A Gas Diffusivity Model Based on Air-, Solid-, and Water-Phase Resistance in Variably Saturated Soil
A Gas Diffusivity Model Based on Air-, Solid-, and Water-Phase Resistance in Variably Saturated Soil
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DOI：
10.2136/vzj2008.0023
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发表时间：
2008-11-01
影响因子：
2.8
通讯作者：
Rolston, Dennis E.
中科院分区：
文献类型：
--
作者：
Thorbjorn, Anne;Moldrup, Per;Rolston, Dennis E.
气体在土壤中的扩散取决于气体扩散系数（D-p）及其随孔隙度的变化。在进行气体迁移和最终结果计算时，准确或上限（风险评估的观点）预测D-p（D-p）至关重要。我们开发了一个相对非结构化的土壤分离的土壤空气，固体和水分的个人阻力D-P的D-P（SDIR）模型。假设总的土壤阻力气体扩散可以描述由三个幂律条款代表空气含量减少，固体引起的曲折，和水引起的断开产生所谓的土壤空气相个别电阻（SAPHIR）模型。SAPHIR模型将D-p预测为实际含水量、颗粒形状因子（p）、土壤体积含水量（theta）和水堵塞因子（w）的函数。在不同的θ条件下，对重填土样和原状土样进行了D-p（θ）测量。新的D-p数据与文献数据相结合，意味着p值在0到1的区间内，w值在1到7的区间内，这取决于颗粒直径、细颗粒含量和压实度。对810个测量的D-p的原状土壤进行测试，SAPHIR与平均值的p = 0.6和w = 3的表现一样好，或优于传统的模型，但是，测试意味着需要不同的参数值为更多的桑迪土壤（低p和高w），以及更多的压实土壤（低p）。
Gas diffusion in soil is governed by the gas diffusion coefficient (D-p) and its variation with air-filled porosity (epsilon). Accurate or an upper-limit (risk assessment standpoint) prediction of D-p(epsilon) is essential when carrying out gas transport and fate calculations. We developed a D-p(epsilon) model for relatively unstructured soil separating the individual resistance of soil air, solids, and moisture to D-p. Assuming the total soil resistance to gas diffusion can be described by three power-law terms representing air-content reduction, solids-induced tortuosity,and water-induced disconnectivity yields the socalled Soil Air Phase Individual Resistances (SAPHIR) model. The SAPHIR model predicts D-p as a function of the actual epsilon, a particle shape factor (p), the volumetric soil water content (theta), and a water-blockage factor (w). The D-p(epsilon) was measured at different theta on repacked and undisturbed soil samples. The new D-p data combined with literature data implied values of p in the interval 0 to 1 and w in the interval 1 to 7, depending on particle diameter, fine-particle content, and compaction. Tested against 810 measurements of D-p on undisturbed soils, SAPHIR with average values of p = 0.6 and w = 3 performed equally well or better than traditional models; however, the test implied a need for different parameter values for more sandy soils (lower p and higher w), as well as for more compacted soils (lower p).