Modelling the Distribution of Heavy Metals between Sediment and Water in the Upper Nile Lake System1

Abstract Sorption isotherms were experimentally determined for copper, lead, cadmium, and chromium with sediments from Lake Victoria, Lake Mobuto, and Lake Kioga in the Upper Nile Lake Basin. The data fitted best Langmuir equations with maximum sorption capacity at aerobic conditions for Pb of 55 μg/g dry matter and minimum sorption capacity for Cd of 2 μg/g dry matter. Under anaerobic conditions the sorption capacity increased depending on metal species. Relations between sorption capacity and pH and redox conditions were established and used in a copper submodel as an example. The submodel was coupled to an existing eutrophication model for Lake Victoria by simple partition coefficients between heavy metal and water and suspended particles generated in the eutrophication model.