Ecologie du phytoplancton du lac Kivu (Afrique de l'Est)

Abstract

With a volcanic origin, Lake Kivu is deep and meromictic, and shows a very particular limnology and some astonishing features. The data available on its limnology and phytoplanktic communities are limited, dispersed or outdated. This is the first deep, long term study (2002-2004) on limnology and phytoplankton ecology of Lake Kivu, combining different techniques: HPLC analysis of marker pigments, flow cytometry, light, epifluorescence and electron microscopy. Recent investigations revealed an increasing methane production in the deep waters during the past three decades, leading to an accumulation of gas and the subsequent lowering of the energy required to trigger a devastating release of gasses. The role of primary producers and the probable changes on the export ratio of the organic matter into deep waters after the introduction of the planktivorous sardine from Lake Tanganyika Limnothrissa miodon, is discussed. The actual primary production, 0.71 g C m-2 d-1 (~ 260 g C m-2 y-1), doesn't seem substantially different from some punctual measurements made in the past, which discards the hypothesis of anthropogenic eutrophication. We believe that the export ratio of organic matter into the deep waters was largely affected by biological changes that could explain part of the methane increase in the past 30 years in Lake Kivu.

Date of Award	29 Sept 2006
Original language	French
Awarding Institution	University of Namur
Supervisor	Jean-Pierre DESCY (Supervisor), Jean-Claude Micha (Jury), Pierre COMPERE (Jury), François Darchambeau (Jury) & Luigi NASELLI-FLORES (Jury)