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  • 1. Kaal, Joeri
    et al.
    Martinez Cortizas, Antonio
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Seasonal changes in molecular composition of organic matter in lake sediment trap material from Nylandssjon, Sweden2015Ingår i: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 83-84, s. 253-262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The origin and degradation/preservation state of organic matter (OM) in lacustrine systems can be studied using its molecular composition. Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) allows rapid assessment of OM-rich samples and has proven a useful tool for peat, lacustrine and marine deposits, but is rarely applied specifically to lake environments prone to the formation of varves (annually laminated sediments), which are used frequently for palaeoenvironmental reconstruction. We applied Py-GC-MS to a 3.5 yr record of sediment trap samples collected from Nylandssjon in northern Sweden to determine the usefulness of the method for improving knowledge of OM dynamics in varved lakes. It appeared that seasonal variation controlled the pyrolysis fingerprints: intact polysaccharides and lignin from vascular plants, chitin from arthropods and chlorophyll from algae were concentrated in spring and summer traps, whereas winter trap samples were enriched mainly in degraded components, as OM slowly trickled down under a thick layer of ice. A secondary diagenetic process involving sulfurisation of phytadienes was recognised via isoprenoid thiophenes, with no clear seasonal trend, probably because it occurred under anoxic conditions at the lake bottom. The N-containing compounds from proteins in algae and chitin in arthropods were abundant in all samples, indicating that the dominant flux of varve OM was autochthonous in origin. We conclude that Py-GC-MS has significant potential for identifying the variability in parent material (source organisms and degradation state) and could become a valuable tool for palaeoenvironmental reconstruction from varved lake sediments. 

  • 2. Norström, Elin
    et al.
    West, Johannes
    Kouli, Katerina
    Katrantsiotis, Christos
    Umeå universitet, Humanistiska fakulteten, Institutionen för idé- och samhällsstudier.
    Hättestrand, Martina
    Smittenberg, Rienk
    Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece2021Ingår i: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The anhydrosugars levoglucosan, mannosan and galactosan have been regarded a suitable molecular indicator of natural biomass combustion. Here we evaluate the summed anhydrosugars (SAS) as paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel throughout the sediment sequence. Modern surface soil samples from the same region were analysed for presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions both on local and regional scale, and regionally widespread arboreal vegetation. Low or absence of SAS in the fossil core is associated with periods of dryness, regional dominance of non-arboreal vegetation and a fen rather than lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months are probably promoting oxidation and biodegradation of the labile SAS molecules compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400-2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece.

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  • 3.
    Soucemarianadin, Laure N.
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Erhagen, Björn
    Nilsson, Mats B.
    Öquist, Mats G.
    Immerzeel, Peter
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Schleucher, Jürgen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Two dimensional NMR spectroscopy for molecular characterization of soil organic matter: Application to boreal soils and litter2017Ingår i: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 113, s. 184-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic soils in boreal ecosystems and peatlands represent a huge global carbon pool and their composition strongly affects soil properties. Nevertheless, the characterization of soil organic matter (SOM) molecular composition, which is essential for elucidating soil carbon processes and turnover, is not easily achieved, and further advances in the area are greatly needed. Two dimensional (2D) liquid state H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy has been used on dimethyl sulfoxide (DMSO) extracts of SOM to achieve molecular level characterization, with signals from many identifiable molecular groups observable. Here we show that a simple and fast sample preparation allows acquisition of 2D H-1-C-13 NMR spectra from extracts of plant litter and organic layers in boreal ecosystems, with fast data acquisition. Our 2D NMR spectra revealed several differences in the DMSO extracts of different tree litter samples, O-horizons of forest soil, peat-forming moss (Sphagnum) and peat. The results mirror established differences between OM in soils and litter of different forest ecosystems (e.g. between deciduous and coniferous litter) but also provide indications for research to untangle previously conflicting results (e.g. cutin degradation in soil or carbohydrate degradation in peat). Thus, combination of 2D NMR methods can greatly improve analysis of litter composition and SOM composition, thereby facilitating the elucidation of their roles in biogeochemical and ecological processes that are critical for foreseeing feedback mechanisms for SOM turnover as a result of global environmental change.

  • 4.
    Soucemarianadin, Laure N.
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Quideau, Sylvie A.
    MacKenzie, M. Derek
    Munson, Alison D.
    Boiffin, Juliette
    Bernard, Guy M.
    Wasylishen, Roderick E.
    Total and pyrogenic carbon stocks in black spruce forest floors from eastern Canada2015Ingår i: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 82, s. 1-11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pyrogenic carbon (PyC), a by-product of recurrent boreal wildfires, is an important component of the global soil C pool, although precise assessment of boreal PyC stock is scarce. The overall objective of this study was to estimate total C stock and PyC stock in forest floors of Eastern Canada boreal forests. We also investigated the environmental conditions controlling the stocks and characterized the composition of the forest floor layers. Forest floor samples were collected from mesic black spruce sites recently affected by fire (3-5 yr) and analyzed using elemental analysis and solid state C-13 nuclear magnetic resonance (NMR) spectroscopy. PyC content was further estimated using a molecular mixing model. Total C stock in forest floors averaged 5.7 +/- 2.9 kg C/m(2) and PyC stock 0.6 +/- 0.3 kg C/m(2). Total stock varied with position in the landscape, with a greater accumulation of organic material on northern aspects and lower slope positions. In addition, total stock was significantly higher in spruce-dominated forest floors than stands where jack pine was present. The PyC stock was significantly related to the atomic H/C ratio (R-2 0.84) of the different organic layers. C-13 NMR spectroscopy revealed a large increase in aromatic carbon in the deepest forest floor layer (humified H horizon) at the organic-mineral soil interface. The majority of the PyC stock was located in this horizon and had been formed during past high severity fires rather than during the most recent fire event.

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