The Change Mechanism of Soil Hydrological Properties in the Permafrost Active Layer of the Qinghai–Tibet Plateau

Abstract

The hydrological properties of the active soil layer are the key parameters that regulate soil water–heat–solute migration and alter hydrologic cycles in a permafrost region. To date, much remains unknown about the interaction mechanism between permafrost degradation and eco-hydrological processes in the permafrost regions of the Qinghai–Tibet Plateau (QTP). In this study, the soil texture, soil hydrological properties, and the soil moisture status of meadow soils with different degrees of degradation were analyzed in the laboratory, and hydrothermal process monitoring was conducted on the QTP. The results showed a close relationship between soil hydrological properties and soil physicochemical properties. Freeze–thaw cycles changed the physicochemical and hydrological properties, resulting in the degradation of frozen soil. In addition, vegetation on the ground delayed the degradation of frozen soil. The actual available soil water content (SWC) in the root layer was a key factor in the ecohydrological process. The actual effective SWC in the root layers of different alpine meadows was ranked as follows: non-degraded meadow (NDM) > moderately-degraded meadow (MDM) > seriously degraded meadow (SDM) (1.8–5.0% at NDM and −2.0–4.2% at SDM). In addition, the weak soil permeability in an SDM intensified the deficiency of the available SWC, thereby increasing the difficulty of ecological restoration. This study provides a basis for ecological environmental protection in permafrost regions and provides a hydrological process model for cold regions under future climate change scenarios.