东北黑土区冻融作用与水蚀过程耦合机理研究

Freeze-thaw action (FTA) has important impacts on soil and water loss in black soil areas in Northeast China, and verifying the mechanism of FTA and quantifying the contribution of FTA to sediment yields are of great significance to soil erosion prediction and soil and water conservation in this area. By filed observation of runoff and sediments in plots and small watersheds, monitoring temperature and moisture in soil profiles, in-situ experiments and laboratory simulation experiments, this project will systematically research a series of theoretical and practical issues including the characteristics of freeze-thaw cycles, impacts of FTA on soil properties, contribution of FTA to sediment yields and so on. This project will propose soil erodibility estimation formula when considering the impacts of FTA, and the temporal and spatial change patterns of melting layer thickness, and determine the contribution of FTA to sediment yields on slope scale and small watershed scale. The research results can provide a theoretical basis for the study of freeze-thaw erosion and enrich the study of soil erosion prediction models. The innovation of this project includes the combination of runoff and sediment observation and monitoring of soil properties, and the establishment of direct relationships between FTA and sediment yield on slope scale and small watershed scale. The expected results contain both the theoretical exploration of process mechanisms and the solutions to practical problems.

冻融作用对东北黑土区的水土流失具有重要影响，探明冻融作用机理、定量评价冻融侵蚀的泥沙贡献对东北黑土区侵蚀预报和防涝保土都具有重要意义。本课题将通过野外小区和小流域径流泥沙观测、土壤剖面温度水分监测、田间原位实验和室内模拟实验等手段，系统研究东北黑土区冻融交替变化规律、冻融作用对土壤性状影响、冻融作用的侵蚀产沙贡献等理论和现实问题，提出考虑冻融作用条件下的土壤可蚀性估算公式和融化层厚度时空变化模式，确定冻融作用对坡面侵蚀和小流域侵蚀的泥沙贡献率。课题研究成果不仅可以为冻融侵蚀研究提供理论基础，也可以丰富和完善我国土壤侵蚀预报模型研究。本课题的创新在于研究手段上将径流泥沙观测和土壤性状变化监测相结合，建立冻融作用与坡面及小流域侵蚀产沙的直接关系。预期研究成果既有理论问题和过程机理探索层面，又有关注实际问题解决的应用层面。

冻融交替循环是我国东北地区土壤侵蚀重要的作用方式之一。冻融交替循环破坏土壤结构，减少径流下渗，加剧区域水土流失，深入研究研究冻融侵蚀发生机理和评价其侵蚀量贡献大小对东北黑土地区的水土保持具有重要意义。本项目通过野外原位监测、径流小区观测、小流域径流泥沙监测和室内模拟实验和野外现场调查等方法，系统研究了不同土地利用下土壤温度及含水量变化、冻融循环对土壤性质的影响、冻融循环对坡面土壤分离过程影响、冻融作用对坡面和小流域产流产沙的影响，以及冻融作用对切沟侵蚀的影响。本课题取得的主要进展和结论概况如下：.1）冻融作用减小了坡面和小流域的产流量，径流系数分别减小0.07 和0.03。受冻融作用影响，土壤可蚀性K值可增大2.67倍。冻融循环影响的结果使小降雨事件也可以引起较为严重土壤侵蚀。.2）冻融期时间长度随深度增加而逐渐缩短。表层土壤往往经历昼融夜冻的频繁冻融交替作用，农地表层土壤温度变化大于草地和林地，冬季最低温度也低于草地和林地。林地冻融循环次数少于草地和农地。.3）冻融循环作用会显著地改变土壤性质。冻融循环作用导致土壤水稳性团聚体含量减少，土壤容重减小，土壤透水性普遍增强。土壤初始含水量的多少对冻融循环作用的影响效果有显著影响。.4）冻融循环作用显著改变土壤分离能力和临界切应力大小，而且不同土壤类型有不同的响应程度。沉积型、原生型和退化型的土壤分离能力分别增大 11.3%、36.5%和 28.6%，细沟可蚀性分别增大 11.1%、36.3%和16.9%。.5) 冻融循环导致切沟沟壁失稳而加剧切沟侵蚀，侵蚀方式为土体剥落和块状崩落，崩落物体积与平均沟深和平均沟宽呈较好的线性关系。.6）土壤磁化率技术可以用于土壤侵蚀与沉积速率估算。利用磁化率技术估算东北黑土区年均土壤侵蚀量为733.5 t/yr，侵蚀模数为4630.5 t/km2/yr，相当于每年侵蚀表土3-4 mm。