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| Titel |
Forest floor methane flux modelled by soil water content and ground vegetation – comparison to above canopy flux |
| VerfasserIn |
Elisa Halmeenmäki, Olli Peltola, Iikka Haikarainen, Kira Ryhti, Üllar Rannik, Mari Pihlatie |
| 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 |
250148179
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| Publikation (Nr.) |
 EGU/EGU2017-12413.pdf |
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| Zusammenfassung |
| Methane (CH4) is an important and strong greenhouse gas of which atmospheric
concentration is rising. While boreal forests are considered as an important sink of
CH4 due to soil CH4 oxidation, the soils have also a capacity to emit CH4. Moreover,
vegetation is shown to contribute to the ecosystem-atmosphere CH4 flux, and it has
been estimated to be the least well known natural sources of CH4. In addition to
well-known CH4 emissions from wetland plants, even boreal trees have been
discovered to emit CH4.
At the SMEAR (Station for Measuring Ecosystem-Atmosphere Relations) II station in
Hyytiälä, southern Finland (61∘ 51’ N, 24∘17’ E; 181 m asl), we have detected small
CH4 emissions from above the canopy of a Scots pine (Pinus sylvestris) dominated
forest. To assess the origin of the observed emissions, we conducted forest floor CH4
flux measurements with 54 soil chambers at the footprint area of the above canopy
flux measurements during two growing seasons. In addition, we measured the soil
volumetric water content (VWC) every time next to the forest floor chamber
measurements, and estimated vegetation coverages inside the chambers.
In order to model the forest floor CH4 flux at the whole footprint area, we combined
lidar (light detection and ranging) data with the field measurements. To predict the
soil water content and thus the potential CH4 flux, we used local elevation, slope, and
ground return intensity (GRI), calculated from the lidar data (National Land Survey of
Finland). We categorized the soil chambers into four classes based on the VWC so
that the class with the highest VWC values includes all the soil chambers with a
potential to emit CH4. Based on a statistically significant correlation between the
VWC and the forest floor CH4 flux (r = 0.30, p < 0.001), we modelled the potential
forest floor CH4 flux of the whole area.
The results of the soil chamber measurements show a few areas of the forest floor with
significant CH4 emissions. The modelled map of the potential CH4 flux is consistent
with the measurements of the flux and the VWC, indicating that the wetter areas have
potential for CH4 emissions, while the drier areas have potential for CH4 uptake.
Preliminary results of the vegetation coverage show a positive correlation between the
first year forest floor CH4 flux and the coverage of Sphagnum spp. mosses (r = 0.55, p
< 0.001). Furthermore, we will include the vegetation coverage to the analysis, and
compare the modelled forest floor CH4 flux with the measured above canopy flux.
This ongoing research will give valuable information about the CH4 sources and
dynamics in boreal forests. |
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