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| Titel |
Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments |
| VerfasserIn |
S. Audry, O. S. Pokrovsky, L. S. Shirokova, S. N. Kirpotin, B. Dupré |
| 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 ; 8, no. 11 ; Nr. 8, no. 11 (2011-11-16), S.3341-3358 |
| Datensatznummer |
250006204
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| Publikation (Nr.) |
 copernicus.org/bg-8-3341-2011.pdf |
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| Zusammenfassung |
| This study reports the very first results on high-resolution sampling of
sediments and their porewaters from three thermokarst (thaw) lakes
representing different stages of ecosystem development located within the
Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the
lake sediments of this and other permafrost-affected regions remain
unexplored regarding their biogeochemical behavior. The aim of this study
was to (i) document the early diagenesic processes in order to assess their
impact on the organic carbon stored in the underlying permafrost, and (ii)
characterize the post-depositional redistribution of trace elements and
their impact on the water column. The estimated organic carbon (OC) stock in
thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to
that reported for peat soils from the same region and denotes intense
organic matter (OM) mineralization. Mineralization of OM in the thermokarst
lake sediments proceeds under anoxic conditions in all the three lakes. In
the course of the lake development, a shift in mineralization pathways from
nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal
electron acceptors in the early diagenetic reactions was suggested. This
shift was likely promoted by the diagenetic consumption of nitrate and
sulfate and their gradual depletion in the water column due to progressively
decreasing frozen peat lixiviation occurring at the lake's borders. Trace
elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides)
and partly sequestered in the sediment in the form of authigenic
Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM
and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate
Sb was observed in the less mature stages. As a result of authigenic sulfide
precipitation, the sediments of the early stage of ecosystem development
were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all
stages of ecosystem development, the sediments were a source of dissolved
Co, Ni and As to the water column. However, the concentrations of these
trace elements remained low in the bottom waters, indicating that sorption
processes on Fe-bounding particles and/or large-size organo-mineral colloids
could mitigate the impact of post-depositional redistribution of toxic
elements on the water column. |
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