Simulation and Seasonal Characteristics of the Intra-Annual Heat Exchange Process in a Shallow Ice-Covered Lake

The intra-annual heat exchange process has a considerable influence on the energy circulation, material metabolism, and ecological succession of lakes. The input and output of heat in an ice-covered lake provide the basic dynamic force driving changes in the biochemical state of the lake. Based on the heat balance between the lake surface and the atmosphere, we established a thermodynamic model for calculating the thermodynamic factors of shallow inland lakes during the ice and open seasons. The data of the Ulansuhai Lake, Inner Mongolia, from two years (2012 and 2013) are used to analyze the seasonal characteristics and associated influences of the heat budget on the ecosystem. The results indicated that the monthly mean lake temperature over the past 10 years was 1.7–2.2 °C lower than in the previous 50 years. The absorbed solar radiation reached up to 210 W/m2 in 2012 and 179 W/m2 in 2013, and there were clear differences in the heat budget between the ice-covered and open seasons. The mean net heat fluxes in the ice season were −33.8 and −38.5 W/m2 in 2012 and 2013, respectively; while in the open season water, these fluxes were 62.5 and 19.1 W/m2. In the simulations, the wind was an important factor for intensive evaporation in summer and the main driver of the ice cover formation patterns in winter, involving the transmission and diffusion of material and energy in the lake. The results provide a theoretical foundation for simulating ice cover growth and ablation processes in shallow lakes. They also present data on the ecological evolution in these lacustrine environments.