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| Titel |
A fertile peatland forest constitutes no major greenhouse gas sink |
| VerfasserIn |
Astrid Meyer, Lasse Tarvainen, Azad Nousratpour, Robert G. Björk, Maria Ernfors, Åsa Kasimir Klemedtsson, Anders Lindroth, Mats Räntfors, Tobias Rütting, Göran Wallin, Per Weslien, Leif Klemedtsson |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076908
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| Zusammenfassung |
| Organic soils drained for agriculture have been identified as potential large sources of
greenhouse gases (GHG), such as CO2, N2O, and CH4. As a mitigation strategy to limit
the GHG effluxes of these soils afforestation has been suggested, because the C
accumulation in tree biomass is assumed to balance soil effluxes of GHG, which would turn
the ecosystem into an overall GHG sink. However, the magnitude of soil GHG
effluxes and the carbon accumulation in tree growth has been shown to be highly
dependent on a number of factors from which the soil nutrient and the drainage level
are of major importance. Year-round measurements of all GHGs of nutrient-rich
afforested organic soils are scarce, so that the overall GHG budget remains uncertain.
The scarcity of studies can partly be explained by the uncertainties involved in
methodology.
This study reports the ecosystem fluxes of CO2, N2O, and CH4 of a spruce dominated
forest on a drained organic soil with an agricultural history in Sweden. A direct (eddy
covariance) as well as an indirect (analysing the different terms of the GHG budget) approach
have been used to determine the net ecosystem CO2 exchange (NEE), so that uncertainties in
the respective method could be evaluated. The annual tree production in 2008 was 30.1 (±
6.2) t CO2eq ha-1yr-1. N2O fluxes were determined by the closed chamber technique and
amounted to 3.3 t CO2eq ha-1yr-1. Independent of the approach applied, the C sequestration
by trees counters large amounts of the soil CO2 effluxes, however according to
the direct approach by the eddy covariance technique, the site acts as a GHG sink
of -4.1 t CO2eq ha-1yr-1. This contrasts the NEE estimate gained through the
indirect approach, which suggests that the site is a net GHG emitter of 3.3 t CO2eq
ha-1yr-1.
Due to major uncertainties involved in the indirect approach, it was concluded that the
direct approach is the more reliable method, suggesting the site to be a GHG sink. However,
as the site was in its optimum growth stage, i.e. the rate of carbon sequestration was at its’
maximum and will decrease with forest age, it will likely turn into a GHG source again. In
general, forests in their younger stage are usually GHG sources or neutral, so that the
overall GHG sink potential of this afforested nutrient-rich organic soil is likely
to be limited to a rather short time period. The long-term GHG sink potential of
nutrient-rich afforested organic soils must thus be questioned and it is recommended
that future GHG mitigation strategies take the site-specific properties into account. |
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