Wildfires in Alaskan Boreal Forests Release Elevated Levels of Polyaromatic Hydrocarbon

Despite the increasing intensity of wildfires in Alaska's extensive and flammable boreal forests, there remains a critical gap in understanding their environmental impacts, particularly on water systems. This study examines water, soil, sediment, and ash samples from the North and Middle Fork regions of the upper Chena River watershed, which faces recurring annual wildfires. Polyaromatic hydrocarbon (∑PAH) concentrations range from 41.1 to 1455.3 ng/L in water and 14.5 to 63.2 microg/kg in sediments, topsoil, and ash. Water primarily contains phenanthrene and trace levels of pyrene and fluorene, while solid samples exhibit elevated levels of naphthalene and phenanthrene, along with trace amounts of acenaphthene, anthracene, and fluorene. Runoff and terrain slope patterns derived from topographical analyses of the Chena River watershed might explain some of these elevated PAH levels, which surpass those found in other wildfire-affected watersheds worldwide. These findings underscore the risks to aquatic ecosystems, as PAHs are toxic, bioaccumulative, and can lead to the formation of harmful disinfection byproducts. Thus, the increasing frequency of wildfires in Alaska poses a significant threat to local communities relying on wildfire-impacted freshwater for fishing and drinking.