冻融条件下黑土团聚体孔隙结构特征及解冻期降雨侵蚀响应研究

Black soil region is generally affected by the freeze-thaw action in northeast China. Repetitive freeze-thaw cycles considerably change the structure and decrease soil anti-erodibility, resulting in more serious erosion during spring thawing period. Aggregate is a key soil structural unit, which is considered to be one of the main soil properties regulating soil erodibility. However, few efforts have been devoted to understanding the effects of freeze-thaw on the characteristics of aggregate pore structure. Besides, it is difficult to interpret and evaluate the relationship between aggregate pore characteristics and soil erosion during spring thawing period accurately. This project is to evaluate the effect of freeze-thaw on the modification of aggregate pore structure with high resolution X-ray micro-computed tomography and the response of aggregate stability and rainfall erosion during spring thawing period in typical black soil of northeast China. The most sensitive pore factors to freeze-thaw will be selected. Based on the above work, the quantitative relationship between aggregate pore characteristics and aggregate stability and rainfall erosion during thawing period will be analyzed. This work provides insights for revealing erosion processes and mechanism under freeze-thaw cycles. Moreover, this work will be beneficial to the research of soil erosion model and to the improvement of soil erosion control in this region.

我国东北黑土区普遍受冻融作用影响，反复的冻融作用影响土壤结构，降低土壤抗蚀性，一旦在春季解冻期产生降雨，极易引发严重的侵蚀。团聚体作为土壤结构的基本单元，是土壤抵御侵蚀外力的最重要的因素之一。目前，我国很少开展有关冻融条件下团聚体孔隙结构的研究，使得难以对春季解冻期降雨侵蚀发生发展规律进行准确的解释与评价。本研究以东北典型黑土为研究对象，结合室内模拟冻融循环试验和人工模拟春季解冻期降雨试验，应用显微CT扫描技术和数字图像分析等技术，开展冻融条件下团聚体孔隙结构特征及解冻期降雨侵蚀过程响应的研究；通过筛选对冻融作用最敏感的孔隙特征因子，建立团聚体孔隙结构和团聚体稳定性与解冻期降雨侵蚀间的量化关系。研究结果可为东北黑土春季解冻期降雨侵蚀预测研究和制定相应的侵蚀治理措施提供可靠的理论依据。

东北黑土受季节性气候变化的影响，遭受多种侵蚀营力作用，加之人类不合理利用，黑土地退化呈加剧趋势，致使该区农业发展受到严重威胁。春季解冻期，反复的冻融作用改变表土结构，导致黑土抗蚀能力降低，在外营力的作用下极易发生侵蚀。因此，弄清解冻期土壤结构特征，探明土壤结构与土壤侵蚀间的关系，是黑土区水土流失防治所面临的重要问题。本项目以冻融—土壤结构—功能为主线，以不同尺度黑土为研究对象，开展室内模拟试验，研究冻融条件下土壤结构变化规律及其与侵蚀的量化关系。主要结果如下：（1）利用医用CT研究了冻融条件下原状土大孔隙结构。结果表明，冻融作用下土壤总孔隙度增大，孔隙数量减少，其中>3 mm孔隙的孔隙度不断增大，1.25–3 mm孔隙的孔隙度减小。（2）明确了冻融过程中土体内部团聚体分布规律。结果表明，原状土在反复冻融过程中结构破碎，>7 mm团聚体含量逐渐减小，5–7 mm团聚体含量变化不大，3–5 mm团聚体及<3 mm的团聚体含量增加。（3）利用SRμ-CT研究了冻融条件下5–7 mm团聚体微结构。结果表明，随冻融循环次数增加，团聚体孔隙度增大，在15次冻融循环后趋于稳定，>100 μm孔隙度和加长型孔隙度占比增加。（4）量化了团聚体孔隙特征因子与团聚体稳定性的关系，其中孔隙度、>100 μm孔隙度和加长型孔隙度对团聚体稳定性起到降低的作用。（5）利用工业CT研究了冻融条件下重塑土的孔隙网络结构。结果表明，随着冻融循环次数的增加，孔隙中轴路径数量显著增大，平均路径长度先增大后减小，节点数量和孔喉数量显著增大，平均孔喉面积先增大后减小。（6）量化了团聚体孔隙特征因子与土壤抗冲性间的关系。结果表明，总孔隙度、加长孔隙度毛管孔隙度和孔隙数量是降低土壤抗冲性的主要特征因子。本研究结果为黑土区土壤侵蚀机制研究及水土保持措施的布设提供理论依据。已发表学术论文3篇，培养学生3名，国内外会议上以学术报告形式介绍本项目研究成果3次。