Dousset S, Thevenot M, Pot V, Simunek J, Andreux F
UMR 5561-Biogéosciences, UFR Sciences Terre and Environnement, Université de Bourgogne, 6 Bd Gabriel, 21000, Dijon, France.
J Contam Hydrol. 2007 Dec 7;94(3-4):261-76. doi: 10.1016/j.jconhyd.2007.07.002. Epub 2007 Jul 17.
In this study, displacement experiments of isoproturon were conducted in disturbed and undisturbed columns of a silty clay loam soil under similar rainfall intensities. Solute transport occurred under saturated conditions in the undisturbed soil and under unsaturated conditions in the sieved soil because of a greater bulk density of the compacted undisturbed soil compared to the sieved soil. The objective of this work was to determine transport characteristics of isoproturon relative to bromide tracer. Triplicate column experiments were performed with sieved (structure partially destroyed to simulate conventional tillage) and undisturbed (structure preserved) soils. Bromide experimental breakthrough curves were analyzed using convective-dispersive and dual-permeability (DP) models (HYDRUS-1D). Isoproturon breakthrough curves (BTCs) were analyzed using the DP model that considered either chemical equilibrium or non-equilibrium transport. The DP model described the bromide elution curves of the sieved soil columns well, whereas it overestimated the tailing of the bromide BTCs of the undisturbed soil columns. A higher degree of physical non-equilibrium was found in the undisturbed soil, where 56% of total water was contained in the slow-flow matrix, compared to 26% in the sieved soil. Isoproturon BTCs were best described in both sieved and undisturbed soil columns using the DP model combined with the chemical non-equilibrium. Higher degradation rates were obtained in the transport experiments than in batch studies, for both soils. This was likely caused by hysteresis in sorption of isoproturon. However, it cannot be ruled out that higher degradation rates were due, at least in part, to the adopted first-order model. Results showed that for similar rainfall intensity, physical and chemical non-equilibrium were greater in the saturated undisturbed soil than in the unsaturated sieved soil. Results also suggested faster transport of isoproturon in the undisturbed soil due to higher preferential flow and lower fraction of equilibrium sorption sites.
在本研究中，在相似降雨强度下，对粉质粘壤土的扰动柱和未扰动柱进行了异丙隆置换实验。由于压实的未扰动土壤的容重比过筛土壤大，溶质在未扰动土壤中在饱和条件下运移，而在过筛土壤中在非饱和条件下运移。这项工作的目的是确定异丙隆相对于溴化物示踪剂的运移特性。对过筛（结构部分破坏以模拟传统耕作）和未扰动（结构保留）土壤进行了三次重复柱实验。使用对流弥散模型和双渗透（DP）模型（HYDRUS-1D）分析溴化物实验突破曲线。使用考虑化学平衡或非平衡运移的DP模型分析异丙隆突破曲线（BTCs）。DP模型很好地描述了过筛土壤柱的溴化物洗脱曲线，而高估了未扰动土壤柱的溴化物BTCs的拖尾现象。在未扰动土壤中发现了更高程度的物理非平衡，其中56%的总水量包含在慢流基质中，而过筛土壤中为26%。使用结合化学非平衡的DP模型，在过筛和未扰动土壤柱中都能最好地描述异丙隆BTCs。对于两种土壤，在运移实验中获得的降解率都高于批量研究中的降解率。这可能是由异丙隆吸附的滞后现象引起的。然而，不能排除更高的降解率至少部分归因于所采用的一级模型。结果表明，在相似降雨强度下，饱和未扰动土壤中的物理和化学非平衡比不饱和过筛土壤中的更大。结果还表明，由于更高的优先流和更低的平衡吸附位点比例，异丙隆在未扰动土壤中的运移更快。
