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| Titel |
Comparison of different methods to determine the degree of peat decomposition in peat bogs |
| VerfasserIn |
H. Biester, K.-H. Knorr, J. Schellekens, A. Basler, Y.-M. Hermanns |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 10 ; Nr. 11, no. 10 (2014-05-21), S.2691-2707 |
| Datensatznummer |
250117418
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| Publikation (Nr.) |
 copernicus.org/bg-11-2691-2014.pdf |
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| Zusammenfassung |
| Peat humification or decomposition is a frequently used proxy to extract past
time changes in hydrology and climate from peat bogs. During the past century
several methods to determine changes in peat decomposition have been
introduced. Most of these methods are operationally defined only and the
chemical changes underlying the decomposition process are often poorly
understood and lack validation. Owing to the chemically undefined nature of
many humification analyses the comparison of results obtained by different
methods is difficult. In this study we compared changes in peat decomposition
proxies in cores of two peat bogs (Königsmoor, KK; Kleines Rotes Bruch,
KRB) from the Harz Mountains (Germany) using C / N ratios, Fourier
transform infrared spectra absorption (FTIR) intensities, Rock
Eva® oxygen and hydrogen indices,
δ13C and δ15N isotopic signatures and UV-absorption
(UV-ABS) of NaOH peat extracts. In order to explain parallels and
discrepancies between these methods, one of the cores was additionally
analysed by pyrolysis gas chromatography mass spectrometry (pyrolysis-GC-MS).
Pyrolysis-GC-MS data provide detailed information on a molecular level, which
allows differentiation of both changes attributed to decomposition processes and
changes in vegetation. Principal component analysis was used to identify and
separate the effects of changes in vegetation pattern and decomposition
processes because both may occur simultaneously upon changes in bog
hydrology. Records of decomposition proxies show similar historical
development at both sites, indicating external forcing such as climate as
controlling the process. All decomposition proxies except UV-ABS and δ15N isotopes show similar patterns in their records and reflect to
different extents signals of decomposition. The molecular composition of the
KK core reveals that these changes are mainly attributed to decomposition
processes and to a lesser extent to changes in vegetation. Changes in the
molecular composition indicate that peat decomposition in the KK bog is
mainly characterized by preferential decomposition of phenols and
polysaccharides and relative enrichment of aliphatics during drier periods.
Enrichment of lignin and other aromatics during decomposition was also
observed but showed less variation than polysaccharides or aliphatics, and
presumably reflects changes in vegetation associated with changes in hydrology
of the bogs. Significant correlations with polysaccharide and aliphatic
pyrolysis products were found for C / N ratios, FTIR-band intensities and
for hydrogen index values, supporting that these decomposition indices
provide reasonable information. Correlations of polysaccharide and aliphatic
pyrolysis products with oxygen index values and δ13C was weaker,
assumingly indicating carboxylation of the peat during drier periods and
enrichment of isotopically lighter peat components during decomposition,
respectively. FTIR, C / N ratio, pyrolysis-GC-MS analyses and Rock Eval
hydrogen indices appear to reflect mass loss and related changes in the
molecular peat composition during mineralization best. Pyrolysis-GC-MS allows
disentangling the decomposition processes and vegetation changes. UV-ABS
measurements of alkaline peat extracts show only weak correlation with other
decomposition proxies and pyrolysis results as they mainly reflect the
formation of humic acids through humification and to a lesser extent mass
loss during mineralization. |
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