Effect of Wildfires on Physicochemical Changes of Watershed Dissolved Organic Matter

Abstract

Physicochemical characterization of dissolved organic carbon (DOC) provides essential data to describe watershed characteristics after drastic changes caused by wildfires. Post‐fire watershed behavior is important for water source selection, management, and drinking water treatment optimization. Using ash and other burned vegetation fragments, a leaching procedure was implemented to describe physicochemical changes to watershed DOC caused by wildfires. Samples were collected after the 2007 and 2009 wildfires near Santa Barbara, California. Substantial differences in size distribution (measured by ultrafiltration), polarity (measured by polarity rapid assessment method), and the origin of leached DOC (measured by fluorescence) were observed between burned and unburned sites. Recently burned ash had 10 times the DOC leaching potential, and was dominated by large size fragments, compared to weathered 2‐year‐old ash. Charged DOC fractions were found to positively correlate with DOC size, whereas hydrophobic and hydrophilic DOC fractions were not. Proteins were only observed in recently burned ash and were indicative of recent post‐fire biological activity.

Temporal variations of disinfection byproduct precursors in wildfire detritus

“…S2 and S3), suggesting that the dissolution/leaching process has contributed to the loss of soluble inorganic and organic materials from the AS to water bodies. The decrease in DOC agrees with Revchuk and Suffet (2014), which showed higher DOC in forest detritus 2 months after fire than detritus 2 years after fire, although the two samples were not from a same site. These observations can explain the highest stream inorganic and DOC concentrations in the first two storm events after fire relative to the later storm events in fire-affected watersheds (Audry et al, 2014;Writer et al, 2014).…”

“…These observations can explain the highest stream inorganic and DOC concentrations in the first two storm events after fire relative to the later storm events in fire-affected watersheds (Audry et al, 2014;Writer et al, 2014). Most field studies observe elevated DOC concentrations in stream water following wild and prescribed fires (Gerla and Galloway, 1998;Mast and Clow, 2008;McEachern et al, 2000;Revchuk and Suffet, 2014;Writer et al, 2014), probably due to a higher degree of allochthonous contribution following fires (Shakesby, 2011).…”

“…Following wildfires, a significant fraction of terrestrial DOM can enter surface waters via surface runoff and soil leaching contributing to increased DBP precursor concentrations in water supplies (Chow et al, 2009;Revchuk and Suffet, 2014). In a study of the 2013 Rim Fire in California (104,131 ha), Wang et al (2015a) found distinct changes in the chemistry of water extractable DOM with burn severity being an important variable affecting the chemical characteristics of the DOM and its reactivity to form DBPs.…”

“…The reactivity of fire-affected DOM showed higher reactivity to form HANs, but comparable reactivity to form THMs and HAAs relative to the unburned site. Revchuk and Suffet (2014) found that the average DOC in source water was elevated by the 2007 Zaca Fire in California (97,208 ha) from 2.8 mg/L pre-fire to~4.8 mg/L one year post-fire (~70% increase), and the THM formation potential was increased to~200e290 mg/L (~49% increase).…”

“…A mechanistic understanding calls for systematic studies on variations in temporal terrestrial and aquatic DBP precursors and the effects of site-specific meteorology, topography, ecosystem types, hydrological conditions, and fire characteristics. Revchuk and Suffet (2014) proposed that precipitation leaching and biological consumption were the primary factors affecting DOC dynamics from wildfire ash. However, it remains unquantified how the leaching process affects the fire-affected terrestrial precursors for different types of DBPs.…”