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| Titel |
Micro-scale elemental composition of organo-mineral associations collected
in situ from a Calcaric Gleysol |
| VerfasserIn |
Selina Tenzer, Karin Eusterhues, Carsten W. Mueller, Lydia Pohl, Thilo Rennert |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150703
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| Publikation (Nr.) |
 EGU/EGU2017-15189.pdf |
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| Zusammenfassung |
| Evaluating the temporal dynamics of the chemical composition and spatial distribution of
organo-mineral associations is crucial for understanding their role in cycling and stabilizing
soil organic matter (SOM).
Especially Fe oxides and hydroxides play an important role for the stabilization of SOM
due to their high reactivity. However, it is not straight forward to study the formation of
organo-mineral associations in situ at intact soil structures. In groundwater-affected
redoximorphic soils, precipitation of Fe oxides occurs directly at the soil-water interface of
coarse pores. Therefore, these soils are particularly suitable to observe the dynamics of Fe
oxides regarding interactions with dissolved organic matter and redox-induced aging of
initially short-range ordered Fe oxides. We therefore chose a dyked marshland
site with a Calcaric Gleysol formed from marine sediments for collecting freshly
precipitated and aged Fe oxides in situ. Sampling was carried out without physical
and chemical disturbance using a special rod with attached glass slides or silicon
wafers. The application of slides enabled us to use a wide range of microscopic and
spectroscopic techniques to analyze the chemical and mineralogical composition of these
precipitates.
Three rods were inserted for half a year (R0.5), one year (R1) and two and a half years
(R2.5). Wafers and glass slides within the Bg-Horizon (oxidizing conditions) were analyzed
starting with field emission scanning electron microscopy (FE SEM) to select suitable spots
for subsequent chemical mapping using nano-scale secondary ion mass spectrometry
(NanoSIMS).
For R0.543 spots on two glass slides were measured, for R1 39 spots on four silicon
wafers and for R2.5 34 spots on four glass slides. For the NanoSIMS measurements
seven masses were chosen, mainly: 16O−, 12C−, 12C14N−, 31P−, 32S−, 27Al16O−,
56Fe16O−.
One plane with 10 ms per pixel (R0.5 + 2.5) and 40 planes with 1 ms per pixel (R1) were
measured. For evaluating a triangle threshold was applied via ImageJ. Look@NanoSIMS was
used to define regions of interest (ROIs). For statistical analysis ratios of different masses will
be calculated and statistically evaluated.
First preliminary results based on selected spots of R0.5and R2.5show a patchy
distribution of organic material on aggregates. The spots of SOM increase over time, which
suggests that larger organo-mineral associations are formed. A tendency for the competition
of adsorption sites between sulfate and organic anions can be assumed for R0.5and R2.5,
demonstrated by larger ratios of 32S− to 56Fe16O− instead of 12C− or 12C14N− to
56Fe16O−. The further evaluation of the data set will give us insight, how organo-mineral
associations are altered over time, e.g. whether the association of organic matter with Fe
oxides becomes more important than the association with phyllosilicates after a larger
number of redox cycles. This would contribute to a long-term SOM stabilization. |
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