坡地壤中流地下侵蚀的动力学过程及携养分流失机理对土壤孔性的响应研究

Interflow is the main component of runoff in mountainous areas. In some hilly areas with severe erosion, interflow accounts for 70-80% of runoff. The proportion of nutrient loss in the interflow is about 50-70% of the total loss, and the soluble organic carbon in the interflow reaches 3-4 times as much as that in the surface flow. The weathering granite residual slopes with strong water erosion are typical of this kind of mountain slope. For that reason, to research on hydrodynamic mechanism and modeling of tunnel erosion by interflow and carrying nutrient loss from slope is the research object, and the water dynamic parameters and nutrient loss patterns in slope soils with different erosion intensity are used as monitoring elements. In-situ rainfall monitoring and indoor artificial simulated rainfall experiments, principles of soil erosion, soil hydrodynamics and solute transport are used to study the characteristics of tunnel erosion and nutrient loss from interflow in different soils with different soil erosion intensity and different depth soil profiles. The following objectives are supposed to be achieved: (1) the tunnel erosion characteristics of interflow on slope soils, hydrodynamics and the mechanism of nutrient carrying loss. (2) the effects of surface erosion intensity on interflow formation, tunnel erosion and nutrient loss. (3) to construct two-dimensional hydrodynamic and nutrient loss models of interflow. The aim of the project is to provide reference for the intervention of sloping land water conservation and interflow regulation, and to provide the basis for human intervention of watershed agricultural non-point source pollution as well as consideration for the improvement of slope hydrology and soil hydrodynamic theory.

壤中流是山区地表径流的主要组成部分，在侵蚀严重的山丘地区，壤中流占径流的70-80%。壤中流携带的养分流失约占总流失量的50-70%，可溶性有机碳高达坡面径流的3-4倍。强烈水蚀的风化花岗岩坡地是这类山丘坡地的典型，为此，本项目以侵蚀性风化花岗岩坡地土壤为研究对象，采用原位降雨监测和室内人工模拟降雨试验方法，应用土壤侵蚀、土壤水动力学与溶质运移原理，通过监测壤中流水动力学参数及养分流失形态要素，分析不同侵蚀强度的土壤孔性、壤中流水流动态及养分（氮、磷、碳）流失特征，研究：（1）坡地壤中流地下侵蚀的水动力学过程及对侵蚀影响下的土壤孔性的响应机制；（2）坡地壤中流携养分流失对水流动态变化的响应机理；（3）构建坡地不同土壤孔隙结构与壤中流孔隙网络模型及携养分流失模型。目标的实现，能为坡地水源涵养、壤中流调节、流域农业面源污染阻断的人为干预提供依据，为坡地水文学和土壤水动力学理论的完善提供思考。

在项目执行期间，经项目组全体人员的共同努力，完成了计划研究内容和预期目标。围绕项目研究内容和目标，以发育于风化花岗岩残积母质上的坡地土壤为研究实例对象，针对不同侵蚀强度下出露土壤层的差异，紧抓砂土层和红土层出露坡地土壤的易侵蚀、易漏肥漏水的特点，通过对不同出露土壤层采用多种方法的综合获得了孔隙度的结构特点，提出了对于大孔隙及优先流通道应采用电阻层析法来获取的提法。采用改进的人工模拟降雨试验径流槽和自动控制的降雨设备，开展了变雨强、变坡度的组合人工模拟降雨试验，获得了大批的壤中流和坡面径流流量及携养分流失的实测数据，得出了在砂土层和红土层出露的坡地土壤，壤中流及携养分流失是坡面水分和养分流失的主体。考虑磷素的易矿化特性，采用了改进式的搅拌流动试验方法，进行了磷素的吸附解吸附测试，获得了不同出露土壤层的磷流失系数。由于壤中流是一个黑箱体，无法直接观察，项目应用多孔隙介质中物质运移理论原理、微分思维和模块组合建模的综合数理推导方法，构建了不同出露土壤层、不同孔隙背景下的壤中流携磷流失的理论机理模型，并应用试验数据得到了充分的验证，为解决预测壤中流水流动态、地下侵蚀和携养分流失提供了估算通用模型。实现了不同侵蚀强度背景下，土壤孔隙特性、壤中流侵蚀及携养分流失响应机制的总体分析和模型构建。研究成果：发表标注有项目资助的论文15篇，其中SCI收录论文12篇，北大核心期刊收录3篇，授权实用新型专利1项，培养博士研究生2名，硕士研究生2名。参加国内外会议5人次并作报告4人次。本项目研究成果的发表和批量试验数据的获得，为壤中流地下侵蚀和养分流失的深入研究提供了启示和数据支撑，为坡地壤中流携氮、磷、碳流失的强度估算提供了模型和计算方法，为提高坡地水源涵养能力、合理改良土壤结构、防治土壤退化和流域水体污染的控制提供了科学依据。