Ren Jianhong, Packman Aaron I
Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, USA.
Environ Sci Technol. 2004 May 15;38(10):2901-11. doi: 10.1021/es034852l.
Contaminant transport in streams can be significantly modified by both stream-subsurface exchange and the presence of colloidal particles, but the interaction of these effects is notwell understood. Exchange with the hyporheic zone exposes contaminants to surface-chemical reactions with streambed sediments, while colloidal particles have a large reactive surface area that allows them to carry pollutants that would otherwise be transported primarily as dissolved species. A new theoretical model is developed to predict the role of colloids in mediating advective contaminant exchange between streams and streambeds. Bedform-induced pumping theory is applied to model physical transport, and colloid filtration and reversible contaminant sorption are used to calculate the local distributions of colloids and contaminants within the streambed. Residence time functions of both colloids and contaminants in the bed are then used to link contaminant concentrations in the pore water and streamwater. Model simulations indicate that, under conditions of low colloid filtration and strong contaminant sorption to colloids, contaminants are mobilized by colloids and there is less retention of contaminants in the streambed. This is the case of "colloid-facilitated contaminant transport" commonly considered in groundwater transport. On the other hand, when colloid filtration is high and contaminants still sorb strongly to colloids, contaminant mobility decreases and there is greater contaminant retention in the streambed. We term this case "colloid-impeded contaminant transport". Thus, we find that a variety of contaminanttransport behavior can occur depending on the concentration and mobility of suspended particles in the system and the relative affinity of contaminants for colloids and other solid phases.
溪流中的污染物输运可因溪流与地下的交换以及胶体颗粒的存在而发生显著改变，但这些效应之间的相互作用尚未得到充分理解。与渗流带的交换使污染物暴露于与河床沉积物的表面化学反应中，而胶体颗粒具有很大的反应表面积，这使得它们能够携带污染物，否则这些污染物将主要以溶解态进行输运。本文建立了一个新的理论模型，以预测胶体在介导溪流与河床之间平流污染物交换中的作用。应用床形诱导抽吸理论对物理输运进行建模，并利用胶体过滤和可逆污染物吸附来计算河床内胶体和污染物的局部分布。然后利用胶体和污染物在河床中的停留时间函数来关联孔隙水和溪水中的污染物浓度。模型模拟表明，在胶体过滤率较低且污染物对胶体吸附较强的条件下，污染物会被胶体带动，河床中污染物的滞留量较少。这就是地下水输运中通常考虑的“胶体促进污染物输运”情况。另一方面，当胶体过滤率较高且污染物对胶体的吸附仍然很强时，污染物的迁移性降低，河床中污染物的滞留量更大。我们将这种情况称为“胶体阻碍污染物输运”。因此，我们发现，根据系统中悬浮颗粒的浓度和迁移性以及污染物对胶体和其他固相的相对亲和力，会出现多种污染物输运行为。
