Controlled Burning of Forest Detritus Altering Spectroscopic Characteristics and Chlorine Reactivity of Dissolved Organic Matter: Effects of Temperature and Oxygen Availability

Abstract

Forest fires occur with increasing frequency and severity in the western United States, potentially altering the chemistry and quantity of dissolved organic matter (DOM) and disinfection byproduct (DBP) precursors exported from forested watersheds. However, little is known concerning effects of the fire triangle (heat, oxygen, and fuel) on DOM alteration. Using detritus from Pinus ponderosa and Abies concolor (dominant species in forests in the western United States), we prepared DOM from unburned and burned detritus under hypoxic (pyrolysis) and oxic conditions (thermal oxidation) at 250 and 400°C. DOM characteristics and chlorine reactivity were evaluated by absorption and fluorescence spectroscopy and chlorination-based DBP formation potential tests. Spectroscopic results suggest that burned-detritus extracts had lower molecular weight (reflected by increased E2:E3 and fluorescence index) and divergent aromaticity (reflected by SUVA 254 ) depending on oxygen availability. Temperature and oxygen availability interacted to alter the chlorine reactivity of fire-affected DOM. Increasing temperature from 50 to 400°C resulted in decreased reactivities for trihalomethane and chloral hydrate formation and divergent reactivities for haloacetonitrile formation (unchanged for pyrolysis and increased for oxidation) and haloketone formation (increased for pyrolysis and decreased for oxidation). We demonstrate that DBP precursors in fire-affected forest detritus are highly dependent on temperature and oxygen availability.

Temporal variations of disinfection byproduct precursors in wildfire detritus

“…4 & Table S11). This observation agrees with a recent study (Wang et al, 2015b) that showed THM and CHD precursors were more dependent on heating temperature, while HAN and HK precursors were highly dependent on oxygen availability. Based on the PCA results, the trends determined for the commonly monitored/ regulated THM and HAA concentrations may not reflect the temporal trends for nitrogenous DBPs, such as HAN and NDMA concentrations.…”

“…In this study, the TS extracts did not show as high SHAN-FP as later extracts of SLS, suggesting that the reactive fire-produced HAN precursors in the AS were possibly photo-/bio-degraded/transformed, or rapidly diluted with less reactive precursors such as the recovered plant/ soil-derived carbon-rich DOM (Wang et al, 2012) under field conditions. Thus, although HANs are an important concern as they are more potent carcinogens than common carbonaceous DBPs such as THMs or HAAs (Richardson et al, 2007) and high SHAN-FP has been found in lab-burned ashes (>10 mg-HAN/mg-DOC; Majidzadeh et al, 2015;Wang et al, 2015b), the extremely high reactivity of DOM to form HANs observed for the sequential AS extracts may not persist in field AS samples (<5 mg-HAN/mg-DOC in Wang et al, 2015a) or source waters ( 2.7 mg-HAN/mg-DOC in Writer et al (2014)). …”

Understanding Organic Nonpoint‐Source Pollution in Watersheds via Pollutant Indicators, Disinfection By‐Product Precursor Predictors, and Composition of Dissolved Organic Matter

“…All fluorescence intensity data were calibrated to values in Raman units. The DBP FP tests were conducted using the dose‐based method to simulate chlorination in drinking‐water treatment plants (Wang et al, 2015). Extracted DBPs were determined using an Agilent 7890A gas chromatograph with an electrolytic conductivity detector, following USEPA Methods 551.1 and 552.2.…”

“…Among organic pollutants, disinfection by‐product (DBP) precursors deserve emphasis because they are ubiquitous, substantial, and threaten the safety of drinking water downstream (Beggs and Summers, 2011; Wang et al, 2015). There are three techniques to measure organic DBP precursors: (i) direct determination of individual compounds (Hanigan et al, 2015), which is commonly used in research; (ii) optical surrogates, such as ultraviolet (UV) absorbance at 254 nm, which are commonly used by water utilities (Weishaar et al, 2003); and (iii) tests of formation potential (FP), which are common in both research and industry (Hanigan et al, 2012).…”

“…It requires time and effort to measure routine organic pollution parameters such as chemical oxygen demand and biochemical oxygen demand (Dogan et al, 2009). Measuring specific and informative organic pollution parameters, such as DBP FP, is much more labor intensive and time consuming than using routine indicators (Wang et al, 2015). Furthermore, most organic solvents (e.g., methyl tertiary‐butyl ether), commonly used in these methods, are volatile, toxic, and hazardous to laboratory workers, which makes researchers hesitant to use them (Lin et al, 2018).…”