Preferential recharge in a reclaimed tailings sand upland: Implications on solute flushing

A peatland watershed was constructed on a post-mined oil sands lease in Northern Alberta, Canada, with the intention of replicating the function of natural wetlands removed by surface mining. Given the potential for moisture limited conditions due to the sub-humid regional climate, ensuring sufficient water availability in these landscapes is a principal concern. This research demonstrates how small recharge basins can modify the hydrology to promote groundwater recharge critical for sustaining saturated conditions in a downgradient wetland. Location was important in determining the efficacy of recharge basins. Specifically, basins placed at the confluence of two hillslopes detained substantial volumes of runoff due to large upslope areas, contributing ~30% of the groundwater budget to the fen, while only occupying 1% of the upland area. Basins situated near low relief hillslopes or altogether isolated from a hillslope did not detain appreciable runoff and therefore had a minor role in recharging groundwater. Groundwater in the vicinity and downgradient of active recharge basins had considerably lower solute concentrations because of dilution. This suggests that basins can not only enhance recharge within engineered landscapes, providing a consistent and focused supply of water to upland aquifers, but offer relatively fresh groundwater to downgradient ecosystems. This could ameliorate the impact of high salinity present in oil sands process-affected materials. •Basins at the base of slopes promote recharge, but are vulnerable to infilling.•Recharge basins contributed 30% of the groundwater budget to the fen.•Location and size determined the efficacy of recharge basins.•Recharge diluted groundwater concentrations, but increased the sodium mass flux.