Metal Reactivity in Laboratory Burned Wood from a Watershed Affected by Wildfires

Abstract

We investigated interfacial processes affecting metal mobility by wood ash under laboratory-controlled conditions using aqueous chemistry, microscopy, and spectroscopy. The Valles Caldera National Preserve in New Mexico experiences catastrophic wildfires of devastating effects. Wood samples of Ponderosa Pine, Colorado Blue Spruce, and Quaking Aspen collected from this site were exposed to temperatures of 60, 350, and 550 °C. The 350 °C Pine ash had the highest content of Cu (4997 ± 262 mg kg), Cr (543 ± 124 mg kg), and labile dissolved organic carbon (DOC, 11.3 ± 0.28 mg L). Sorption experiments were conducted by reacting 350 °C Pine, Spruce, and Aspen ashes separately with 10 μM Cu(II) and Cr(VI) solutions. Up to a 94% decrease in Cu(II) concentration was observed in solution while Cr(VI) concentration showed a limited decrease (up to 13%) after 180 min of reaction. X-ray photoelectron spectroscopy (XPS) analyses detected increased association of Cu(II) on the near surface region of the reacted 350 °C Pine ash from the sorption experiments compared to the unreacted ash. The results suggest that dissolution and sorption processes should be considered to better understand the potential effects of metals transported by wood ash on water quality that have important implications for postfire recovery and response strategies.

Organic Functional Group Chemistry in Mineralized Deposits Containing U(IV) and U(VI) from the Jackpile Mine in New Mexico

“…These findings are within range of those of another study in the Grants Belt . The low H/C ratio (0.513) indicates high aromaticity as suggested in other studies. , Moreover, low O/C (0.243) and (O + N)/C (0.247) ratios indicate low hydrophilicity and polarity. − Elemental analyses require a pure organic sample to avoid accounting for the C, O, H, and N from the minerals contained in the sample. The C detected with this technique is within the range identified by TGA and LOI.…”

“…53,54 Moreover, low O/C (0.243) and (O + N)/C (0.247) ratios indicate low hydrophilicity and polarity. 53-56 Elemental analyses require a pure organic sample to avoid accounting for the C, O, H, and N from the minerals contained in the sample. The C detected with this technique is within the range identified by TGA and LOI.…”

Wildland–urban interface wildfire increases metal contributions to stormwater runoff in Paradise, California

“…The primary components of wood ash include Ca (13-34%), K (1-13%), Mg (0.1-9%), Al (0.5-1.9%), and Mn (<1%), and Fe (<1%). 46,47 The metals Ca and Mg tend to form carbonate minerals, while Al, Mn, and Fe tend to be in the form of oxides. 46,47 In addition to carbonate minerals and oxides, silicate minerals that include Al, Ca, Fe, K, and Mn can be a component of ash, and the presence of phosphate and sulfate minerals (e.g., apatite, gypsum) have also been reported.…”

“…46,47 The metals Ca and Mg tend to form carbonate minerals, while Al, Mn, and Fe tend to be in the form of oxides. 46,47 In addition to carbonate minerals and oxides, silicate minerals that include Al, Ca, Fe, K, and Mn can be a component of ash, and the presence of phosphate and sulfate minerals (e.g., apatite, gypsum) have also been reported. 47,48 The observation of increased hardness during early season ushing is explained by the presence of the readily dissolved mineral forms while later season storms with more energy mobilized the oxide forming, less soluble particulates.…”

Quantification of Bioaccessible and Environmentally Relevant Trace Metals in Structure Ash from a Wildland–Urban Interface Fire

“…Following severe burns, slopes lose the vegetation that prevents erosion, increasing vulnerability to debris flow landslides during rainstorms . Erosion and wind events deposit ash onto soils − and surface waters, − thus contaminating water sources , and increasing sediment load …”