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Titel |
DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles? |
VerfasserIn |
K.-H. Knorr |
Medientyp |
Artikel
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Sprache |
Englisch
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ISSN |
1726-4170
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Digitales Dokument |
URL |
Erschienen |
In: Biogeosciences ; 10, no. 2 ; Nr. 10, no. 2 (2013-02-07), S.891-904 |
Datensatznummer |
250017507
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Publikation (Nr.) |
copernicus.org/bg-10-891-2013.pdf |
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Zusammenfassung |
Dissolved organic carbon (DOC) exports from many catchments in Europe and
North-America are steadily increasing. Several studies have sought to explain
this observation. As possible causes, a decrease in acid rain or sulfate
deposition, concomitant reductions in ionic strength and increasing
temperatures were identified. DOC often originates from riparian wetlands;
but here, despite higher DOC concentrations, ionic strength in pore waters
usually exceeds that in surface waters. In the catchment under study, DOC
concentrations were synchronous with dissolved iron concentrations in pore
and stream water. This study aims at testing the hypothesis that DOC exports
are mediated by iron reduction/oxidation cycles. Following the observed
hydrographs, δ18O of water and DOC fluorescence, the wetlands were
identified as the main source of DOC. Antecedent biogeochemical conditions, i.e.,
water table levels in the wetlands, influenced the discharge patterns of
nitrate, iron and DOC during an event. The correlation of DOC with pH was
positive in pore waters, but negative in surface waters; it was negative for
DOC with sulfate in pore waters, but only weak in surface waters. Though, the positive
correlation of DOC with iron was universal for pore and surface water. The decline of DOC and iron concentrations in transition from anoxic
wetland pore water to oxic stream water suggests a flocculation of DOC with
oxidising iron, leading to a drop in pH in the stream during high DOC fluxes.
The pore water did not per se differ in pH. There is, thus, a need to consider processes more
thoroughly of DOC mobilisation in wetlands when
interpreting DOC exports from catchments. The coupling of DOC with iron
fluxes suggested that increased DOC exports could at least, in part, be caused
by increasing activities in iron reduction, possibly due to increases in
temperature, increasing wetness of riparian wetlands, or by a shift from
sulfate dominated to iron reduction dominated biogeochemical regimes. |
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