Carbon and nutrient cycles in the tropical meromictic Lake Malawi (East Africa)

Lake Malawi, one of the largest and deepest (700 m) lakes in the World, is known for its great biodiversity with over 800 species of fish, and its importance for the local populations as the major source of fresh water and fish protein. However, like other East African Great Lakes, Lake Malawi is under considerable stress from climate warming and anthropogenic changes in its watershed. Increases in agricultural activity have led to further losses of forest cover and altered river discharges, which may have increased nutrient loadings into the lake affecting the biogeochemistry and primary productivity.

The recent changes in physical and geochemical characteristics of Lake Malawi is poorly documented, and the sediment carbon and nutrient budgets remains largely unavailable. We investigate the sediment geochemistry in Lake Malawi, characterize carbon and nutrient distributions and fluxes, and quantifies the role of sediments in the lake's geochemical budgets.


Publications: - Li, J., E. T. Brown, S. A. Crowe, and S. Katsev. 2018. Sediment geochemistry and contributions to carbon and nutrient cycling in a deep meromictic tropical lake: Lake Malawi (East Africa). Journal of Great Lakes Research: https://doi.org/10.1016/j.jglr.2017.12.001 (link)- Katsev S., Verburg P., Lliros M., Minor E., Kruger B., and Li J.. 2017. Tropical meromictic lakes: Specifics of meromixis and case studies of Lakes Tanganyika, Malawi, and Matano. In Ecology of Meromictic Lakes, edited by R. Gulati, A. Degermendzhy, and E. Zadereev. Springer. (PDF)
Fig. 1 Sampling sites in Lake Malawi

The merometic tropical Lake Malawi is permanently stratified and remain anoxic below 200 meters (Fig. 2). Temperatures in the deep waters (N300 m) are now the highest since the first measurements in the 1940s

Fig. 2 A) Vertical distributions of temperature and dissolved oxygen in the water column of Lake Malawi. Horizontal dashed lines indicate lake bottom. B) Deep water (N 300 m) temperature in Lake Malawi. C) Vertical distributions of dissolved oxygen in the sediment at S2.
Sediment records from different parts of the lake.

Geochemical profiles in the water column and sediments of Lake Malawi (scroll down to see more profiles):

Profiles.pdf

Freshwater lakes in comparison to the Oceans

Fig. 8 Comparison between sediments in Lake Malawi and marine and temperate large lakes sediments. (A) Organic carbon degradation rates as a function of water depth. (B) Export efficiency (organic carbon fluxes/primary productivity) as a function of water depth. (C) Organic carbon burial efficiency (relative to amount deposited to the sediment surface) against oxygen exposure time (OET). OET was estimated as the depth of oxygen penetration divided by the average burial velocity. (D) Organic carbon burial efficiency as a function of sedimentation rate.