Integrated hydrogeological and geophysical study of depression-focused groundwater recharge in the Canadian prairies

In the northern prairie region of North America, numerous seasonal wetlands and ephemeral ponds form as snowmelt water is trapped in small topographical depressions. A detailed hydrogeological investigation is combined with electrical resistivity imaging (ERI) to evaluate the roles of the wetlands and ponds on depression-focused groundwater recharge at the St. Denis National Wildlife Area in Saskatchewan, Canada. The analysis of groundwater samples indicated two distinct geochemical zones: a zone of salt leaching under Wetland 109 and zones of salt accumulation under the adjacent uplands. Two intermediate zones were identified as partially leached or mixed leached-unleached and premodern or mixed saline-nonsaline water. The resistivity images of the areas around 109 were classified using the correlation between ERI-derived electrical conductivity (EC) and the groundwater EC. The ERI data clearly showed that depression-focused recharge occurs under all depressions regardless of size. Leaching is observed to the depth of a regional intertill aquifer, indicating that depression-focused recharge contributes to the regional groundwater system. The ERI data also revealed the complex pattern of salt distribution that could not have been recognized by hydrogeological observations alone. The complex distribution of salts appears to be caused by interaction between wetlands and variations in topography.