Chemical characterization of dissolved organic matter as disinfection byproduct precursors by UV/fluorescence and ESI FT-ICR MS after smoldering combustion of leaf needles and woody trunks of pine (Pinus jeffreyi)

Forested land plays an essential role in water supply across the United States (US). Smoldering commonly existing in wildfires contributes significantly to biomass consumption and gas emission, but its influence on source water quality has been rarely studied. Here, we investigated the impact of smoldering temperature (i.e., no burn, 250, 400, and 600 °C) on the nutrients, elements, and dissolved organic matter (DOM) of water extracts from the residues of the leaf needles and woody trunks of pine (Pinus jeffreyi) under the lab-simulated smoldering fire. Results showed the increase of pH and the yields of the dominated exchangeable cations of K⁺ and Mg²⁺, P, PO₄³⁻-P, and SO₄²⁻ with increasing temperature increasing from 250 to 600 °C, whereas significant decreases in the fraction of dissolved organic C in residue C with increasing temperature and the yields of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) after burnings. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) presented consistent results with UV/fluorescence, suggesting that the unburned materials contained more biodegradable tyrosine/tryptophan/soluble microbial byproduct-like compounds with high molecular weight (MW), whereas the 600 °C-smoldering materials composed of more aromatic, humified, fulvic/humic acid-like, and oxidized compounds with a potentially high density of C=C bonds had less reactivity in forming trihalomethanes (THMs) and haloacetonitriles (HANs). Our study indicates the smoldering-dominated prescribed fire as a potential forest management strategy for reducing biomass fuel and disinfection byproducts (DBPs) precursors in source water from forested lands.