西南喀斯特地区坡面壤中流过程及其驱动机制

Karst region of southwestern China is characterized by its thin soil cover as well as dual structure of hydrological processes, consequently almost all rainfall water infiltrates into the soil as subsurface flow and deep percolation. Although subsurface flow has been recognized as an important component of infiltration water, its generation conditions and driving mechanism have been unclear up to now, which will consequentially prevent a full understanding of the hydrological cycle of the Karst region and hinder the rational utilization of the inherent limited water resources in this region. To solve the above problem, three types of hillslopes with typical land uses (including bushland, grassland, sloping land) are to be selected as our study objects in this project to achieve a deeper understanding of the subsurface flow generation and development machanism in this area. After vegetation and soil profiles investigation, soil hydrological components including subsurface flow of in situ experimental plots (2m × 1m) will be observed in the upper, middle, and lower slope positions under both simulated and natural rainfall events. During the experiments, the comprehensive methods combining the traditional hydrological monitoring methods with the techniques of stable oxygen and hydrogen isotope tracer as well as the ground-penetrating radar are to be adopted to investigate and evaluate the subsurface flow. Based on the above experiments, we attempt to clarify how plant-soil-rock coupled architecture and deep percolation influence on the subsurface flow processes of Karst region of southwestern China, and to investigate how subsurface flow response to environmental factors, such as vegetation coverage, rainfall intensity, rainfall amount, rainfall duration, and initial soil water content, etc. After achieving this project, we intend to reveal the generation and development characteristics of subsurface flow and its main driving machanism on hillslopes in Karst region of southwestern China. The results will provide scientific basis for the rational land use planning and rocky desertification control in karst region of southwestern China.

西南喀斯特地区地表地下二元结构发育，降水几乎全部下渗，壤中流作为下渗水的一个重要去向，其发生条件和主要驱动机制尚不清楚，这阻碍了对喀斯特地区水文循环的深入认识，限制了有限水资源的合理利用。项目以喀斯特地区灌木丛、草地、坡耕地等3种典型土地利用方式坡面作为研究对象，运用传统水文监测的方法，结合模拟降雨试验，通过监测不同坡位（上、中、下）土壤水文过程，研究植物-土壤-岩石耦合构造、外部环境因子、深层渗漏等对壤中流过程的影响，明确壤中流的主要影响因素和发生条件；同时，在试验过程中结合探地雷达和稳定性氢氧同位素示踪的方法，探讨壤中流运移路径和新旧水组成，深化对壤中流产流机制的认识。通过以上研究阐明西南喀斯特地区坡面壤中流过程及其驱动机制，为该地区土地利用合理布局和石漠化综合治理提供科学依据。

喀斯特地区水循环方式独特，水流以垂向运动为主，水文过程与降雨、土壤、植被、岩性、表层岩溶带结构等密切相关。然而，从三维立体的视角，将喀斯特关键带作为一个整体进行水文过程的研究还明显不足。针对喀斯特坡面地表径流少、水分去向不明的问题，通过开挖深入基岩的断面（深4m），采用模拟降雨的方法，研究了喀斯特坡面植被-土壤-表层岩溶带体系中多界面水文过程及其影响因素，同时结合水量平衡方程，初步探讨了壤中流发生机制和表层岩溶带水文调蓄功能，并提出喀斯特地上地下三维多界面产流概念模型。研究的主要结论如下：（1）在差异化岩溶作用下，喀斯特表层岩溶带地形起伏剧烈，土壤-表层岩溶带系统表现出极其复杂的三维耦合构造。（2）地表径流仅在高雨强条件下出现且产流量少（2%-15%），起始产流时间与壤中流基本一致，表现为蓄满产流机制。（3）壤中流为主要产流过程（15%-45%），具有极强的空间变异，其产流后快速上升，降雨停止后快速下降，表现为优先流的特点；壤中流起始产流降雨量主要受到前期水分状况的影响，受降雨强度的影响小，表现出蓄满产流的特征。（4）表层岩溶带在降雨水分的调蓄过程中表现出主导性作用（33%-63%）；其水文调蓄功能具有极大的变化幅度（68mm-273mm），且主要受控于前期含水量，而受到降雨强度的影响较小。以上研究为构建喀斯特近地表水文过程模型提供了理论参考，同时能为该区有限水资源的合理配置以及植被恢复提供现实指导。同时，在项目执行过程中，创造发明了在喀斯特地区开展原位水土过程模拟监测的“可升降便携式模拟降雨器”、“微型土壤水文监测系统”、“检测坡面产流位置的装置”等设备方法，解决了传统方法在类似喀斯特等异质性强的地区开展入渗、侵蚀研究的技术难题。