东南丘陵区高砾石坡面三维土壤水文过程与机制解析研究

Soil hydrological process is a key controlling factor of the biological, physical and biochemical processes in earth critical zone, as well as one main driving factor which results in serious eco-environmental issue on the southeast hilly region of China. As for the difficulties in sampling and complexities of physical mechanisms, the hydrological processes of stony soils, which are widely distributed on the southeast hilly region of China, are still needed to be thoroughly studied. This study selects a representative stony-soil hillslope on southeast hilly region of China as the study region. Based on the electrical resistivity tomography (ERT) survey, automatic monitoring system of water-soil interaction processes on the study hillslope, and the laboratory experiments, the three-dimensional spatial distributions of soil rock fragment contents on this study hillslope will be derived. Accordingly, the soil water content – soil resistivity petrophysical relationships of stony soils will be established on the hillslope and the spatial distributions of soil water content will be retrieved based on the periodically ERT survey. Therefore, coupling the observed and retrieved soil water data into the HYDRUS-3D model, to optimize the soil hydraulic parameters of stony soils, the long time serial information of three-dimensional soil water distributions and movements on the stony-soil hillslope will be derived. Thus the spatio-temporal variation characteristics and controlling factors of soil hydrological processes on the stony-soil hillslope will be revealed. This study will help to accurately identify the hot moments and spots of the soil hydrological processes and the pathways of the subsurface flow on the stony-soil hillslope, these will lay the foundation for revealing the coupling mechanisms of soil water-carbon-nitrogen on the stony-soil hillslope.

土壤水文过程是地球关键带中生物、物理和化学过程的关键控制因子，也是我国东南丘陵区面源污染物迁移的主要驱动因素之一。在东南丘陵区广泛分布的砾石性土壤，其水文过程由于监测困难、机制复杂，在研究中尚存许多不足。本项目选择东南丘陵区典型高砾石坡面为研究对象，基于ERT扫描、野外水土过程监测和室内控制实验，提取坡面土壤砾石三维空间分布，构建砾石性土壤的土壤水分-电阻率的岩土物理学关系并反演土壤水分；将观测和反演的数据耦合到HYDRUS-3D模型，优化砾石性土壤水力参数，最终获取长时间序列的高砾石坡面三维土壤水分分布和运动信息，并解析其时空变化特征和主控因素。该研究有助于准确识别高砾石坡面土壤水文过程时空变化热点及壤中流发生路径，为揭示高砾石坡面土壤水-碳-氮耦合机制打下基础。

土壤水文过程是陆面过程的核心环节之一，对地表物质输移循环、作物生长等具有重要作用。砾石（粒径> 2 mm的矿物颗粒）在丘陵山区土壤广泛分布，且其存在可影响土壤水文过程。精确解析丘陵山区砾石性土壤水文过程对太湖流域丘陵山区水土污染防控、生态环境保护等具有重要意义。基于此，研究选择从坡面尺度、流域尺度乃至全球尺度等不同尺度出发，集合ERT扫描、野外采样、背景数据搜集、相关文献整理、模型优化模拟等不同方法，首先提出了坡面土壤砾石含量三维空间分布的ERT土壤电阻率反演方法，阐明了土壤砾石含量的空间分布机制。在此基础上，揭示了砾石对土壤质地、容重、碳氮浓度、持水导水参数、土壤含水量的影响机制，以及进一步总结了砾石对土壤水文过程的影响机理。通过构建土壤电阻率与土壤含水量的关系模型，基于ERT扫描数据反演揭示了坡面三维土壤水分分布特征；引入多峰持水方程，构建了坡面砾石性土壤水力参数的精确空间表达方法，从而利用HYDRUS-3D模型实现了高砾石坡面土壤水文过程的精确模拟。在此基础上，分别从土壤水分分布和水分渗漏两方面揭示高砾石坡面土壤水文过程的时空特征及主控因子。结果表明，土壤水分分布渗漏均表现出强烈的时空变异性。其中，土壤水分分布受土层厚度、土壤质地和地形的综合影响，而土壤水分渗漏则主要受土层厚度和砾石含量控制，地形影响有限。