The Contribution of Ground Ice Meltwater to Vegetation Growth in Retrogressive Thaw Slumps: A Case Study at Ebo Ridge, China

Abstract

The intensification of global warming has accelerated permafrost degradation in the Qilian Mountains on the Qinghai–Tibet Plateau (QTP), leading to frequent secondary impacts such as thermokarst and significantly altered regional hydrological processes. In permafrost zones, a drastic reduction in ground ice has profoundly restructured the surface to groundwater hydrological connectivity. However, exactly how this restructuring affects the dynamic responses and ecological impacts of varied water sources for vegetation in thermokarst areas remains unclear. This study focuses on δD and δ18O isotope data from various water bodies with a Bayesian mixing model (MixSIAR) to quantify the water utilization strategies of herbaceous plants in the retrogressive thaw slumps (RTSs) that characterize the Ebo Ridge in China's Qilian Mountains. Results show that the dominant source of water for vegetation comes from 40‐ to 80‐cm soil moisture (48.7%) and meltwater from ground ice (26.1%), while precipitation contributed 25.3%, which is notably lower than in nonthermokarst areas (30%–50%). Isotopic analysis further reveals that RTSs disrupt the impermeable layer of permafrost, enhancing deeper water recharge and enabling vegetation to access water more evenly across various soil depths (14.8%–17.9%). These changes have enhanced plant dependence on ground ice meltwater, driving the emergence of adaptive water‐use strategies. However, ongoing permafrost degradation may trigger positive feedback: Accelerated ice melt stimulates deeper rooting, but the consequent decline in accessible soil moisture and inherent physiological constraints on root elongation are likely to undermine this adaptation, ultimately leading to ecosystem instability. This cascading sequence of impacts presents substantial risks to both the resilience of regional water resources and the persistence of carbon sequestration capacity. Based on these findings, this study highlights the critical importance of preserving permafrost integrity and proposes an ecological restoration framework, emphasizing coordinated regulation of microtopography–vegetation–hydrology for sustaining alpine ecosystems in permafrost regions under climate change.