冻融过程对祁连山区土壤导水率影响的实验研究

Soil hydraulic conductivity in frozen soil is one of most important and sensitive parameters of the research on land surface process and the study of eco-hydrological processes in cold high mountainous regions, because melt water from glacier and snow and precipitation go into next water cycle through soil water redistribution. As global warming, ground temperature rise, active layer thickening and permafrost degradation change the distribution proportion of frozen and thawed soil both in time and space pattern in cold regions. The changes of soil hydraulic conductivity in frozen soil with ground temperature rise, and the difference of soil hydraulic conductivity between frozen and thawed soil, change water cycle and eco-hydrological processes, and lead to the change of ecological environment in high mountainous area. With the lacking of field measured data of soil hydraulic conductivity, the necessary basic data and key parameters of research on hydrological processes and model in high mountainous area in China, come from the high latitude permafrost regions, which are difference in soil type and climate condition with high mountainous area. Rely on the Qilian Ecology-Hydrology Experimental Research Station (location: Qilian County in Qinghai Province), CAREERI(Cold and Arid Regions Environmental and Engineering Research Institute), CAS(Chinese Academy of Science), the project plans to measure hydraulic conductivity in variety of soil type during freezing and thawing processes, with field observation and laboratory experiment, in typical clod regions in Qilian mountains. With the observational data, we try to understand the influence of soil texture, frozen soil temperature and soil solid and liquid content on hydraulic conductivity in frozen soil, and find the impedance parameter, which accounts for the blocking effect of ice on hydraulic conductivity in frozen soil, to contribute to research on water movement process, land-atmosphere-water process and water cycle, and eco-hydrological processes and relative model in Qilian mountain and whole alpine mountainous regions.

寒区冰川/积雪融水和降雨都要经过土壤再分配进入下一步水循环，冻土导水率因而成为寒区水文和生态水文过程的重要敏感参数，特别是在全球变暖大背景下，冻土温度升高引起了其自身导水率的变化，而融土与冻土导水率的差异及其时空分布格局的变化，必将影响水循环和生态水文过程，导致区域生态环境的变化。我国高海拔冻土区土壤导水率实测数据相对缺乏，导致相关过程研究和模型研究必需基础数据和关键参数多参考土壤类型和气候条件并不一致的高纬度冻土区。为此，本项目拟以中科院寒旱所祁连站为依托，野外试验和室内实验相结合，利用多种方法实测祁连山区野外实地土壤在冻融不同阶段的土壤导水率；分析土壤质地、温度和含水量对土壤导水率的影响；探索我国高寒山区冻土导水率计算所必需的关键参数，为区域土壤水运动、陆面水文过程和水循环、生态水文过程研究和相关模型模拟提供关键参数。

寒区冰川/积雪融水和降雨都要经过土壤再分配进入下一步水循环，冻土导水率因而成为寒区水文和生态水文过程的重要参数。在祁连山黑河上游葫芦沟流域，开挖多个土壤剖面，分层取样进行土壤导水率实验，获取了流域尺度的饱和导水率数据集，为葫芦沟土壤研究，水文过程及其相关过程研究和模拟提供了重要基础数据。在葫芦沟流域的高寒草原试验点附近布设7种不同尺寸的双环入渗仪，对比观测结果推荐山区使用内径20 cm，外径40 cm的入渗仪。利用4种不同方法实测高寒山区土壤导水率，结果显示单环入渗法、环刀法和Hood入渗仪实测结果均高于双环入渗法，其相对于双环入渗仪的修正系数分别为1.25、1.40和1.67。葫芦沟流域多种不同土壤质地的饱和导水率实测结果显示，高寒山区土壤中砾石的存在对土壤导水率影响较大，通过土壤粒径组成来模拟高寒山区土壤饱和导水率必须考虑砾石组成。利用野外实地实验和室内控温实验相结合，分析了温度对高寒山区土壤饱和导水率的影响，冻土的饱和导水率远小于融土，差距至少一个数量级以上。构建了冻土导水率的冰阻系数简易公式，为高寒山区冻土水热耦合及相关水文过程研究和模拟提供有效简易参数化方案。实测蒸散发和气象要素的相关回归分析显示在非冻结期，影响蒸散发的主要因素为净辐射；而在冻结期则为地表温度和气温。不同海拔和下垫面的蒸散发和水量平衡结果显示，海拔是影响山区降水和蒸散发的重要因素，无植被的高山寒漠区是高寒山区的主产流区。全球变暖情况下，植被线上移可能增加蒸散发占降水比例，减少产流系数。青藏高原和祁连山区多个流域的多年降水和径流数据显示，高寒山区流域夏季降水与冬季径流相关性呈现明显增加趋势，表明冻土退化增加土壤下渗率，使更多的降水下渗转为地下水，从而在冬季补充径流，成为冬季径流的主要水源。项目发表论文5篇，接收1篇，其中SCI收录4篇，完成了预设目标。