Freeze-thaw cycles of Arctic thaw ponds remove colloidal metals and generate low-molecular-weight organic matter

High-latitude boreal and arctic surface/inland waters contain sizeable reservoirs of dissolved organic matter (DOM) and trace elements (TE), which are subject to seasonal freezing. Specifically, shallow ponds and lakes in the permafrost zone often freeze solid, which can lead to transformations in t...

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Bibliographic Details
Published in:Biogeochemistry 2018-02, Vol.137 (3), p.321-336
Main Authors: Pokrovsky, Oleg S., Karlsson, Jan, Giesler, Reiner
Format: Article
Language:English
Subjects:
Aquatic ecosystems
Biodegradation
Biogeosciences
Bog
Bogs
Carbon
Carbon dioxide
Climate change
Cycles
Dissolved organic carbon
Dissolved organic matter
Earth and Environmental Science
Earth Sciences
Ecosystems
Environmental Chemistry
Fen
Fens
Freeze thaw cycles
Freeze-thawing
Freezing
Global warming
Heavy metals
Hydroxides
Inland waters
Iron
Lakes
Life Sciences
Metal
Metals
Mires
Organic matter
ORIGINAL PAPERS
Peat
Permafrost
pH effects
Ponds
Removal
Supersaturation
Surface water
Trace elements
Ultrafiltration
Water
Weight
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Summary:High-latitude boreal and arctic surface/inland waters contain sizeable reservoirs of dissolved organic matter (DOM) and trace elements (TE), which are subject to seasonal freezing. Specifically, shallow ponds and lakes in the permafrost zone often freeze solid, which can lead to transformations in the colloidal and dissolved fractions of DOM and TE. Here, we present results from experimental freeze-thaw cycles using iron (Fe)- and DOM-rich water from thaw ponds situated in Stordalen and Storflaket palsa mires in northern Sweden. After ten cycles of freezing, 85% of Fe and 25% of dissolved organic carbon (DOC) were removed from solution in circumneutral fen water (pH 6.9) but a much smaller removal of Fe and DOC (< 7%) was found in acidic bog water (pH 3.6). This removal pattern was consistent with initial supersaturation of fen water with respect to Fe hydroxide and a lack of supersaturation with any secondary mineral phase in the bog water. There was a nearly two- to threefold increase in the low-molecular-weight (LMW) fraction of organic carbon (OC) and several TEs caused by the repeated freeze-thaw cycles. Future increases in the freeze-thaw frequency of surface waters with climate warming may remove up to 25% of DOC in circumneutral organic-rich waters. Furthermore, an increase of LMW OC may result in enhanced carbon dioxide losses from aquatic ecosystems since this fraction is potentially more susceptible to biodegradation.
ISSN:0168-2563
1573-515X
1573-515X
DOI:10.1007/s10533-018-0421-6