural eutrophication. Turbidity favors the dominance of diatoms especially centric diatoms which are able to attach on detritus. Eight fish families (with 19 fish species) were found and were dominated the Cyprinidae group. We recommend improved catchment management, agricultural practices and protection existing forest areas with long-term river monitoring program.