Characterization and biodegradation of water-soluble biomarkers and organic carbon extracted from low temperature chars

This study demonstrates that wildfires/biomass combustion may be an important source of labile pyrogenic water-soluble organic matter (Py-WSOM) in aquatic systems. Spectroscopic analysis (solid char and Py-WSOM) with Fourier transform infrared spectroscopy (FTIR) indicated that the Py-WSOM extracted from two low temperature chars (one wood, one grass) was dominated by polar moieties (–OH and C–O) derived from depolymerization and fragmentation of lignocellulose. Incubation experiments under aerobic conditions with unsterilized river water suggested that Py-WSOM and associated biomarkers may have a turnover rate of the order of weeks to months, consistent with mixing and transport conditions of riverine systems. For example, pyrogenic dissolved organic carbon (Py-DOC) had a half-life of 30–40 days. Turnover rate for the combustion biomarkers was shorter, with levoglucosan and free lignin phenols having a half life around 3–4 days and polymeric lignin components 13–14 days. The latter observations contradict earlier studies of the biodegradation of dissolved lignin and point to the need for re-assessment of lignin degradation kinetics in well-mixed riverine systems, particularly when such lignin components are derived from thermally altered plant material that may exist in a form more labile than that in highly processed riverine DOM.