The timing of groundwater recharge is poorly understood in high-latitude, cold temperate systems, particularly in formerly glaciated cratonic interiors such as the Canadian Shield. Repeated glacial scouring and minor deposition in these regions left a thin, patchy veneer of low-permeability glacial till atop Precambrian fractured bedrock. In these regions, the interplay of frost dynamics with precipitation and snowmelt exerts a strong control on recharge processes due to the impact of seasonally-frozen ground on infiltration and surface runoff.
We explored this relationship in a Northeastern Minnesota watershed using a combination of low-cost soil-moisture and thermistor arrays, continuous monitoring of groundwater levels and streamflow, stable-isotope analysis of surface and subsurface waters, and field observations. Preliminary results for summer 2019–spring 2020 suggest that a significant amount of recharge occurred in the fall, after plant senescence but before soil freeze-up, and that recharge in the spring was a gradual response to snowmelt and spring rain. In spring 2020, soil frost likely did not inhibit significantly the groundwater response to snowmelt due to a large and quickly established snowpack that limited soil exposure to cold air and thus prevented deep soil frost. Rather, the low-permeability soils (tills) likely had a stronger influence on delaying infiltration and recharge. This study will continue in spring 2021 and will provide insight into the complex dynamics between frost, snowmelt, and groundwater recharge in these systems.
Speaker(s)
Mitchell Ihlang, John Swenson, Salli Dymond, University of Minnesota Duluth