Published in April 2021
Lake Victoria is Africa’s largest freshwater body with a surface area of ca. 68,000 km2 . It is shared by Kenya (6%), Tanzania, (49%), and Uganda (45%) while Rwanda and Burundi forms part of its drainage basin. The Lake is of great socio-economic and ecologic value not only in Eastern Africa but also in the Nile basin countries. It supports a fast growing population estimated at 45 million people (World Bank, 2018). The functions of the Lake in the region ranges from provision of basic needs and services (food, fresh water, and transport) to economic resources like hydroelectric power, commercial water, wildlife and tourism, minerals, cash crops, trade, industry, and fishery. In addition, it is the source of the White Nile River. However, Lake Victoria’s ecosystem health has tremendously degraded in the last five decades due to eutrophication. Eutrophication is the biological effect caused by nutrient enrichment in aquatic ecosystems. In the Lake Victoria, eutrophication is manifested by the growth of dense algal blooms and water hyacinth infestation (Fig1).
Nitrate concentrations varied spatially in the three river basins. The mixed agriculture land use of the Nyando basin recorded the highest nitrate levels (Fig. 2 & 3). This land use is characterised by mixed farming of food crops, livestock and a commercial flower farm. Significantly high nitrate concentration ranging 23 - 56 mg L-1 was obtained in a stream located downstream of a commercial flower farm (Fig. 3). In addition, the urbanized areas of the Nzoia basin and the large-scale tea estates of the Sondu Miriu basin recorded highest nitrate concentrations for their respective river basins (Fig. 2). On the other hand, upstream areas of the river basins characterized by forests and small scale tea farms recorded low nitrate concentrations. This reveals the influence of land use on river nitrate concentrations, i.e. nitrate concentration increases with human population density and intensity of land use activities.