Hydrological contaminant mobilisation from thawing permafrost in Alaska

Daniëlle Kraak , Jan Nitzbon , Simone Stuenzi, Soraya Kaiser, Alexander Oehme, Christina Himmelsbach, Pernille Erland Jensen, Sebastian Westermann, Jorien E. Vonk, Moritz Langer

Global warming and permafrost thaw increasingly threaten contaminated sites across Alaska, altering contaminant mobilisation risks in sensitive ecosystems and communities. To assess this threat, we used the SIRIUS database to identify 1261 active contaminated sites within Alaska’s permafrost region, noting that many sit near lakes, rivers, and coastlines. We evaluated current and future hydrological mobilisation potential at these sites using the CryoGridLite model under SSP1-2.6 and SSP5-8.5 climate scenarios, accounting for how permafrost thaw and shifting precipitation alter groundwater levels. We then determined overall aquatic hazard potential by integrating site-specific characteristics, including contaminant toxicity, solubility, and proximity to water bodies. Our results show that across Alaska 428 contaminated sites already carry a 'high' to 'very high' mobilisation risk. In the Alaska Tundra ecoregion, about 48% (238) of contaminated sites fall into these categories, while the Alaska Boreal Interior (110 sites, 9.6%) and Boreal Cordillera ecoregions (36 sites, 29.3%) contain fewer high-risk sites and show limited future change. These regional differences reflect distinct environmental controls: in tundra regions, proximity to water bodies and extensive wetland networks heighten mobilisation potential despite generally lower contaminant toxicity, whereas higher contaminant toxicity dominates the drier Boreal Interior where hydrological pathways are limited. While northern coastal regions show the largest relative increases in hydrological mobilisation potential, absolute values remain low, causing minor changes in risk classification. Conversely, drying in central Alaska, likely driven by increased evapotranspiration, could reduce future contaminant mobilisation potential despite enhanced permafrost thaw. Ultimately, these findings highlight the complex and regionally distinct controls on contaminant mobilisation under climate change, offering crucial guidance for targeted northern environmental management.