Groundwater data improve modelling of headwater stream CO<sub>2</sub> outgassing with a stable DIC isotope approach

Marx, Anne; Conrad, Marcus; Aizinger, Vadym; Prechtel, Alexander; van Geldern, Robert; Barth, Johannes A. C.

doi:https://doi.org/10.5194/bg-15-3093-2018

Articles | Volume 15, issue 10

https://doi.org/10.5194/bg-15-3093-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-15-3093-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 10

Research article

|

18 May 2018

Research article |

| 18 May 2018

Groundwater data improve modelling of headwater stream CO₂ outgassing with a stable DIC isotope approach

Anne Marx, Marcus Conrad, Vadym Aizinger, Alexander Prechtel, Robert van Geldern, and Johannes A. C. Barth

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Final revised paper (published on 18 May 2018)
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Preprint (discussion started on 14 Sep 2017)
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Status: closed

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

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RC1: 'Review', Anonymous Referee #1, 27 Oct 2017
- AC1: 'Response to Anonymous Referee #1', Anne Marx, 21 Dec 2017
RC2: 'Review of article', Anonymous Referee #2, 24 Nov 2017
- AC2: 'Response to Anonymous Referee #2:', Anne Marx, 22 Dec 2017

Peer-review completion

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

ED: Reconsider after major revisions (05 Jan 2018) by Steven Bouillon

AR by Anne Marx on behalf of the Authors (08 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Feb 2018) by Steven Bouillon

RR by Anonymous Referee #2 (23 Mar 2018)

Suggestions for revision or reasons for rejection

Having been a critical reviewer (referee Nr 2) on the earlier version of this manuscript, I am now happy with how this manuscript has developed and improved. In fact, I want to congratulate the authors on these improvements.

The main focus of the paper has been well revised and puts it more into context on the recent advances in the field of estimating CO2 evasion of small headwater streams. The comparison with the work based on k-values (which is also extrapolated ot the entire globe)) is a pleasured to read. Also the presentation and discussion of the ‘no PP’ assumption is now well done. Thus, and despite the earlier criticism that there is ‘little data’, I find the manuscript now a good and, more importantly very relevant contribution to the field.

This reasoning can also be seen in my overall rating within the editorial system: (not sure if the authors can see these, thus I’ve copied them in here and added a comment to each):
1) Scientific significance
Does the manuscript represent a substantial contribution to scientific progress within the scope of this journal (substantial new concepts, ideas, methods, or data)?
My rating: ‘Excellent’. Given the new focus on presenting this new method and the comparison with other headwater studies this is excellent!

2) Scientific quality
Are the scientific approach and applied methods valid? Are the results discussed in an appropriate and balanced way (consideration of related work, including appropriate references)?
My rating: ‘Good’ – there remains the somewhat limited data resolution. But good it is!

3) Presentation quality
Are the scientific results and conclusions presented in a clear, concise, and well-structured way (number and quality of figures/tables, appropriate use of English language)?
My Rating: ‘Excellent’. With the revised figures and other improvements, the find the presentation now very well.

With this I suggest to the editor that this manuscript shall published in the Journal Biogeosciences without further reservations.

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ED: Publish subject to minor revisions (review by editor) (23 Mar 2018) by Steven Bouillon

Dear Anne,
Thank you for your detailed author replies and revised manuscript, which has now been re-evaluated by one of the original reviewers. I agree with their conclusion that you have adequately handled the suggestions and comments raised by both reviewers. I am therefore pleased to accept your revised version for publication in BG, pending a minor suggestion from my side (DOC & d13C-DOC data, see comment below), related to
one of the questions by Referee #1:
Ref#1: P.6 L.24. The authors state that they use δ13C of POC instead of the d13 of SOM. In soils,DOC is often more important than POC and CO2 is more often linked to DOC than POC.Please explain why you use d13C of POC and not DOC or TOC. If d13C-POC = d13C-SOM, then explain.
Author Reply: In our opinion, POC is the best representative of soil organic matter in the catchment. It is the material that is closest to the original plant and soil material. We did not choose DOC, because it is known to have recalcitrant phases that are poorly decomposed (Cauwet and Sidorov 1996; Laudon et al. 2011). This would introduce a non-representative value for organic matter input.
-->I would argue here that there are similarly recalcitrant pools in the soil POC, I do not find this line of reasoning supported by strong arguments or data. Currently, the manuscript mentions that both DOC concentrations and d13C-DOC data were measured (described in the Methods section), but neither the DOC data nor the d13C-DOC are presented or discussed. At the minimum, the d13C-DOC data should be presented, and you could briefly discuss to which extent using d13C-DOC rather then d13C-POC would change the output. Secondly, since DOC data were measured it would be a small extra effort to compare the DIC fluxes (incl CO2 outgassing) to export fluxes of DOC, then at least these data add something extra (in case you decide this is not wanted, then remove these analyses from the Materials & Methods section).

Best regards
Steven Bouillon

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AR by Anne Marx on behalf of the Authors (31 Mar 2018) Author's response Manuscript

ED: Publish as is (04 Apr 2018) by Steven Bouillon

AR by Anne Marx on behalf of the Authors (04 Apr 2018)

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Short summary

CO₂ outgassing from small streams causes one of the main uncertainties in global carbon budgets. These are caused by variable flow conditions, changing stream surface areas, and groundwater seeps. Here we used groundwater data to improve a novel stable carbon isotope modelling approach. We found that CO₂ outgassing contributed more than three-fourths of annual stream inorganic carbon loss in a small, silicate catchment. We underline the potential of this approach for global applications.

Groundwater data improve modelling of headwater stream CO2 outgassing with a stable DIC isotope approach

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Groundwater data improve modelling of headwater stream CO₂ outgassing with a stable DIC isotope approach