Laboratory combustion-induced transformation of pyrogenic dissolved organic matter from vegetation and its impact on disinfection byproduct formation.

Wildfires can threaten the drinking water quality by introducing pyrogenic dissolved organic matter (PyDOM) into watersheds. However, the role of flammable vegetation distributed across forest strata, especially lower-stratum fuels, in shaping PyDOM composition and its consequences for source water remains unclear. Five representative French forest plant species-oak (canopy), pine (canopy), heather (understory), gorse (shrub) and fern (herb)-were combusted at 550 °C to generate PyDOM. Compared with DOM extracted from unburned plants, PyDOM showed 5.2 to 59.8-fold higher relative abundances of condensed aromatic molecular features (CAs), accompanied by a decrease in dissolved organic carbon (DOC) content and an increase in inorganic ion concentrations, including halides. Notably, PARAFAC modelling isolated two hydroxybenzoic acid-like components (m- and o-isomers) with spectral properties matching reported pure organic compounds. These components were predominantly present in PyDOM extracted from gorse, with the lowest abundance observed in burned fern and heather. Combustion-induced changes in DOM were highly vegetation-dependent. PyDOM from heather, oak, and pine contained greater CA abundances than that from other plants. Increased precursors of halogenated organic formulas (HOCs) were mainly observed in burned oak and pine. Chlorination of PyDOM enhanced the formation of brominated and nitrogenous DBPs, likely correlated to elevated levels of black nitrogen (BN) and bromide. Nitrogenous DBPs accounted for over 50 % of identified DBPs in both PyDOM from gorse and heather. Our findings indicate how vegetation across forest strata interacts with high-temperature combustion to potentially reshape DOM composition and DBP formation potential relevant to forested source waters.