Study on the retention effect of condensed water at different soil levels in exposed areas of Hoh Xil lake upon water recession

Abstract

Abstract In order to investigate the absorption and retention characteristics of condensed water at different soil layers in the bare desertification area at the bottom of a receding lake in Hoh Xil, Qinghai Province, the characteristics of condensate variation, condensate formation time, condensate volume, and its absorption capacity were investigated in July 2021 using a micro-osmometer. The research area was the artificial water retention layer and bare ground of the exposed sandy bottom formed under the influence of the warming–wetting trend that occurs when water recedes in the salt lake area of the Qinghai-Tibet Plateau, as well as the two conditions of underpass and underseal. According to the results, the time of condensation generation during the observation period in the salt lake area of Hoh Xil begins at about 0:00 and ends at about 10:00. The artificial water retention layer had little influence on the condensation generation time, and the trend of the condensation rate is the same. The unidirectional condensation phenomenon of water vapor in the near-surface air at a depth range of 0–5 cm when an artificial water retention layer is applied is clearly superior to that of other layers; accordingly, its frequency of condensation phenomenon is also the highest. The amount of condensed soil water vapor from the lower part of the ground when an artificial water retention layer is applied at depth ranges of 0–5 cm, 5–10 cm, and 0–10 cm were 3.60, 6.39, and 10.27 times that of the near-surface air, respectively. The total amount of bidirectional condensed water under the condition of the artificial water retention layer at 0–10 cm was the largest. Conversely, the total amount of condensed water from the near-surface air at a depth range of 0–5 cm under the unidirectional condensation condition was the highest, being twice as great as the total amount of condensed water in other layers, which demonstrates the promoting effect that the artificial water retention layer has on the adsorption of water vapor in the near-surface air. Due to the existence of permafrost in the Qinghai-Tibet Plateau, the heat zero-flux plane in the area of the Salt Lake has a migration range of divergence of approximately 30 cm from the surface to the ground. An analogous humidity coefficient characterizes the retention effect of condensed water in certain areas, which serve to demonstrate how the artificial water retention layer distributed at a depth of 0–5 cm, regardless of bidirectional or unidirectional condensation, has the best capacity for adsorption. The results of this study provide a theoretical basis for condensate absorption capacity and vegetation restoration in the bare ecologically degraded areas of the lake bottom.