Assessment of streamwater age using water stable isotopes in a headwater catchment of the central Tibetan Plateau

Mechanisms of Suprapermafrost Groundwater Recharge Streamflow in Alpine Permafrost Regions: Insights From Young Water Fraction Analysis

“…Second, at sampling site G3 in the YZR, which is geographically close to the research basin of S. Wang, He, Kang, Hong, et al. (2023), the SPG MTT in G3 (113 days) was consistent with the streamflow MTT (107 days) in that study, whereas the F yw of the G3 watershed streamflow (0.151) was significantly lower than that of the SPG (0.548). This further demonstrates that streamflow in permafrost regions is replenished by the mixing and transformation of various water bodies within the active layer (Gui et al., 2023), resulting in smaller amplitude variations in streamflow isotopes compared to those in the SPG (the magnitude of isotopic variations in streamflow and SPG is illustrated in Figures 4 and 6, respectively).…”

“…In a previous study, the water age was calculated for 254 streams worldwide, revealing an average F yw of 0.26, with 89% > 0.05 (Jasechko et al., 2016). Recent studies calculated the F yw of streamflow for several small basins with permafrost, resulting in values of 0.151 (Song et al., 2017), 0.23 (Yang et al., 2021), 0.3 (S. Wang, He, Kang, Yan, et al., 2023), and 0.151 (S. Wang, He, Kang, Hong, et al., 2023), which are consistent with the results of this study (Table 2). These findings indicate that the F yw of streamflow in permafrost regions is generally lower than that of global rivers.…”

“…While Jasechko et al. (2016) found that young streamflow originates from less than 0.1% of global groundwater storage, in permafrost regions, permafrost confines groundwater to the shallow subsurface, leading to higher proportions of young streamflow compared to that in temperate regions (Song et al., 2017; S. Wang et al., 2022; S. Wang, He, Kang, Hong, et al., 2023; S. Wang, He, Kang, Yan, et al., 2023). Recent studies have emphasized the critical role of suprapermafrost groundwater (SPG) in cold region hydrology (Lamontagne‐Hallé et al., 2018; O'Connor et al., 2019).…”

“…The combination of F yw and MTT provides crucial information on the TTDs of water migration within a watershed (Hu et al., 2020). Although previous studies have attempted to estimate the water ages of small tributaries in certain permafrost regions (Song et al., 2017; S. Wang, He, Kang, Hong, et al., 2023; S. Wang, He, Kang, Yan, et al., 2023; Yang et al., 2021), the scarcity of observational data has resulted in limited research on F yw and MTT in other water bodies. Moreover, relying solely on the water age of individual hydrological components within a basin is inadequate for understanding hydrological processes across the entire basin (Sprenger et al., 2019).…”

Reply on RC2

“…The Fyw in Hehuan streams, which ranged from 19% to 38%, is comparable to values reported in other alpine environments. For example, in the alpine grasslands of the Qinghai-Tibet Plateau in western China, Fyw values ranged from 18% to 39% as reported in various studies (Song et al, 2017;Wang et al, 2023;Yang et al, 2021). In Switzerland, a Fyw of 34% was noted (Ceperley et al, 2020).…”