祁连山高山灌丛区粗骨性土层水分运移及其储水动态研究

In shrub distributed area of the arid alpine mountain, influenced by local climatic and topographic conditions, there exists a thin surface soil and under which lays a weathered or semi-weathered soil mainly composed of coarse rock fragment with different thicknesses named coarse-fragment soil layer. The alpine shrub area distributed with coarse-fragment soil is the main runoff area in Qilian Mountains and this runoff plays an important role in supplying and regulating water resources in arid areas. However, former studies about soil hydrology in the shrub area of Qilian Mountains focused more on the upper homogeneous soil layer compared with the lower coarse-fragment layer. As a result, the knowledge of soil water transport and water storage capacity is limited. Up to now, the regulatory mechanism that the coarse-fragment soil layer is to runoff in mountain region is still unknown, which lead to great uncertainty of quantitative simulation of basin hydrological processes. Thus, the coarse-fragment soil layer in the alpine shrub area of Qilian Mountains was taken as the research object. We use integrated methods including field transects investigation, sampling analysis, located observation and CT scanning to (1) identify the characteristics of coarse-fragment soil layer and its water transport, (2) quantify the spatio-temporal variation of water storage in coarse-fragment soil layer, (3) to reveal the regulation mechanism of coarse-fragment soil layer on slope runoff in alpine shrub area. This study would provide scientific basis for quantifying soil hydrological cycle of alpine shrub area in arid area.

在干旱区高寒山地灌丛分布地段，受气候和地形条件影响，不仅表土层薄，而且表土层下即为不同厚度的粗骨性碎屑组成的风化或半风化土壤层，将其称为粗骨性土层。粗骨性土层对应的高山灌丛区是祁连山区的主要产流地段，对干旱区水资源起到了重要的补给和调节功能。然而，以往针对祁连山灌丛区土壤水文的研究中，多侧重于上部均质土壤层，对下部粗骨性土层考虑不够，导致对祁连山高山灌丛区土壤的水分传输过程和储水能力认识有限，尚不清楚粗骨性土层对山地径流的调控机制，导致对流域水文过程的定量模拟存在很大的不确定性。本项目以祁连山高山灌丛区粗骨性土层为研究对象，利用野外样带调查、钻孔和径流场定位观测、室内测试分析和CT扫描等手段，识别高山灌丛区粗骨性土层特征及其水分运移规律，量化高山灌丛区粗骨性土层储水量时空变化，揭示高山灌丛区粗骨性土层储水量对坡面径流的调控机制，为准确量化干旱区高山灌丛土壤水文循环过程提供科学依据。

探究祁连山高山灌丛区粗骨性土层水分运移规律及其储水量对坡面径流的调控机制，对于准确量化干旱区山地高山灌丛区土壤水文循环过程具有重要的科学意义。本项目以祁连山高山灌丛区风化碎石广泛分布的粗骨性土层为研究对象，借助野外调查、长期定位监测和模型模拟等方法，开展了高山灌丛区粗骨性土层结构特征识别、水分传输过程的直接观测、储水动态评估量化和坡面径流产流机制研究。.主要结论：（1）基于粗骨性土层剖面野外调查和深钻技术，构建了高山灌丛区粗骨性土层的三维空间结构；（2）通过对降雨事件、季节性冻融循环、钻孔水位和粗骨性土层水分传输的连续监测，揭示了高山灌丛区粗骨性土层水分的垂直分布特征，阐明了高山灌丛区粗骨性土层的水分运移规律及其影响因素，确定了植被、地形和土壤质地深刻地影响山地灌丛系统土壤水文过程，其中土壤属性和含水量是该区冻融点控制的关键因素；（3）借助野外调查和定点观测，估算了粗骨性土层储水量的空间分布，解析了高山灌丛区粗骨性土层储水量的时空差异性，阐明了高山灌丛区粗骨性土层储水量变化的影响机制，发现前期土壤储水量和降水阈值不仅表明一个存储阈值，而且表明一个水源面积阈值，如果超过该阈值，则随着集水区贡献面积的增大，上坡-下坡-河流连通性增加；（4）在流域尺度上，分析了粗骨性土层水分运移、储水量和坡面径流过程的关系，探讨了粗骨性土层的产流形式和产流阈值，初步阐明了干旱区山地坡面地表径流以超渗-蓄满产流相互作用为主，降雨强度超过阈值或土-石界面的稳渗率，导致表土层-粗骨性土层蓄满产生地表径流；壤中流则表现为填充-溢出过程，表土层-粗骨性土层蓄满导致坡上、坡下的饱和区域联通，土壤层-粗骨性土层界面壤中流产流。.项目已积累了大量的粗骨性土层调查和水文过程监测数据，并在临泽站网站共享。已发表学术论文6篇，以第一作者发表SCI论文2篇，圆满完成了项目预期设定的目标。