耕作破碎母岩作用下坡面水文过程的变化机制

The bedrocks have been crushed by manual hoeing in practice for a long period of time, for the purpose of weathering into soil to combat soil erosion in hilly areas of purple soils. Yet, previous studies on hillslope hydrological processes have not dealt with effects of soil-rock fragment mixture formed by the action of bedrock crushing, but only confined to the soil itself. This study will examine the flux and translocation rate of rock fragments using the dyed rock fragment tracing technique; and determine the vertical and downslope distribution pattern of rock fragments using the gravely-magnetic tracer technique and the profile and slope position analysis combined. The porosity of the rock fragment layer will be measured by the 3D laser scanning technique. By establishing the runoff plot and using the simulated raining method, we will examine effects of the rock-soil interface induced by bedrock fracturing due to hoeing on hillslope hydrological features, such as infiltration, inflow, overland flow; and will explore changes in hydrological processes of the soil-rock fragment mixture of different rock contents and rock fragment size compositions, and elucidate effects of rock fragment redistribution in soil induced by tillage on hydrological processes. Given the feature of strong weathering of rock fragments, we will study the effects of rock contents and rock fragment size compositions at different stages of weathering over time, by means of a simulation of soil-rock fragment mixture with different rock fragment sizes and contents. At last, we will comprehensively study hydrological effects of rock crushing areas on non-rock fracturing areas, and elucidate the mechanism of effects of rock crushing by hoeing on hillslope hydrological processes as a whole. The novelty of this study lies in directly linking rock crushing by hoeing to hillslope hydrological processes. This program will exhibit an important theoretical and practical significance to a comprehensive understanding of effects of tillage activity on hillslope hydrology and soil erosion, and an appropriate application of tillage practices in watershed management.

过去对紫色土丘陵区坡面水文过程的研究并未考虑耕作破碎母岩而产生的影响，而仅仅局限于土壤本身。本研究拟分别利用多种示踪法测定耕作产生的母岩碎屑通量、位移速率及岩屑在土壤中再分布速率，结合剖面与坡位解析确定耕作侵蚀过程中岩屑在坡面的垂直与沿坡分布格局；并利用3D激光扫描测定母岩碎屑层孔隙度变化。利用人工模拟降雨方法研究耕作破碎母岩产生的不同岩—土界面、混合体的不同粒径岩屑组成及耕作产生的岩屑再分布对坡面水文过程的影响；模拟不同粒径岩屑及含量的土体，研究风化导致的岩屑含量及岩屑等效粒径减小的不同阶段坡面水文过程的变化；通过研究坡面岩石破碎区（上坡）对非岩石破碎区（下坡）的水文特征的作用，整体上揭示耕作破碎母岩对坡面水文过程的影响机制。本项目创新在于将耕作破碎母岩与坡面水文过程进行直接联系。该研究对于全面认识耕作活动与紫色土坡面水文、土壤侵蚀的关系及耕作措施的合理运用等具有重要理论和实践意义。

紫色土土层浅薄，耕作破碎母岩是常用的提高土壤生产力措施，其伴随的耕作传输过程会引起岩屑在土壤剖面和坡面中的再分布，进而对坡面水文过程产生影响。本项目通过田间模拟耕作，染色示踪，模拟降雨等实验方法研究了紫色土耕作破碎母岩产生的岩屑垂直与顺坡变化对坡面水文过程的影响机制。耕作破碎母岩深度是影响岩屑构型的重要因素，在耕作层底部形成岩屑>80%，其厚度和大粒径岩屑含量均随母岩耕作深度的增大而增大。当破碎母岩耕作深度由0 cm增大至6 cm，耕作层的饱和导水率值分别由5.0 m d−1增大至30.5 m d−1和8.8 m d−1增大至44.4 m d−1。随着破碎母岩深度增加，耕作层的饱和导水率显著增大，岩屑层的饱和导水率最高。对于近地表浅层母岩，耕作破碎母岩能促进裂隙优先流的发育，在一定程度上增强其饱和导水率，但是没有表现出随耕作破碎母岩深度增大而明显的变化趋势。室内模拟降雨实验结果指出，岩屑层的存在导致壤中流产流量增大了30–110%，而深层入渗的产流量减少了4–48%，地表径流的产流量变化不明显。耕作破碎母岩深度大对降水转化为壤中流的促进作用则强。降雨强度和坡度对降水在各种水流之间的转化和分配特征的影响受到岩屑层的控制。当岩屑层具有较大的厚度和较高的大粒径岩屑含量时，随着降雨强度（或坡度）的增大，壤中流产流量的增量较大，而深层入渗产流量的增量较小。顺坡岩屑含量变异减小会削弱地表径流，但增强壤中流和深层入渗流。同时，顺坡岩屑含量变异减小能减缓地表径流流速。当顺坡岩屑含量变异为20%、40%、60%时，影响壤中流和深层入渗的临界降雨强度为60 mm h−1；当顺坡岩屑含量变异为0%时，则为90 mm h−1。同时，当顺坡岩屑含量变异较小时，随着坡度在15°临界坡度范围内增大，壤中流和深层入渗产流强度的增量均较大。本研究对于认识耕作活动与坡面土壤水文的关系，探索水土保持措施的适宜性提供了重要参考。