Abstract
Large wildfires generate smoke that greatly compromises 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 wildfires had a detectable effect on
ion content in a mountain river in an unburned watershed. Significant
local wildfire 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 wildfire smoke) in
smoke years compared to no-smoke years, and was the primary route of
atmospheric deposition. Similarly, river water in smoke years had
elevated concentrations of K+ and
Ca2+, with a higher ratio of K+ to
Ca2+ compared to no-smoke years. River concentrations
were generally unrelated to river discharge and observed
K+ concentrations in smoke and no-smoke years could be
accounted for atmospheric deposition. Our study provides early evidence
that wildfires affect water quality far beyond the watersheds where they
occur. Wildfires are increasing in frequency and extent worldwide,
widely distributing vast quantities of smoke containing nutrients,
toxins and microbes. Potassium is a routinely-measured water quality
parameter that can act as a sentinel of 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.