Dynamics of charcoal alteration in a tropical biome: a biochar-based study

Ascough, Philippa L., Bird, Michael I., Meredith, William, Snape, Colin, Large, D., Tilston, Emma, Apperley, David, Bernabé, Ana, and Shen, Licheng (2018) Dynamics of charcoal alteration in a tropical biome: a biochar-based study. Frontiers in Earth Science, 6. 61. pp. 1-15.

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Abstract

Pyrogenic carbon (PyC) is a polyaromatic residue of the incomplete combustion of biomass or fossil fuels. There is a growing recognition that PyC forms an important part of carbon budgets, due to production rates of 116–385 Tg C yr, and the size and ubiquity of PyC stocks in global carbon reservoirs. At least a proportion of PyC exists in a highly recalcitrant chemical form, raising the prospect of long-term carbon sequestration through soil amendment with “biochar,” which is generally produced with the aim of making a particularly recalcitrant form of PyC. However, there is growing evidence that some PyC, including biochar, can be both physically and chemically altered and degraded upon exposure to the environment over annual timescales, yet there is a lack of information concerning the mechanisms and determining factors of degradation. Here, we investigate three main factors; production temperature, feedstock composition, and the characteristics of the environment to which the material is exposed (e.g., pH, organic matter composition, oxygen availability) by analysis of biochar samples in a litterbag experiment before and after a year-long field study in the tropical rainforests of northeast Australia. We find that non-lignocellulosic feedstock has lower aromaticity, plus lower O/C and H/C ratios for a given temperature, and consequently lower carbon sequestration potential. The rate at which samples are altered is production temperature-dependant; however even in the highest temperature samples loss of the semi-labile aromatic carbon component is observed over 1 year. The results of 13C-MAS-NMR measurements suggest that direct oxygenation of aromatic structures may be even more important than carboxylation in environmental alteration of biochar (as a subset of PyC). There is a clear effect of depositional environment on biochar alteration even after the relatively short timescale of this study, as changes are most extensive in the most oxygenated material that was exposed on the soil surface. This is most likely the result of mineral ingress and colonization by soil microbiota. Consequently, oxygen availability and physical or chemical protection from sunlight and/or rainwater is vital in determining the alteration trajectory of this material.

Item ID: 57555
Item Type: Article (Research - C1)
ISSN: 2296-6463
Keywords: pyrogenic carbon; black carbon; PAH's; charcoal; biochar
Copyright Information: Copyright © 2018 Ascough, Bird, Meredith, Snape, Large, Tilston, Apperley, Bernabé and Shen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funders: Natural Environment Research Council (NERC), Carnegie Trust (CT)
Projects and Grants: NERC NE/F017456/1
Date Deposited: 08 Apr 2019 22:48
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 50%
04 EARTH SCIENCES > 0402 Geochemistry > 040204 Organic Geochemistry @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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