Reply on RC1

Abstract

Pyrogenic materials generated by wildfires are negatively impacting many aquatic ecosystems. At least ~10 % of dissolved organic matter (DOM) pools may be comprised of pyrogenic organic matter (PyOM) that is generally considered to be more refractory than DOM from other sources. However, there has been no systematic evaluation of bioavailability across a full spectrum of PyOM chemistries. We assessed the potential bioavailability of PyOM in relation to measured and globally ubiquitous DOM compounds using a substrate-explicit model to predict the energy content, metabolic efficiency, and aerobic decomposition of representative PyOM compounds. Overall, we found similar potential bioavailability between PyOM and sediment and surface water DOM. Predicted thermodynamics and carbon use efficiencies of PyOM and DOM were statistically indistinguishable. Within PyOM, phenols and black carbon (BC, defined by Wagner et al. (2017)) had lower metabolic efficiency than other PyOM and DOM compounds, and oxygen limitation had less impact on BC metabolism than on other PyOM classes. Our work supports the recent paradigm shift where PyOM bioavailability may be more comparable to natural organic matter than previously thought, highlighting its potential role in global C emissions and providing a basis for targeted laboratory investigations into the bioavailability of various PyOM chemistries.