Seasonal Fluctuations in Iron Cycling in Thawing Permafrost Peatlands

Monique S. Patzner; Nora Kainz; Erik Lundin; Maximilian Barczok; Chelsea Smith; Elizabeth Herndon; Lauren Kinsman-Costello; Stefan Fischer; Daniel Straub; Sara Kleindienst; Andreas Kappler; Casey Bryce

doi:10.1021/acs.est.1c06937

Seasonal Fluctuations in Iron Cycling in Thawing Permafrost Peatlands

Monique S. Patzner, Nora Kainz, Erik Lundin, Maximilian Barczok, Chelsea Smith, Elizabeth Herndon, Lauren Kinsman-Costello, Stefan Fischer, Daniel Straub, Sara Kleindienst, Andreas Kappler, Casey Bryce

Plant-Soil Interactions

Research output: Contribution to journal › Article › peer-review

25 Scopus citations

Abstract

In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether reactive iron minerals could act as a stable sink for carbon or whether they are continuously dissolved and reprecipitated during redox shifts remains unknown. We deployed bags of synthetic ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify the formation and dissolution of reactive Fe(III) (oxyhydr)oxides. We found that the bags accumulated Fe(III) under constant oxic conditions in areas overlying intact permafrost over the full summer season. In contrast, in fully thawed areas, conditions were continuously anoxic, and by late summer, 50.4 ± 12.8% of the original Fe(III) (oxyhydr)oxides were lost via dissolution. Periodic redox shifts (from 0 to +300 mV) were observed over the summer season in the partially thawed areas. This resulted in the dissolution and loss of 47.2 ± 20.3% of initial Fe(III) (oxyhydr)oxides when conditions are wetter and more reduced, and new formation of Fe(III) minerals (33.7 ± 8.6% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions, which also led to the sequestration of Fe-bound organic carbon. Our data suggest that there is seasonal turnover of iron minerals in partially thawed permafrost peatlands, but that a fraction of the Fe pool remains stable even under continuously anoxic conditions.

Original language	English
Pages (from-to)	4620-4631
Number of pages	12
Journal	Environmental Science and Technology
Volume	56
Issue number	7
DOIs	https://doi.org/10.1021/acs.est.1c06937
State	Published - Apr 5 2022

Funding

The authors acknowledge the Abisko Scientific Research Station and ICOS Sweden (Swedish Research Council: 2019-00205) for their support during sampling missions and providing the context data (precipitation, air temperature, soil temperature, soil moisture), with special thanks to Annika Kristoffersson and Jutta Holst. They thank Merritt Logan (Colorado State University, Fort Collins, Colorado) and Hanna Joss (University Tuebingen, Germany) for assistance in the field and for carbon analyzes. This work was supported by the University of Tuebingen (Programme for the Promotion of Junior Researchers award to Casey Bryce) and by the German Academic Scholar Foundation (scholarship to M.S.P.). A.K. acknowledges infrastructural support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy, cluster of Excellence EXC2124, project ID 390838134. The authors thank the German Research Foundation DFG (INST 37/1027-1 FUGG) for financial support provided for the acquisition of the cryogenic focused ion beam scanning electron microscope.

Funders	Funder number
German Academic Scholar Foundation
University of Tuebingen
Deutsche Forschungsgemeinschaft	EXC2124, 390838134, INST 37/1027-1 FUGG

Keywords

Abisko
Arctic
bioavailability
iron
microbial Fe(III) reduction and Fe(II) oxidation
permafrost collapse
seasonal fluctuations
soil organic carbon

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10.1021/acs.est.1c06937

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title = "Seasonal Fluctuations in Iron Cycling in Thawing Permafrost Peatlands",

abstract = "In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether reactive iron minerals could act as a stable sink for carbon or whether they are continuously dissolved and reprecipitated during redox shifts remains unknown. We deployed bags of synthetic ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify the formation and dissolution of reactive Fe(III) (oxyhydr)oxides. We found that the bags accumulated Fe(III) under constant oxic conditions in areas overlying intact permafrost over the full summer season. In contrast, in fully thawed areas, conditions were continuously anoxic, and by late summer, 50.4 ± 12.8% of the original Fe(III) (oxyhydr)oxides were lost via dissolution. Periodic redox shifts (from 0 to +300 mV) were observed over the summer season in the partially thawed areas. This resulted in the dissolution and loss of 47.2 ± 20.3% of initial Fe(III) (oxyhydr)oxides when conditions are wetter and more reduced, and new formation of Fe(III) minerals (33.7 ± 8.6% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions, which also led to the sequestration of Fe-bound organic carbon. Our data suggest that there is seasonal turnover of iron minerals in partially thawed permafrost peatlands, but that a fraction of the Fe pool remains stable even under continuously anoxic conditions.",

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AU - Patzner, Monique S.

AU - Kainz, Nora

AU - Lundin, Erik

AU - Barczok, Maximilian

AU - Smith, Chelsea

AU - Herndon, Elizabeth

AU - Kinsman-Costello, Lauren

AU - Fischer, Stefan

AU - Straub, Daniel

AU - Kleindienst, Sara

AU - Kappler, Andreas

AU - Bryce, Casey

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N2 - In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether reactive iron minerals could act as a stable sink for carbon or whether they are continuously dissolved and reprecipitated during redox shifts remains unknown. We deployed bags of synthetic ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify the formation and dissolution of reactive Fe(III) (oxyhydr)oxides. We found that the bags accumulated Fe(III) under constant oxic conditions in areas overlying intact permafrost over the full summer season. In contrast, in fully thawed areas, conditions were continuously anoxic, and by late summer, 50.4 ± 12.8% of the original Fe(III) (oxyhydr)oxides were lost via dissolution. Periodic redox shifts (from 0 to +300 mV) were observed over the summer season in the partially thawed areas. This resulted in the dissolution and loss of 47.2 ± 20.3% of initial Fe(III) (oxyhydr)oxides when conditions are wetter and more reduced, and new formation of Fe(III) minerals (33.7 ± 8.6% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions, which also led to the sequestration of Fe-bound organic carbon. Our data suggest that there is seasonal turnover of iron minerals in partially thawed permafrost peatlands, but that a fraction of the Fe pool remains stable even under continuously anoxic conditions.

AB - In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether reactive iron minerals could act as a stable sink for carbon or whether they are continuously dissolved and reprecipitated during redox shifts remains unknown. We deployed bags of synthetic ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify the formation and dissolution of reactive Fe(III) (oxyhydr)oxides. We found that the bags accumulated Fe(III) under constant oxic conditions in areas overlying intact permafrost over the full summer season. In contrast, in fully thawed areas, conditions were continuously anoxic, and by late summer, 50.4 ± 12.8% of the original Fe(III) (oxyhydr)oxides were lost via dissolution. Periodic redox shifts (from 0 to +300 mV) were observed over the summer season in the partially thawed areas. This resulted in the dissolution and loss of 47.2 ± 20.3% of initial Fe(III) (oxyhydr)oxides when conditions are wetter and more reduced, and new formation of Fe(III) minerals (33.7 ± 8.6% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions, which also led to the sequestration of Fe-bound organic carbon. Our data suggest that there is seasonal turnover of iron minerals in partially thawed permafrost peatlands, but that a fraction of the Fe pool remains stable even under continuously anoxic conditions.

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KW - bioavailability

KW - iron

KW - microbial Fe(III) reduction and Fe(II) oxidation

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KW - seasonal fluctuations

KW - soil organic carbon

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Seasonal Fluctuations in Iron Cycling in Thawing Permafrost Peatlands

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