Eutrophication Model For Simulating The Transport Of Total Nitrogen And Total Phosphorus In Winam Gulf Lake Victoria

ABSTRACT

Lake Victoria has experienced eutrophication problems. These problems may be attributed to pollution due to expanding population, a rapidly developing technology and increased industrial and food production. Eutrophication in Lake Victoria is evident from the average total nitrogen to total phosphorus (TN: TP) ratio in Winam Gulf Lake Victoria of 5.89 which is below 16.1 the ratio of a balanced aquatic system. Low TN: TP ratio promotes excessive growth of algae which during decomposition depletes the water of available oxygen causing deaths of aquatic organisms. It is with this understanding that a numerical model for simulating the spatial and temporal variation of concentration of TN and TP has been developed. In the simulations, the sources discharge the nutrients in the lake and the nutrients are dispersed by both advection and diffusion. The transport rate of nutrients in Winam Gulf depends on several properties including advection velocity, diffusivity coefficient and wind speed and direction which vary with time of the day. TN and TP loads from the sub-basins were set as the initial conditions for the numerical simulation. A non staggered block centered grid for spatial discretization of Winam Gulf was used to enable the simulator track TN and TP movement through various blocks with increasing time. The governing equation describing the mathematical model was discretized explicitly by integral finite difference and solved using C# computer codes. The model was validated using data obtained from Lake Victoria Environment Management Project (LVEMP). The calculated TN: TP ratio from the simulated results in all the blocks was between 4.0 and 14.0. The model can be used to determine the dispersion of TN and TP in Winam Gulf with an aim of seeing how a given input affects the Lake ecosystem and which input gives a balanced aquatic ecosystem.