Downstream variation of environmental tracers in Strawberry Creek reveals potential interaction with a buried-valley aquifer (Alberta, Canada)

Buried bedrock valleys in North America are often filled with coarse-grained deposits that form productive buried-valley aquifers, providing a valuable water source for human use. However, the role of buried-valley aquifers in the hydrology of watersheds, including baseflow generation and supporting ecosystems, is not widely recognized. This study demonstrates that the presence of a buried-valley aquifer influences near-surface hydrology, specifically the interaction of a creek coaligned with the bedrock valley thalweg. We combine synoptic sampling of environmental tracers and geochemistry of the creek during low flow conditions and regional groundwater data to determine downstream variation in groundwater interaction. Modelled downstream variation suggests that the greatest amount of groundwater discharge occurs where the buried-valley aquifer is present beneath, but not necessarily in direct contact with the creek. Further, a shift in baseflow source to the creek occurs depending on the depth to bedrock, indicated by a change in water isotopic and chemical composition similar to that of groundwater located in the sediments above bedrock to a signature similar to groundwater in the underlying bedrock formations. This study demonstrates that buried-valley aquifers can focus groundwater flow to a modern-day creek valley, providing a unique source of baseflow in the Canadian Prairies and midwestern United States. The interaction between buried-valley aquifers and streams has implications for water allocation and land use planning, whereby a critical baseflow source may also be a target aquifer to develop with good quality water.