First interactions with the hydrologic cycle determine pyrogenic carbon's fate in the Earth system

Abstract

Fires produce an aromatic particulate residue commonly referred to as pyrogenic carbon (PyC).Particulate PyC is low density, high porosity, and is predominantly deposited on the soil surface in post-fire landscapes. These characteristics create a material that is prone to mobility, both vertically down the soil profile and laterally across the landscape even in low-relief landforms.Because of its tendency for lateral mobilization, we argue here that PyC's first interaction with water determines its environmental fate and persistence, not its interactions with soil minerals or microbes. PyC's first interactions with water determine: the amount of PyC that will enter the soil profile and experience microbial and geochemical alterations, whether it will be buried in depositional environments and stored on the landscape, or if it will be transported to streams and eventually to the ocean. Here we posit that this crucial first interaction with the hydrologic cycle This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Key drivers of pyrogenic carbon redistribution during a simulated rainfall event

“…4). Therefore, our data confirms that the fate and mobility of PyC on short timescales depends to a great extent on its initial interaction with water (Masiello and Berhe, 2020). The portions of PyC relocated by runoff (% of total added PyC; Fig.…”

“…Initial rainfall not only determines the redistribution of PyC on the surface, but also the quantity of PyC that moves into the soil (Masiello and Berhe, 2020). We recovered part of the initially added PyC (PyC fraction) at 1-3 and 3-10 cm depth at the upslope position where it was initially applied, especially for the Cambisol (6.8 % (Cambisol) and 1.3 % (Luvisol); Fig.…”

“…In post-fire landscapes erosion by water is very often substantially enhanced (Abney and Berhe, 2018;Masiello and Berhe, 2020;Vieira et al, 2018). The removal of the protective vegetation cover during wildfires increases the impact of raindrops on the soil surface (Certini, 2005;Johansen et al, 2001;Pierson et al, 2013), which can cause aggregate breakdown and surface sealing (Moody et al, 2013;Shakesby, 2011).…”

“…The PyC particles produced during a fire that remain on the soil surface may be more redistributed by water erosion during the first rainfall than other soil particles (Abney et al, 2019b;Rumpel et al, 2009Rumpel et al, , 2006. This high mobilization of PyC is partially caused by its physical properties, in particular its low density and high porosity, but also due to the lack of organo-mineral interactions between the PyC and soil matrix that prevent either wash-out (surface erosion by interrill or splash) or wash-in (to deeper soil horizons) during initial rainfall (Brewer et al, 2014;Masiello and Berhe, 2020;Pyle et al, 2017). Most PyC materials have a high initial hydrophobicity, which can promote floating and transport by water (Abney and Berhe, 2018;Rumpel et al, 2015).…”

“…However, to which extent these drivers affect the magnitude of post-fire PyC erosion and deposition still need to be elucidated (Abney and Berhe, 2018;Berhe et al, 2018;Santín et al, 2016). It is difficult to assess the redistribution of PyC directly after a fire because substantial redistribution occurs during the first major rainfall event (Masiello and Berhe, 2020). Rainfall simulation experiments allow controllability and comparability between drivers, so that a diverse set of drivers can be repeatedly studied https://doi.org/10.5194/bg-2020-361 Preprint.…”