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| Titel |
Sulfur and carbon isotope biogeochemistry of a rewetted brackish fen |
| VerfasserIn |
Franziska Koebsch, Matthias Gehre, Matthias Winkel, Stefan Koehler, Marian Koch, Gerald Jurasinski, Alejandro Spitzy, Susanne Liebner, Torsten Sachs, Iris Schmiedinger, Lisett Kretzschmann, Anke Saborowski, Michael E. Böttcher |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112837
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| Publikation (Nr.) |
 EGU/EGU2015-13016.pdf |
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| Zusammenfassung |
| Coastal wetlands are at the interface between terrestrial freshwater and marine and exhibit
very specific biogeochemical conditions. Intermittent sea water intrusion affects metabolic
pathways, i. e. anaerobic carbon metabolism is progressively dominated by sulfate reduction
with lower contribution of methanogenesis whilst methane production is increasingly shifted
from acetoclastic to hydrogenotrophic. Due to expanding anthropogenic impact a large
proportion of coastal ecosystems is degraded with severe implications for the biogeochemical
processes.
We use concentration patterns and stable isotope signatures of water, sulfate, dissolved
carbonate, and methane (δ2H, δ13C, δ18O, δ34S) to investigate the S and C metabolic cycle in
a rewetted fen close to the southern Baltic Sea border. Such studies are crucial to
better predict dynamic ecosystem feedback to global change like organic matter
(OM) decomposition or greenhouse gas emissions. Yet, little is known about the
metabolic pathways in such environments. The study site is part of the TERENO
Observatory „Northeastern German Lowlands“ and measurements of methane emissions
have run since 2009. High methane fluxes up to 800 mg m-2 hr-1 indicate that
methanogenesis is the dominant C metabolism pathway despite of high sulfate concentrations
(up to 37 mM). The presented data are part of a comprehensive biogeochemical
investigation that we conducted in autumn 2014 and that comprises 4 pore water
profiles and sediment samples within a transect of 300-1500 m distance to the Baltic
Sea.
Depth of organic layers ranged from 25 to 140 cm with high OM contents (up to 90
dwt.%). Sulfate/chloride ratios in the pore waters were lower than in the Baltic Sea for most
sites and sediment depths indicated a substantial net sulfate loss. Sulfide concentrations were
negligible at the top and increased parallel to the sulfate concentrations with depth to values
of up to 0.3 mM. One pore water profiles situated 1150 m from the Baltic Sea coast line
exhibited a significant excess of sulfate. Preliminary sulfur isotope analysis of pore
water sulfate from a location nearest to this profile revealed an enrichment in 34S
(24.9 to 41.8oÂ) in comparison to Baltic Sea sulfate (21oÂ). This confirms high
degrees of net sulfate reduction. Considering the yet high sulfate concentrations we
hypothesize that local processes might supply additional sulfate and that the sulfide
produced from sulfate reduction might either be lost by upwards diffusion towards the
atmosphere or converted into other S compounds such as pyrite or organic compounds.
The isotopic signatures of methane (δ13C: -68 to -57oÂand δ2H: -133 to -157o
respectively) indicated acetoclastic methanogenesis to be the most dominant methane
production pathway. However, estimated fractionation factors are comparatively high
(1.050-1.065). Enrichment of heavy 13C in methane at the top of the sediment was either
caused by methane oxidation or variation in substrate availability (e. g. due to peat
degradation).
The interpretation of our data in the light of further results will provide deeper insights
into metabolic pathways and possible interactions between both coupled element cycles for
coastal ecosystems. |
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