Rolle der Torfzersetzung für die Akkumulation und Freisetzung von Metallen aus Torfmooren
Mineralogie, Petrologie und Geochemie
Zusammenfassung der Projektergebnisse
Peatlands have the ability to store large amounts of major and trace elements from atmospheric deposition. Sphagnum spp., a dominant species in boreal peatlands, readily takes up and retains soluble cations of trace elements. However, the role of Sphagnum degradation on trace element uptake and release in peatlands and its relation to seasonal and climatic changes is not well understood. The aim of the SMAP project was to determine the effect of Sphagnum litter decomposition on the release of trace elements into the hydrological system or their retention in the peat deposit. Objectives included: characterizing moss degradation and its relationship with microhabitat conditions, relating degradation to metal accumulation, and relating results to field studies on dissolved organic matter (DOM) and trace element export from peatlands. We examined variation in the composition fo organic matter (OM) in short moss cores from different microhabitats from a ombrotrophic peatland using Fourier-transform infrared spectroscopy (FTIR) and Pyrolysis- and THM-GC-MS analysis in an in-vitro degradation experiment. Our results were compared with other degradation proxies such as carbon to nitrogen ratios (C/N) and mass loss. We compared our findings to the composition of the peatland outflow to investigate the relationship between the organism matter degradation and metal releases in a peatland affected by historical mining pollution. We found that FTIR analysis showed minimal differences between cores from different microhabitats, mostly due to differences in vegetation. The main differences in decomposition observed with FTIR were between fresh moss and peat layers, as well as early and late stages. FTIR ratios pinpointed the most active decomposition layer (in the limit of the seasonal water table changes) that was supported by C/N ratios. Overall, we found that FTIR is useful for studying moss and peat organic matter degradation, but has limitations in identifying changes in early stages of degradation. Therefore, Py-GC-MS and THM-GC-MS were better suited for examining molecular changes during early stages of moss tissue degradation in 400-day decomposition experiments. We identified two distinct degradation processes: long-term decay in anaerobic conditions, characterized by the gradual loss of polysaccharides and the preservation of lignin and aliphatic OM; and the initial stages of aerobic degradation, characterized by the formation of microbial-origin OM, the degradation of labile phenolic compounds (including 4-isopropenylphenol from sphagnum acid, 4IPP) and its mobilization by leaching along with free carbohydrates. These processes were found to be spatially-separated, with anaerobic decay being the initial process in hollows and aerobic degradation through leaching being the dominant process in hummocks. This suggests that the presence of 4IPP in peat cores might not only depend on general peatland water table fluctuations but also on position in the microrelief during peat accretion. Our data suggests the total mass loss of the samples after incubation was lower when the original sample contained a higher amount of structural carbohydrates. Additionally, we observed that decreases in C/N ratios during the decomposition experiment were not significantly correlated with higher mass loss, as is commonly observed in millennial peat records; suggesting that in natural conditions, the initial stages of OM degradation may not be consistently characterized by decreasing C/N values. Although the degradation patterns of OM in incubated samples differed between hollows and hummocks compared to naturally decomposed samples, we were able to identify the transport of trace metals from the peatland, which is associated with phenols and driven by leaching from hummocks or surface aerobic layers, through comparison of our THM products with THM products from the peatland outflow. Future studies will evaluate the effect of moss core degradation on metal accumulation by combining the molecular characterization of surface core OM with metal concentration analysis.
Projektbezogene Publikationen (Auswahl)
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Sensitivity of river catchments to discharge-controlled dissolved carbon export: a study of eight catchments in southern Patagonia. Biogeochemistry, 160(2), 177-197.
Pérez-Rodríguez, Marta & Biester, Harald
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Explicit microrelief-controlled decoupling of initial aerobic (in hummocks) and anaerobic (in hollows) decay in superficial layers of Sphagnum-dominated peatlands. (2023, 1, 30). American Geophysical Union (AGU).
Pérez-Rodríguez, Marta; Alten, Alexandra; Miler, Miloš & Kaal, Joeri
