Date of Award

Spring 1-1-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Fernando L. Rosario-Ortiz

Second Advisor

R. Scott Summers

Third Advisor

Deborah Martin

Abstract

Wildfires are a natural and ubiquitous phenomenon that leave behind a perturbed hydrologic environment. Post-fire landscapes become susceptible to erosion, decreased infiltration capacity, and soil hydrophobicity, which facilitate transport of post-fire residue into surface waters serving potable water sources. The risks posed by post-fire residue deposition to raw water sources and subsequent impairment of water quality are difficult to understand due to the complex nature of wildfire effects. Research indicates that soil organic matter (SOM) and plant material undergo chemical and structural changes following heating. As a result, water extractable organic matter from forest floor material altered by heat may be significantly different from that of unaltered material in quantity and quality. To address the impacts of ash on water quality, surface soils and litter were progressively heated to a range of temperatures (150 to 550˚C) and subsequently leached in water to evaluate changes in the release of dissolvable constituents as a function of burn temperature. Water quality parameters assessed include dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved inorganic nitrogen (DIN), fractions of water extractable organic carbon and nitrogen (WEOC and WEON), and soluble elements. The quality of dissolved organic matter (DOM) from unaffected and heat-impacted soil and litter was assessed using ultraviolet absorbance at 254 nm (SUVA254). Following heating, the quantity and solubility of DOC and DON from soil were enhanced at 250˚C to 350˚C while the litter decreased drastically after material was heated above 150˚C. DOC contributions from litter across all temperatures exceeded that from soil while DON contributions for both materials were comparable. Soluble element trends varied; however, litter concentrations were magnitudes higher than soil for all except for Al and Mn, which were comparable. For both soil and litter leachates, SUVA254 increased with increasing temperature, indicating a higher concentration of aromatic moieties for leachates of heat-impacted material. Findings contribute to the growing understanding of impacts wildfires have on water quality and helps identify major contributors (soil or litter) to water quality risk based on fire severity.

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