大孔隙数量和孔径组合对土壤溶质运移影响研究

大量野外观测与试验表明, 土壤因植物根系发育、蚯蚓活动等形成的不同密度、数量和孔径的大孔隙优势通道影响水分和溶质优势流运移特征。当前对大孔隙度影响的关注较多, 而对相同大孔隙度条件下因数量和孔径组合不同带来的影响关注不足。文章通过相同大孔隙度的 3 组不同数量和孔径组合的土柱及对照均质土柱的溶质运移试验, 探究其对土壤水分和溶质运移的影响, 并利用 Hydrus 中的双重渗透模型探究其在数值模拟中的影响。结果表明: 相同大孔隙度条件下细而多的大孔隙组合土柱出流速度更快, 溶质平均停留时间更短, 优势流程度更高; 在双重渗透模型中大孔隙数量和孔径组合的改变由参数 a 体现, 且细而多的大孔隙组合 a 取值更小; a 对溶质运移结果的影响表现为 a 值越小, 溶质穿透更快、更集中, 峰值质量浓度更高, 但是初始穿透更晚。

A large number of field observations and experiments have shown that the macropore preferential channels with different densities, numbers and sizes formed by plant root development and earthworm activities affect the transport characteristics of water and solute preferential flow. Currently, more attention has been paid to the effect of macroporosity, while less to the effect of different number and size combinations with the same macroporosity. In this paper, solute transport experiments of soil columns with three different macropore number and size combinations with the same macroporosity and one homogeneous soil column were conducted to explore the effects of the combinations on water and solute transport in soil. The dual permeability model in Hydrus was used to investigate their effects in numerical simulation. The results show that under the same macroporosity, the discharge rate of the soil column with fine and more macropore combination is faster, the average residence time of solute is shorter, and the degree of preferential flow is higher. In the dual permeability model, the change of the number and size combination of macropores is reflected by the parameter a, and the value of a is smaller for fine and more macropore combination. The effect of a on solute transport is that, with a smaller value of a, the breakthrough will be faster and more concentrate, and peak concentration value is higher, but initial penetration is later.