EGU2020-1465, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-1465
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Organic carbon sorbed to reactive iron minerals released during permafrost collapse

Monique S. Patzner1, Merritt Logan4, Carsten W. Mueller2, Hanna Joss1, Sara E. Anthony1, Thomas Scholten3, James M. Byrne1, Thomas Borch4, Andreas Kappler1, and Casey Bryce1
Monique S. Patzner et al.
  • 1Geomicrobiology, Center for Applied Geoscience, University Tuebingen, Germany (monique-sezanne.patzner@student.uni-tuebingen.de)
  • 2Chair of Soil Science, Technical University Muenchen, Freising, Germany
  • 3Chair of Soil Science and Geomorphology, University of Tuebingen, Germany
  • 4Department of Soil & Crop Sciences, Colorado State University, Fort Collins, US

The release of vast amounts of organic carbon during thawing of high-latitude permafrost is an urgent issue of global concern, yet it is unclear what controls how much carbon will be released and how fast it will be subsequently metabolized and emitted as greenhouse gases. Binding of organic carbon by iron(III) oxyhydroxide minerals can prevent carbon mobilization and degradation. This “rusty carbon sink” has already been suggested to protect organic carbon in soils overlying intact permafrost. However, the extent to which iron-bound carbon will be mobilized during permafrost thaw is entirely unknown. We have followed the dynamic interactions between iron and carbon across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost retreat. Using both bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS), we found that up to 19.4±0.7% of total organic carbon is associated with reactive iron minerals in palsa underlain by intact permafrost. However, during permafrost collapse, the rusty carbon sink is lost due to more reduced conditions which favour microbial Fe(III) mineral dissolution. This leads to high dissolved Fe(II) (2.93±0.42 mM) and organic carbon concentrations (480.06±34.10 mg/L) in the porewater at the transition of desiccating palsa to waterlogged bog. Additionally, by combining FT-ICR-MS and greenhouse gas analysis both in the field and in laboratory microcosm experiments, we are currently determining the fate of the mobilized organic carbon directly after permafrost collapse. Our findings will improve our understanding of the processes controlling organic carbon turnover in thawing permafrost soils and help to better predict future greenhouse gas emissions.

 

How to cite: Patzner, M. S., Logan, M., Mueller, C. W., Joss, H., Anthony, S. E., Scholten, T., Byrne, J. M., Borch, T., Kappler, A., and Bryce, C.: Organic carbon sorbed to reactive iron minerals released during permafrost collapse , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1465, https://doi.org/10.5194/egusphere-egu2020-1465, 2019

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  • CC1: Comment on EGU2020-1465, Ben Fisher, 27 Apr 2020

    Hello,

    I thought this was a very interesting presentation and also read your pre-print. I'm interested in the dithionite extraction method and just had a few questions about it that I wondered if you had the data for.

    1.  You perform the dithionite extraction at room tempreature for 16h, did you try the standard 80 degree C 15 minute extraction and if so was there any difference in the two?

    2. Do you have the data for the %OC which was removed in the control (sodium chlordie) step?

    3. I like the way you subtract background DOC of the organic reagents, how significant was this when calcualting the final amount of Fe bound OC?

    Thanks!

    Ben 

    • AC1: Reply to CC1, Monique S. Patzner, 27 Apr 2020

      Hi Ben, 

      Thanks for your feedback! Really appreciated!

      1. Yes, we performed the dithionite extraction at room temperature, rather than at 80 degree, because we also want to further characterise the carbon which was previously Fe-bound. High temperatures could effect the carbon fate. So far, we didn’t perform the high temperature dithionite extraction. 

      2 and 3. Concerning the organic carbon simply leached from the soil (sodium chloride bicarbonate extraction, same pH and ionic strength as the dithionite citrate following Lalonde et al), I added the absolute values (mg/g) in the Supplementaries of the preprint, Table S1. The amounts are low: An example, for the Palsa transition zone, it was 3 to 10 mg carbon per g soil for the sodium chloride bicarbonate control and 31 to 53 mg carbon per g for the sodium dithionite citrate extraction (already control corrected, means originally 31+3 and 53+10 mg carbon per g soil). 

      Does this help? 

      Best, 

      Monique

      • CC2: Reply to AC1, Ben Fisher, 27 Apr 2020

        Hi Monique,

        Thanks for getting back. It's understandable that you have decreased the tempreature, it'd be interesting to know if this has any effect on the efficency of Fe extraction compared to the 80 degree treatment. 

        And on 2 & 3 that's exactly what I was looking for, I hadn't seen the supplementaries so I'll check that out but good to know the background DOC is low.

        Thanks! 

