Potable water sources in a contaminated temperate peatland resistant to acute impacts but vulnerable to legacy effects of extreme wildfire

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.