Evidence of Smoke From Wildland Fire in Surface Water of an Unburned Watershed

Large wildland fires generate smoke that can compromise air quality over a wide area. Limited studies have suggested that smoke constituents may enter natural water bodies. In an 18-year water monitoring study, we examined whether smoke from distant wildland fires had a detectable effect on ion content in a mountain river in an unburned watershed. Significant local smoke occurred in six years as traced by MODIS satellite data of fires, regional and local atmospheric fine particulate matter (PM2.5), and the amount of potassium (K+) in PM2.5 as a marker of vegetation combustion. Rainwater had elevated K+ and calcium (Ca2+, also associated with wildland fire smoke) in high-smoke years compared to low-smoke years, and was the primary route of atmospheric deposition. Similarly, river water in high-smoke years had elevated concentrations of K+ and Ca2+, with a higher ratio of K+ to Ca2+ compared to low-smoke years. River concentrations were generally unrelated to river discharge and observed K+ concentrations in high-smoke and low-smoke years could be accounted for by atmospheric deposition. Our study provides early evidence that wildland fires affect water quality far beyond the watersheds where they occur. Wildland fires distribute vast quantities of smoke containing nutrients, toxins and microbes and are increasing in North America. Potassium is a routinely-measured water quality parameter that can act as an indicator of biomass smoke inputs. Further work is needed on the patterns and processes by which wildfire smoke enters water as well as on the consequences for ecosystems and human health.