Skip to main content
U.S. flag

An official website of the United States government

Wildfires influence mercury transport, methylation, and bioaccumulation in headwater streams of the Pacific Northwest

July 30, 2024

The increasing frequency and severity of wildfires are among the most visible impacts of climate change. However, the effects of wildfires on mercury (Hg) transformations and bioaccumulation in stream ecosystems are poorly understood. We sampled soils, water, sediment, in-stream leaf litter, periphyton, and aquatic invertebrates in 36 burned (one-year post fire) and 21 reference headwater streams across the northwestern U.S. to evaluate the effects of wildfire occurrence and severity on total Hg (THg) and methylmercury (MeHg) transport and bioaccumulation. Suspended particulate THg and MeHg concentrations were 89 and 178% greater in burned watersheds compared to unburned watersheds and increased with burn severity, likely associated with increased soil erosion. Concentrations of filter-passing THg were similar in burned and unburned watersheds, but filter-passing MeHg was 51% greater in burned watersheds, and suspended particles in burned watersheds were enriched in MeHg but not THg, suggesting higher MeHg production in burned watersheds. Among invertebrates, MeHg in grazers, filter-feeders, and collectors was 33, 48, and 251% greater in burned watersheds, respectively, but did not differ in shredders or predators. Thus, increasing wildfire frequency and severity may yield increased MeHg production, mobilization, and bioaccumulation in headwaters and increased transport of particulate THg and MeHg to downstream environments.

Publication Year 2024
Title Wildfires influence mercury transport, methylation, and bioaccumulation in headwater streams of the Pacific Northwest
DOI 10.1021/acs.est.4c00789
Authors Austin K. Baldwin, James Willacker, Branden L. Johnson, Sarah E. Janssen, Collin Eagles-Smith
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Science & Technology
Index ID 70257008
Record Source USGS Publications Warehouse
USGS Organization Forest and Rangeland Ecosys Science Center; Idaho Water Science Center; Upper Midwest Water Science Center