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Modeling Reactive Solute Transport in Permafrost-Affected Groundwater Systems
Water Resources Research ( IF 5.4 ) Pub Date : 2021-07-07 , DOI: 10.1029/2020wr028771
Aaron A. Mohammed 1 , Victor F. Bense 2 , Barret L. Kurylyk 1 , Rob C. Jamieson 1 , Lindsay H. Johnston 1 , Amy J. Jackson 1
Affiliation  

Understanding the interactions between ground freeze-thaw, groundwater flow, and solute transport is imperative for evaluating the fate of contaminants in permafrost regions. However, predicting solute migration in permafrost-affected groundwater systems is challenging due to the inherent interactions and coupling between subsurface mass and energy transport processes. To this end, we developed a numerical model that considers coupled groundwater flow, subsurface heat transfer, and solute transport, including water-ice phase change, solute-dependent porewater freezing, and temperature-dependent solute reaction rates. As an illustrative example, we present simulations to investigate the potential for contamination from a municipal wastewater lagoon in the Canadian sub-arctic. Two-dimensional groundwater models assuming varying permafrost conditions were developed to evaluate possible contaminant migration scenarios associated with groundwater flow from the lagoon to a river, including the transport of conservative, degradable, and sorbing solutes. Model results reveal important transport mechanisms controlling the behavior of aqueous contaminants in permafrost landscapes as well as the hydrogeologic factors affecting reactive transport in cold regions. Seasonal freeze-thaw episodically restricts connectivity of transport pathways, which attenuates both transport and reaction rates. However, elevated solute concentrations can depress the freezing temperature of porewater and produce thaw-induced solute transport. Both thermally driven and solute-enhanced thaw can decrease ice content in permafrost, which can have significant implications for solute migration. Therefore, thermo-hydrogeologic process controlling reactive transport in cold-region groundwater systems must be considered when quantitatively assessing the impact of changing environmental conditions on contaminant hydrogeology.

中文翻译:

模拟受多年冻土影响的地下水系统中的反应性溶质输运

了解地面冻融、地下水流和溶质迁移之间的相互作用对于评估永久冻土地区污染物的归宿至关重要。然而,由于地下物质和能量传输过程之间固有的相互作用和耦合,预测受永久冻土影响的地下水系统中的溶质迁移具有挑战性。为此,我们开发了一个数值模型,该模型考虑了耦合地下水流、地下传热和溶质传输,包括水冰相变、溶质相关孔隙水冻结和温度相关溶质反应速率。作为一个说明性的例子,我们提供了模拟来调查加拿大亚北极地区市政污水泻湖的污染可能性。开发了假设不同永久冻土条件的二维地下水模型,以评估与地下水从泻湖流向河流相关的可能污染物迁移情景,包括保守、可降解和吸附性溶质的迁移。模型结果揭示了控制永久冻土景观中含水污染物行为的重要传输机制以及影响寒冷地区反应性传输的水文地质因素。季节性冻融偶尔会限制运输途径的连通性,从而减弱运输和反应速率。然而,升高的溶质浓度会降低孔隙水的冻结温度并产生解冻诱导的溶质迁移。热驱动和溶质增强解冻都可以减少永久冻土中的冰含量,这可能对溶质迁移产生重大影响。因此,在定量评估不断变化的环境条件对污染物水文地质的影响时,必须考虑控制冷区地下水系统反应性输运的热水地质过程。
更新日期:2021-07-22
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