Wildfires significantly alter terrestrial carbon pools through the production of pyrogenic organic matter (PyOM), with a complex chemical makeup thought to determine its fate in aquatic systems. Our current molecular level understanding of dissolved-phase PyOM chemistry is rooted in experiments specifically linked to burn temperature (e.g., Heat Temperature Treatments), which in the environment can be heterogenous and is not directly linked to field assessments of burn severity. In this study, we seek to understand the relationship between PyOM production and vegetation burn severity through a comprehensive characterization of dissolved PyOM generated along a burn severity continuum. We used a combination of optical techniques, ultra-high resolution mass spectrometry, and benzene polycarboxylic acids to characterize leachates from chars generated in open-air conditions at varying degrees of burn severity with vegetation representative of Pacific Northwest land cover types. We highlight an independence in PyOM molecular signatures across vegetation types from raw and lower burn severities that ultimately converge at higher severities into uniform signatures characteristic of degraded, aromatic DOM with enriched nitrogen containing functionality. The results of this study improve our understanding of the production of PyOM across burn severities that will enhance our understanding of wildfire impacts on ecosystem processes and our predictive understanding of wildfire impacts on terrestrial and aquatic biogeochemical cycles.

Primary Presenter: Alan Roebuck, Pacific Northwest National Laboratory (alan.roebuck@pnnl.gov)

Authors:

Alan Roebuck, Pacific Northwest National Laboratory  (alan.roebuck@pnnl.gov)

Samantha Grieger, Pacific Northwest National Laboratory  (sammigrieger@gmail.com)

Morgan Barnes, Pacific Northwest National Laboratory  (morgan.barnes@pnnl.gov)

Riley Barton, Rensselaer Polytechnic Institute  (bartor2@rpi.edu)

Sasha Wagner, Rensselaer Polytechnic Institute  (wagnes3@rpi.edu)

Kevin Bladon, Oregon State University  (kevin.bladon@oregonstate.edu)

Emily Graham, Pacific Northwest National Laboratory  (emily.graham@pnnl.gov)

Tim Schiebe, Pacific Northwest National Laboratory  (tim.schiebe@pnnl.gov)

Allison Myers-Pigg, Pacific Northwest National Laboratory  (allison.myers-pigg@pnnl.gov)