Boron isotopes and FTIR spectroscopy to identify past high severity fires
Boron isotopes and FTIR spectroscopy to identify past high severity fires
Bushfires have played a crucial role in shaping the landscape and biodiversity for millennia. As fire regimes continue to alter with climate change, greater understanding becomes critical in mediating future events. Existing records are largely historically limited or do not accurately identify fire severity; therefore, there is a need to develop new proxies that can extend our fire records significantly. Here, we test whether changes in carbon (C) and nitrogen (N) content, boron (B) isotopes and Fourier Transform Infrared (FTIR) spectra in sediment deposits can identify past fire events. To achieve this, we investigated sediments deposited in small order creek beds of the Upper Nepean Catchment in southeastern Australia. In each deposit, layers associated with past fire events were independently identified based on visual inspection of higher charcoal abundance. Radiocarbon dating of charcoal fragments was used to approximate the age of the fire events. Neither C and N abundances nor C/N ratios show association with charcoal-rich layers, suggesting they are not useful proxies to identify past fires. Conversely, FTIR spectra show increased aromatic/aliphatic ratios in sediment layers recording past fire events. This observation suggests that those fires were hot enough to reduce long-chain aliphatic compounds to more temperature- and decomposition-resistant aromatics. In each deposit, an increase in δ11B by 2–7 ‰ is associated with charcoal-rich sediment layers. Leaves and fine branches, which burn only during high severity fires, are enriched in 11B, possibly causing the increase in the δ11B value of the sediment clay size fraction. These results suggest that, even in these small order creek beds which are typically transient environments, both FTIR spectra and B isotopes are potentially useful proxies to identify past fire events.
Boron, Bushfires, FTIR Spectroscopy, Isotopes, Radiocarbon
Ryan, Rebecca
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Dosseto, Anthony
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Lemarchand, Damien
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Dlapa, Pavel
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Thomas, Zoë
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Simkovic, Ivan
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Bradstock, Ross
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1 March 2023
Ryan, Rebecca
1f9fae0f-a259-4964-9f50-85b4bac0bdb2
Dosseto, Anthony
75da8a0d-f420-4d80-87b2-b3df9f22cc64
Lemarchand, Damien
17801f84-7da0-4511-8ebb-dda7ed7f179f
Dlapa, Pavel
da45835e-4c42-44cf-831c-beb82108206e
Thomas, Zoë
4b512d3a-3478-4270-9fdd-61256aa640d3
Simkovic, Ivan
061703f8-0c42-4bc3-98ce-eab71d54ea76
Bradstock, Ross
42af40d2-1a04-487d-b7b6-d9d5fab0cb9b
Ryan, Rebecca, Dosseto, Anthony, Lemarchand, Damien and Thomas, Zoë
,
et al.
(2023)
Boron isotopes and FTIR spectroscopy to identify past high severity fires.
CATENA, 222 (3), [106887].
(doi:10.1016/j.catena.2022.106887).
Abstract
Bushfires have played a crucial role in shaping the landscape and biodiversity for millennia. As fire regimes continue to alter with climate change, greater understanding becomes critical in mediating future events. Existing records are largely historically limited or do not accurately identify fire severity; therefore, there is a need to develop new proxies that can extend our fire records significantly. Here, we test whether changes in carbon (C) and nitrogen (N) content, boron (B) isotopes and Fourier Transform Infrared (FTIR) spectra in sediment deposits can identify past fire events. To achieve this, we investigated sediments deposited in small order creek beds of the Upper Nepean Catchment in southeastern Australia. In each deposit, layers associated with past fire events were independently identified based on visual inspection of higher charcoal abundance. Radiocarbon dating of charcoal fragments was used to approximate the age of the fire events. Neither C and N abundances nor C/N ratios show association with charcoal-rich layers, suggesting they are not useful proxies to identify past fires. Conversely, FTIR spectra show increased aromatic/aliphatic ratios in sediment layers recording past fire events. This observation suggests that those fires were hot enough to reduce long-chain aliphatic compounds to more temperature- and decomposition-resistant aromatics. In each deposit, an increase in δ11B by 2–7 ‰ is associated with charcoal-rich sediment layers. Leaves and fine branches, which burn only during high severity fires, are enriched in 11B, possibly causing the increase in the δ11B value of the sediment clay size fraction. These results suggest that, even in these small order creek beds which are typically transient environments, both FTIR spectra and B isotopes are potentially useful proxies to identify past fire events.
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More information
Accepted/In Press date: 21 December 2022
Published date: 1 March 2023
Additional Information:
Funding Information:
We would like to thank Dominique Tanner for her help with the FTIR spectroscopy work. We would also like to thank WaterNSW and Crown Lands for permitting access to sites and sample collection. Funding was provided by ARC Discovery Grant DP200101123, and RR acknowledges an APA PhD scholarship. We also thank Solomon Buckman, Braiya White, Shawn Lu and Mark Quoyle for their assistance in the field.
Funding Information:
We would like to thank Dominique Tanner for her help with the FTIR spectroscopy work. We would also like to thank WaterNSW and Crown Lands for permitting access to sites and sample collection. Funding was provided by ARC Discovery Grant DP200101123, and RR acknowledges an APA PhD scholarship. We also thank Solomon Buckman, Braiya White, Shawn Lu and Mark Quoyle for their assistance in the field.
Publisher Copyright:
© 2022 Elsevier B.V.
Keywords:
Boron, Bushfires, FTIR Spectroscopy, Isotopes, Radiocarbon
Identifiers
Local EPrints ID: 476109
URI: http://eprints.soton.ac.uk/id/eprint/476109
ISSN: 0341-8162
PURE UUID: f5c78129-2425-4cb9-98f0-37bb491efc3f
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Date deposited: 12 Apr 2023 14:17
Last modified: 18 Mar 2024 04:10
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Contributors
Author:
Rebecca Ryan
Author:
Anthony Dosseto
Author:
Damien Lemarchand
Author:
Pavel Dlapa
Author:
Zoë Thomas
Author:
Ivan Simkovic
Author:
Ross Bradstock
Corporate Author: et al.
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