SEDIMENTATION STATUS OF LAKE VICTORIA: LOADING FROM RIVER MOUTH AND IN-LAKE SEDIMENTATION

Abstract

Lake sediments consist of the input of suspended solids by river discharges, the autochthonous produced particulatematter in the water column and the settled material on the lake bottom. The loading, transport, formation and decay ofthe sediments entering the Lake Victoria from Tanzanian side was monitored for the period 2000 to 2005. Thesedimentation study focused on; quantification of settling fluxes of particulate nutrients and organic carbon at the off-shore(Pelagic) and near-shore(Littoral) monitoring stations. Monitored data on sedimentation rate and settlingvelocities has been sampled and analysed in the period November 2000 to March 2005. The mean sedimentation rate atlittoral stations for total particulate phosphorous (TPP) was about twice as compared to pelagic stations. The samesituation was observed for total particulate carbon (TPC), however, total particulate silica did not show a clear patternof variability between littoral and pelagic stations though there was a general tendency of decreasing towards thepelagic stations. Mean value for TPC /TPP sedimentation rate ratio was 117.61 for littoral and 90.74 for pelagic stationsrespectively compared to TBSi/TPP which was 3.15 for littoral and 2.10 for pelagic stations. The results show thatsedimentation rates are highest at the littoral stations compared to pelagic stations. The differences in settling velocitiesindicate that the settling material consists dead and living material with a contribution of diatoms. The stoichiometriccomposition of the settling material indicates nitrogen limitation and a non-dominance of diatoms.