土壤溶质迁移至地表径流过程的室内模拟试验

Laboratory simulation experiment on chemical transport from soil to surface runoff

关于土壤溶质迁移到地表径流,现有研究大多是概念性的认识,对迁移过程中各个部分的定量研究却很少。该文为了量化研究土壤溶质迁移流失过程及其作用机理,通过设计2种水文条件即土壤水分饱和和土壤渗流条件,其中土壤渗流条件设置了2种水头(5cm,10cm),采用人工模拟5组不同地表径流流速,分别研究土壤溶质迁移到地表径流过程中4种途径:土壤侵蚀、伯努利效应、扩散和对流。试验结果表明了伯努利效应导致土壤溶质迁移量增加;特别是在土壤水分饱和条件下,当地表径流流速从55mL/s升到200mL/s时,伯努利效应引起的土壤溶质流失通量占总流失通量的比例从14%升到53%,在土壤水分饱和条件下,混合层深度小于5mm;但是在土壤渗流条件下,混合层深度随着水头的高低和径流流速的大小而变化。土壤溶质迁移过程同地表径流流速和地下水位高低有着重要关系。

Although there is a conceptual understanding on chemical transport from soil to surface runoff, there are little literature and research results actually quantifying those individual processes. A laboratory flow cell and experimental procedures to quantify chemical transport from soil to runoff by each of the individual processes： i.e., 1 soil erosion; 2 Bernoulli effect; 3 diffusion; and 4 convention were developed. Different vertical hydraulic gradients were imposed by setting the flow cell to saturation condition and artesian seepage conditions. Additional quantitative data describing the contribution from each individual chemical loading process under different surface runoff and soil hydrologic conditions were obtained. The experimental data clearly demonstrated that Bernoulli effect caused increased chemical transport from soil into surface runoff. Under saturation condition, with increasing of runoff flow rate from 55 mL/s to 250 mL/s, bromide loss flux caused by Bernoulli effect was augmented from 14% to 53% from soil into surface runoff. According to the data, the mixing zone depth was gotten by mixing theories under saturation condition and artesian seepage conditions. The mixing zone depth was less than 5 mm under saturation condition, and it changed as hydraulic head and runoff flow rate under artesian seepage conditions. Chemical transport has a significant relationship to surface runoff flow rate and groundwater table.