Lake thermal dynamics and its potential impact on lake ecological system on the Tibetan Plateau

Lake thermal stratification is of great importance to hydrodynamics and transport of nutrients, oxygen, and primary production, which influence limnology and local climate. The thermal regime of the lakes over Tibetan Plateau (TP) was summarized as follow. During summer, solar radiation unevenly heats the water column in the vertical direction, resulting in a stratified thermal structure. The stratification dissipates in October, after which time a more uniform vertical distribution of temperature is observed. This occurs because the increased temperature gradient between the air and lake surface, combined with strong winds, drives considerable energy transfer from the lakes to the overlying air, and leads to a rapid decrease in surface water temperature. This result increases in density of the upper layers and then drives vertical convection that deepens the mixed layer. When the lakes have been completely frozen, the vertical water circulation stops; weak thermal stratification then develops and persists during winter. However, lake water near the surface warms rapidly, and rest water layer does not change much when lakes are covered with ice. When the lake ice disappears, wind-driven turbulence develops and promotes lake vertical mixing. Due to sparse observation, the lake modeling was an alternative method to simulate the seasonal lake thermal change induced by local climate change. Using lake model, the seasonal variation and magnitude of water temperature at different layers were reproduced fundamentally. The interaction heat flux and water exchange with overlying air also were simulated with reasonable error. Both the simulation and observation have shown that the thermal characteristic and ice phenology has altered: warming water and shorter ice duration, impacted by climate change. Meanwhile, the future projection of thermal response of lakes over TP to climate change shows that remarkable water temperature increase and winter ice loss which indicates less mixing frequent and shifting mixing regime. The Lake mixing events can channel the epilimnion and hypolimnion and release large amounts of potent greenhouse gases into the upper surface layer and the atmosphere in autumn, making lakes generally being considered as a weak net carbon source. The epilimnion depth show significant implications on the algal distribution, photosynthesis rates and establishing food web basis. Thus, the seasonal variations of thermal stratification and mixing in lakes can influence the aerobic life, prevent anoxia and impact on local climate and it is one of the most important factors in limnology and climate change.