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| Titel |
Seasonal qualitative and quantitative dynamics of dissolved organic carbon in a boreal mire complex in Northwest Russia. |
| VerfasserIn |
A. Avagyan, B. Runkle, C. Knoblauch, N. Hennings, H. Haupt, B. Brockmeyer, A. Spitzy, J. Hartmann, L. Kutzbach |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065813
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| Zusammenfassung |
| Dissolved organic carbon (DOC) is a poorly characterized component of the carbon cycle in
the boreal regions of Russia, home to a considerable portion of global carbon-rich peatlands.
However, due to the variable substrates, nutrient availability, and hydrological regime,
different parts of a mire complex may exhibit distinctively different DOC concentrations.
Therefore, the objective of the current study is to investigate the spatial variability of
DOC, and to distinguish DOC temporal hot-spots during the course of the annual
cycle.
Water samples were collected from the forest-fen transitional zone (lagg), from fen and
bog zones, and from the peatland outflow into the river fluvial system in the Ust-Pojeg mire
complex (61Ë 56’N, 50Ë 13’E) in the Komi Republic, Northwest Russia. The bulk
DOC was separated from particulate organic matter with pre-combusted glass fiber
filters. Afterwards, tangential flow filtration was used for fractionating the bulk DOC
into colloidal and ‘truly dissolved’ fractions The organic carbon content of these
fractions was analyzed via wet combustion, and the δ13C value of this organic matter
was determined through isotope-ratio mass spectrometry. This isotopic analysis
allows determining the degree of degradation, as degradation increases the δ13C
signature of the remaining carbon due to microbial metabolic preference for lighter
isotopes.
During the summer-autumn period, surface- and pore-waters from different parts
of the mire complex exhibited clearly differing DOC concentrations. The highest
DOC concentrations (41-55 mg L-1) were detected at the transitional or lagg zone
between forest and fen while the lowest concentrations were observed at the bog site
(20-28 mg L-1). During the spring snowmelt period, a significant amount (2.3 g
C m-2) of DOC was flushed away from the mire into the nearby regional Pojeg
River.
The DOC composition, particularly with respect to the proportion of colloids, differed
significantly between outflow, lagg, fen and bog surface waters. During the summer period,
the highest relative contribution of the truly dissolved organic carbon to the bulk DOC
was detected at the bog site (47% of the total) while after the snowmelt period its
highest relative contribution was at the transitional (lagg) site (12% of the total).
The δ13C analyses showed that during the summer period under high temperature
and low water table conditions the bog contained the most decomposed organic
material, which may contribute to its large observed CO2 emissions during the hot
season.
We conclude that lagg, bog and fen zones represent separate hydrological and
biogeochemical units within the single mire complex. Particularly, the transition
(lagg) zones between mires and the surrounding mineral soils appear to be of major
importance for organic matter export from boreal mire-forest landscapes into the
fluvial system. The presented data suggest that further investigation of processes
governing DOC dynamics is needed to understand the spatial-temporal variability of
fluxes and to scale up aggregated fluxes for regional carbon budget estimations. |
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