Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden

Deng, J.; Li, C.; Frolking, S.; Zhang, Y.; Bäckstrand, K.; Crill, P.

doi:https://doi.org/10.5194/bg-11-4753-2014

Articles | Volume 11, issue 17

https://doi.org/10.5194/bg-11-4753-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-11-4753-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 11, issue 17

Research article

|

09 Sep 2014

Research article |

| 09 Sep 2014

Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden

J. Deng, C. Li, S. Frolking, Y. Zhang, K. Bäckstrand, and P. Crill

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Final revised paper (published on 09 Sep 2014)
Preprint (discussion started on 11 Mar 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C1205: 'Referee Comment', Nigel Roulet, 22 Apr 2014
- AC C2478: 'Responses', Changsheng Li, 15 Jun 2014
RC C1671: 'review of Deng et al., Assessing effects of permafrost thaw on C fluxes', Anonymous Referee #2, 16 May 2014
- AC C2479: 'Responses', Changsheng Li, 15 Jun 2014

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Changsheng Li on behalf of the Authors (19 Jun 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Jun 2014) by Paul Stoy

RR by Anonymous Referee #2 (14 Jul 2014)

Suggestions for revision or reasons for rejection

The paper has been substantially improved by revision, and provides an important addition to the body of work on observing and understanding trace gas exchange in thawing peatlands. I have just a couple of lingering concerns related to what the sites represent in terms of thaw sequence, and the resulting discussion language.

59 “As a result of climate warming, degradation of permafrost has been observed…” This phrasing seems to overstate the evidence of cause and effect – in part because some amount of degradation has been ongoing in the discontinuous permafrost zone – these are dynamic systems. Perhaps, “Many recent studies have argued that with climate warming, the rate (or extent) of permafrost degradation is increasing….”? Something like this.

87 “therefore disregarding” and “ignoring”: Consider rewording. Perhaps not disregarding/ignoring so much as effectively making assumptions about scaling effects that have not been (well) tested.

146 qualifying phrase was inserted in response to my initial comments but here seems redundant. I meant to ask for more complete description of the plant species assemblages present at these sites. This information seems critical for understanding the paper, and as someone who has worked in peatlands a little, but not this one, I’m curious. Also, has there been work done on the age of this peatland? How long has C been accumulating?

149 “representing intermediate thaw features” – Is this based on dating, field observation of thaw progression, or some other evidence? The authors have responded to previous comments along these lines, but in this section and elsewhere the terminology of “gradient of thaw” and “intermediate” still seem to imply a time sequence, while the phrase “converted into Sphagnum or Eriophorum” at line 158 implies two alternate thaw scenarios. What I’m looking for here is just clarity about what relationships are known or hypothesized, and what the supporting evidence is. I see that the thaw depths are greater in Erioph than in Sphag but this doesn’t require that the Eriophorum scenario follows the Sphagnum (and I appreciate that there is a simple wetness gradient here). Given the difference in observed methane efflux, it seems important to be careful about the implication of time sequence vs. wetness gradient or alternate thaw scenarios represented (or if either may be true). Later (see comments below), it appears the authors interpret these sites as thaw scenarios – maybe? – but this really should be clarified to appropriately understand the results and, e.g., what’s represented in Figure 6 and with change in land cover areas in terms of outcomes. The response comment of “intact, diminishing, or gone” implies a sequence of events. Since observations were made only to a meter and the authors state that palsa may re-form, caution in this wording and articulation of supporting evidence are important.

151 grammar, “with water table levels fluctuate”

347-348 “rate of summer thaw accelerated along the gradient of soil moisture” – The slopes in Figure 2 don’t look different (and are not quantified); do you just mean that the Sphagnum took longer than Eriophorum to go deeper than a meter? Or that both went deeper than Palsa? Please clarify.

539 “increased along the thaw gradient”; this implies a thaw sequence that turns on understanding the Sphagnum site as representing an intermediate state between the palsa and the Eriophorum site. Is this the understanding here and if so, based on what evidence (see comment on line 149)?

558-559 “Given that the soil thaw rate accelerated under wet conditions (Figure 2), this trend toward a wetter ecosystem may further accelerate permafrost degradation.” Do you mean this very generally for the two site types vs. palsa, or from palsa to Sphagnum to Eriophorum? Please clarify and make parallel with the site type distinctions in methods at 149-158.

665-667 Here it seems that the site types represent two thaw scenarios relative to palsa. This should be clarified at points indicated above.

729 “should have set a sound basis for the model to incorporate” – consider rewording as “provide a sound approach to incorporating”

1101 Figure 4 caption is a bit confusing with respect to a-g symbols vs. those in next two columns. This should be clarified. The figure could be changed so that the first column looks more distinct.

1133 Thanks for the addition of Figure 5. Consider adding labels (eg, “Sphagnum; WT>-10 cm) to the panels for clarity.

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ED: Publish subject to minor revisions (Editor review) (18 Jul 2014) by Paul Stoy

AR by Changsheng Li on behalf of the Authors (27 Jul 2014) Manuscript

ED: Publish as is (01 Aug 2014) by Paul Stoy

AR by Changsheng Li on behalf of the Authors (01 Aug 2014)