基于同位素示踪技术的黄河源区水力联系变化研究

Under a warming climate and degrading permafrost, in the Source Area of the Yellow River (SAYR) on northeastern Qinghai-Tibet Plateau, one of the most sensitive regions to climate warming and of extensive and persistent concerns, the hydraulic connections of surface- and subsurface-waters have changed greatly. This, directly or indirectly, has affected, is affecting, and will continue to affect the dynamics and seasonal allocation of water resources among its numerous components, those at shallow depths in particular, and subsequently the hydrological cycling. With its high sensitivity and resolution, the rapidly developing and extensively applied stable and radiative isotope techniques have provided the crucial support for tracing the movements of mositure (water, ice and vapor) in many ungauged or data-poor cold regions watersheds. Therefore, it is very important to study the dynamic changes in the rechardge (supply), runoff (flow) and discharge (drainage) paths and hydraulic connections of the permafrost-controlled, coupled surface and subsurface water (ice) flow systems using the latest technologies in isotopic hydrology and hydrogeology. The proposed program aims at studying the spatiotemporal distribution of and changes in environmental isotopes such as 222Rn, δ2H and δ18O in precipitation, different layers of river and lake waters, groundwater and ground-ice, and soil moisture in the five carefully-chosen zones with varied stages of degrading permafrost in the SAYR, in order to comparatively evaluate the changes in hydraulic connections and channels (preferred paths) due to the degrading permafrost conditions in the SAYR. Additionally, the program also will investigate the radiative isotopes (14C and 3H) of groundwater (ice) and talik aquifers in order to understand the distribution of formation ages of groundwater (ice) and aquifers and the evolutionary processes of the coupled flow systems, and to comprehensively evaluate the changes in hydraulic connections in the SAYR by taking into account the spatiotemporal scale changes. The program results will lead to interdisciplinary breakthroughs and integrated innovations in the applications of stable and radiative isotope tracing techniques in hydrology, hydrogeology, geocryology and isotope environmental geochemistry, and provide key parameters and theorectical supports for understanding the mechanisms for the changes in and for prudently exploitation of water resources in the SAYR.

随气候变暖、冻土退化，黄河源区水力联系已经改变，并影响到水文循环过程。由于源区缺乏系统的实测水文地质资料，深入探究其流域水循环特征及其变化机制，就需利用同位素示踪技术来探索研究冻土控制下的水流系统的水力联系变化过程及趋势。本项目拟在黄河源5个不同冻土退化阶段的试验区开展降水、湖水、冰雪融水、地下水（冰）及河水样品的调查和采集，通过分析水体的222Rn、2H和18O同位素分布和变化，评价降水和不同层位的河湖、地下水（冰）以及土壤水之间的水力联系，比较研究冻土退化导致的水力联系变化。此外，通过测定地下水（冰）和融区含水层中14C和3H同位素，查明地下水（冰）年龄分布与冻土区含水层协同演化关系，并通过时空尺度转换综合分析源区水力联系的动态变化。本项目的开展将在水文地质、冻土学和同位素环境地球化学领域交叉融合方面取得重要进展，并为揭示冻土区水资源动态变化机制和水资源合理利用提供理论依据。

黄河源区水力联系已显著改变，并影响到水文过程。同位素技术为寒区流域水（冰）流耦合系统的水资源动态变化研究提供了重要手段。通过分析不同水体和土壤水样的222Rn、2H和18O同位素分布和变化，可在黄河源区调查和评价水力联系及其变化。自项目启动以来，基于同位素示踪技术分别开展了以下四项研究：1）利用氢氧同位素定性分析黄河源区水力联系；2）利用氡同位素研究冻融作用对产汇流影响；3）利用放射性同位素研究地下水（冰）滞时和水力联系；4）综合考虑同位素时空分布，分析水力联系变化。项目取得成果如下：1）开展了黄河源区冻土产汇流过程试验研究，查明了地表水与地下水动态变化规律和趋势以及地表水、河水等互相补给过程，完成了双岔沟试验小流域及整个黄河源区同位素水文变化研究；2）在不同冻土退化程度的小流域开展了水位、活动层等基础观测，利用放射性氡同位素，构建地下水-地表水交互模型，分析冻土退化程度对水文过程的影响；3）通过同位素定年方法研究冻土与河湖融区之间的水力联系，以及；4）构建同位素湖泊模型定量分析不同冻土区，水文过程、水资源量的差异。以上研究表明，地下冰融水和地下水补给在黄河源区水文过程中具有重要作用，冻土退化已经产生了显著的水文效应。冻土退化导致的水力联系变化主要体现在径流深度增大和径流路径延长，并显著增加了地下水储量和水量平衡的各个方面。但是，定量评估冻土退化的水文效应还需要进一步的细化、分析。本项目瞄准冻土水文学科前沿和江河源区可持续发展等国家重大需求，完成了源区气象水文、活动层、径流、热融湖塘等系列数据库和图件，其实施产生了较多重要原创性成果。基于上述工作，目前项目发表论文总数17篇，其中 SCI收录10篇。本项目圆满完成了各项任务，显著推进了我国黄河源区冻土水文过程、生态过程、冻土环境变化过程和水文地质循环过程等研究， 提高了国际知名度。