长江源多年冻土区土壤冻融对径流形成的影响机理研究

The water resources security in major rivers of Asia depends on the runoff supply in the Qinghai-Tibet Plateau and its surrounding mountains. The soil freeze-thaw cycle processe is the key link of runoff generation in these regions, which greatly affects the water resource for large rivers in Asia, especially under the influence of global climate change. Water resources in the Yangtze River Headwater Region (YRHR) have declined in recent years. In particular, the causes and magnitude of declining runoff in the region remain unclear. Therefore, this study choose a permafrost watershed as the objectives, which located in the YRHR, in the hinterland of the Tibetan plateau. This study base on water cycle observation system, containing soil water and heat, groundwater, and surface runoff field. Firstly, field contract method will be used to clarify the relationships between freeze-thaw processe, the soil profile distribution of soil water, and rainfall infiltration process were analyzed. The influence of freeze-thaw processes on the characteristics of m groundwater igration will be analyzed. Secondly, the study applied water stable isotope techniques (δD vs δ18O) to infer sources and mixing of active layer soil waters, the contribution of precipitation, seasonal and permafrost ice to soil water and surface runoff will be studied, the rainfall infiltration dynamatics, and determine the supply source of soil moisture in the active layer at different periods. The seasonal difference of runoff composition and its response to freeze-thaw processes and active layer fluctuation change will be analyzed. The hydrological response to future climate and permafrost changes will be preliminary forecasted. In a word, on the basis of field contract method and stable isotope, the effect of freeze-thaw cycle processes and active layer fluctuation on runoff generation mechnism will be studied. These will enrich and develop the theory system of frozen soil hydrology and eco-hydrology. Moreover, these are important for understanding alpine region water cycle and water resource evolution under climate change, regional environmental protection, and water management decisions.

亚洲主要江河的水资源安全与青藏高原的河流径流补给密切相关，其中土壤冻融是该区域径流形成的关键环节，认识和揭示土壤冻融对径流形成的影响机理具有重要的科学意义。本研究立足于对气候变化敏感的长江源区多年冻土区，基于前期建立和补充的土壤水热、地下水和径流观测系统，以系统的野外对比观测试验为手段，研究活动层土壤冻融循环对土壤水分剖面分布和地下水迁移规律的影响，分析冻融锋面迁移对降雨入渗过程的影响，初步探索冻土-径流形成作用机制。结合氢氧稳定同位素技术，分析降水、河水、土壤水的稳定同位素特征，描述活动层土壤水中稳定同位素组成随深度变化特征，推断活动层表层水体和地下孔隙水的混合过程，确定不同时期活动层土壤水分的补给来源，识别降雨入渗规律，分析冻融过程对径流形成的影响。本研究将为认识气候变化下的寒区流域水循环过程和水资源演变过程提供理论基础，为区域水资源安全提供技术支撑。

亚洲主要江河的水资源安全与青藏高原的河流径流补给密切相关，其中土壤冻融是该区域径流形成的关键环节，认识和揭示土壤冻融对径流形成的影响机理具有重要的科学意义。本研究立足于长江源区多年冻土区，基于前期建立和补充的土壤水热、地下水和径流观测系统，以系统的野外对比观测试验为手段，研究活动层土壤冻融循环对坡面土壤水分剖面分布的影响，分析冻融锋面迁移和植被退化对降雨入渗过程的影响，探索冻土径流形成作用机制。结合氢氧稳定同位素技术，分析降水、河水、土壤水的稳定同位素特征，描述活动层土壤水中稳定同位素组成随深度变化特征，确定不同时期活动层土壤水分的补给来源。. 结果表明：（1）从坡顶到坡脚，地表覆被从裸地演替至高寒草甸、沼泽草甸，开始冻结时间和融化时间不断推迟。随着土壤有机质含量增加，坡面土壤水分呈增加趋势。这与坡脚植物根系发达，从而导致土壤较高的有机质含量、更多的细颗粒含量有关。（2）土壤水分垂向变化明显，活动层都存在一个土壤干层和活动层底部高含水层。植被退化后，土壤干层向下迁移且呈现加厚趋势，表明地表良好的植被状况是活动层底部土壤水分富集的关键。（3）土壤水、河水、地下水同位素点分布于局地大气降水线两侧(LMWL)，表明降水为上述水体的主要来源，并且在转换过程中经历了一定程度的蒸发。（4）各坡面壤中流对河流的补给机制表现出一定的差异性，高寒草甸以深层壤中流和地下水为河水的主要补给，沼泽草甸以浅层壤中流和深层壤中流为主要补给。（5）沼泽草甸根系主要用水为0~10cm土壤水，而高寒草甸植物根系最大摄水深度可达60cm。初步判断风火山流域的坡面径流形式机制与山前倾斜平原类似，冻融锋面和沼泽草甸泥炭层承担着弱透水层的角色，可能呈现为坡面中上部呈现为下渗-壤中流/地下径流，坡面中下部呈现壤中流/地下径流-蓄满产流特征。本研究将为认识气候变化下的寒区流域水循环过程和水资源演变过程提供理论基础，为区域水资源安全提供技术支撑。