Biogeochemistry study on Lake Tanganyika in Tanzania

Lake Tanganyika is the worlds longest freshwater lake, with a north-south expansion of 673 km, and it sustains the second largest inland fishery of the African continent. Unfortunately, its fish stocks are declining, and previous investigations have identified overfishing and climate change as the main causes. Hence, Lake Tanganyika provides the opportunity to study direct (overfishing) as well as more subtle, global human alterations (climate change) on a large lake ecosystem. By heating the surface waters, global warming enforces the stable layering of the water column (stratification). The strong thermal layers reduce the vertical transport of nutrients from the deep waters into the nutrient-poor, sunlit surface waters. The nutrient scarcity slows down algal growth, which in turn has implications on the entire food web. In an aquatic food web, all higher organisms depend on the biomass produced by algae and bacteria. Thus, nutrients in the productive surface zone mean fewer algae and, ultimately, less fish. Our project attempts to better understand the biogeochemical processes and hence, nutrient cycling in Lake Tanganyika, such as the nitrogen fixation or nitrogen loss through the activities of bacteria living in deep waters.