Pyrogenic carbon from tropical savanna burning: production and stable isotope composition

Saiz, G., Wynn, J.G., Wurster, C.M., Goodrick, I., Nelson, P.N., and Bird, M.I. (2015) Pyrogenic carbon from tropical savanna burning: production and stable isotope composition. Biogeosciences, 12. pp. 1849-1863.

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Widespread burning of mixed tree–grass ecosystems represents the major natural locus of pyrogenic carbon (PyC) production. PyC is a significant, pervasive and yet poorly understood "slow-cycling" form of carbon present in the atmosphere, hydrosphere, soils and sediments. We conducted 16 experimental burns on a rainfall transect through northern Australian savannas with C4 grasses ranging from 35 to 99% of total biomass. Residues from each fire were partitioned into PyC and further into recalcitrant (HyPyC) components, with each of these fluxes also partitioned into proximal components (>125 μm), likely to remain close to the site of burning, and distal components (<125 μm), likely to be transported from the site of burning. The median (range) PyC production across all burns was 16.0 (11.5) % of total carbon exposed (TCE), with HyPyC accounting for 2.5 (4.9) % of TCE. Both PyC and HyPyC were dominantly partitioned into the proximal flux. Production of HyPyC was strongly related to fire residence time, with shorter duration fires resulting in higher HyPyC yields. The carbon isotope (δ13C) compositions of PyC and HyPyC were generally lower by 1–3‰ relative to the original biomass, with marked depletion up to 7‰ for grasslands dominated by C4 biomass. δ13C values of CO2 produced by combustion were computed by mass balance and ranged from ~0.4 to 1.3‰. The depletion of 13C in PyC and HyPyC relative to the original biomass has significant implications for the interpretation of δ13C values of savanna soil organic carbon and of ancient PyC preserved in the geologic record, as well as for global 13C isotopic disequilibria calculations.

Item ID: 41151
Item Type: Article (Research - C1)
ISSN: 1726-4189
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© Author(s) 2015. This work is distributed under the Creative Commons Attribution 3.0 License.

Funders: Australian Research Council (ARC)
Projects and Grants: ARC DP1096586, ARC FF0883221
Date Deposited: 03 Nov 2015 03:46
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040204 Organic Geochemistry @ 100%
SEO Codes: 96 ENVIRONMENT > 9602 Atmosphere and Weather > 960201 Atmospheric Composition (incl. Greenhouse Gas Inventory) @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960510 Ecosystem Assessment and Management of Sparseland, Permanent Grassland and Arid Zone Environments @ 50%
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