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JPR Advance Access published online on October 9, 2007
Journal of Plankton Research, doi:10.1093/plankt/fbm078
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© The Author 2007. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Phytoplankton primary productivity characteristics in response to Photosynthetically Active Radiation in three Kenyan Rift Valley saline-alkaline lakes

S. O. Oduor1 and M. Schagerl2

1 Department of Biological Sciences, Egerton University, Kenya

2 corresponding author; Department of Marine Biology, University of Vienna, Althanstraße 14, A-1090 Vienna, Austria email: michael.schagerl{at}univie.ac.at

Received on January 11, 2007; revised on July 10, 2007; accepted on October 8, 2007


  Abstract

Phytoplankton photosynthetic characteristics in the Kenyan Rift Valley lakes Bogoria, Nakuru and Elmentaita were studied between November 2003 and February 2005. In these world-famous saline-alkaline lake systems, long-term continuous monitoring and photoautotrophic primary productivity modelling has been done for the first time. High light attenuation coefficients were observed with lakes means around 13 m–1reflecting the huge phytoplankton biomass. No photoinhibition was observed in the primary productivity field measurements. High values of the P-E curve initial slope ({alpha}) up to 0.85 (mg O2 mg Chl a –1 hr–1)(µmol photons m–2 s–1)–1 and a low onset of productivity saturation (Ek) down to 11.4 µmol photons m–2 s–1 as an acclimation to poor light supply were found. For the trophogenic zone, high mean net primary production (NPP) rates of 6.8, 10.7 and 8.5 g O2 m–2 d–1 were recorded for Bogoria, Nakuru and Elmentaita. For the whole water column, NPP decreased to - 1.4, 1.6 and 7.2 g O2 m–2 d–1 because of high community respiration. Modelling of the gross primary production (GPP, Chlorophyll a, light supply, initial slope {alpha}, maximum production rates considered) gave annual values of 4.9, 6.8 and 4.2 kg O2 m–2 yr–1 respectively for Bogoria, Nakuru and Elmentaita, annual NPP values down to the compensation depth were 70%, 65% and 55% of the GPP.

Key Words: saline-alkaline • Arthrospira • phytoplankton • productivity

Communicating Editor: K. J. Flynn


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