Estimation of water pollution sources in Lake Victoria, East Africa: Application and elaboration of the rapid assessment methodology

Abstract

Pollution resulting from increased human activities is threatening Lake Victoria, its effects being characterised by eutrophication and the occurrence of dramatically low dissolved oxygen levels. This study applies a system of pollution inventory methods to estimate waste loads from pollution sources on the basis of functional variables and pollution intensities. Penetration factors are used to incorporate the effects of treatment facilities and of natural ‘purification’ in rivers and wetlands. The application of a basic error analysis provides insight into the reliability of results. A one-dimensional model is applied to assess the overall nutrient balance.Results show that biological oxygen demand (BOD) load is highest on the Kenyan side. Domestic BOD loads exceed industrial loads in all regions, and management policies should therefore be directed primarily towards a reduction of domestic pollution. It was concluded that through effective operation of existing treatment facilities alone BOD loads on the Kenyan side could be reduced by 50%.Nutrient input appears to originate mainly from atmospheric deposition and land runoff, together accounting for approximately 90% of phosphorous and 94% of nitrogen input into the lake. The increase in eutrophication is most probably due to an increase in nutrient input from these sources, as a result of increased human activities in the lake surroundings, such as land exploitation for agriculture and forest burning. Policies for sustainable development in the region, including restoration and preservation of the lake's ecosystem, should therefore be directed towards improved land-use practices and a control over land clearing and forest burning.