Wildfire-driven changes in hydrology mobilize arsenic and metals from legacy mine waste

Science of the Total Environment
By: , and 



Wildfires burning in watersheds that have been mined and since revegetated pose unique risks to downstream water supplies. A wildfire near Boulder, Colorado that burned a forested watershed recovering from mining disturbance that occurred 80-160 years ago allowed us to 1) assess arsenic and metal contamination in streams draining the burned area for a five-year period after the wildfire and 2) determine the fire-affected hydrologic drivers that convey arsenic and metals to surface water. Most metal concentrations were low in the circumneutral waters draining the burned area. Water and sediment collected from streams downstream of the burned area had elevated arsenic concentrations during and after post-fire storms. Mining-related deposits were the main source of arsenic to streams. An increased proportion of overland flow relative to infiltration after the fire mobilized arsenic- and metal- rich surface deposits and wildfire ash into streams within and downstream of the burned area. The deposition of this sediment into stream channels resulted in the remobilization of arsenic for the five-year post-fire study period. It is also possible that enhanced subsurface flow after the fire increased contact of water with arsenic-bearing minerals exposed in underground mine workings. Other studies have reported that wildfire ash can be an important source of arsenic and metals to surface waters, but wildfire ash was not an important source of arsenic in this study. Predicted increases in frequency, size, and intensity of wildfires in the western U.S., a region with widely dispersed historical mines, suggest that the intersection of legacy mining and post-wildfire hydrologic response poses an increasing risk for water supplies.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Wildfire-driven changes in hydrology mobilize arsenic and metals from legacy mine waste
Series title Science of the Total Environment
DOI 10.1016/j.scitotenv.2020.140635
Volume 743
Year Published 2020
Language English
Publisher Elsevier
Contributing office(s) WMA - Earth System Processes Division
Description 140635, 15 p.
Country United States
State Colorado
City Boulder
Other Geospatial Four Mile Creek
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