西南岩溶山区坡地水文过程及其影响机制

Hydrological processes are special and have high spatial variability in karst regions with soil-rock dual structures. Due to the lack of the effects of the heterogeneity of soil distribution and epikarst structure on the processes of rainfall infiltration and runoff generation, the hydrological processes and their influencing mechanisms on karst hillslopes are unclear, which heavily restrict the effectiveness of vegetation restoration and the improvement of water conservation function. From the point of view of atmosphere-vegetation-soil-bedrock system, this project focuses on clarifying the interaction of hydrological processes in soil and epikarst. Based on field in situ observation with stable isotope tracer and dye tracing techniques as well as ground-penetrating radar techniques, the effects of spatial variability of soil depths, soil physical properties and epikarst structure on infiltration-runoff processes will be analyzed, and the mutual transformation relationships among rainwater, soil water, surface water and groundwater will be investigated on karst hillslopes. After the achieved results, we try to understand the laws of water infiltration into soil and epikarst and their water holding and transport capacities at different slope positions, to discuss the hydrological adjusting function of epikarst and its influencing factors, and to investigate the rainfall-runoff characteristics on different interfaces of karst hillslopes. Fuerthermore, a hydrological modle will be set up to simulate the processes of rainfall infiltration and runoff generation, and the influencing mechanisms of hydrological processes on karst hillslopes will be revealed finally. The results of this project can not only promote the development of hillslope hydrology with dual structures, but also provide scientific basis for vegetation restoration in karst mountainous regions of southwest China.

岩溶山区具有地表地下二元结构，其水文过程独特且空间异质性高。由于土体非均匀性和表层岩溶带结构多变性对入渗产流影响的了解不清，岩溶坡地水文过程及其影响机制不明，严重制约了该区植被恢复重建和水源涵养功能提升的成效。本项目拟从大气-植被-土壤-岩石系统出发，以土壤和表层岩溶带水文过程的相互作用为核心，通过野外定位监测，应用稳定同位素示踪技术、染色示踪技术和地质雷达探测技术，分析土层厚度、土壤物理性质和表层岩溶带结构的空间变化对入渗产流的影响，研究大气降水、土壤水、地表水、地下水的相互转化关系，弄清不同地貌部位土壤和表层岩溶带水分入渗规律及水分蓄持与传导能力；探讨表层岩溶带水文调节功能及其影响因素；阐明坡地不同界面降雨产流特征；建立坡地降雨入渗产流模型，揭示二元结构岩溶坡地水文过程的影响机制。本项目的研究成果不仅可以促进二元结构坡地水文学的发展，而且可以为西南岩溶山区植被恢复重建提供科学依据。

岩溶山区水文过程独特、复杂，具有很强的空间异质性。已有研究大多侧重地表水文过程或地下水补给机制，对二元结构岩溶坡地降雨入渗产流特征及其影响机制缺乏深入了解，严重影响了该区植被恢复重建和水资源综合调控措施的成效评估。本项目针对典型岩溶小流域，在调查小流域地形地貌、土壤-岩石空间分布、植被分布格局和表层岩溶带结构的基础上，综合应用原位模拟降雨、稳定同位素示踪、染色示踪、探地雷达等技术，探明了岩溶坡地土壤-表层岩溶带三维结构特征及其水力学特性，揭示了坡地降雨产流机制；明确了峰丛洼地小流域主要水文路径及其主控因素，探讨了土壤和表层岩溶带水文调蓄功能；提出了二元结构岩溶坡地降雨入渗产流概念模型，并以此模型为参考，分析了小流域尺度水文过程和土壤侵蚀特征。研究主要结论如下：（1）土壤性质和基岩风化程度沿坡分异明显；土-岩界面地形起伏剧烈，土壤-表层岩溶带系统呈现极为复杂的三维复合构造；不同地貌部位土壤-表层岩溶带水分入渗率高，但坡脚和洼地土层较厚，对水文过程有较大的阻滞和平缓作用。（2）坡面地表产流在较高降雨强度下才发生，符合超渗（降雨强度大于土-石界面稳定入渗率）-蓄满（降雨量大于土壤-表层岩溶带水分亏缺量）产流机制；壤中流产流符合“充满-溢出”理论，具有优先流特征，且作为主要产流过程表现出极强的空间变异。（3）表层岩溶带具有较高的水分蓄持能力和对快速水文过程的延缓功能，其变幅主要受控于表层岩溶带结构和前期含水量；即使表层岩溶带管道系统发育程度不高，但连通性较好，仍是重要的排水介质。（4）二元水文结构发育的岩溶坡地，地表产流少，地表水下渗比例高且速度快，运用传统径流冲刷模型估算坡面地表土壤侵蚀速率必须做参数修正或校正。研究结果不仅加深了对二元结构岩溶坡地水文-侵蚀过程的认识，能为类似地区的相关研究提供有力借鉴，而且可为西南岩溶山区植被恢复重建的生态水文效应评估提供坚实的理论依据。