Phosphorus supply to a shallow tropical lake and its consequences - Lake Naivasha, Kenya

The ecological stability of Lake Naivasha is unpredictable, as it lies in an endorrheic basin situated in an intensive agricultural region with diversified climatic conditions. The situation is getting worse as increase in agricultural activities and hence human population continues, consequently resulting in an increase in water demand and abstraction.;An investigation in phosphorus dynamics, interactions and possible sources was carried out both in the inflowing waters and the lake. During the "El Nino" rains approximately 9 times more TP was transported into the lake from the catchment mainly in particulate form (PP). The river Malewa transported almost 30 times more total phosphorus (TP) than the other two rivers. Most of the TP input arose from the middle course of the river, mainly in PP form bound in suspended solids. Watering of the livestock in the river was found to elevate the concentration of TP, PP and total suspended solids (TSS), although its influence downstream depended on discharge, intensity and frequency of disturbance.;The phosphorus lake loading to the lake varied significantly between the two hydrological phases encountered with 1.41 and 0.21 g m-2 yr-1 for the "extremely" wet and "normal" wet years respectively classifying the lake as eutrophic. However the overall quotient between the mean in-lake phosphorus (P) and the inflow phosphorus (Pi) concentration from the river Malewa portrayed an equilibrium state with an overall P/Pi ratio of 0.62.;The Naivasha sediments are poorly sorted with inorganic phosphorus dominance. The lake sediment has low phosphorus buffering capacity as portrayed by a low phosphorus sorption index (PSI), indicating a phosphorus source rather than sink.