Eutrophication of Kigoma bay Lake Tanganyika, Tanzania

Abstract

Studies carried out in Kigoma bay (Tanzania) and at a deep water offshore station in lakeTanganyika showed marked differences in the water characteristics at the two locations. At the pelagic station, the water was more transparent (mean 11.47 m) and poor in phosphorus (mean 6.46 mg p/1 and 2.23 p/1 total and soluble reactive p, respectively). The mean transparency value for the bay was 4.05 m, and the levels of total and soluble reactive phosphorus were 14.75 mg p/1 and 4.34 mg p/1, respectively. The high water transparency coupled with low phosphorus levels in the pelagic zone indicate that the pelagic region is oligotrophic, while the values for the bay show that it is meso – eutrophic. Nitrogen levels in the bay were also much higher (mean 61 mg n/1) than in the open waters (44 mg n/1). Phytoplankton biomass, expressed as chlorophyll a, was higher in the bay (mean 2.42 mg /1) than in the pelagic region (mean 1.55 mg /1). The high nutrient levels in the bay may have caused the high chlorophyll a values in there. During October 1998, very high chlorophyll a values (4.80 mg /1) and low transparency (7.70 m) were obtained at the offshore station. High chlorophyll a levels and low water transparency in the pelagic zone of the lake during October has also been reported by other workers. The high chlorophyll a levels are believed to result from Anabaena spp. blooms that occur during this period. High levels of nitrogen levels have also been observed during October.

Keywords: Lake Tanganyika, Kigoma bay, eutrophication, nutrients, chorophyll a.