鄂东南红壤区不同母质组合对坡面土壤侵蚀的影响

The red soil area in the Southeastern Hubei Province is one of the most delicate areas suffering from serious soil erosion in China. Due to complex geological background, the soil parent materials vary for different parts of the same hillslope. The combination patterns of the parent materials on the hillslope has a significant impact on the soil erosion-deposition process, but the degree and mechanism of this impact is not clear. Thus, the red soil hill-slope with different combination patterns of parental materials in the southeastern Hubei Province was taken as the study area. Through sampling, in situ observations and laboratory experiments of slope erosion for different combinations of parent material, the physical and hydraulic properties and erosion processes were recorded in detail to reveal the response of soil erosion-deposition processes for different combinations of parent materials of red soil on the hillslope. The main contents of the study include: (1) study the difference in physical properties and hydraulic parameters of red soils between different parent materials under similar landform and vegetation conditions; (2) study the upper-slope red soil’s effects on the hydraulic properties of the middle and lower slope with different parent material during the erosion process; (3) study the law of parent material type and the erosion and sediment yield on the slope through the source-sink relationship between the deposition on the bottom of slope and the slope material. This project is of great theoretical significance to the adjustment of parameters in soil erosion model and can provide scientific basis for soil and water conservation and ecological construction in red soil region of Southern China.

鄂东南红壤区是我国土壤侵蚀较为严重的地区之一。该区域地质背景复杂，同一坡面的不同部位，成土母质不尽相同。坡面不同母质的组合对土壤侵蚀-堆积过程有明显的影响，而影响的程度和机理尚不明确。基于此，本项目以鄂东南丘陵区不同母质组合的红壤坡面为研究对象，通过采样分析、野外原位观测以及设计不同母质红壤组合的坡面冲刷实验，分析土壤物理和水力参数、侵蚀产沙的过程和数据，揭示土壤侵蚀-堆积过程对坡面不同母质红壤组合的响应。主要研究内容包括：（1）在相近的地貌和植被条件下，不同母质红壤物理性质和水力参数的差异；（2）在不同母质组合的坡面侵蚀过程中，坡上土壤对坡中和坡下土壤的物理和水力性质的影响；（3）坡底堆积物与坡面物质的源-汇关系，研究母质类型的组合方式与坡面侵蚀产沙规律。本项目对土壤侵蚀模型中参数的调整具有重要理论意义，且能为南方红壤区水土保持与生态建设提供科学依据。

成土母质对土壤水力性质和侵蚀过程有直接影响。本项目选取咸宁通山县的丘陵缓坡，以发育于泥质灰岩、泥质瘤状灰岩和灰岩角砾岩的红壤为研究对象(三种土壤分别以NL、NAL和SS表示)；设计了单一母质红壤坡面(单一坡面)与组合母质红壤坡面(异质性坡面)两个大类共计9种类型的坡面，研究了在放水冲刷和模拟降雨条件下的土壤侵蚀过程；选取长江中游典型的网纹红土剖面，研究了不同物源网纹红土的水力性质。结果表明：.(1)在放水冲刷条件下：对于单一坡面，SS的产沙量和径流量都是最大的，且产沙量是NL的1.76倍，是NAL的3.91倍；相比于单一坡面，各类异质性坡面之间的总产沙量与总产流量差异较小，且产沙量要大于单一母质红壤坡面；说明在放水冲刷的条件下，不同母质的组合降低了坡面的整体抗侵蚀能力。对于异质性坡面，稀土元素示踪结果显示，上坡段的产沙量均大于下坡段，即上坡段的侵蚀更为剧烈，主要原因是上坡段的流水具有更强的携沙能力，但每种组合的产沙量及其在坡面的分布又有所不同。.(2)在模拟降雨条件下：单一坡面的侵蚀量均大于异质性坡面，其中SS坡面在侵蚀初期的含沙率高达60.0g·kg-1，远高于NAL和NL两种单一坡面及异质性坡面。总体而言，单一坡面的产沙量都呈现随时间而降低趋势，在产沙25min后渐趋平稳。对于异质性坡面而言，在其他因子不变的前提下，两种土壤在坡面所处的位置(位于上坡段还是下坡段)对侵蚀产沙过程有着较大的影响，主要原因是下坡段的流量要远大于上坡段，当抗侵蚀能力较弱的土壤位于坡下时，所受到的侵蚀动能更大，故侵蚀量大。在模拟降雨条件下，增加坡面的异质性可以有效地减少水土流失。.(3)成土母质为不同物源的网纹红土，其水力性质有明显的差异。母质为风尘沉积物的网纹红土，其持水能力和抗侵蚀能力均强于发育于水成沉积物的网纹红土。.本项目的研究结果为减缓坡面土壤侵蚀和提高坡面水土资源利用效率提供了科学依据。.