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| Titel |
Characterizing adsorptive properties and DOC concentrations in soils of Northern European Russian tundra and taiga. |
| VerfasserIn |
Marieke Oosterwoud, Erwin Temminghoff, Sjoerd van der Zee |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044140
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| Zusammenfassung |
| Subarctic river basins have an enormous potential to mobilize and transport terrestrial OC to
the Arctic Ocean, because 23-48% of the worlds soils organic carbon (SOC) is
stored in the high latitude region. Currently the Arctic drainage basin (~24 x 106
km2) processes about 11% of the global dissolved organic carbon (DOC), which
is exported to the ocean. About 10-25% of annual C input to the organic surface
layer with litter is leached from the organic surface layers. As climate changes, the
amount and chemical composition of DOC exported from these basins are expected to
change.
Adsorption of DOC on mineral phases is the key geochemical process for the release and
removal of DOC from this potentially soluble carbon pool. Most DOC leached from organic
horizons is adsorbed and retained in the subsoils. The adsorption depends much on the
content of sesquioxides and amount of carbon previously accumulated in soils. Besides
adsorption, polyvalent metal ions in solution, such as Al and Ca, can cause precipitation of
DOC. Along with the decrease of DOC concentrations on its passage through mineral soil,
there are major biochemical alterations of DOC composition. Hydrophobic compounds
(humic and fulvic acids) of high molecular weight that are rich in acidic functional groups
and aromatic compounds adsorb most strongly. Hydrophilic compounds can contribute
to DOC adsorption but are also easily desorbed because of the weaker bonding
strength.
The aim of this study was to characterize the DOC concentrations and their chemical
composition as well as the DOC adsorptive properties of soils found in a tundra and
taiga catchment of Northern Russia. We sampled soil and soil solution from two
catchments in the Komi Republic of European Northern Russia: a tundra (67N/62E) and
a taiga (62N/50E). The soil samples were analysed for total organic carbon (Ct)
and the content of sequioxides. By extracting soil samples with water we got an
impression of the potentially extractable organic carbon (EOC). Besides DOC, the easily
dissolvable part of the adsorbed organic carbon and precipitated organic carbon will also
be extracted. The soil solution and extraction samples were analysed for DOC,
DOC composition and cations. Based on the methodological relationship between
Ct, EOC and DOC we will demonstrate that for the release of DOC from these
soils the chemical process of adsorption and desorption are more important than
mineralization.
Our laboratory results showed that adsorbed organic carbon that can easily dissolve can
provide a quick release of DOC. We found that about 80-90% of the released EOC was
previously adsorbed. Because the process of desorption is quick it is not dependent on
mineralization or degradation. Consequently, leaching of DOC as a result of desorption will
have a large impact on the transport of DOC, especially under climate change. By being able
to model the amount of adsorbed organic carbon we would be able to predict the amount of
organic carbon that could be desorbed under different soil and climatic conditions. Using the
chemical speciation model Orchestra we modelled the adsorption of humic, and
fulvic acids to cations according to the NICA-Donnan model. This model describes
the specific binding of cations to the humic reactive sites (NICA) as well as the
nonspecific (electrostatic) binding of cations due to the negative charge of the humic
substances (Donnan). We compared the modelled amount of adsorbed hydrophobic acids
with the measured amounts of adsorbed hydrophobic acids to see if the model is
able to reproduce the amount of potentially available organic carbon found in the
soils.
Acknowledgement: This work is part of CARBO-North project (036993) funded by EU
FP6 Global Change and Ecosystems |
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