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| Titel |
Seasonal dynamics of organic carbon and metals in thermokarst lakes from the discontinuous permafrost zone of western Siberia |
| VerfasserIn |
R. M. Manasypov, S. N. Vorobyev, S. V. Loiko, I. V. Kritzkov, L. S. Shirokova, V. P. Shevchenko, S. N. Kirpotin, S. P. Kulizhsky, L. G. Kolesnichenko, V. A. Zemtzov, V. V. Sinkinov, O. S. Pokrovsky |
| 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 ; 12, no. 10 ; Nr. 12, no. 10 (2015-05-21), S.3009-3028 |
| Datensatznummer |
250117944
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| Publikation (Nr.) |
 copernicus.org/bg-12-3009-2015.pdf |
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| Zusammenfassung |
| Despite relatively good knowledge of the biogeochemistry of Siberian
thermokarst lakes during summer base flow, their seasonal dynamics remains
almost unexplored. This work describes the chemical composition of
~130 thermokarst lakes ranging in size from a few m2 to several
km2, located in the discontinuous permafrost zone. Lakes were sampled
during spring flood, just after the ice break (early June), the end of summer
(August), the beginning of ice formation (October) and during the full
freezing season in winter (February). The lakes larger than 1000 m2 did
not exhibit any statistically significant control of the lake size on
dissolved organic carbon (DOC), the major and trace element concentrations
over three major open water seasons. On the annual scale, the majority of
dissolved elements including organic carbon increased their concentration
from 30 to 500%, with a statistically significant (p < 0.05) trend
from spring to winter. The concentrations of most trace elements (TEs)
increased in the order spring > summer > autumn > winter. The ice
formation in October included several stages: first, surface layer freezing
followed by crack (fissure) formation with unfrozen water from the deeper
layers spreading over the ice surface. This water was subsequently frozen and
formed layered ice rich in organic matter. As a result, the DOC and metal
(Mn, Fe, Ni, Cu, Zn, As, Ba and Pb) concentrations were highest near the
surface of the ice column (0 to 20 cm) and decreased by a factor of 2
towards the bottom. The main implications of discovered freeze-driven solute
concentrations in thermokarst lake waters are enhanced colloidal coagulation
and removal of dissolved organic matter and associated insoluble metals from
the water column to the sediments. The measured distribution coefficients of
a TE between amorphous organo-ferric coagulates and lake water
(<0.45 μm) were similar to those reported earlier for Fe-rich
colloids and low molecular weight (<1 kDa, or <1–2 nm) fractions
of thermokarst lake waters, suggesting massive co-precipitation of TE with
amorphous Fe oxyhydroxide stabilized by organic matter. Although the
concentration of most elements was lowest in spring, this period of maximal
water coverage of land created a significant reservoir of DOC and soluble
metals in the water column that can be easily mobilized to the hydrological
network. The highest DOC concentration observed in the smallest
(<100 m2) water bodies in spring suggests their strongly
heterotrophic status and, therefore, a potentially elevated CO2 flux
from the lake surface to the atmosphere. |
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