Hydrological functions of a mine-impacted and natural peatland-dominated watershed, James Bay Lowland

• The hydrology of a peatland-dominated watershed under aquifer depressurization/dewatering was evaluated over 3 years.
• Deep seepage in bogs and fens showed the greatest variation from natural systems.
• Evapotranspiration rates were found to be slightly lower than in natural systems.
• As the headwaters were unaffected by the mine, runoff was not noticeably hindered.
• The extent of the mine drawdown was not enough to out-weigh the variations in climate.

Study regionThis study was conducted in Northern Ontario, Canada, in the middle of the Hudson-James Bay. Lowland: one of the world’s largest wetland complexes.Study focusNorthern latitudes are expected to be the most impacted by climate change in the next century and adding to this stressor are increased mineral exploration activities, such as the De Beers Victor Mine, a large open-pit diamond mine. Because of the extremely low relief and presence of marine sediments, horizontal runoff and vertical seepages losses are minimal. As a consequence of this aquifer dewatering must occur to keep the open-pit mine dry. What is unknown is how the aquifer dewatering would impact the water balance of a peatland-dominated watershed. This study examines 3 years of aquifer dewatering from 2009 to 2011.New hydrological insightsDeep seepage (groundwater recharge) varied with marine sediment thickness and represented a significant loss to the local system. Large downward fluxes were also measured in fen systems that are typically local discharge zones. Evaporation rates were also found to be lower in the bogs and fens and where impacted by lower water tables. When evaluating the water balance, with only 14.5% of the watershed impacted by the mine, the hydrological function of the entire watershed is more driven by seasonal climate variations than mine dewatering.