Towards a global assessment of pyrogenic carbon from vegetation fires

Abstract

The production of pyrogenic carbon (PyC; a continuum of organic carbon (C) ranging from partially charred biomass and charcoal to soot) is a widely acknowledged C sink, with the latest estimates indicating that~50% of the PyC produced by vegetation fires potentially sequesters C over centuries. Nevertheless, the quantitative importance of PyC in the global C balance remains contentious, and therefore, PyC is rarely considered in global C cycle and climate studies. Here we examine the robustness of existing evidence and identify the main research gaps in the production, fluxes and fate of PyC from vegetation fires. Much of the previous work on PyC production has focused on selected components of total PyC generated in vegetation fires, likely leading to underestimates. We suggest that global PyC production could be in the range of 116-385 Tg C yr À1 , that is~0.2-0.6% of the annual terrestrial net primary production.According to our estimations, atmospheric emissions of soot/black C might be a smaller fraction of total PyC (<2%) than previously reported. Research on the fate of PyC in the environment has mainly focused on its degradation pathways, and its accumulation and resilience either in situ (surface soils) or in ultimate sinks (marine sediments). Off-site transport, transformation and PyC storage in intermediate pools are often overlooked, which could explain the fate of a substantial fraction of the PyC mobilized annually. We propose new research directions addressing gaps in the global PyC cycle to fully understand the importance of the products of burning in global C cycle dynamics.

Quantifying Changes in Total and Pyrogenic Carbon Stocks Across Fire Severity Gradients Using Active Wildfire Incidents

“…The lack of available data for PyC from a full range of fire-prone forest types has been a challenge identified in the literature, especially in regards to data needed for modeling fire and carbon dynamics (North et al, 2009;Liu et al, 2011). Important advancements in providing this muchneeded data Santín et al, 2015a;Reisser et al, 2016) led to a recent modeling study of global PyC TABLE 4 | Post-fire PyC (estimated as PyC CTR via chemical oxidation) proportions of post-fire C, C affected, and post-fire total ecosystem C for plots measured before and after fire in mixed-conifer forest type.…”

“…Seiler and Crutzen (1980) produced the first global estimate of PyC production using a simple model based on burned area, biomass stock and burning efficiency. Since then, charcoal research has reached important milestones in determining the fate of PyC once it become embedded in the soil matrix; however, the production rate of PyC during wildfire in natural conditions still represents a poorly addressed research gap (Santín et al, 2015a). Biomass type and formation conditions (i.e., temperature, oxygen availability) influence PyC stocks and characteristics (Baldock and Smernik, 2002;Hammes et al, 2006;McBeath et al, 2011;Hatton et al, 2016), and natural PyC is known to exhibit a range of physical and chemical characteristics depending on fire characteristics (McBeath and Smernik, 2009;McBeath et al, 2013;Michelotti and Miesel, 2015;Uhelski and Miesel, 2017).…”

A New Perspective on the Apparent Solubility of Dissolved Black Carbon

“…The chemical composition of BC is heterogeneous (Masiello, 2004), ranging from mildly thermally altered biomolecules (Myers-Pigg et al, 2015) to condensed aromatic structures produced during high temperature combustion (Schneider et al, 2010). It is estimated that global production of BC from biomass burning is up to 383 Tg per year and most of the BC produced through fire is deposited on the landscape (Santín et al, 2015). The stability of BC which is incorporated into soils is highly variable, with residence times ranging from days to millennia (Bird et al, 2015).…”

“…As such, it was estimated that DBC accounts for ∼10% of the total DOC flux exported annually by global rivers to the oceans . It seems clear that fluvial transfer of DBC to the ocean represents a key component of global C cycles (Santín et al, 2015). However, very little is known regarding the geochemical mechanisms which control the release of soil BC to inland waters as DBC.…”

Flux of Dissolved and Particulate Low-Temperature Pyrogenic Carbon from Two High-Latitude Rivers across the Spring Freshet Hydrograph

“…These fires release 1.6-2.8 petagrams of carbon (Pg C) to the atmosphere worldwide (Santín et al, 2016), mostly as gaseous CO 2 . However, inefficient combustion conditions in the environment regularly leave a proportion of the fire-affected carbon pool as carbonaceous residues, called pyrogenic carbon (PyC), which varies in molecular structure and environmental reactivity.…”