Estimation of Nutrient Export Coefficients in Lake Victoria Basin

Abstract

Lake Victoria in East Africa is the second largest freshwater lake in the world by surface area. Pollution of the lake is an increasing concern because it compromises the ecosystem integrity of the lake. Past studies estimated the runoff load using borrowed nutrient export coefficients from other regions. Borrowed export coefficients were not necessarily modified to match the attributes of the local area. This study estimated the nutrient export coefficients for three land uses using river runoff data measured at river mouths of watersheds on the Kenyan side of Lake Victoria. Measured nutrients at river mouths were distributed back to the watersheds using a model equation. Factors that influence the export of nutrients were also assessed and incorporated in the model. Land use areas and rainfall-runoff coefficient values were used as main variables to explain runoff load. Two sets of data were used, one to set up the model and the other to validate the model. The range of export coefficients were estimated at 95% confidence interval. Land use and rainfall-runoff coefficient factors are adequate to estimate the export coefficients. Agricultural activities are the dominant land use and cover 87% of the catchment and are the major source of runoff load.