Nutrient cycling and methane production in Lake Kivu

Swiss Coordinator : Alfred Wüest, Limnological Research Centre, EAWAG
Main Foreign partner : Boniface Kaningini, Institut Supérieur Pédagogique de Bukavu
Cooperation with : Congo, Rwanda
Disciplines : Hydrology, Geochemistry

Lake Kivu, one of the large East African rift lakes, contains enormous amounts of dissolved carbon dioxide (CO2) and methane (CH4). On the one hand these gases are a tremendous hazard for this densely populated region since their sudden potential release, triggered by volcanic or tectonic activity, could have catastrophic consequences of unprecedented dimensions. On the other hand, the dissolved CH4 should become a valuable renewable energy source for the two bordering countries Rwanda and DR Congo. A most recent study indicates that the CH4 production in Lake Kivu has substantially increased in the past decades. This increase could be due to a significant change in the lake-internal nutrient cycling. The present project aims at creating a better quantification and understanding of the main nutrient sources and the lake-internal fluxes of nutrients and CH4. The external nutrient sources will be determined by measuring the atmospheric deposition of nitrogen (N) and phosphorus (P) and by determining the inputs of N, P and silica (Si) by the main surface inflows. The internal nutrient fluxes will be studied by regularly measuring vertical profiles of nutrient concentrations and the spatial heterogeneity of nutrient concentrations and photosynthetic active radiation (PAR) in the epilimnion while satellite pictures will be used to determine the spatial variability of chlorophyll concentrations. The nutrient export from the epilimnion and the net sedimentation will be quantified with sediment traps and its historic development will by determined by analyzing sediment cores. The physical mixing processes and the geochemical cycling will be studied by representing the system with a one-dimensional numerical model. A detailed water column profile of CH4 concentration and its carbon and deuterium isotopic composition will be measured to determine the CH4 oxidation in the water column, and the corresponding nutrient fluxes as well as the microbial community responsible for the CH4 oxidation will be examined. The measurements and the comparison with model simulations and internal nutrient balancing will allow estimating the current CH4 production. In addition we seek for resolving the influence of the external nutrient inputs and the change in the internal nutrient cycling due to the introduction of the sardine L. miodon. The project will be implemented in cooperation between ISP Bukavu (DR Congo), UNR Butare (Rwanda) and EAWAG. Each institution will be in tight collaboration with the project ECOSYKI where ISP and UNR together with the Universities of Namur and Louvain-la-Neuve investigate the pelagic ecosystem of Lake Kivu. A workshop will be organized towards the end of the project to disseminate the results to decision makers and responsible Governmental representatives to discuss options for the future management of the lake, especially the CH4 exploitation.

Contact Addresses:
Alfred Wüest, Seestrasse 79, 6047 Kastanienbaum, Tel. 041 349 21 81, Fax 041 349 21 62, alfred.wueest@eawag.ch
Martin Schmid, Seestrasse 79, 6047 Kastanienbaum, Tel. 041 349 21 93, Fax 041 349 21 62, martin.schmid@eawag.ch
Boniface Kaningini, Institut Supérieur Pédagogique de Bukavu, Bukavu, DR Congo, Tel. +243 813 186 602, bkaningini@yahoo.fr