Detachment and transport of particles by raindrop impact and runoff determine the characteristics of soil aggregate loss, which are largely related to surface hydrologic conditions. The water ponding and sediment deposition in furrow areas within contour ridge systems complicate the effects of raindrop impact and runoff on soil aggregate loss responding to surface hydrologic conditions. The objective of this study was to determine the effect of raindrop impact and runoff to macro-aggregate and micro-aggregate losses under surface hydrologic conditions within contour ridge systems. The losses of 16 size aggregates were measured under three surface hydrologic conditions (free drainage, soil saturation, and seepage) and two soil surface conditions (with and without raindrop impact) through simulated rainfalls. Results showed that raindrop impact was the dominant factor controlling soil aggregate loss under free drainage condition, while soil aggregate loss was mostly affected by runoff under soil saturation and seepage conditions. Under free drainage condition, raindrop impact accounted for 44.6 %–100 % of the loss of each size aggregate, with maximum losses from 0.5 to 1 mm and 20–50 μm aggregates. Raindrop impact mainly caused the breakdown of >0.5 mm and 50–250 μm aggregates, and enhanced the transport of 20–50 μm aggregates by saltation. Under soil saturation and seepage conditions, runoff contributed 25.5 %–247.6 % to the loss of each size aggregate, and most dramatically to the losses of 2–5 mm and 10–50 μm aggregates. The role of runoff was mainly characterized by the breakdown of 0.25–1 mm and 50–250 μm aggregates, exhibiting a propensity toward transporting 2–5 mm aggregates by rolling, following 10–50 μm aggregates by suspension/saltation. This study highlights the need to understand the effects of raindrop impact and runoff on erosion processes associated with surface hydrologic conditions for better erosion modeling, and provides guidance for soil erosion control within contour ridge systems.

雨滴撞击和径流引起的颗粒的分离和迁移决定了土壤团聚体损失的特征，这主要与地表水文条件有关。等高线脊系统内沟区域的积水和沉积物沉积使雨滴撞击和径流对响应于地表水文条件的土壤聚集体损失的影响变得复杂。这项研究的目的是确定在轮廓脊系统内地表水文条件下，雨滴的影响和径流对宏观集料和微观集料损失的影响。通过模拟降雨，在三种地表水文条件（自由排水，土壤饱和度和渗水）和两种土面条件（有无雨滴影响）下测量了16种骨料的损失。结果表明，雨滴影响是控制自由排水条件下土壤团聚体损失的主要因素，而土壤团聚体损失主要受土壤饱和度和渗流条件下的径流影响。在自由排水条件下，雨滴影响占每种尺寸骨料损失的44.6％–100％，最大损失为0.5-1 mm和20-50μm骨料。雨滴的撞击主要导致> 0.5 mm的聚集体和50–250μm的聚集体破裂，并通过盐化增强20–50μm聚集体的运输。在土壤饱和度和渗流条件下，径流对每种尺寸骨料的损失贡献了25.5％–247.6％，对2-5 mm和10-50μm骨料损失的贡献最大。径流的作用主要表现为0.25–1 mm和50–250μm聚集体的分解，表现出倾向于通过滚动运输2–5 mm骨料的趋势，其次是通过悬浮/盐化10–50μm骨料。这项研究强调需要了解雨滴的影响和径流对与地表水文条件有关的侵蚀过程的影响，以便更好地进行侵蚀建模，并为轮廓contour系统内的土壤侵蚀控制提供指导。