Nutrient Dynamics of Lake Tanganyika Based on the High-resolution Diatom Fossil Record from the Southern Basin
High-resolution fossil diatom records from the southern basin of Lake Tanganyika, one of Africa’s Great Rift Valley lakes, provide valuable insights into long-term nutrient dynamics and ecosystem variability. As the world’s second-deepest freshwater lake, Tanganyika supports diverse biological communities that are highly sensitive to climatic and hydrological fluctuations. Changes in lake stratification, mixing depth, and nutrient availability have profound effects on primary productivity, which are effectively recorded in fossil diatom assemblages preserved in its sediments.
Analysis of diatom records from both nearshore (core 6B) and offshore (core 11A) regions reveals distinct spatial and temporal variations in ecological conditions. In both littoral and pelagic cores, diatom concentrations were relatively high before approximately 1860 CE, followed by a sharp decline, signalling major shifts in nutrient cycling and water column stability.
In core 6B, elevated abundances of the euplanktonic Stephanodiscus muelleri and smaller proportions of Aulacoseira species before ca. 1860 CE suggest high phosphorus availability and moderately low silica concentrations. After 1860 CE, dominance shifted toward long, needle-shaped Nitzschia species, indicating reduced phosphorus and silica concentrations linked to intensified and prolonged thermal stratification. A later decline of Nitzschia and resurgence of small and large centric euplanktonic diatoms around ca. 2015 CE points to enhanced mixing and renewed nutrient inputs.
In core 11A, S. muelleri and needle-shaped Nitzschia species dominated throughout the record, reflecting persistently moderate phosphorus and low silica levels. A temporary increase in Aulacoseira species between ca. 1900–1950 CE suggests stronger vertical mixing and higher silica availability. The brief dominance of Gomphonema clevei between 2000 and 2005 CE indicates the expansion of periphytic habitats associated with rising lake levels and increased transport of benthic diatoms into the pelagic zone. From ca. 2005–2020 CE, the dominance of planktonic forms and the reduction of meroplanktonic and benthic taxa imply slightly elevated nutrient levels, while a sharp increase in S. muelleri after 2005 signals higher soluble reactive phosphorus concentrations.
Collectively, these findings highlight spatial heterogeneity in nutrient regimes and water-column processes within Lake Tanganyika, underscoring that nearshore and offshore ecosystems respond differently to climatic and limnological shifts over the past two centuries.
Light micrograph image of Stephanodiscus muelleri with scale bar.
Light micrograph image of different diatoms with scale bar.
Sristika Adhikari is a Ph.D. student in Paleolimnology at the Department of Earth and Environmental Systems, Indiana State University. She previously served as a Research Assistant at the Nepal Academy of Science and Technology. She holds dual master’s degrees—an M.Sc. in Limnology and Wetland Management from IHE–Institute for Water Education, Delft, Netherlands, and an M.Sc. in Environmental Science from Tribhuvan University, Nepal. Her research focuses on the conservation and reconstruction of freshwater ecosystems, emphasizing the impacts of climate and land-use change on lakes and rivers and developing strategies for their sustainable management.
Position: PhD candidate
Current Affiliation/Laboratory: Indiana State University
Supervisor Name: Jeffery Stone