Solute depletion and reduced hydrological connectivity in subarctic patterned peatlands disturbed by mine dewatering.

Patterned bog and fen peatlands of the Hudson Bay Lowlands, which form one of the largest continuous peatland complexes in the world, are globally significant stores of carbon and important water conveyance and storage features on the landscape. However, expansion of resource exploration and extraction combined with warmer temperatures associated with climate change may result in reduced water availability to these peatland complexes, potentially disrupting peatland hydrological connectivity and hydrogeochemical cycling. A case study on the effects of reduced water availability on peatland hydrological and geochemical function was conducted near the De Beers Victor Diamond Mine, located 90 km west of Attawapiskat. Active dewatering occurred here over a 12-year period (2007-2019) during which a 1.5 km transect was monitored within the mine impacted radius. Hydrological (streamflow and groundwater levels) and chemical (porewater and surface water samples) parameters were collected at the impacted transect and two nearby unimpacted reference sites. Results demonstrated that impacted peatlands had depleted water storage and spent an average of 50 % less time hydrologically connected than unimpacted peatlands. By the end of the study period, increasingly depleted water storage within the dewatering radius resulted in disproportionately lower flowrates in two tributaries downgradient of the mine-impacted peatlands when compared with the reference sites. Moreover, diminished water storage allowed solute-depleted precipitation to reach greater depths within the peat profile, while stronger downwards gradients suppressed upwards flow into fens, limiting the amount of solute-enriched water reaching the surface. The recovery of fen solute concentrations will be a prolonged process (i.e., decades to centuries) due to the slow rate of upwards diffusion, which may result in the transition of these systems towards ombrotrophic bogs. Further studies should focus on the susceptibility of these impacted systems to further reductions in water availability due to climate change.