Hydrochemical characteristics of ground ice in permafrost regions of the Qinghai-Tibet Plateau

Ground ice is a distinctive feature of permafrost terrain. The vertical distribution and factors controlling the hydrochemistry of ground ice are important for studying soil moisture and salt migration during the freeze-thaw process in soil These factors arc also important components of hydrological cycles in cold regions. The hydrochemical characteristics of ground ice on the Qinghai-Tibetan Plateau (QTP) are not well known. We examined the characteristics of ground ice hydrochemistry using data from 9 soil profiles in permafrost regions of the central QTP. The isotopes and anion concentrations of subsurface water on the QTP were higher than those in Arctic polygonal ground regions. The spatial distribution of anions was complex. Well-developed hydrochemical depth gradients occurred within the soil profile. Isotopes decreased and anions increased with depth, suggesting general vertical patterns of soil hydrochemistry across different permafrost regions. Cl- and SO42- concentrations in soil water increased with depth, while NO3- concentration did not change with depth. Freeze-out fractionation, self-purification, and desalination greatly impact soil hydrochemistry. The major factors controlling variation of soil water chemistry were soil moisture, an temperature, and active layer thickness. The results could provide a framework for understanding ground ice origins and the moisture and salt migration pathways in the context of permafrost changes. This information could be useful in developing process-based permafrost hydrologic models. (C) 2018 Elsevier B.V. All rights reserved.