Where there's fire, there's smoke: estimating smoke emissions from Hudson Bay Lowland mining

Recent Canadian wildfires have generated daily mean PM_2.5 values nearly 10 times the World Health Organization recommended limits in urban centers. Northern peatlands present a unique risk to air quality conditions as they: (i) store globally significant quantities of belowground carbon (C) in peat, which may fuel multiyear fires; and (ii) are prone to smouldering combustion, an inefficient low-temperature reaction that produces more smoke with increased particulate matter than flaming combustion. The same mechanisms that allow C to accumulate also support the accumulation of other deposited elements, including arsenic, mercury, lead, and nickel. Historically, northern peatlands have been resistant to burning due to the high near-surface water content and low bulk density of peat; however, water table drawdown alters these ecological protections, rendering peatlands susceptible to increased wildfire frequency, severity, and areal extent.

The Hudson Bay Lowlands (HBL) of Ontario, Canada, represent one of the largest intact peatland complexes remaining on Earth, yet ~5,000 km² has been claimed for mining of critical minerals. Dewatering practices required to facilitate mine development and operations can reduce the water table in surrounding peatlands by up to 75 cm. Drying at the soil surface and along the peat profile increases risk for wildfire ignition and subsequent smouldering combustion, potentially forming an additional potent source for smoke emissions and particulate matter while threatening HBL C stores. Therefore, the objective of this study was to estimate the impact of several mine dewatering scenarios on potential smoke emissions from the peatlands of HBL. We simulated the potential effect of mine dewatering on soil moisture profiles using Hydrus 1D with hydrophysical properties derived from HBL peat profiles. Hydrus 1D simulations were used to assess susceptibility to combustion and, consequently, estimates of smoke emissions based on antecedent weather conditions measured prior to wildfires in the study region.

Preliminary results suggest that wildfire vulnerability will increase, which will lead to greater smoke emissions as a direct result of drying from mining and infrastructure development. Furthermore, due to increased human activity, ignition sources will also increase, leading to peatlands that are both more vulnerable to severe burning and an increased risk of fires igniting.

Although the focus of this study has been on the HBL, this work can be applied to other peatland systems that may undergo drying scenarios in the future, be it from mining, climate change, or drainage. Northern landscapes that have traditionally been resistant to wildfire may not necessarily remain as such, and the implications for human health may be far-reaching, with potentially compounding effects of smoke and the additional toxic elements that may be released as a result of burning.