BOOK OF ABSTRACTS 87 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Environment, Agriculture, and Forestry SL39 Wildfires Increase the Molecular Heterogeneity of Soil Dissolved Organic Matter across Mediterranean-climate Forest Ecoregions Jingyi Zeng1, Kathleen Murphy2, Carlos Afonso3, Marie Hubert-Roux3, Yingying Xiang4, Jean-Philippe Croué1 1 Université de Poitiers, Institut de Chimie des Milieux et des Matériaux de Poitiers (IC2MP), UMR 7285, Centre National de la Recherche Scientifique (CNRS), Poitiers 86073, France, jingyi.zeng@univ-poitiers.fr 2 Department of Architecture and Civil Engineering, Chalmers University of Technology, Gothenburg 41298, Sweden 3 CARMeN institute, UMR 6064, CNRS, University of Rouen Normandie, Mont Saint Aignan 76821, France 4 School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States Wildfires are increasing in frequency, scale, and severity worldwide. These events cause extreme transformations in soil organic matter and subsequently release pyrogenic dissolved organic matter (PyDOM) into forested watersheds [1, 2]. Across wildfireaffected landscapes, PyDOM quantity and composition vary with fire regime, soil properties, and forest ecoregion. This variability leads to fluctuating abundances of pyrogenic condensed aromatic organics (CAs) [3]. However, fire-modified DOM impacts water treatment performance and potable water quality by increasing disinfection byproduct (DBP) formation [4]. It is crucial to understand the consistency and diversity of PyDOM from soil across different geographic regions. This study investigates postfire changes in soil DOM across six Mediterranean-type forest ecoregions in France, Chile, and Australia. By comparing burned soil samples (n = 11) with unburned counterparts (n = 4), DOM was characterized using general chemical parameters (e.g., DOC, and pH), UV/ Fluorescence with parallel factor analysis (PARAFAC), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The potential formation of DBP (THM4, HAA9, HAN5, Dalapon acid and HAcAm2) was further evaluated by chlorination of soil DOM leachates. Overall, burned soil samples released higher levels of leachable organic carbon and nitrogen compared to unburned counterparts. Wildfireinduced thermal degradation led to increased pH, conductivity, and anion concentrations in soil leachates. SUVA254 values generally decreased in soil PyDOM, except for samples from the Altos de Cantilliana Reserve (Chile). Fluorescent and biological indices
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