The Role of Environmental Factors in Driving Phytoplankton Communities in Winam Gulf, Lake Victoria, Kenya
Keywords:
phytoplankton, environmental variables, Winam Gulf, Lake Victoria, eutrophicationAbstract
Winam Gulf, a shallow bay of Lake Victoria, Kenya, is increasingly affected by anthropogenic activities that alter its water quality. This study examined the key environmental drivers of phytoplankton community dynamics in the gulf. Physicochemical variables were measured in situ, while nutrients (total phosphorus, total nitrogen, nitrate, nitrite and ammonia) were analysed in the laboratory using standard methods. Phytoplankton were identified and counted microscopically, and diversity indices, including the Shannon-Wiener index, were calculated. One way analysis of variance, repeated-measures analysis of variance, principal component analysis, canonical correspondence analysis and non-metric multidimensional scaling assessed spatial and temporal patterns, while Spearman's correlation and Mantel tests explored relationships between phytoplankton and environmental variables. Influence category significantly affected water depth, total dissolved solids, electrical conductivity, dissolved oxygen, biochemical oxygen demand, pH, Secchi depth and total nitrogen, while season significantly influenced temperature, total dissolved solids, electrical conductivity, dissolved oxygen, biochemical oxygen demand, pH, Secchi depth, nitrite, nitrate, ammonia nitrogen, soluble reactive phosphorus and total nitrogen. Significant category × season interactions occurred for total dissolved solids, dissolved oxygen, pH, Secchi depth and total nitrogen, showing that seasonal change varied among influence categories. Thirty-four phytoplankton genera from five phyla: Cyanophyta, Bacillariophyta, Chlorophyta, Charophyta and Dinophyta were recorded, with Cyanophyta dominant (44.1%), followed by Chlorophyta, Bacillariophyta, Dinophyta and Charophyta. Nutrients, especially total phosphorus, together with electrical conductivity, dissolved oxygen, pH and temperature, emerged as key environmental correlates of phytoplankton communities in Winam Gulf.
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