Metals export to streams during base flow and storm events in the 416 Fire, southwest Colorado
Date
2021
Authors
Pulver, Bryce A., author
Kampf, Stephanie K., advisor
Ross, Matthew R. V., committee member
Leisz, Stephen J., committee member
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Abstract
With approximately two thirds of the Western U.S. relying on fresh water from forested areas, it is vital to understand how wildfires can affect the release of metals into soil water and streams. Moderate to high intensity fires can alter the physical and chemical properties of soil, allowing elevated release of sediment, organic matter, and nutrients to streams. While many studies have focused on how fires affect sediment loading, nutrient export, and organic matter; less research has been conducted on how wildfire impacts the export of metals. This study examines metals export from the 2018 416 fire near Durango, CO during baseflow and storm events. Six tributaries (3.88-38.8 km2) and five sites on Hermosa Creek (152-435 km2) were sampled and analyzed for metal concentrations. We examine how metal concentrations relate to burn severity and watershed characteristics under different flow conditions using both univariate correlation analysis and multivariate models. Metal concentrations were significantly greater in burned baseflow samples compared to unburned locations for As, Ca, K, Mg, Mo, Si, Sr, and Zn. Concentrations of As in baseflow exceeded the Environmental Protection Agency's (EPA's) primary drinking water maximum contaminant level (MCL). Metal concentrations in baseflow were positively correlated with percentage of watershed burned, burn severity, and basin slope, and negatively correlated with basin elevation, drainage area, and average annual precipitation. Metal concentrations increased significantly (mean factor change = 20.6) in storm samples compared to pre-storm samples for Al, As, Ba, Ca, Cr, Fe, K, Li, Mg, Mn, Si, and Zn with Al, As, Ba, Be, Cd, Cr, Fe, Mn, Ni, and Pb being above an EPA or World Health Organization (WHO) MCL. Although storm samples were limited, metal concentrations were correlated with watershed burn severity (r ~ 0.8), indicating elevated metal concentrations likely came from burned areas. Overall, this study demonstrated that wildfires cause elevated metal concentrations in both baseflow and stormflow, but with the exception of As, only the stormflow metal concentrations posed water quality concerns, with 10 metals exceeding both EPA and WHO MCL's for drinking water.
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Subject
post-fire
trace metals
base flow
water quality
storm events