侵蚀泥沙分选对土壤团聚体胶结特征的响应

Soil erosion by water involves two main processes: (1) detachment of soil material from the soil mass by raindrop impact and/or runoff shear, and (2) transport of the resulting sediment by raindrop splash and/or flowing runoff water. The transport of sediment includes a process of sediment sorting, due to different size and density of soil particles and varied entrainment capacity of overland flow. Fine soil particles are preferentially transported while coarse soil particles are prone to deposition. Accordingly, sediment sorting can provide basic information regarding erosion processes. Improved knowledge of sediment sorting has been seen as a basis for a better understanding of fluvial transport dynamics and the development of improved transport relationships. Previous research has focused on the effects of erosive forces and aggregate breakdown mechanisms on sediment sorting. Aggregate breakdown essentially depends on their binding agents. Binding agents, such as organic matters, oxides and clay, are crucial for the process of soil aggregate formation, influencing the stability of aggregates, as well as the water-soil interface. There is limited information regarding impacts of the type and content of binding agents and their binding mechanisms on sediment sorting. In this project, we selected typical soils cemented by different binding agents from Red soil zone in southern China and the Loess Plateau in northwestern China. The objectives of this project are to (1) investigate impacts of flow hydraulic characteristics and aggregate breakdown on sediment size distribution of soils cemented by various binding agents, (2) compare the difference of binding agents and their binding mechanisms between aggregates from eroded sediment and soils, and (3) identify sediment sorting associated with different aggregate binding agents during the water erosion process. The study may provide a better understanding of soil erosion by water and be a necessity for more accurate prediction of sediment movement.

坡面土壤水蚀过程中，泥沙的运动形式及其搬运和沉积状态不仅取决于坡面径流水动力学特征，还与泥沙的颗粒大小、密度等性质相关。泥沙颗粒源于侵蚀动力对土壤团聚体的破坏，不同胶结特征团聚体在侵蚀外力作用下的破碎程度及其产物存在较大差异，因而土壤团聚体胶结特征对坡面侵蚀泥沙的分选搬运过程有重要影响。鉴于此，本项目选择氧化物—有机质胶结为主的红壤和棕红壤，碳酸盐胶结为主的黑垆土和黄绵土为研究对象，研究不同胶结特征土壤的侵蚀泥沙分选规律，通过土壤与侵蚀泥沙中团聚体胶结特征的对比分析，揭示胶结特征对侵蚀过程中团聚体破碎产物的影响，阐明土壤团聚体胶结特征对侵蚀泥沙分选的作用机制，结果有助于进一步理解坡面侵蚀—搬运—沉积过程。

坡面土壤水蚀过程中，泥沙的运动形式及其搬运和沉积状态不仅取决于坡面径流水动力学特征，还与泥沙的颗粒大小、密度等性质相关。泥沙颗粒源于侵蚀动力对土壤团聚体的破坏，不同胶结特征团聚体在侵蚀外力作用下的破碎程度及其产物存在较大差异，因而土壤团聚体胶结特征对坡面侵蚀泥沙的分选搬运过程有重要影响。鉴于此，本项目以碳酸盐胶结为主的黄土以及有机质—氧化物胶结为主的红壤为研究对象，通过野外原位人工模拟降雨和室内人工模拟降雨监测坡面侵蚀过程，系统分析了坡面侵蚀形态演变过程中的土壤团聚体破碎特征与泥沙颗粒变化规律，明确了降雨-径流耦合作用对侵蚀过程中土壤团聚体演变的影响，对比分析了土壤与侵蚀泥沙中团聚体胶结物质组成差异，识别了影响侵蚀泥沙物质组成的关键因子，揭示了侵蚀外力与土壤团聚体胶结特征耦合作用下泥沙分选规律。研究结果有助于深入理解坡面侵蚀—搬运—沉积过程。项目实施3年，在Water Resources Research、Journal of Hydrology、Agriculture Ecosystems & Environment等期刊发表论文5篇，培养硕士2人。