西南黄壤区不同尺度土壤侵蚀与泥沙运移规律耦合关系

The yellow soil area in Southwest China is one of the most serious areas that suffer from soil erosion and water loss. There are severe eco-environmental problems in this area with unique geographical environment, in which the soil erosion processes are complicated and they have not been well investigated. Therefore, it is necessary to study the multi-scale coupling of soil erosion and sediment transport in this area. By applying various methods like field investigation, data collection, plot observation, small watershed monitoring, tracer technique, remote sensing and GIS, this project plans to implement researches in four aspects including quantitative assessment of soil erosion at plot scale, soil erosion characteristics and sediment transport processes at small watershed scale, sediment transport relationships at plot, small watershed and river watershed scales, sediment delivery ration in the Karst area and its impacting factors. Based on these researches, it is expected to identify the characteristics of runoff and sediment yield on the steep and short slopes with thin soil layer and underlying bedrock fissures and other Karst environment conditions, to achieve the quantitative assessment of the factors influencing soil erosion in this area, to develop the plot scale soil erosion prediction model, to propose the small watershed sediment estimation model, to build up the technique and method for soil erosion and water loss assessment at large river watershed scale, to provide a standard, reliable and comparable plot observation dataset, to enrich the research and theory of soil erosion process, to promote the development of the national soil erosion prediction model and the relating factors data base, and to afford theoretical guidance for the soil erosion and water loss prevention and the rocky desertification control in the yellow soil area of Southwest China.

西南黄壤区是我国水土流失危害最严重的地区之一，生态环境问题突出，地理环境独特，侵蚀过程复杂，研究积累相对薄弱，在该区域开展不同尺度土壤侵蚀与泥沙运移规律耦合关系研究十分必要。项目拟通过野外调查、资料收集、小区观测、小流域监测、示踪技术、遥感与GIS等方法和手段，开展坡面侵蚀特征及其定量评价；小流域侵蚀特征及泥沙输移过程；坡面－小流域－河流泥沙输移变化规律；喀斯特地区泥沙输移比及其影响因素等四方面研究。以期探明坡度陡坡长短、土层薄、下覆基岩裂隙发育等喀斯特环境条件下的坡面产流产沙特征，解决该区域土壤侵蚀影响因子的定量评价问题，建立坡面土壤侵蚀预报模型；提出小流域侵蚀泥沙估算模型；构建大流域尺度水土流失评价技术方法；积累一组规范统一、可比性强的小区观测资料，丰富和完善土壤侵蚀基本过程及其理论研究，促进全国侵蚀预报模型和相关因子数据库的建立，为西南黄壤区水土流失防治和石漠化治理提供理论指导。

围绕研究目标，针对研究内容，采用多方法融合、多尺度耦合和多途径互证等技术手段，对喀斯特地区的土壤侵蚀及泥沙运移规律开展了系统研究。取得了以下主要结果：1）黄壤分离强度小，农地和裸地平均土壤流失量分别只有121.4和543.6 t•km−2•yr−1。土壤可蚀性小，K因子值仅为0.0029 t•hm2•h•hm-2•MJ-1•mm-1；B值更小，其中农作物平均B值为0.073，草地为0.0087，人工林为0.0374。2）块石出露显著影响土壤入渗：裸岩率不足10%时，对入渗影响不显著；大于40%时显著减少入渗，但超过80%时又会增加入渗。块石出露对产沙也存在双重作用，小强度降雨时抑制侵蚀发生，但高强度降雨时又促进土壤侵蚀。坡面侵蚀强度随裸岩率的增加先增后减，转折点在裸岩率13-43%。3）喀斯特地区地下漏失现象存在，但漏失强度很小。在已被土壤充填的裂隙中，土壤细颗粒淋溶下移深度最多只有8cm，且不随降雨年限的增长而加深。地表土壤充填裂隙的平均速率在百年和千年尺度上分别为20.34和24.26 t•km−2•yr−1，但1963年之后只有1.72 t•km−2•yr−1。近两年在洞穴监测到的石漠化农地和高覆盖林地的地下漏失模数分别为0.35和0.05 t•km−2•yr−1。4）建立了多元经验模态分解模型和状态空间方程，可对喀斯特区的月输沙量进行准确预测，其精度要远优于经典的“Sediment Rating Curves”。5）如今的石漠化景观是经过漫长的地质历史过程演化而来，只是近300年来人类过度干扰导致石漠化加速扩张。喀斯特石漠化区的土地利用历程存在“林地-草地-农地-草地-林地”的转化模式。近60年来典型石漠化小流域的土壤流失减少了约88%。不同石漠化程度的小流域洼地沉积2m厚的泥沙经历了0.7-1.27万年。6）喀斯特区极端降雨的侵蚀产沙贡献占比很大。坡面尺度上，同样1%的极端降雨事件，黄壤坡面产生的径流分别是黄土和红壤的1.81倍和1.86倍，产生的泥沙分别是黄土和红壤的2.77倍和3.37倍。流域尺度上，最大5天、10天、15天的日输沙量分别占年输沙量的56%、69%和83%。上述研究成果对喀斯特地区土壤侵蚀与泥沙运移过程以及土壤侵蚀与石漠化时空耦合关系的解析具有重要意义，也可为喀斯特地区的侵蚀输沙预报模型构建及其参数量化提供科学依据。