The hydrogeologic connectivity of a low-flow saline-spring fen peatland within the Athabasca oil sands region, Canada

Saline springs can provide clues as to the nature of groundwater flow, including how it relates to subsurface wastewater storage and the distribution of solutes in the landscape. A saline-spring peatland neighboring a proposed in-situ oil facility was examined near Fort McMurray, Alberta (Canada). The study area is situated just north of a saline groundwater discharge zone, which coincides with the erosional edge of the Cretaceous Grand Rapids Formation. Na⁺ (mean 6,949 mg L⁻¹) and Cl⁻ (mean 13,776 mg L⁻¹) were the dominant salts within the peatland, which increased by an order of magnitude in the opposite direction to that of the local groundwater flow. Rivers and freshwater wetlands within the study area had anomalously high salinities, in some cases exceeding 10,000 mg L⁻¹ total dissolved solids within deeper sediments. Saline-spring features were observed as far as 5 km from the study area. A low-permeability mineral layer underlying the peatland restricted vertical groundwater exchange (estimated to be less than several mm over the 4-month study period). Sand and gravel lenses underlying the fen’s high-salinity zone may function as areas of enhanced discharge. High Cl/Br ratios point to halite as a potential source of salinity, while δ¹⁸O and δ²H signatures in groundwater were lower than modern-day precipitation or Quaternary aquifers. The complex connectivity of saline-spring wetlands within the landscape has implications for industry and land-use managers, and justifies incorporating them into monitoring networks to better gauge the magnitude and flow history of natural saline discharge in the oil sands region.