Modelling and simulation of the cyanobacteria blooms dynamics in lake Taihu, China

Abstract

The present work deals with the modeling of the cyanobacteria blooms phenomenon from Lake Taihu in China by a 3D hydro-ecological model and the implementation of this model for the simulation. The model is composed of: (1) a model of the lake hydrodynamics in two di- mensions: we used the Shallow Water equations which are a particular case of Navier- Stokes equations, where the vertical dimension is neglected; (2) a Water Quality Model (WQM): we used the Water Quality Analysis Simulation Program(WASP) model in which are represented the reactions between ecological variables such as phytoplankton, oxygen, nitrogen and phosphorus, and the transport and diffusion of these substances by the fluid (in our case the water). For the numerical resolution of the partial differential equations involved, the finite volume method was used with a non-uniform triangular mesh of the lake. The Navier- Stokes equations were solved independently in a first time to compute the current values. For this purpose, the free software called Finite Volume Coastal Ocean Model (FVCOM) was used. For the coupled hydro-ecological simulation, we developed a programme that performs the numerical resolution of the reaction-convection-diffusion equations, using the currents as inputs of the model. The simulations focus on the current effect and the coupling between hydrodynamics and water quality variables. Finally, to analyze the model, we applied the Morris method, which is a Sensitivity Analysis method, to the water quality model. It gives us the most important param- eters of the model which will be useful in the next step to calibrate the model for the specific case of the lake Taihu.