Dynamics of vertical mixing in a shallow lake with submersed macrophytes

A model for vertical turbulent diffusion and stratification in a shallow lake with submersed macrophytes is formulated on the basis of a one-dimensional equation for production, transport, and dissipation of turbulent kinetic energy, coupled with a vertical heat transfer equation. Numerical solutions of the coupled equations allow simulation of the hourly variation of water temperature profiles in a shallow lake as a function of varying weather parameters. The model can be used to simulate water temperature and turbulent kinetic energy profiles in locations of a shallow lake with either dense macrophyte beds or relatively open water. The water temperature simulations are in good agreement with field data from a shallow lake. During the day, macrophyte beds are found to increase the strength of temperature stratification and to reduce the mixed layer depth compared to open water. Macrophyte beds are found to have relatively little effect on nighttime deepening of the mixed layer because of surface cooling. Lateral transport between open water and macrophyte beds of finite horizontal dimensions (patchiness) may limit the accuracy of one-dimensional transport models. Vertical diffusivity coefficient profiles found in this study may be useful to investigate mass transport in shallow lakes with macrophytes.