Abbey Marcotte

Climate change is increasing wildfire frequency and severity, expanding into ecosystems less historically prone to wildfires, such as temperate peatlands. These peatlands are significant potable water sources that have accumulated legacy contaminants for decades. A major concern and uncertainty for ecosystem health and drinking water supply is the timing and magnitude of pollutant release, particularly potentially harmful metals, following extreme disturbances. Here, we examine mobilisation of legacy metals in a contaminated temperate blanket peatland following extreme drought and wildfire occurrence, focussing on key metal sources, transport pathways and deposition on the lake-bed of the receiving reservoir. We found that erosion of metal-rich hillslope peat and ash peaked three months post-wildfire, particularly in extreme burn severity areas, contributing to substantial deposition of metal-rich material in the receiving reservoir. Elevated metal concentrations in suspended sediments were observed nine months post-wildfire during spring rainstorm events. Dissolved metals in the streamflow were comparatively orders of magnitude lower, but displayed similar timing in concentration increases. Together this indicates limited acute but potential chronic impacts that extend beyond our study’s monitoring period. These pathways can present different challenges for managing water supplies. Our findings provide critical insights into the spatio-temporal dynamics of metal transport in peatlands following severe drought and wildfire. Understanding these pathways is essential for assessing current and future risks to water quality and developing targeted management strategies in northern peatland regions that are reliant on peat-rich catchments for drinking water and that are increasingly vulnerable to climate-induced disturbances.

Intact peatlands provide hydrological ecosystem services, such as regulating water regimes and immobilizing pollutants within catchments. Climate change impacts including drought and wildfire may impair their functioning, potentially impacting ecosystem service delivery. Here we investigate stream water quality changes following the combined impacts of a summer drought and wildfire in a peat-dominated catchment in the UK during 2018. The study catchment stores legacy pollutants (i.e., metals) due to past industrial activity, thus making it particularly susceptible to pollutant release during wildfires. We quantified changes in water chemistry during five storm events over a 9-month period following the wildfire. Concentration-discharge (C-Q) relationships for nine solutes were analyzed to explore changes in activation and connectivity of solute source zones. Hysteresis and flushing indices of C-Q responses further described solute dynamics during storm events. We found that most nutrient and base cation concentrations in the stream discharge were highest in the immediate post-fire storm events and decreased during subsequent autumn and spring storms. Metal concentrations increased during autumn and spring storms, indicating delayed mobilization from within-peat or distal headwater sources. Our findings suggest that seasonal re-wetting and hydrologic connectivity following disturbance influenced solute source zone activation and transport in the study catchment. Water quality responses associated with wildfire and drought were primarily observed in the months following the wildfire, suggesting mobilization of pollutants peaks shortly after fire. Our results contribute to a critical understanding of the future of water quality risks in temperate peatland catchments subject to disturbances exacerbated by climate change.