Lake Tanganyika, East Africa, is one of the world’s most unique freshwater ecosystems. This lake is approximately 10 million years old and contains an extremely diverse fauna with high levels of endemicity. Most of the biodiversity in the lake is concentrated along the rocky shoreline, and this dissertation focuses on the land-water interactions that may affect this ecosystem as human population densities increase.

First, I used carbon and nitrogen stable isotopes of sedimentary organic matter in river deltas as indicators of human impact. Carbon isotopes were enriched with increasing watershed disturbance and size, while nitrogen isotopes were enriched only with increasing watershed disturbance. Stable isotope analyses of cores taken at two sites were consistent with patterns seen in surface sediments. These results suggest that nitrogen isotopes may be a better indicator of land use than carbon isotopes and that watershed size can be a confounding factor in the interpretation of geochemical signals in lake sediments.

Secondly, I compared benthic productivity at disturbed and undisturbed sites along the shoreline. Benthic net productivity does not differ significantly between the disturbed and undisturbed watersheds, but benthic respiration and algal biomass are significantly higher at the disturbed site. Further evidence of disturbance is given by greater amounts of inorganic material on the rocks and lower ambient oxygen concentrations at the impacted site. Seasonal variation in net productivity, respiration and biomass are not significant at the northern site but are significant in the southern area of the lake.

Finally, I used stable isotopic analyses of the littoral and pelagic food webs to determine food web structure. Carbon isotopes clearly distinguished between phytoplankton and epilithic carbon sources. Diet specificity is not apparent in the littoral food web, suggesting that broad dietary preferences may help stabilize the food web during environmental perturbations. For the pelagic food web, there was a slight depletion of 15-N from phytoplankton to upper level consumers instead of expected enrichment. This isotope structure suggests that upwelled nitrate is a nutrient source rapidly consumed by phytoplankton but diluted by temporal integration in the upper trophic levels.