Modeling Contaminant and Nutrient Transport in Permafrost-Affected Groundwater Systems

Presenter:

 

Aaron Mohammed – aaron.mohammed@dal.ca

 

Authors:

 
A.A. Mohammed – Dalhousie University, Halifax, NS, Canada
V.F. Bense – Wageningen University, Wageningen, Netherlands
B.L. Kurylyk – Dalhousie University, Halifax, NS, Canada
R.C. Jamieson – Dalhousie University, Halifax, NS, Canada
J.A. Guimond – Dalhousie University, Halifax, NS, Canada
 

Summary:

Understanding the impacts of permafrost freeze-thaw dynamics on groundwater flow and solute transport is imperative to quantify terrestrial feedbacks to climate change, and for understanding the fate of anthropogenic contamination in arctic and subarctic regions. Meaningful prediction of solute migration in cold regions is challenging however, due to the inherent interactions and coupling between mass and energy transport processes in the subsurface. 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 chemical reactions. We present simulations evaluating groundwater flow and transport dynamics under various permafrost scenarios, considering the mobilization of dissolved organic carbon released by permafrost thaw, as well as potential groundwater contamination from wastewater lagoons underlain by permafrost. Results reveal important transport mechanisms controlling the behavior of solutes in permafrost landscapes. Seasonal freezing in the active layer causes the temporary immobilization of water and solutes, and restricts connectivity of transport pathways, which attenuates both transport and reaction rates. Elevated solute concentrations can depress the freezing temperature of porewater and produce thaw-induced transport which enhances solute migration. Simulations show that solute depression of freezing characteristics, and temperature effects on solute reaction properties, can strongly influence solute movement and subsurface biogeochemical processes. Such model development and ongoing improvement will be critical for further understanding the hydrogeologic processes controlling the fate and transport of contaminants and nutrients in warming permafrost environments. 

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