Temporal variations of disinfection byproduct precursors in wildfire detritus

Abstract

a b s t r a c tThe Rim Fire ignited on August 17, 2013 and became the third largest wildfire in California history. The fire consumed 104,131 ha of forested watersheds that were the drinking water source for 2.6 million residents in the San Francisco Bay area. To understand temporal variations in dissolved organic matter (DOM) after the wildfire and its potential impacts on disinfection byproduct (DBP) formation in source water supply, we collected the 0e5 cm ash/soil layer with surface deposits of white ash (high burn severity) and black ash (moderate burn severity) within the Rim Fire perimeter in Oct 2013 (pre-rainfall) for five sequential extractions, and in Dec 2013 (~87 mm cumulative precipitation) and Aug 2014 (~617 mm cumulative precipitation) for a single water extraction. Water-extractable DOM was characterized by absorption and fluorescence spectroscopy and DBP formation tests. Both increasing cumulative precipitation in the field or number of extractions in the lab resulted in a significant decrease in specific conductivity, dissolved organic carbon, and DBP formation potential, but an increase in DOM aromaticity (reflected by specific UV absorbance). However, the lab sequential leaching failed to capture the increase of the NO x À -N/NH 4 þ -N ratio and the decrease in pH and dissolved organic carbon/nitrogen ratio of ash/soil extracts from Oct 2013 to Aug 2014. Increasing cumulative precipitation, inferring an increase in leaching after fire, led to an increase in DOM reactivity to form trihalomethanes, haloacetic acids, and chloral hydrate, but not for haloketones, haloacetonitrile, or N-nitrosodimethylamine, which were more related to the original burn severity. This study highlights that fire-affected DBP precursors for different DBP species have distinct temporal variation possibly due to their various sensitivity to biogeochemical alterations.

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

“…2a). This observation is consistent with previous findings where recently generated ash had higher DOC leaching potential than did weathered/leached ash (Wang et al, 2016). Overall, these findings indicate that while fires consume large amounts of litter/vegetation, they can generate more mobile DOC that is quickly flushed (<1 year) from the burned watersheds in the post-fire runoff.…”

“…Soil pH increases after wildfire due to the mineralization and release of acidic volatiles (Certini, 2005;Wang et al, , 2016, and the concentration of Ca 2þ , Mg 2þ , K þ, and Na þ as oxides, hydroxides, and carbonates (Certini, 2005), especially in newly burned organic matter (Revchuk and Suffet, 2014). Therefore, postfire stream runoff may increase the pH of downstream surface waters (Son et al, 2015), possibly resulting in a higher solubility of DOM.…”

“…With rapid population growth and a changing climate, these vital water sources are vulnerable to both natural and human-made disturbances. For example, forest fires are of particular concern because they rapidly consume biomass, convert forest vegetation into pyrogenic organic matter (PyOM) and change the physical and chemical properties of upper soil layers (Goforth et al, 2005;Oliveira-Filho et al, 2018;Santín et al, 2015;Vergnoux et al, 2011;Wang et al, 2016). Consequently, surface run-off regimes that strongly affect the quantity and quality of water exported from forested catchments are markedly altered (Ellis et al, 2004;Knoepp et al, 2008).…”

“…Fire temperature and oxygen availability during a wildfire are the principal factors affecting the consumption of detrital biomass and the formation of PyOM in wildfire ash. Thus, fire characteristics have a substantial effect on the quality and quantity of terrestrially-derived dissolved organic matter (DOM) exported from burned watersheds (Hohner et al, 2016;Wang et al, , 2016. Higher fire temperature is expected to increase detritus pyro-mineralization (Gray and Dighton, 2006).…”

“…Higher fire temperature is expected to increase detritus pyro-mineralization (Gray and Dighton, 2006). Therefore, the amount of water leachable DOM, expressed as dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations, might be expected to be lower in PyOM than in the unburned organic matter from which it originated (Wang et al, 2016). However, higher DOC and DON concentrations are frequently reported in stream waters following wildfires (Hohner et al, 2016;Revchuk and Suffet, 2014;Writer et al, 2014).…”