Mining and Climate Change Alters Water Storage and Streamflow Dynamics of Northern Peatland‐Dominated Catchments

Abstract The Hudson Bay Lowlands (HBL) of northern Ontario, a globally significant carbon store, are characterized by expansive peatland complexes of patterned bogs and fens, which play a vital role in regional water regulation. These peatlands are threatened by disturbance from large‐scale resource extraction and projected climate change, both of which have the potential to compromise their ecohydrological function. Field measurements and numerical modeling were used to investigate the hydrological responses of peatlands and downgradient streamflow as a consequence of disturbance from mining and shifts in climate, individually and in combination. Mine dewatering reduced groundwater storage by as much as 150 mm, equivalent to a water table lowering of 75 cm, thereby decreasing annual streamflow by 66% in impacted tributaries. Although the projected increases to precipitation and evapotranspiration due to climate change were approximately balanced, resulting in minor changes to storage, there were pronounced shifts in the temporal patterns of streamflow, with a diminished snowmelt and spring freshet occurring a month earlier. When considering the cumulative impacts of climate change coupled with mining, a potential shift in peatland ecohydrology toward new equilibria is plausible, implying altered water movement across the landscape and compromised ecosystem function. This study emphasizes the critical need for further monitoring and modeling efforts to characterize the thresholds and mechanisms driving these ecohydrological changes. This research will guide future investigations on the implications of disturbance on local and regional hydrologic connectivity and facilitate the protection of peatland ecosystems in the HBL and other northern peatland‐dominated landscapes.