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Peat humification or decomposition is a frequently used proxy to extract pasttime changes in hydrology and climate from peat bogs. During the past centuryseveral methods to determine changes in peat decomposition have beenintroduced. Most of these methods are operationally defined only and thechemical changes underlying the decomposition process are often poorlyunderstood and lack validation. Owing to the chemically undefined nature ofmany humification analyses the comparison of results obtained by differentmethods is difficult. In this study we compared changes in peat decompositionproxies in cores of two peat bogs (Königsmoor, KK; Kleines Rotes Bruch,KRB) from the Harz Mountains (Germany) using C / N ratios, Fouriertransform infrared spectra absorption (FTIR) intensities, RockEva® oxygen and hydrogen indices,δ13C and δ15N isotopic signatures and UV-absorption(UV-ABS) of NaOH peat extracts. In order to explain parallels anddiscrepancies between these methods, one of the cores was additionallyanalysed by pyrolysis gas chromatography mass spectrometry (pyrolysis-GC-MS).Pyrolysis-GC-MS data provide detailed information on a molecular level, whichallows differentiation of both changes attributed to decomposition processes andchanges in vegetation. Principal component analysis was used to identify andseparate the effects of changes in vegetation pattern and decompositionprocesses because both may occur simultaneously upon changes in boghydrology. Records of decomposition proxies show similar historicaldevelopment at both sites, indicating external forcing such as climate ascontrolling the process. All decomposition proxies except UV-ABS and δ15N isotopes show similar patterns in their records and reflect todifferent extents signals of decomposition. The molecular composition of theKK core reveals that these changes are mainly attributed to decompositionprocesses and to a lesser extent to changes in vegetation. Changes in themolecular composition indicate that peat decomposition in the KK bog ismainly characterized by preferential decomposition of phenols andpolysaccharides and relative enrichment of aliphatics during drier periods.Enrichment of lignin and other aromatics during decomposition was alsoobserved but showed less variation than polysaccharides or aliphatics, andpresumably reflects changes in vegetation associated with changes in hydrologyof the bogs. Significant correlations with polysaccharide and aliphaticpyrolysis products were found for C / N ratios, FTIR-band intensities andfor hydrogen index values, supporting that these decomposition indicesprovide reasonable information. Correlations of polysaccharide and aliphaticpyrolysis products with oxygen index values and δ13C was weaker,assumingly indicating carboxylation of the peat during drier periods andenrichment of isotopically lighter peat components during decomposition,respectively. FTIR, C / N ratio, pyrolysis-GC-MS analyses and Rock Evalhydrogen indices appear to reflect mass loss and related changes in themolecular peat composition during mineralization best. Pyrolysis-GC-MS allowsdisentangling the decomposition processes and vegetation changes. UV-ABSmeasurements of alkaline peat extracts show only weak correlation with otherdecomposition proxies and pyrolysis results as they mainly reflect theformation of humic acids through humification and to a lesser extent massloss during mineralization

Comparison of different methods to determine the degree of peat decomposition in peat bogs