KMFRI, P. O. Box 1881, Kisumu. E-Mail: sitoki@hotmail.com

Nutrient enrichment in Lake Victoria, a cause for concern

Phytoplankton species composition, numerical abundance and total biomass measured as chlorophyll concentration were studied between October, 2000 and August, 2001 in relation to water quality parameters in the Kenyan water of lake Victoria (Nyanza Gulf). A total of 52 algal genera were recorded. There were mainly three algal families of which Cyanophyceae were the most dominant followed by Bacillariophyceae and Chlorophyceae.

The nutrient levels were found to be generally high (averages, nitrates - 1 µg/1, phosphates 46 µg/1 and silicate 10mg/1) as were the chlorophyll a and cell densities. Therefore, the systems can be classified as eutrophic. Higher chlorophyll a was recorded in stations with high nitrate contents. Using hierarchical clustering the sampled stations differed mainly in conductivity, silicates, total hardness, and total alkalinity.

The findings obtained from the Nyanza Gulf were compared to those from the small water bodies and were found to differ substantially in their water quality status. Higher nitrates, phosphates, and silicates were recorded in smaller water bodies than in the Nyanza Gulf. On average, all measured parameters were higher in the small water bodies than in the Gulf.

The trend of having steady increases in the nutrient concentrations in recent years has had a profound effect on the natural functioning of the ecosystem. This trend raises significant concerns on the future of our ecosystems and welfare in general.