基于稀土元素示踪的植物篱对三峡库区坡耕地侵蚀-沉积分布的影响机制

The hedgerow is one of vital soil and water conservation technology used on sloping farmland in the Three Gorges Reservoir Area (TGRA), which influences the process of detachment, transportation and deposition by retaining the sediment and changing the continuity of runoff. However, the research on the impact of hedgerow on the distribution of soil erosion and deposition and the related mechanism remain largely unexplored. An indoor physical model of purple sloping farmland in the TGRA will be constructed and three kinds of slope conditions including control slope, hedgerow and only hedgerow root will be designed. Six kinds of rare earth element will be applied to distinguish the in this project. The effects of hedgerows on the erosion process of sloping farmland will be clarified by comparing the results of sediment yield process, hydrologic process, sediment particle size distribution and hydrodynamic parameter between the control slope and hedgerow slope. The impact of hedgerow on the distribution of soil erosion and deposition will also be illuminated after analyzing the difference in spatial distribution of soil erosion and deposition between the control slope and hedgerow slope by using rare earth element tracing method. The relation of the distribution of soil erosion and deposition with hydrologic process, size selectivity of sediment and hydrodynamic parameter will be established and the effect of aboveground and belowground part of the hedgerow will be evaluated to systematically elucidate the influence mechanism of hedgerow on the distribution of soil erosion and deposition. The study will strengthen the understanding of mechanism of hedgerow for erosion resistance and provide a scientific basis for the sustainable use of the water and soil resources and the ecological construction in the TGRA.

植物篱是三峡库区坡耕地的重要水土保持措施之一，能够发挥物理挡沙和改变坡面径流连续性作用，影响坡面泥沙剥离-搬运-沉积过程。目前关于植物篱对坡耕地侵蚀-沉积分布影响及其影响机制的研究较为薄弱。本项目以三峡库区紫色土坡耕地为研究对象，建造室内实体模型，设置裸坡对照、植物篱和仅有植物篱根系3种坡面条件，使用6种稀土元素分段布设坡面。分析不同坡面条件下产沙过程、水文过程、侵蚀泥沙粒径分布和水动力学参数结果，阐明植物篱对坡耕地侵蚀过程的影响；基于稀土元素数据判别坡面侵蚀-沉积空间分布，对比不同坡面条件结果探明植物篱对坡耕地侵蚀-沉积分布的影响；分析水文过程、泥沙分选、水动力学参数与坡面侵蚀-沉积分布之间的关系，确定植物篱地上和地下部分对坡面侵蚀-沉积分布的影响，系统揭示植物篱对坡耕地侵蚀-沉积的影响机制。以期深入理解植物篱侵蚀阻控机理，为三峡库区水土资源的持续利用与生态环境建设提供科学依据。

植物篱是三峡库区坡地的重要水土保持措施之一，影响着坡地侵蚀-沉积过程。选用香根草植物篱，使用稀土元素示踪方法，采用模拟降雨试验，设置3个降雨强度（60、90和120 mm/h）、2个坡度（15º和25º）和3种坡面条件（裸坡对照CK、植物篱P和仅有植物篱根系R），针对香根草植物篱对三峡库区坡耕地侵蚀-沉积分布的影响机制开展了系统研究。得到以下结论：（1）阐明了植物篱对坡地侵蚀的影响，明确了植物篱地上地下部分对减流减沙贡献。植物篱可以有效地延缓坡面产流时间、减少径流率和侵蚀率；植物篱地上部分和地下部分对减流效益的平均贡献率为66.01%和33.99%，对减沙效益的平均贡献率为60.09%和39.91%。（2）弄清了植物篱对坡地侵蚀分布的影响。与CK坡面条件相比，R和P坡面条件下坡面下部侵蚀贡献率减少，坡面上部侵蚀贡献率增加，植物篱造成坡面侵蚀位置往坡上方移动。（3）厘清了植物篱对坡地沉积分布的影响。侵蚀泥沙主要沉积于坡面下部，坡面沉积量基本上呈现CK<R<P；坡面各示踪坡段沉积量均呈现Sm > Ce > La > Yb > Eu，不同示踪段对总沉积量贡献受到植物篱影响存在显著差异。（4）揭示了植物篱对坡面侵蚀-沉积影响机制。从水文过程、泥沙分选以及植物篱地上部分和地下部分作用的角度系统揭示了植物篱对坡地侵蚀-沉积分布的影响机理。研究结果可为优化植物篱设计以及三峡库区水土资源的持续利用与生态环境建设提供科学依据。