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| Titel |
Partitioning of organic carbon in European Russian tundra and taiga ecosystems |
| VerfasserIn |
M. R. Oosterwoud, E. J. M. Temminghoff, S. E. A. T. M. van der Zee |
| 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 |
250028475
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| Zusammenfassung |
| Sorption of dissolved organic carbon (DOC) on mineral phases is an important process for
carbon preservation and element cycling in soils. Sorption of DOC to active minerals results
in its fractionation because hydrophobic compounds (humic and fulvic acids) will be
preferentially sorbed. Binding of cations (Ca2+, Mg2+, Al3+, Fe3+) by the DOC reduces the
negative charge and thus its water solubility. At low pH and high cation concentrations,
cations may cause coagulation of DOC. The sorption and/or coagulation are important factors
in relation to DOC transport.
Little is known about DOC partitioning between the soil solid and solution phases
of arctic ecosystems. As a consequence of future warming arctic ecosystem will
shift from surface water dominated to groundwater dominated systems. In general,
permafrost affected soils with shallow active layers, having lateral flow towards the
stream with only short contact time to mineral layers, lead to higher hydrophobic
(humic and fulvic acid) DOC concentrations in streams compared to permafrost free
soils where a larger share of hydrophilic DOC is expected to be discharged into
streams. Changes in the delivery of DOC, nutrients and major ions to arctic rivers
may have important consequences for primary production and carbon cycling. The
partitioning of DOC is a fundamental process needed for modelling current and
future stream water quality and solute transport. Therefore, the objective of this
study is to determine the sorption and consequent fractionation of DOC in arctic
ecosystems.
During fieldwork carried out in the summer of 2007 and 2008 in the Russian Komi
Republic, we collected soil, soil solution and surface water samples in both a forested taiga
and a permafrost affected tundra catchment. The liquid samples were analysed for total
organic carbon and inorganic cations. A rapid batch procedure was used for determining the
humic-, fulvic- and hydrophilic acid fractions. Using the chemical speciation model
Orchestra we modelled the adsorption of humic, and fulvic acids (hydrophobic compounds)
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).
Our first results show that DOC concentrations in surface water in taiga are higher than in
tundra. By comparing total (TOC) and dissolved (DOC) organic carbon concentrations in
surface water we can conclude that particulate organic carbon (POC=TOC-DOC) is hardly
present. Large differences between 2007 and 2008 surface water DOC concentrations in
tundra reveal the large annual fluctuations in surface water DOC fluxes that may occur. For
the inorganic concentrations the differences between 2007 and 2008 are much smaller than
for DOC. In the permafrost affected tundra ecosystem, DOC concentrations in surface
water decreased with increasing cation concentrations. The composition of the
DOC in both taiga and tundra surface water consists dominantly of fulvic acids
with a minor contribution of hydrophilic acids. Only in a large thermokarst lake in
the tundra and in upstream, fen peat draining, locations in taiga humic acids are
found.
Acknowledgement: This work is part of CARBO-North project (036993) funded by EU
FP6 Global Change and Ecosystems |
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