Lipid and PAH composition as indicators for conditions of thermal degradation
Zusammenfassung der Projektergebnisse
Burning residues have been frequently analysed in the past due to their potential harmful properties on the one hand and their high persistence in environmental matrices compared to other components of bulk organic matter. Amongst others also molecular proxies like alkanes and polycyclic aromatic carbons (PAH) have been shown to be of diagnostic character for the assessment of burning residues. However, limited available data did not allow for detailed reconstructions of burning conditions. By the help of burning experiments carried out under controlled conditions and the comparison of the results with natural wild fires this project was designed to significantly improve our understanding on the diagnostic significance of molecular proxies like alkanes and PAH for fire tracing, i.e. the reconstruction of burning conditions like temperature, oxygen limitation, duration and burning fuel. The alkane and PAH distribution patterns changed with increasing temperature especially between 250°C and 400°C. Furthermore, total lipid extracts contents revealed a relative increase from 300°C to 350°C, which indicated the degradation of high molecular weight compound. However, oxygen supply, burning fuel and duration of thermal degradation revealed less significant changes in molecular patterns than temperature. Therefore, alkanes and PAH can be preferentially used to reconstruct burning temperature, but none of the other burning conditions, if during the thermal degradation the temperature exceeded 350°C. Below this temperature, alkanes enable the tracing of burning fuel due to the chemotaxonomic significance of alkanes. In other words, wood or grass derived fires could be reconstructed at low burning temperatures, where the burning is incomplete. Natural wild fires confirmed the proposed burning conditions with intermediate temperature regimes, which could enable tracing of burning fuel for forest vs. grassland fires, whereas the fireplace history at the archaeological site Wachtberg/Krems enabled also a differentiation of the different thermal degradation within the sample set of the fireplace. In conclusion, the presence of comparatively low total lipid extract contents, PAH and shortchain even numbered alkanes as well as the absence of long-chain odd alkanes allows for tracing of fires in natural sample sets. But especially at higher temperatures than 450°C other tracers than alkanes and PAH such as benzene polycarboxylic acids (BPCA) or atomic ratios of oxygen and hydrogen towards carbon (O/C and H/C) enable better reconstruction of burning conditions.
Projektbezogene Publikationen (Auswahl)
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2010. Reconstruction of anthropogenic activities on the excavations of a fireplace sequence from the Krems-Wachtberg site (Austria) using molecular proxies. Geophysical Research Abstracts, Vol. 12, 13518
Wiesenberg, G.L.B., Hambach, U.
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2011. Neo-formation of a ferrimagnetic phase during thermal degradation of plant tissues: implications for the magnetic properties of top soils. EGU General Assembly 2011, 03.-08. Apr. 2011, Vienna, Austria
Hambach, U., Wiesenberg, G.L.B.
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2013. Reconstruction of past fire regimes by geochemical analyses of charcoal. Organic Geochemistry 55, 11-21
Wolf, M., Lehndorff, E., Wiesenberg, G.L.B., Stockhausen, M., Schwark, L. & Amelung, W.
