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| Titel |
Snow and ice properties and melt water dynamics control the methane fluxes during early spring in two boreal mires in north Eastern Europe |
| VerfasserIn |
P. Schreiber, L. Kutzbach, I. Forbrich, M. Gažovič, M. Wilmking |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029642
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| Zusammenfassung |
| High-latitude peatlands are globally important sources of the atmospheric trace gas methane
(CH4). CH4 emissions from boreal peatlands are characterised by a pronounced small-scale
spatial heterogeneity and a high seasonal variability due to extreme climatic contrasts
between seasons. Although winter is the predominant season in boreal climates, most CH4
studies were conducted during the vegetation period whereas wintertime data are
sparse.
Here, we present the results of two intense field campaigns in two boreal peatlands
starting close to the end of winter until the start of the vegetation period, focussing on CH4
fluxes during the very dynamic spring thaw periods. The mire complex Salmisuo in North
Karelia (Finland, 62.46Ë N, 30.58Ë E) was investigated during spring 2006, and the mire
complex Ust Pojeg in the Komi Republic (Northwest Russia, 61.56Ë N, 50.13Ë E) was
studied during spring 2008. Both peatlands represent transition mire complexes in which both
fen and bog types of vegetation can be found with three typical micro-site types: hummocks
(dry), lawns (intermediate) and flarks (wet). CH4 fluxes were measured by the snow gradient
approach (according to Fick’s first law) until the snow was nearly completely melted,
followed by closed dark chamber measurements. Fluxes were measured every second or third
day.
During the spring thaw period, CH4 fluxes were highly dynamic due to rapidly changing
snow and ice properties, hydrological characteristics and temperature variations. Due to
melting and refreezing of snow-melt water and surface water, ice layers were created which
acted as efficient barriers for CH4 efflux from the peatlands. In both peatlands,
an 8 to 15 cm massive ice layer developed during winter in or above the peat soil
depending on microtopography and water level. The surface was covered by snow
with an average height of 50 cm (Salmisuo) and 65 cm (Ust Pojeg). During the
ongoing snowmelt, the CH4 fluxes decreased from highest values (up to 0.5 mg m-2
h-1) to lowest fluxes (< 0.05 mg m-2 h-1) when a layer of fresh melt water at the
bottom of the snow cover was blocking the diffusive pathways for CH4 emission
from the superficially frozen peatlands. After the snow ablation, the massive ice
layer melted; however, the CH4 fluxes were then limited by the high surface water
levels resulting from the snow melt and small rain events. Only after the water
level started to decrease due to outflow and evaporation during the transition period
between snowmelt and start of the vegetation period, CH4 emission was gradually
increasing. In general, closed chamber CH4 fluxes during the transition period were
lower in Salmisuo (hummocks: 0.01 ± 0.007 to 2.0 ± 0.14 mg m-2 h-1, lawns:
0.08 ± 0.01 to 4.2 ± 0.3 mg m-2 h-1, flarks: 0.05 ± 0.03 to 5.7 ± 0.4 mg m-2
h-1) than in Ust Pojeg (hummocks: 0.09 ± 0.02 to 2.8 ± 0.6 mg m-2 h-1, lawns:
0.1 ± 0.03 to 7.01 ± 1.7 mg m-2 h-1, flarks: 0.05 ± 0.01to 3.7 ± 0.8 mg m-2
h-1).
Interestingly, the contribution of the micro-sites to the CH4 emission from the peatlands
differed substantially between the cold seasons and the vegetation period when the flarks are
known to be hot spots of CH4 emission. In winter and early spring, the CH4 fluxes
from the wet flarks were strongly limited by ice and melt water layers which were
acting as diffusion barriers. During the early spring, the control of CH4 fluxes from
peatlands has to be considered highly heterogeneous in space and time. During this
period, the CH4 flux dynamics are mainly controlled by physical factors influencing
the gas transport processes whereas biological processes dominate the CH4 flux
control later during the vegetation period. Since climate change in high-latitudes is
expected to be most extreme during winter, the influence of cryospheric processes on
the carbon cycle will be particularly important for future carbon balance changes. |
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