Metals Export to Streams in the 416 Fire Burn Area During Base Flow and Storm Events

Abstract:

With approximately two thirds of the Western U.S. relying on fresh water from forested areas it is vital to understand how wildfires may affect the transport of metals in watersheds. Moderate to high intensity fires can alter the physical and chemical properties of soil, allowing elevated release of sediment, metals, organic matter, and nutrients. These substances can be mobilized by overland flow and surface erosion during storm events. This causes metals to be transported into streams, potentially impairing water quality. Many studies have focused on how fires affect sediment loading, nutrient export, and organic matter, but less research has been conducted on how wildfire affects the export of metals. This study examines metal export from the 2018 416 fire near Durango, CO. Six tributaries (388-3884 ha) and five sites on the main stream (15203-43511 ha were sampled during baseflow and storm events to examine general water chemistry and metals. We examine how metal concentrations relate to burn severity and watershed characteristics under both low and high flow conditions using both univariate correlation analysis and multivariate models. At low flows metal concentrations generally increased with percentage of watershed burned, burn severity, and basin slope, and decreased with basin elevation, drainage area, and average annual precipitation. At high flows large increases of concentrations to metals were observed in the tributaries that were captured during storm events, ranging from 0-1.47 x 10⁵ percent increase. This presentation will discuss what variables are directly and inversely related to the concentration of metals observed in the burn area.