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| Titel |
Water movement and solute transport in permafrost wetlands: implications for inorganic carbon cycling |
| VerfasserIn |
Søren Jessen, Hanne Dahl Holmslykke, Kristine Rasmussen, Niels Richardt, Peter Engelund Holm |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098506
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| Publikation (Nr.) |
 EGU/EGU2014-14188.pdf |
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| Zusammenfassung |
| Carbon dioxide emissions from thawing permafrost wetlands are an expected consequence of
global warming. Addressing the pathways by which carbon is emitted, we investigated the
hydrological and geochemical controls on the pore water chemistry of a permafrost wetland,
with a shallow geological sequence comprising loam overlain by sphagnum peat, in Ilulissat,
Greenland. A 400 m transect parallel to the general flow direction was established, along
which water table measurements and slug tests were conducted, and the active layer thickness
recorded (typically ~0.5 m). Also, in three detailed profiles along the transect,
the vertical distributions of stable isotopes of water and major ion chemistry were
investigated, by analysis of active layer pore water and water of melted core sections
of permafrost. Concentrations of chloride (0.3-0.4 mM) did not show variation
with depth, dismissing solute movement by ion freeze-out during fall freeze-up
as a main control on the water chemistry. In addition, the observed vertical δ18O
distribution did not to any extent conform to modelled Rayleigh distillation curves for the
preferential inclusion of H218O into ice, which could be a scenario for fall freeze-up.
The δ18O data therefore suggests either a rapid freeze-up or a simultaneous phase
transition at all depths of the active layer, which in either case also would minimize
potential ion freeze-out effects. Nevertheless, concentrations of major ions generally
increased with depth. A conceptual model for water and solute transport was therefore
established, according to which solutes are mobilized by weathering reactions in the
loam and then transported upwards to the peat by diffusion. In the peat, lateral
advective solute transport dominates. We applied the model to observed profiles of
Ca, Mg, HCO3 and the partial CO2 pressure (PCO2). Concentrations of Ca, Mg
and HCO3 increased with depth, reaching ~2 mM, ~2 mM and ~8 meq/L at the
bottom of the active layer. Pore water at all depths was of Ca-Mg-HCO3 type (1:1:4
stoichiometry), and was subsaturated for calcite and dolomite. Immediately below the
permafrost table, however, Ca, Mg and HCO3 showed an abrupt decrease. Similarly,
highly elevated PCO2 of up to 1.8 atm were observed in the active layer, followed
by an abrupt decrease to |
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