A simple model of the eco-hydrodynamics of the epilimnion of Lake Tanganyika

1. The ecosystem response of Lake Tanganyika was studied using a four-component, nutrient-phytoplankton-zooplankton-detritus, phosphorus-based ecosystem model coupled to a nonlinear, reduced-gravity, circulation model. The ecosystem model, an improved version of the earlier eco-hydrodynamics model developed for Lake Tanganyika, was used to estimate the annual primary production of Lake Tanganyika and its spatial and temporal variability. The simulations were driven with the National Centres for Environmental Protection (NCEP) records for winds and solar radiation forcing. 2. The simulated annual cycles of the four ecosystem variables and the daily net primary production were compared with the observations. The comparison showed that simulations reproduced realistically the general features of the annual cycles of epilimnial phosphate, net primary production and plankton dynamics. 3. The climatic simulations for the years 1970-2006 yielded a daily averaged integrated upper layer net production ranging from 0.11 to 1.78 g C m(-2) day(-1) and daily averaged chlorophyll-a (chl-a) from 0.16 to 4.3 mg m(-3). Although the nutrient concentrations in the epilimnion during the strong wind years were high, the net production was low, which is partly because of the greater vertical mixing, produced by strong winds, exposing the phytoplankton to low light conditions in deeper waters. The simulated annual net production and chl-a agreed quite well with observed production available in the literature. 4. We envisage using this model to predict the future scenarios of primary productivity in the lake