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

Environmental Science & Technology
By: , and 

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Abstract

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.

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Publication type Article
Publication Subtype Journal Article
Title Wildfires influence mercury transport, methylation, and bioaccumulation in headwater streams of the Pacific Northwest
Series title Environmental Science & Technology
DOI 10.1021/acs.est.4c00789
Volume 58
Issue 32
Year Published 2024
Language English
Publisher ACS Publications
Contributing office(s) Forest and Rangeland Ecosys Science Center, Idaho Water Science Center, Upper Midwest Water Science Center
Description 14 p.
First page 14396
Last page 14409
Country United States
State Idaho, Oregon, Washington
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