IMPLICATIONS FOR SIGNIFICANT LOSS OF LABILE PYROGENIC DOC IN MAJOR ARCTIC RIVERS

Recent attention to the characterization of pyrogenic dissolved organic carbon (Py-DOC) in fire-impacted watersheds has highlighted the quantitative importance of its transfer to the coastal ocean. However, quantification of Py-DOC has predominantly been constrained to the most condensed and biologically refractory fractions of the Py-C continuum. The low temperature portion of the Py-C continuum contains a higher proportion of oxygen-rich, non-aromatic functional groups. Because of their high solubility, these organics may bypass soil sorption and act as important contributors to exported DOM in fire-impacted watersheds, or potentially influence riverine respiration rates. In this study, we report the first evidence for the presence of highly reactive biomass combustion by-products (half-lives of days to weeks) in DOM of major Arctic rivers. A strong relationship between stream flow and Py-DOC (r²=0.61 for all rivers) suggests that fire-altered carbon is an intrinsic component of the DOC pool mobilized by hydrologic events and may be controlled by soil active layer thickness. Gymnosperm combustion, from the southern portions of the watersheds, is the primary source of this labile Py-DOC to Arctic rivers. Up to 55% of estimated Py-DOC may be lost during transit time (20-40 days) from fire source to river mouth, showing that fire-derived DOC contains a highly reactive pool in addition to the recalcitrant dissolved black carbon characterized in earlier studies.