Assessing the Ecological Dynamics of Lake Tanganyika: Remote Sensing Insights into Seasonal Hydrodynamics and Human or Climate-Induced Changes

Lake Tanganyika, one of the world’s largest freshwater body and located in East Africa, is under threat from both anthropogenic activities and climate change. The region strongly depends on it as a vital resource for water and food for the surrounding populations while pollution is increasing and fish catches and size are decreasing.

The characterization of Lake Tanganyika’s hydrodynamics, surface primary productivity and their changes over the past decades has not often benefited from remote sensing observations. In this study, we use satellite-derived estimates of surface chlorophyll-a concentration from ESA’s CCI Lakes dataset to enhance our understanding of Lake Tanganyika's hydrodynamics and more particularly the seasonal spatial patterns. Then, we focus on the analysis of the spatiotemporal changes of this variable over the past two decades with a subsequent effort to discern the underlying factors contributing to these observed changes.

After applying the DINEOF method for spatiotemporal interpolation, we comprehensively described the seasonal dynamics in surface chlorophyll-a concentration. We showed that the main patterns are the contrasting dynamics in the coastal and pelagic regions of the lake, explaining nearly 80% of the variance. The observed 20-year trends in primary productivity confirmed the hypothesis that primary productivity is decreasing in the pelagic regions of Lake Tanganyika, as asserted by earlier studies. This phenomenon can be attributed to the impact of climate change on air temperature and wind velocities in the region. These negative trends were found most dominant between March and June, and amount to around -0.5 mg.m^-3.decade^-1. We also showed a relative sharp increase in primary productivity (+0.5 to 2 mg.m^-3.decade^-1) in coastal regions near urban centres and river mouths, most notably in the North near Bujumbura and the outlet of the Ruzizi river. This most certainly illustrates the growing impact of the surrounding populations on the lake’s water quality.