Recent work demonstrates that a leachable fraction of pyrogenic organic matter (PyOM, aka ‘black carbon’) is transported hydrologically to the ocean where it contributes to the long-cycling pool of dissolved organic carbon. Like PyOM, dissolved PyOM (PyDOM) properties vary predictably along a combustion continuum, but the effects of environmental aging on PyDOM characteristics are not well-established. Wildfire-derived chars aged for 1, 4, and 30 (GDS-30) years were collected from the Great Dismal Swamp, USA and analyzed for their solid and aqueous leachate chemical characteristics. Solid ¹³C NMR spectroscopic and elemental analyses show GDS-30 to have the highest %O and lowest %C and aromatic C contents suggesting it to have the lowest charring extent of the 3 study chars. However, benzenepolycarboxylic acid (BPCA) marker analyses reveal GDS-30 to have the highest BPCA yield and highest degree of aromatic condensation consistent with the opposite conclusion (highest charring extent). In PyDOM leachates, increased char aging correlates with increased DOC and BPCA yields and FTICR-MS-derived aromatic and low O/C molecular formulas. We hypothesize that hydrological and oxidative aging processes 1) deliver allochthonous materials yielding higher PyOM H/C and O/C ratios, and 2) selectively remove an oxygenated, less aromatic portion of the initial PyOM. Subsequently, only the most highly condensed aromatic compounds are available for oxidation and transport as PyDOM, and PyDOM molecular characteristics are better explained by an aging continuum than a combustion continuum.

Primary Presenter: Andrew Wozniak, University of Delaware (awozniak@udel.edu)

Authors:

Siddhartha Mitra, East Carolina University  (mitras@ecu.edu)

Alex Goranov, Old Dominion University  (agoranov@odu.edu)

Kyle Bostick, Fugro  (k.bostick@fugro.com)

Andrew Zimmerman, University of Florida  (azimmer@ufl.edu)

Patrick Hatcher, Old Dominion University  (phatcher@odu.edu)