        Ben

  • CC3: Comment on EGU2020-1465, Natalie Kashi, 04 May 2020

    Really nice work and presentation!  Thanks for highlighting the importance of iron biogeochemistry in permafrost peatlands!  Looking forward to reading your manuscript, this is great support for my work with phosphorus at the Stordalen mire.

    • AC2: Reply to CC3, Monique S. Patzner, 05 May 2020

      Thanks! I also saw your great presentation! I am especially interested in your "peat incubation fertilisation experiments". 

      It would be great if we can get in touch after the session today or in the next days to talk a little bit more about ongoing research. :) 

      • CC5: Reply to AC2, Natalie Kashi, 05 May 2020

        That would be great!

  • AC3: Comment on EGU2020-1465, Monique S. Patzner, 05 May 2020

    In case you are interested, here is the link to the preprint of the manuscript: 

    https://eartharxiv.org/52w47/

    We are happy for feedback and suggestions! 

  • CC4: Comment on EGU2020-1465, Prokushkin Anatoly, 05 May 2020

    You have indeed important findings! thanks for presentation! In our work we are trying to get insight into soil carbon storage patterns related to Al and fe forms along latitudinal gradient in Siberia (58-73N). It is really good idea to look into Fe(II) there also.

    Best ishes,

    Anatoly Prokushkin

    • AC4: Reply to CC4, Monique S. Patzner, 05 May 2020

      Thanks for your positive feedback!

       

      How much carbon is bound to Al and Fe forms at your site? Do you find similar carbon amounts (mg Fe-bound carbon per g soil), Fe-bound carbon in % of the TOC?

       

      Let me know if you can detect aqueous Fe2+ concentrations at your site. I am curious. :) 

       

      Best,

      Monique

  • CC6: Comment on EGU2020-1465, Aaron Thompson, 05 May 2020

    Nice Work Monique! I am curious if you tried to quantify total cells using some kind of staining or other method? The MPN of the Fe reducers are pretty low overall (10^4), but maybe the total microbial counts are also low in these environments. I also wonder if you tried any additions of Fe(III) or carbon to gauge the limitations on Fe reduction (i.e., was it the Fe(III), the labile C source, or the presence/activity of the microbes).  Thanks!!! - Aaron T.

    • AC5: Reply to CC6, Monique S. Patzner, 05 May 2020

      Aaron! I was waiting for your question. We even have Mössbauer results now for the solid phase along the thaw gradient, just prepared for you. : ) Before you ask, it perfectly fits to our selective extraction and EXAFS data :) 

       

       

      Coming to your questions:

       

      • (1) The advantage of our field site is that there is extensive context data from the Abisko scientific community available. Stordalen mire is therefore often referred to as “the best studied permafrost peatland mire in the world”. Woodcroft et al (2018) reported 2.6 times more cells per g fen soil relative to the palsa and bog soils, so also show a general cell increase along the thaw gradient. In the fen, they found around 0.6*10^9 cells per g soil – question remains how many are active. In the fen transition zone, we determined 3.1*10^5 Fe(III)-reducing cells per g soil via the growth-dependent approach, means direct proof for Fe(III) reduction. In an iron sulfur spring in Switzerland, just one example, we find similar abundance of Fe(III)-reducing bacteria (10^5). MPNs seem to be the best current way to determine the abundance of Fe(III) reducers due to the fact that for molecular work (DNA/RNA analysis) specific genes for Fe(III) reducers are lacking. 

       

      • (2) We set up microcosms (with increasing water filled pore space to simulate permafrost thaw) where we add either Fe2+/ferrihydrite/labile carbon to this “rusty carbon sink” material to further determine microbial community shifts (DNA and RNA level) over time with different amendments, differences in Fe(III) reduction rates and its direct contribution to CO2 and CH4 emissions. I hope that this will help to further answer the question what limitations on Fe(III) reductions we are facing.

       

      Does this help?

       

      Thanks for your input here! / Best, Monique 

  • CC7: Comment on EGU2020-1465, Prokushkin Anatoly, 05 May 2020

    Hi again, your study is somehow unexplored yet side in our research... which is really good to know. we followed really common practice: measured dithionite-citrate-, oxalate- and pyrophosphate-extractable Fe and Al in soil profiles and searched for a relationship with TOC content. the XRD was planned in March in Germany, but COVID has broken our plan...

    we can contact later for details, if you have an interest.

    my email: prokushkin@ksc.krasn.ru 

    • AC6: Reply to CC7, Monique S. Patzner, 05 May 2020

      Sounds great! I am definitely interested!  / Best, Monique 

      • CC8: Reply to AC6, Prokushkin Anatoly, 05 May 2020

        great! i am particularly  interested to discuss some details about Fe(II) and Fe (III) :-) i indeed thought that there is much Fe(II)  in our permafrost soils...

        all the best, Anatoly