Using stable isotopes to illuminate thermokarst lake hydrology in permafrost regions on the Qinghai-Tibet plateau, China

摘要

Thermokarst lakes are widespread and developing on the Qinghai-Tibet Plateau (QTP), and they have modified hydrological processes and water balance in the region. Despite increasing attention, our understanding of the hydrological behaviors of thermokarst lakes under permafrost degradation remains limited on the QTP. In this study, water stable isotope tracers were used to characterize the spatial and seasonal hydrological changes of thermokarst lakes on the central QTP. Significant seasonal variations and factors influencing the isotopic hydrology of lakes were revealed through the ice-free season. Substantial differences in lake-specific input water isotope compositions (delta(I)) among the lakes indicate two lake-recharge regimes: rain-dominated, and snowmelt/permafrost thaw-dominated. We suggest that precipitation and active-layer hydrology controlled these hydrological changes in the ice-free season. However, under ice cover, melting of the surrounding permafrost (including ground ice) dominated the hydrology of thermokarst lakes. Importantly, a conceptual model delineates the hydrological evolution of thermokarst lakes under permafrost degradation. This study serves as a baseline for future investigations of hydrological processes and water balance relating to thawing permafrost on the QTP.