Temporal changes in total alkalinity, ionic composition and nutrient concentrations were studied in the saline, alkaline endorheic Kenyan Rift Valley Lakes Bogoria, Nakuru and Elmentaita to understand the association of these variables with phytoplankton community structure. In total, 24 taxa were found, with L. Bogoria having the fewest species. Although the cyanobacterium Arthrospira fusiformis dominated the phytoplankton biomass, especially in L. Bogoria, other groups came into play especially during high water levels in L. Nakuru and L. Elmentaita. Cluster analysis based on species biomass resulted in four groups, characterised by 13 indicator taxa. Most of the variation in these groups appeared to be associated with hydrological stability and perhaps biological factors rather than water chemistry, which only explained 44% of the variance in taxa composition on the first four axes derived from redundancy analysis. Species numbers decreased with elevated conductivity and water temperature. Synechocystis sp. occurrence coincided with phosphorus, water temperature and conductivity increase, whereas the distributions of Arthrospira fusiformis and Arthrospira platensis were mainly influenced by both light attenuation and elevated nitrate concentrations. Increases in silica and ammonium and declines in conductivity, total phosphorus and water temperature enhanced diatom abundances. Not only do the results of the present study indicate the unexpectedly high variability of phytoplankton community composition and water chemistry in these three alkaline tropical lakes, but also the data assist our understanding of the factors influencing flamingo populations on these lakes, which are significant conservation reserves and tourist attractions.

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We hypothesised that changes in nutritional composition and quality of the pelagic phytoplankton community influence the occurrence of Lesser Flamingo populations in two Kenyan salinealkaline lakes, Nakuru and Bogoria. This was achieved by carrying out a detailed time series assessment of the phytoplankton community composition and nutritional components (carbohydrates, crude protein and lipids) from

The human health risks posed by exposure to cyanobacterial toxins such as microcystin (MC) through water and fish consumption remain poorly described. During the last two decades, coastal regions of Lake Victoria such as Nyanza Gulf (Kisumu Bay) have shown severe signs of eutrophication with blooms formed by Microcystis producing MC. In this study, the spatial variability in MC concentration in Kisumu Bay was investigated which was mostly caused by Microcystis buoyancy and wind drifting. Small fish (<6 cm) mainly composed of Rastrineobola argentea were examined for MC content by means of biological methods such as ELISA and protein phosphatase inhibition assay (PPIA) and partly by chemical-analytical methods such as LC-MS/MS. Overall, the MC content in small fish was related to the MC content observed in the seston. When comparing the MC content in the seston in relation to dry weight with the MC content in small fish the latter was found three orders of magnitude decreased. On average, the ELISA-determined MC contents exceeded the PPIA-determined MC contents by a factor of 8.2 ± 0.5 (SE) while the MC contents as determined by LC-MS/MS were close to the detection limit. Using PPIA, the MC content varied from 25–109 (mean 62 ± 7) ng/g fish dry weight in Kisumu Bay vs. 14 ± 0.8 ng MC/g in the more open water of L. Victoria at Rusinga channel. Drying the fish under the sun showed little effect on MC content, although increased humidity might indirectly favor photocatalyzed MC degradation.

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This study, carried out between November 2003 and February 2005, aimed to investigate the temporal trends of conductivity, ions, nutrient concentrations and phytoplankton biomass expressed as chlorophyll a in the Kenyan Rift Valley saline-alkaline lakes namely Nakuru, Bogoria and Elmentaita. The influence of environmental variables on phytoplankton biomass has always been of much interest in understanding phytoplankton dynamics. Being shallow and endorheic, these lakes' chemical, physical and biological properties were found to be strongly influenced by the hydrologic cycle within their catchment area. The lakes are characterised by high nutrient concentrations but with low Ntot : Ptot ratios. Significant differences between surface and near-bottom samples for water temperature, chlorophyll a and some nutrients were found in these lakes. A stepwise Discriminant Analysis with lakes as defined groups resulted in a significant model with SRP, nitrate-N, conductivity and light supply being of major importance. A significant correlation between specific conductivity and total alkalinity (Kendalls s = 0.85, n = 132) was calculated. While L. Bogoria showed the least temporal variation in conductivity -(65-73 mS cm -1 ), larger variations were observed in L. Elmentaita (21-77 mS cm -1 ). Na + and K + form the main cations with Cl -, HCO 3 -and CO 3 2-being the major anions in all the three lakes. Flouride was detected in high quantities (mean values L. Bogoria 72 meq l -1 , L. Nakuru 17 meq l -1 and L. Elmentaita 71 meq l -1 ). A PCA followed by multiple regression analysis with chlorophyll a as dependent variable showed that nitrate-N, conductivity, phosphorus and light supply were the key variables influencing algal biomass in these lakes.

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