喀斯特坡地土—岩结构对降雨入渗产流特征的影响机制

Due to the special geological background and strong karstification processes, karst regions exhibit dual structures. Because of the uneven horizontal distribution of surface soil and outcrops and the different vertical combination of soil-bedrock, hydrological processes in karst regions are complicated and changeable. However, present studies mainly focus on surface hydrological processes, and the understanding of underground processes and their dominating factors are still unclear. Therefore, it is hard to detect the influence of soil-bedrock structure on water infiltration and runoff processes in different slope positions, and also restricts the understanding of the influencing mechanisms of the hydrological processes on karst dual-structured hillslopes. In this project, we take soil-bedrock system as the study object. Based on field investigation by marking pin and ground penetrating radar, the spatial variability of soil-bedrock structure could be clarified. Moreover, water infiltration features of soil profile and epikarst will be illuminated. Stable isotopic tracer technology will be employed to study the relationships between rainwater, soil water and shallow groundwater. Based on these results, we try to understand the runoff generation features under different interfaces, and to reveal the control mechanism of soil-bedrock structure on hydrological processes on karst hillslopes. The results of this project can not only promote the development of karst hillslope ecohydrology, but also provide scientific basis for vegetation restoration and the improvement of water conservation functions in karst regions in southwest China.

由于特殊的地质背景和强烈的岩溶作用，西南喀斯特地区具有地表地下二元空间结构。由于水平方向地表土壤和出露岩石的非均匀性、垂直方向土壤－岩石结构特征的差异性，喀斯特地区水文过程具有复杂多变性。但目前针对喀斯特地区水文过程的研究，大多侧重地表过程，对地下水文过程的空间变异性及其控制因素还缺乏深入了解，无法阐明不同地貌部位土－岩结构对降雨入渗产流过程的影响，难以揭示二元结构喀斯特坡地水文过程的影响机制。本项目拟以土壤－岩石系统为研究对象，结合测钎和探地雷达，调查分析土－岩结构的空间分布特征，弄清不同地貌部位土壤剖面及表层岩溶带的水分入渗特征；应用氢氧稳定同位素示踪技术，研究大气降水、土壤水、浅层地下水的相互关系，探讨坡地不同界面降雨产流特征，揭示土－岩结构对喀斯特坡地水文过程的影响机制。本项目的研究结果不仅可以促进喀斯特坡地生态水文学的发展，而且可以为西南喀斯特地区植被恢复重建提供科学依据。

西南喀斯特地区具有地表地下二元三维空间结构，其水文过程十分复杂且与其他类型区显著不同。但是，现有研究主要侧重地表过程，对地下水文过程尤其是土－岩结构对其的影响机制尚不明确。本项目选定不同植被类型样方，采用小网格方式调查分析土壤—岩石结构及出露基岩对土壤理化性质的影响；采用单环入渗，分析不同岩土构型剖面土壤水分入渗特征。基于野外长期定位观测，结合氢氧稳定同位素技术，探讨土壤水分动态变化特征及水分运移机制。结果表明，出露基岩对岩周土壤物理性质影响明显，越靠近出露基岩，土壤饱和导水率越高，而容重越小；雨季土壤含水量越靠近出露基岩越高，而旱季正好相反。不同土壤剖面的持水、导水性能主要受其不同层次土壤颗粒组成特征及剖面构型的影响。浅层土壤含水率大多数时间处于凋萎系数附近，指示着依赖浅层水分的植物极易受到水分胁迫的影响。在喀斯特土壤低持水能力和亚热带地区高蒸发蒸腾的综合影响下，降雨对土壤的影响时间大多只能持续两周到三周，最多一般不超过五周。研究区坡地土壤水分运移速度约为1.7~12.5mm/d，土壤含水量对降雨响应明显，且一周后回复至雨前水平。本项目研究结果加深了对喀斯特坡地水文过程的理解，可为喀斯特地区植被的恢复重建提供理论依据。