Comparison of hydrogeochemical characteristics of thermokarst lake water in the Qinghai–Tibet Plateau under active layer freeze–thaw conditions

Abstract

With the gradual increase of global temperature, thermokarst lakes are widely developed and become major environmental disasters in the Tundra Plateau which have impacted the stability of the project such as the Qinghai–Tibetan highway. In this study, some typical thermokarst lakes in the Qinghai–Tibet Plateau (QTP) were selected as the research object. And four samples were taken from different freezing–thawing processes of the lakes in 2019 to analyze the hydrogeochemical process of the thermokarst lake in the context of climate change. Results show that the main hydrogeochemical types of the lake water in the northern part of the study area were HCO3·Cl − Na·Ca·Mg or Cl·HCO3 − Na·Mg, whereas in the central and southern parts were mainly Cl − Na·Mg. The variations of hydrogeochemical concentration in thermokarst lake water are mainly affected by evaporation concentration, rock differentiation, freezing desalination in the active layer, and plant photosynthesis, which are mainly due to temperature changes. Furthermore, the results of the saturation index (SI) show that dolomite and calcite leaching control the hydrogeochemical composition in thermokarst lakes. In addition, the evaporation-to-inflow (E/I) ratios of the lake reach the maximum in the middle and later periods of the active layer thawing. On the contrary, the E/I values of the lakes decrease during the initial thawing or freezing periods of the active layer.

Variation of water bodies along highways in the Qinghai–Tibet Plateau over the past 20 years: A case study of G109 and G219

“…Variations in water bodies in the seasonally frozen ground zone are closely related to meteorological aspects, while in the permafrost zone the weak permeability of the permafrost layer will affect the transformation relationship between surface water and groundwater (Fang et al 2022). In addition, the variation of surface water bodies is affected not only by the meteorological environment but also by the degradation or development of the frozen soil.…”

“…Due to the low reflectivity and high heat storage capacity of the ponded area, solar radiation will accelerate the temperature increase in it and the underlying permafrost. Therefore, once the thermokarst lake is formed, its thermal convection process will cause the underlying permafrost to continue to thaw and form a thaw zone (Fang et al 2022), which performs an expansion of water body and the rise of water level on the ground surface.…”