Civil Engineering ETDs

Publication Date

Summer 7-14-2018

Abstract

Massive amounts of wood ash are deposited into nearby streams as a result of runoff from storm events after increasing frequency of wildfire events that negatively affect water quality. Ash and debris from burned vegetation can alter the pH, turbidity and dissolved oxygen (DO) in water and can release heavy metals, organic matter, and nutrients. 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 decrease 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) v 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 are essential 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.

Keywords

Wildfire, Wood Ash, Metal, Valles Caldera, Metal Reactivity, Water Chemistry

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Jose M. Cerrato

Second Committee Member

Abdul Mehdi Ali

Third Committee Member

Mark C. Stone

Fourth Committee Member

Rebecca Bixby

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