Observation and Analysis of Water Temperature in Ice-Covered Shallow Lake: Case Study in Qinghuahu Lake

Water temperature serves as a key environmental factor of lakes and the most basic parameter for analyzing the thermal conditions of a water body. Based on the observation and analysis of the water temperature of Qinghuahu Lake in the Heilongjiang Province of China, this paper analyzed the variation trend of the heat flux, effective thermal diffusivity of the icebound water, and revealed the temporal and spatial variation law of the water temperature and the transfer law beneath the ice on a shallow lake in a cold region. The results suggested a noticeable difference existing in the distribution of water temperature beneath the ice during different periods of ice coverage. During the third period, the water temperature vertically comprised three discrete layers, each of which remained unchanged in thickness despite the alternation of day and night. Sediment–water heat flux and water–ice heat flux both remained positive values throughout the freezing duration, averaging about 3.8–4.1 W/m2 and 9.8–10.3 W/m2, respectively. The calculated thermal diffusivity in late winter was larger than molecular, and the time-averaged values increased first and then decreased with water depth, reaching a maximum at a relative depth of 0.5. This research is expected to provide a reference for studies on the water environment of icebound shallow lakes or ponds in cold regions.