Phytoplankton community relationship to environmental variables in three Kenyan Rift Valley saline-alkaline lakes
Michael Schagerl A C and S. O. Oduor BA Department of Marine Biology, University of Vienna, Althanstraße 14, A-1090 Vienna, Austria.
B Department of Biological Sciences, Egerton University, P.O. Box 536 Njoro, Nakuru, Kenya.
C Corresponding author. Email: michael.schagerl@univie.ac.at
Marine and Freshwater Research 59(2) 125-136 https://doi.org/10.1071/MF07095
Submitted: 9 May 2007 Accepted: 7 January 2008 Published: 27 February 2008
Abstract
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.
Additional keywords: biomass, community, diversity, phytoplankton, saline-alkaline, soda lake.
Acknowledgements
The present study was funded by the Austrian Exchange Service OEAD. We thank the Kenya Wildlife Services (KWS) for granting us free access to L. Nakuru, the L. Bogoria Game Reserve authorities for free access to L. Bogoria and the Delamere estates for access to L. Elmentaita through their farm. We acknowledge and appreciate the assistance given by Geoffrey Ongondo during the sampling and laboratory analyses exercises. We extend our appreciation to Christian Fesl and Romana Limberger for their constructive suggestions on the draft.
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