Li Na, Ren Li
Department of Soil and Water Sciences, China Agricultural University, Key Laboratory of Plant-Soil Interactions, MOE, Beijing 100193, China.
J Contam Hydrol. 2009 Sep 1;108(3-4):134-51. doi: 10.1016/j.jconhyd.2009.07.002. Epub 2009 Jul 12.
Continuous time random walk (CTRW) formulations have been demonstrated to provide a general and effective approach that quantifies the behavior of solute transport in heterogeneous media in field, laboratory, and numerical experiments. In this paper we first apply the CTRW approach to describe the sorbing solute transport in soils under chemical (or) and physical nonequilibrium conditions by curve-fitting. Results show that the theoretical solutions are in a good agreement with the experimental measurements. In case that CTRW parameters cannot be determined directly or easily, an alternative method is then proposed for estimating such parameters independently of the breakthrough curve data to be simulated. We conduct numerical experiments with artificial data sets generated by the HYDRUS-1D model for a wide range of pore water velocities (upsilon) and retardation factors (R) to investigate the relationship between CTRW parameters for a sorbing solute and these two quantities (upsilon, R) that can be directly measured in independent experiments. A series of best-fitting regression equations are then developed from the artificial data sets, which can be easily used as an estimation or prediction model to assess the transport of sorbing solutes under steady flow conditions through soil. Several literature data sets of pesticides are used to validate these relationships. The results show reasonable performance in most cases, thus indicating that our method could provide an alternative way to effectively predict sorbing solute transport in soils. While the regression relationships presented are obtained under certain flow and sorption conditions, the methodology of our study is general and may be extended to predict solute transport in soils under different flow and sorption conditions.
连续时间随机游走（CTRW）公式已被证明是一种通用且有效的方法，可用于量化现场、实验室和数值实验中非均质介质中溶质运移的行为。在本文中，我们首先应用CTRW方法，通过曲线拟合来描述化学（或）物理非平衡条件下土壤中吸附性溶质的运移。结果表明，理论解与实验测量结果吻合良好。若CTRW参数无法直接或轻易确定，则提出一种替代方法，可独立于待模拟的突破曲线数据来估算此类参数。我们使用HYDRUS-1D模型生成的人工数据集，针对广泛的孔隙水速度（υ）和阻滞因子（R）进行数值实验，以研究吸附性溶质的CTRW参数与这两个可在独立实验中直接测量的量（υ，R）之间的关系。然后根据人工数据集建立了一系列最佳拟合回归方程，这些方程可轻松用作估算或预测模型，以评估稳定流条件下吸附性溶质在土壤中的运移。使用了几个农药的文献数据集来验证这些关系。结果在大多数情况下表现合理，从而表明我们的方法可为有效预测土壤中吸附性溶质的运移提供一种替代方法。虽然所呈现的回归关系是在特定的流动和吸附条件下获得的，但我们研究的方法具有通用性，可扩展用于预测不同流动和吸附条件下土壤中的溶质运移。
