Published Date:
November 2018

José M. Cerrato, Asifur Rahman

We investigated interfacial processes affecting metal mobility in wood ash burned under laboratory-controlled conditions using aqueous chemistry, microscopy, and spectroscopy analyses. Wood was collected from the Valles Caldera National Preserve in New Mexico, which has experienced two wildfires since 2011 that have caused devastating effects. Wood samples (e.g., Ponderosa Pine, Quaking Aspen, and Colorado Blue Spruce) collected from this site were exposed to temperatures of 60°C, 350°C and 550°C. Pine ashes burned at 350°C and 550°C were associated with high concentrations of metals (i.e., Cu, Cr, Si, Ni, Fe, K and Mg). Pine ash burned at 350°C had the highest content of Cu (4997 + 262 mg kg-1), Cr (543 + 124 mg kg-1), and labile dissolved organic carbon (DOC, 11.3 + 0.28 mg L-1). Metal sorption experiments were conducted by reacting 350°C Pine ash separately with 10μM solutions of Cu(II) and Cr(VI), as examples of a cation and an oxyanion found in high concentrations in water following wildfire events near VALL. High decreases in Cu(II) concentration (up to 92%) was observed in solution while Cr(VI) showed limited decrease (up to 13%) in concentration after 180 mins of reaction. X-ray photoelectron spectroscopy (XPS) analyses detected increased association of Cu(II) on the near surface region of the reacted ash from the sorption experiments compared to the unreacted ash. The results from this investigation suggest that dissolution and sorption processes should be considered to understand the transport of metals in water following wildfires. This study provides relevant insights about the potential effects of metals transported by wood ash on water quality that have important implications for post-fire recovery and response strategies

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Wildfires, Wood Ash, Metal Reactivity, Dissolved Organic Carbon, Metal Mobility, Metal Sorption, Post-fire Recovery, Valles Caldera National Preserve