Evidence of eutrophication in the Tanzania sector of Lake Victoria

Abstract

Lake Victoria has experienced accelerated eutrophication with elevated phosphorus, nitrogen and chlorophyll-a concentrations, coupled with decreased transparency as a result of the growing human activities in the catchment area. A survey in Tanzanian waters from 2011-2016 provided data on phosphorus, nitrogen, dissolved oxygen and transparency from littoral (bays and gulfs) and pelagic stations. The differences between the two groups of stations were generally small, with the exception of chlorophyll-a, which was generally higher at the littoral stations. The molar TN:TP ratio indicated nitrogen limitation in most of the lake thus favouring the dominance of nitrogen-fixing cyanobacteria, which currently dominate the phytoplankton. The trophic status of the lake was assessed using the OECD criteria, yielding four ‘eutrophic’ and two ‘hypertrophic’ assessments. A similar assessment in 2005-2005 gave two ‘eutrophic’ and four ‘hypertrophic’ classifications, suggesting that the lake may have not deteriorated over the last decade and may have stabilised.Keywords: Eutrophication, Lake Victoria; Nitrogen, Phosphorus, Transparency, Trophic status