黄土区牧草控制侵蚀动力学机制及有效性研究

Based on filed surveys and sampling analysis, position monitoring, and laboratory simulated rainfall experiments, the mechanism on four grasslands of Bothriochloa ischaemum, Lolium perenne, Astragalus adsurgens Pall, Artemisia capillaries controlling soil erosion were studied using advanced measuring techniques and methods of mathematical physics. The grass roots improving soil anti-erodibility by the direct impact of combining the soil, and the indirect effect through improving soil physical and chemical properties would be clarified. The grass covers effects raindrop splash erosion would be studied and the relationship between grasses covers or leaves area index and rainfall splash force or energy would be analyzed. The grass stems effects on overland flow hydraulics and soil erosion dynamics would be analyzed, and the resistance equation of grasslands would be established. Based on the comparative tests of runoff plot experiments, the contribution rates of the grass roots, litter, stems and leaves to erosion control would be quantified. Further some sensitive vegetative parameters would be choosen and the grassland erosion dynamics equation including rainfall splash and flow scouring impacts could be established, which can clarify the dynamic mechanism of grasses controlling soil eorison and their effectiveness. This study can provide a theory basis for establishing soil erosion physical model considering vegetation effects, and be beneficial to ecological construction for soil and water conservation on the loess plateau of China.

以黄土高原几种常见牧草- - 黑麦草（禾本科）、白羊草（禾本科）、沙打旺（豆科）、茵陈蒿（菊科）草地为研究对象，通过野外调查取样、定位监测和室内外模拟降雨试验等手段，采用较先进的监测技术和数理分析方法，区分根系通过固结缠绕土体以及改善土壤特性增强土壤抗侵蚀性能的直接和间接贡献。研发降雨击溅力测定装置，并探讨草地冠层、枯落物对降雨击溅侵蚀的影响，构建草地坡面土壤溅蚀量模型。从圆柱绕流理论出发探讨坡面流水动力参数与阻力关系，并研究建立草地坡面流阻力表达式。结合不同类型牧草及其地上、地下各部分减沙效益分析，筛选牧草控制侵蚀的共性敏感参数，构建综合考虑地上部分控制侵蚀动力，地下根系增强土壤抗侵蚀性能的草地坡面侵蚀动力方程，并系统阐明不同类型草地控制侵蚀动力学机制及有效性，为黄土区水土保持生态环境建设和草地坡面侵蚀物理模型构建提供理论依据。

本项目以人工和自然牧草为研究对象，从牧草地上部分对降雨击溅和坡面流侵蚀动力参数的影响，以及地下根系对土壤抗侵蚀性能的作用机理出发，以草地茎杆和叶片削减降雨侵蚀力和增强坡面流阻力，以及根系改善土壤理化特性进而发挥水土保持作用为突破点，探讨草地植被控制侵蚀的作用机理。主要取得的成果有1）退耕初期的禾本科和菊科牧草由于其细根含量较大而控制侵蚀效果较好，且土壤的根系含量控制侵蚀作用显著，其贡献率在75%以上，这充分说明草地根系在一般的水流冲刷条件下（根据流量折算大约为常见1年1遇暴雨）控制侵蚀的重要性。2）植被的减水减沙效果与雨型关系密切，草地对于雨强和历时中等的降雨减水作用较强，而对黄土区出现频率较高的短历时强降雨减沙效果更为显著。3）牧草种植可有效拦截上方来沙，尤其是盖度较大的成行分布的草地。雨滴打击对陡坡草地的坡面流水动力参数影响不明显，而雨滴动能的增大明显增强了坡面泥沙的输移，降雨增强草地坡面输沙主要来自雨滴动能，而并非改变径流侵蚀动力参数，因此在以后的坡面流输沙方程研究中需要增加雨滴动能的相关指标。4）牧草种植可明显增大坡面流阻力，且在流量更大或下坡条件下增阻效果更加显著，降雨条件下草地叶片对阻力贡献占50%以上，因此在流域洪水防控中尽量减少牧草的割刈。5）控制侵蚀覆盖较好的草地显著增大坡面流阻力近100倍，并减少95%的径流剪切力。这说明草地种植一方面可通过根系改善固土减沙侵蚀产沙量，同时覆盖良好的草地显著减小了作用于侵蚀的径流作用力，径流的大部分能量均消耗于草地茎秆。以上研究结果为黄土区水土保持和生态环境建设以及推动土壤侵蚀物理模型的发展提供理论依据。