Seasonal dynamics of suprapermafrost groundwater and its response to the freeing-thawing processes of soil in the permafrost region of Qinghai-Tibet Plateau

The suprapermafrost groundwater in permafrost region not only is an important component of the water cycle and land surface process, but also is closely associated with the charges of ecological environment in cold region. However, the seasonal dynamics, driving factors, and mechanism of suprapermafrost groundwater are not well understood. Based on observation at slope scale on suprapermafrost groundwater dynamics of typical alpine meadows in the Qinghai-Tibet Plateau, the seasonal dynamics, spatial distribution and driving factors of suprapermafrost groundwater were analyzed. The results showed that there were close relationships between the seasonal dynamics of suprapermafrost groundwater and the freezing-thawing processes of active soil in permafrost region. The seasonal dynamics of suprapermafrost groundwater and its slope distribution pattern were controlled by soil temperature of active layers. The phase and range of the suprapermafrost groundwater dynamics are determined by deep soil (below 60 cm depth) moisture and groundwater recharging sources. The relationship between active soil temperatures and dynamics of suprapermafrost groundwater levels was better described by Boltzmann functions. However, the influencing thresholds of soil temperature on groundwater dynamics varied at different depths of active layers and in different slope positions, which resulted in the significant spatial heterogeneity of suprapermafrost groundwater dynamics in slope scale. Land cover change and global warming certainly altered the dynamics of suprapermafrost groundwater and the hydraulic interaction between groundwater and rivers, and consequently altered the overall hydrologic cycle of watershed scale.