Lay summary
Lake Kivu, one of the large East African rift lakes, contains enormousamounts of dissolved carbon diox-ide (CO2) and methane (CH4). On the onehand these gases are a tremendous hazard for this densely populated regionsince their sudden potential release, triggered by volcanic or tectonicactivity, could have catastrophic consequences of unprecedenteddimensions. On the other hand, the dissolved CH4 should become a valuablerenewable energy source for the two bordering countries Rwanda and DRCongo. A most recent study indicates that the CH4 production in Lake Kivuhas substantially increased in the past decades. This increase could bedue to a significant change in the lake-internal nutrient cycling. Thepresent project aims at creating a better quantification and understandingof the main nutrient sources and the lake-internal fluxes of nutrients andCH4. The external nutrient sources will be deter-mined by measuring theatmospheric deposition of nitrogen (N) and phosphorus (P) and bydetermining the inputs of N, P and silica (Si) by the main surfaceinflows. The internal nutrient fluxes will be studied by regularlymeasuring vertical profiles of nutrient concentrations and the spatialheterogeneity of nutri-ent concentrations and photosynthetic activeradiation (PAR) in the epilimnion while satellite pictures will be used todetermine the spatial variability of chlorophyll concentrations. Thenutrient export from the epilimnion and the net sedimentation will bequantified with sediment traps and its historic development will bydetermined by analyzing sediment cores. The physical mixing processes andthe geochemical cy-cling will be studied by representing the system with aone-dimensional numerical model. A detailed wa-ter column profile of CH4concentration and its carbon and deuterium isotopic composition will bemeas-ured to determine the CH4 oxidation in the water column, and thecorresponding nutrient fluxes as well as the microbial communityresponsible for the CH4 oxidation will be examined. The measurements andthe comparison with model simulations and internal nutrient balancing willallow estimating the current CH4 production. In addition we seek forresolving the influence of the external nutrient inputs and the change inthe 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 intight collaboration with the project ECOSYKI where ISP and UNR togetherwith the Universities of Namur and Louvain-la-Neuve investigate thepelagic ecosystem of Lake Kivu. A workshop will be organized towards theend of the project to disseminate the results to decision makers andresponsible Governmental representatives to discuss options for the futuremanagement of the lake, especially the CH4 exploitation.