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| Titel |
Uplifting of palsa peatlands by permafrost identified by stable isotope depth profiles |
| VerfasserIn |
Jan Paul Krüger, Franz Conen, Jens Leifeld, Christine Alewell |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104020
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| Publikation (Nr.) |
 EGU/EGU2015-3440.pdf |
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| Zusammenfassung |
| Natural abundances of stable isotopes are a widespread tool to investigate biogeochemical
processes in soils. Palsas are peatlands with an ice core and are common in the discontinuous
permafrost region. Elevated parts of palsa peatlands, called hummocks, were uplifted by
permafrost out of the influence of groundwater. Here we used the combination of δ15N values
and C/N ratio along depth profiles to identify perturbation of these soils. In the years 2009
and 2012 we took in total 14 peat cores from hummocks in two palsa peatlands near Abisko,
northern Sweden. Peat samples were analysed in 2 to 4 cm layers for stable isotope ratios and
concentrations of C and N. The uplifting of the hummocks by permafrost could be detected
by stable isotope depth patterns with the highest δ15N value at permafrost onset, a so-called
turning point. Regression analyses indicated in 11 of 14 peat cores increasing δ15N values
above and decreasing values below the turning point. This is in accordance with
the depth patterns of δ13C values and C/N ratios in these palsa peatlands. Onset
of permafrost aggradation identified by the highest δ15N value in the profile and
calculated from peat accumulation rates show ages ranging from 80 to 545 years
and indicate a mean (±SD) peat age at the turning points of 242 (±66) years for
Stordalen and 365Â(±53) years for Storflaket peatland. The mean peat ages at turning
points are within the period of the Little Ice Age. Furthermore, we tested if the
disturbance, in this case the uplifting of the peat material, can be displayed in the
relation of δ15N and C/N ratio following the concept of Conen et al. (2013). In
unperturbed sites soil δ15N values cover a relatively narrow range at any particular
C/N ratio. Changes in N cycling, i.e. N loss or gain, results in the loss or gain of
15N depleted forms. This leads to larger or smaller δ15N values than usual at the
observed C/N ratio. All, except one, turning point show a perturbation in the depth
profile, with most of the adjacent sampling points also indicating perturbation. This
perturbation shows the changes in N cycling, in this case N loss, from these depths due
to permafrost aggradation. Deeper parts of some profiles at Stordalen peatland
indicate with the same approach an N gain, maybe due to lateral N input to these
nutrient poor ecosystems. Most of the uppermost samples in the δ15N depth profiles
show no perturbation, potentially due to the adaptation of these soils to the new
conditions. Both stable isotope (δ15N and δ13C) depth profiles are suitable to detect
palsa uplifting by permafrost. The perturbation of the peat by uplifting as well
as the potential nutrient input can be detected by δ15N when related to the C/N
ratio.
Conen, F., Yakutin, M. V., Carle, N., and Alewell, C. (2013): δ15N natural abundance may
directly disclose perturbed soil when related to C:N ratio. Rapid Commun. Mass Spectrom.
27: 1101-1104. |
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