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| Titel |
Smouldering bog wildfires and possible implications in palaeoenvironmental reconstructions |
| VerfasserIn |
C. Zaccone, G. Rein, V. D'Orazio, R. Hadden, C. M. Belcher, T. M. Miano |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062709
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| Zusammenfassung |
| Ombrotrophic (i.e., rainwater-fed) peat bogs have been recognized as providing
excellent records of past environmental changes over the last millennia. They are well
known to provide information on both climatic and vegetational changes, and the
deposition of organic and inorganic pollutants from anthropogenic vs. lithogenic
sources. Whether they also record well past fire activity is an unresolved issue to
date.
Peatland ecosystems are most at risk from smouldering fires, especially in drought
conditions. Smouldering fires are slow, low temperature, flameless and the most persistent
form of combustion of organic matter (OM) in porous form. It is known to consume dozen of
times more peat mass than flaming fires. Importantly, the in-depth oxidation reaction in
smouldering leaves few charred remains, which hampers their identification in
palaeoenvironmental analyses. Smouldering even consumes the possible pyrogenic char
produced by flaming wildfires. Most studies on smouldering peatland fires to date have
focused on ignition and carbon losses/emissions, leaving a significant gap in our
understanding of OM changes following fires.
In the present work, we present new data which suggest that variations in the chemical
signature of OM in peatlands provides a possibility of identifying past peatland
fires. In particular, we show results from a laboratory study about the physical,
chemical and spectroscopic changes in OM features following a smouldering fire. We
initiated a smouldering fire on top of three sphagnum peat columns (26 cm deep) each
having a different initial moisture content (MC) designed to reflect dry conditions
(55% MC), undisturbed conditions (90% MC), and wet conditions (210% MC). The
fires were allowed to propagate downwards until they self-extinguished at some
distance from the top. After the fire, we tracked chemical variations in the residual
columns to determine the possible signature of natural past smouldering peatland
fires.
The analysis shows a consistent variation in the vertical direction of chemical markers
below the point at which the fire front propagated the columns. The depth over which the
chemical markers vary is apparent down to 5 cm in 55% MC (the whole residual column),
and 8 cm deep in 90% MC. No significant variation of any of the chemical parameters was
observed in the 210% MC column.
The results of this study show that smouldering fires could occur also when bogs are in
undisturbed hydrological conditions (e.g., near 100%MC), and that zone affected by
smouldering fire is revealed by the presence of: 1) a strong increases of pH and ash content;
2) higher contents of aromatic and condensed molecules (as suggested by higher C/H values
and by fluorescence spectra); 3) higher total N content leading to a decrease in C/N
ratio.
These data show potential to track similar variations in cores taken from peat bogs where
they may serve as new proxies for the identification of past fire events. Moreover, these
findings suggest the possibility that similar chemical and physical signatures detected in
previous peatland cores may have been ascribed to the wrong past climatic or hydrological
variations, as fire induced changes had not been considered before. In particular, peaks in ash
content, such as those observed in our study (e.g.. ca. 13% in the 90% MC residue vs. 3%
in the undisturbed peat), have in the past been ascribed to an increase of either
dust depositions or mineralization processes typically linked to climatic changes.
Similarly, large variations in pH values (e.g., >6 in the 90% MC residue vs. |
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