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| Titel |
Effect of leaf litter degradation and seasonality on D/H isotope ratios of n-alkane biomarkers |
| VerfasserIn |
Michael Zech, Nikolai Pedentchouk, Björn Buggle, Katharina Leiber, Karsten Kalbitz, Slobodan Marković, Bruno Glaser |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056003
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| Zusammenfassung |
| During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n-alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of early diagenesis on the deltaD values of n-alkanes. We therefore investigated the n-alkane patterns and deltaD values of long-chain n-alkanes from three different C3 higher plant species (Acer pseudoplatanus L., Fagus sylvatica L. and Sorbus aucuparia L.) that have been degraded in a field leaf litterbag experiment for 27 months.
We found that after an initial increase of the total long-chain n-alkane mass (up to ~50%), decomposition took place with mean turnover times of 11.7 months. Intermittently, the total mass of mid-chain n-alkanes increased significantly during periods of highest mass losses. Furthermore, initially high odd-over-even predominance declined and long-chain n-alkane ratios like n-C31/C27 and n-C31/C29 started to converge to the value of 1. While bulk leaf litter became systematically D-enriched especially during summer seasons (by ~8‰ on average over 27 months), the deltaD values of long-chain n-alkanes reveal no systematic overall shifts, but seasonal variations of up to 25‰ (Fagus, n-C27, average ~13‰)).
These findings suggest that a microbial n-alkane pool sensitive to seasonal variations of soil water deltaD rapidly builds up. We propose a conceptual model that accounts for the decomposition of plant-derived n-alkanes and the build-up of microbial n-alkanes. Model results are in good agreement with measured n-alkane deltaD results. Since microbial ‘contamination’ is not necessarily discernible from n-alkane concentration patterns alone, care may have to be taken not to over-interpret deltaD values of sedimentary n-alkanes. Furthermore, since leaf-water is generally D-enriched compared to soil and lake waters, soil and water microbial n-alkane pools may help explain why soil and sediment n-alkanes are D-depleted compared to leaves. |
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