Groundwater recharge during spring thaw in the Prairie Pothole Region via large, unfrozen preferential pathways

Snowmelt is an important source for replenishing groundwater in the Prairie Pothole Region of North America. Snowmelt collects in landscape depressions (forming temporary ponds) as a result of frozen soil impeding infiltration. These ponds aid in replenishing groundwater during spring thaw. Little is known, however, about the dynamic changes in groundwater and the associated physical state of the soil at the time of recharge. In February 2000, the water table within a 2-ha landscape depression rose by 1 m within 24 h after a pond (surface area of 2000 m(2)) had formed as a result of snowmelt runoff. Recharge of groundwater occurred despite a 0.85-m thick layer of frozen soil. Five unfrozen pathways or conduits were found within the soil profile underlying the pond. These vertical conduits had a surface area that varied from about 0.1 to 0.4 m(2). Two conduits were completely thawed and protruded through (bypassed) the frozen layer of soil. All conduits were located in the bottom of the depression within an area of about 10 m(2). The structure and texture of soil within these conduits were similar to soil adjacent to the conduits. Recharge of groundwater within a prairie pothole during snowmelt is a seemingly localized process where surface water drains through thawed conduits or pathways located near the bottom of landscape depressions. The importance of these pathways in groundwater hydrology warrants further investigation into their formation.