Mercury in Lake Victoria (East Africa): Another emerging issue for a beleaguered lake

Total mercury cycling and the food web structure are investigated in Lake Victoria, East Africa. Lake Victoria is not only the largest tropical lake in the world by area, but also supports the largest freshwater fishery in the world. This lake is threatened by several environmental pressures. Methylmercury, a serious neurotoxic chemical, has the potential to be a major environmental concern in Lake Victoria as it is easily bioaccumulated in aquatic biota. Any potential negative impact on the valuable fisheries can have serious ramifications.; Because food web structure is important in terms of total mercury (THg) bioaccumulation, the food web structures in Napoleon and Winam Gulfs were characterized using stable nitrogen and carbon isotope analyses. Similar biota in Napoleon Gulf had significantly lighter δ15N values and heavier δ13C values than similar biota in Winam Gulf, indicating different basal isotopic values but the fractionation rates remained consistent between trophic transfers. Stable isotope data are consistent with Nile perch feeding on a restricted set of fish and macroinvertebrate species, including its own young, and indicate that Nile perch populations may be self-limited by cannibalism.; THg concentrations in the food-webs and water of Napoleon Gulf (Uganda) and Winam Gulf (Kenya) in northern Lake Victoria were determined. Water Hg concentrations in Lake Victoria are higher than in temperate great lakes, but the top predator Nile perch has relatively low THg concentrations compared to temperate piscivorous fish. While the water Hg concentrations are similar between Napoleon and Winam Gulfs, the THg concentrations in biota are significantly higher in Napoleon Gulf than in the same species from Winam Gulf.; Patterns in THg in water, soil and 210Pb-dated sediment cores from northern and central Lake Victoria were determined. There were no apparent differences in THg water concentrations between Napoleon and Winam Gulfs in northern L. Victoria.; Data were compiled from published and unpublished studies in the three countries sharing Lake Victoria, namely Tanzania, Uganda and Kenya. (Abstract shortened by UMI.)...