Temperature stratification and mixing dynamics in a shallow lake with submersed macrophytes

This paper describes an investigation of temperature stratification and vertical mixing in lacustrine macrophyte beds. Field measurements in a shallow lake show pronounced diel temperature dynamics, driven by surface heat transfer. The temperature stratification data also indicate a significant dependence of vertical mixing characteristics on macrophyte stand height. While natural convective mixing during night-time cooling was rather uniform between measurement sites, wind-driven mixing during the day was significantly attenuated in dense, full-depth macrophyte beds, resulting in increased stratification and higher maximum surface temperatures. An unsteady, one-dimensional heat transfer model has been formulated to simulate temperature dynamics in shallow lakes with submersed macrophytes. Surface mixed layer dynamics are successfully modeled at time scales down to 1 hour, using an integral energy model formulated to include the effect of light attenuation and turbulent kinetic energy dissipation by submersed macrophytes. The results of this study have implications for the management of water quality and ecology of shallow lakes, as variation of thermal stratification and mixing likely has corresponding effects on the transport of dissolved oxygen and nutrients.