Wang Shaoyong, He Xiaobo, Kang Shichang, Yan Fangpin, Fu Hui, Hong Xiaofeng, Xue Yuang, Feng Zijing
State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
Sci Total Environ. 2023 Mar 25;866:161337. doi: 10.1016/j.scitotenv.2022.161337. Epub 2023 Jan 2.
Improving our understanding of streamwater age knowledge is critical for revealing the complex hydrological processes in alpine cryosphere catchments. However, few studies on water age have been conducted in alpine cryosphere catchments due to the complicated and inclement environment. In this study, the Buqu catchment, a typical alpine catchment covered by glaciers and permafrost on the central Tibetan Plateau (TP), was selected as the study area. Using the sine-wave approach and a gamma model based on the seasonal cycle of stable isotopes in water, the young water fraction (F) and mean transit time (MTT) of the Buqu catchment outlet and 23 sub-catchments was estimated to comprehensively reveal the potential driving mechanism of water age variability. The streamwater MTT for the entire catchment was 107 days, and 15.1 % of the streamwater was younger than 41 days on average. The estimated water age showed significant spatial heterogeneity with shorter water ages in high-elevation and glacier catchments and longer water ages in low-elevation and non-glacier catchments. Precipitation was the primary driver for spatial variations in water age, while the thickness of the permafrost active layer may function as an intermediate hub to drive water age variability. Mechanically, the thickness of the permafrost active layer controls the water ages by modifying the flow direction and length of water flow path. Spatially, this control mechanism is indirectly driven by the elevation gradient. The TDS concentration in streamwater is significantly related to water age, thus revealing a close link between water quality and hydrology. Our findings suggest that cryosphere retreats likely alter water age, thereby slowing water circulation rates and affecting water quality security under global warming. This study provides insights into the evolution of water ages, thereby deepening our understanding of the hydrological processes and guiding the protection of water resources in alpine headwater catchments.
增进我们对河流水龄知识的理解对于揭示高寒冰冻圈流域复杂的水文过程至关重要。然而，由于环境复杂恶劣，在高寒冰冻圈流域开展的水龄研究较少。本研究选取了位于青藏高原中部、被冰川和多年冻土覆盖的典型高寒流域——布曲流域作为研究区域。利用基于水中稳定同位素季节循环的正弦波方法和伽马模型，估算了布曲流域出口及23个次级流域的年轻水比例（F）和平均滞留时间（MTT），以全面揭示水龄变化的潜在驱动机制。整个流域的河流水MTT为107天，平均15.1%的河水年龄小于41天。估算的水龄显示出显著的空间异质性，高海拔和冰川流域的水龄较短，低海拔和非冰川流域的水龄较长。降水是水龄空间变化的主要驱动因素，而多年冻土活动层的厚度可能作为一个中间枢纽来驱动水龄变化。从机制上讲，多年冻土活动层的厚度通过改变水流方向和流程长度来控制水龄。在空间上，这种控制机制是由海拔梯度间接驱动的。河流水体中的总溶解固体（TDS）浓度与水龄显著相关，从而揭示了水质与水文之间的密切联系。我们的研究结果表明，在全球变暖的情况下，冰冻圈退缩可能会改变水龄，从而减缓水循环速率并影响水质安全。本研究为水龄的演变提供了见解，从而加深了我们对水文过程的理解，并为高寒源头流域的水资源保护提供了指导。
