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| Titel |
Stable carbon isotopic signature of methane from high-emitting wetland sites in discontinuous permafrost landscape |
| VerfasserIn |
Maija Marushchak, Maarit Liimatainen, Saara Lind, Christina Biasi, Pertti Martikainen |
| 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 |
250150479
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| Publikation (Nr.) |
 EGU/EGU2017-14949.pdf |
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| Zusammenfassung |
| The rising methane concentration in the atmosphere during the past years has been associated
with a concurrent change in the carbon isotopic signature: The atmospheric methane is
getting more and more depleted in the heavy carbon isotope. The decreasing 13C/12C ratio
indicates an increasing contribution of methane from biogenic sources, most importantly
wetlands and inland waters, whose global emissions are still poorly constrained. From the
climate change perspective, arctic and subarctic wetlands are particularly interesting
due to the strong warming and permafrost thaw predicted for these regions that
will cause changes in the methane dynamics. Coupling methane flux inventories
with determination of the stable isotopic signature can provide useful information
about the pathways of methane production, consumption and transport in these
ecosystems.
Here, we present data on the emissions and carbon isotopic composition of
methane from subarctic tundra wetlands at the Seida study site, Northeast European
Russia. In this landscape, underlain by discontinuous permafrost, waterlogged fens
represent sites of high carbon turnover and high methane release. Despite they
cover less than 15% of the region, their methane emissions comprise 98% of the
regional mean (± SD) release of 6.7 (± 1.8) g CH4 m−2 y−1 (Marushchak et al.
2016).
The methane emission from the studied fens was clearly depleted in 13C compared to the
pore water methane. The bulk mean δ13CH4 (± SD) over the growing season was -68.2 (±
2.0) ‰ which is similar to the relatively few values previously reported from tundra
wetlands. We explain the depleted methane emissions by the high importance of
passive transport via aerenchymous plants, a process that discriminates against the
heavier isotopes. This idea is supported by the strong positive correlation observed
between the methane emission and the vascular leaf area index (LAI), and the inverse
relationship between the δ13CH4 of emitted methane and LAI. The latter cannot be
explained by greater dominance of acetoclastic methanogenesis on densely vegetated
sites, since this would lead to the opposite: more enriched methane with higher
LAI.
While the spatial variability of methane emission was related to the differences in the
vascular plant cover, the seasonal dynamics followed closely the local temperatures. Height
of the water table level was an unimportant regulator of methane emissions in these fens,
where floating peat surface follows the water table fluctuations. This implies that
these fens have high potential for increased methane release in the future warmer
climate, due to enhanced microbial methane production and vascular plant growth. |
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