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Titel |
Stable isotopes, radiocarbon signature and C loss as an indicator for soil degradation in a drained peatland, northern Germany |
VerfasserIn |
Jan Paul Krüger, Jens Leifeld, Stephan Glatzel, Christine Alewell |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250089560
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Publikation (Nr.) |
EGU/EGU2014-3765.pdf |
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Zusammenfassung |
Peatlands are an important component of the global carbon cycle. Even though they cover
only about 3% of the global land area, they store approximately 600 Pg carbon (C) in their
soils. Drainage for agriculture use, for example as grassland, induces oxic conditions in the
upper part of a peat profile and increases the carbon dioxide emissions. Peatlands thus change
from a carbon sink in pristine status to a carbon source under drainage and land use
intensification.
Detailed peat profile analyses in a drained peatland under grassland use in northern
Germany were used to study the influence of drainage and land use management on stable
isotope depth profiles and to calculate retrograde C losses by the ash method. Peat profiles
(n=3) were taken from one semi-natural bog as reference and two adjacent drained peatlands
located at the former peat bog which has been used as grassland (extensive, intensive use) for
the last decades. The peatland drainage started at the beginning of the 20th century and land
use was intensified in the middle of the 20th century. The semi-natural peatland is
unmanaged, the extensive grassland is neither fertilized nor manured and only cut once per
year and the intensive grassland is cut 4-5 times per year and fertilized with mineral fertilizer
and manure.
All grassland peat cores show a clear ash peak in the upper most centimetre of the profile
indicating an accumulation of ash caused by the oxidation of the organic material. Calculated
carbon losses since the drainage of the peatland are 540 (±156) and 290 (±36) t C ha-1for
the intensive and extensive used grassland, respectively. The constant background ash values
from the lower profile were taken as reference values, because even the semi-natural site
accumulated ash in the topsoil and has lost 144(±98) t C ha-1 based on this method. A
likely drainage influence by the surrounding area is also reflected in the δ13C values of the
semi-natural site with an increase of the δ13C values with depth in the upper part
which is also displayed in the drained sites. Furthermore, the δ15N values show
clear difference between the sites with low δ15N at the semi-natural site, slightly
negative values at extensive and positive values at the intensive grassland site. The
latter is most likely caused by the application of fertilizer and manure as well as the
advanced decomposition of peat material in the upper part, which is supported by
the lower C/N ratios in this depth. Radiocarbon pMC values confirmed stronger
peat decay under grassland compared to the semi-natural situation. These were
90.2 (±2.6) and 91.6 (±2.3) pMC in the extensive and intensive grassland (8-14
cm depth), referring to calibrated radiocarbon ages of around 1000 – 1500 years
BP whereas the corresponding pMC value for the semi natural site (112.8 ±4.0)
indicated dominance of organic matter fixed during the second half of the last century. |
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