黄土丘陵区不同土地利用下的土壤大孔隙与优先流特征研究

Vegetation restoration on the loess plateau is facing with soil desiccation and river flow decrease which threaten the regional water recycling and water safe. The traditional unsaturated infiltration theories aggravated the anxiety about safety of water. The research on macropores from root system and Preferential flow is theoretically beneficial to study the mechanism of groundwater recharge and improve the infiltration models of inhomogeneous medium. In practice, evaluating the change of recharge intensity and retardation time of preferential flow impacted by Vegetation restoration can offer the basis of layout and pattern of ecological restoration. Taking cropland forestry and grassland in different utilization years as research objects, acquiring the root characteristics by the soil core method, plus the image scanning techniques and the software of root analysis, the relation between root development and the formation of macropores in the process of vegetation restoration can be set up. The model of relation about pores characteristics - preferential flow can be built and the parameters of dual permeability model in HYDRUS can be revised by using undistributed soil columns, precisely analyzing the characteristics of columns through CT and image scanning techniques, using the Hood permeameter to measure the infiltration process on different land uses in filed, and regarding the breakthrough curves and water characteristic curve as the additional indoor experiments. At last, the model could be used to evaluate the influence on the soil recharge ability to groundwater under some ways and durations about restoring arable land to nature, which can help deeply understood of the regional hydrological response caused by Land Use and Land Cover Change and provide national ecological construction with some reliable basis.

黄土高原植被恢复面临土壤干燥化和河川径流锐减的水循环与水安全压力，土壤的非饱和入渗理论加深了对水安全的忧虑。研究植被根系形成的大孔隙及其大孔隙优先流，理论上有助于完善地下水补给机制、改进非均匀介质入渗模型；实践上则通过评价植被恢复形成的优先流补给强度变化、滞后时间等提供生态恢复布局、模式依据。研究以不同利用年限的农林草地为对象，以根钻法和图像扫描技术、根系分析软件获取根系特征，建立植被恢复进程中根系发育与土壤大孔隙形成的联系。利用原状土柱，以CT扫描和图像分析软件精确解剖原状土土柱孔隙特征，辅以野外Hood入渗仪测定不同土地利用下的近饱和入渗过程、室内穿透曲线法/水分特征曲线法补充实验，建立孔隙特征-优先流关系模型，给出HYDRUS中的双重渗透模型参数；最终利用模型评价农地退耕方式、年限对土壤补给地下水能力的影响，深入理解土地利用/覆被变化引起的区域水文响应，为国家生态建设提供可靠依据。

项目通过4年执行，先后在甘肃平凉官山林场、陕西长武建立了18个不同土地利用的野外测定样点，完成了野外土壤物理性质测定、土壤圆盘入渗试验、室内土柱CT实验室扫描，土壤水分特征特征曲线测定等，取得了丰富的试验数据。主要结论有：.1)土地利用方式会影响土壤有机质积累，有机质增加能促进土壤团聚体稳定性，使得团聚体粒径增大、颗粒之间空隙的等效孔径增加，叠加上根系作用下的土壤大孔隙，大大增强了土壤入渗能力。.2)植被类型及其年限一起影响着土壤的空隙结构。土壤CT扫描、圆盘入渗试验数据分析表明：土壤大孔隙数量和孔隙的几何特征是植被影响土壤发育的结果，包括以增加团聚体粒径和稳定性促进土壤导水性，以及根孔发育提升导水能力的双通道机制。土壤有机质含量是主要内在影响因素。 .3)林灌草植被对于土壤有机质积累、土壤结构的改良明显优于耕地， 退耕还林草在退耕年限达到25年后能有效地修复土壤水文环境，其时土壤入渗能力远远高于农地，可有效地化解暴雨引起的产流和水土流失。草地和林地的作用有所差别，对于不同深度土层的土壤涵养能力能够互补；常绿林（侧柏、油松）对于土壤性质的改善能力上不及刺槐、山杏等落叶林。.4)林草地而言，土壤中>1 mm可传导水分的有效孔隙体积虽然仅占土壤体积的不足0.05%，但是却可以解释52.16～82.54%的饱和水通量。>0.5mm的孔隙占土壤体积的0.5%，却为饱和导水率做出了70.92～91.58%的贡献。土壤表层相通的大孔隙会缩短整个湿润锋运移时间。土壤湿润峰运移速度取决于孔隙深度、孔隙扭曲度及倾斜角度等。Hydrus-2d模型可以模拟黄土中的入渗行为，提供了黄土地区发育的黑垆土的基本水力参数。. 项目深化了植被修复土壤性质的基本理论，阐明了土壤入渗能力的提升机制和刻画方法。提供了黄土区减轻水土流失的科学依据。.项目共发表了9篇科技论文，其中4篇为SCI收录（其中1篇农林科学领域TOP期刊）。团队成员参加国际国内会议6人次，会议交流论文2篇。培养研究生7名，硕士毕业4名，博士毕业1名。