Direct O<sub>2</sub> control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

Cojean, Adeline N. Y.; Zopfi, Jakob; Gerster, Alan; Frey, Claudia; Lepori, Fabio; Lehmann, Moritz F.

doi:https://doi.org/10.5194/bg-16-4705-2019

Articles | Volume 16, issue 23

https://doi.org/10.5194/bg-16-4705-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-16-4705-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 23

Research article

|

10 Dec 2019

Research article |

| 10 Dec 2019

Direct O₂ control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

Adeline N. Y. Cojean, Jakob Zopfi, Alan Gerster, Claudia Frey, Fabio Lepori, and Moritz F. Lehmann

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

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RC1: 'Review', Anonymous Referee #1, 13 Aug 2019
- AC1: 'Response to comments by Anonymous Referee #1', Adeline Cojean, 30 Aug 2019
RC2: 'Review of Cojean et. al.', Anonymous Referee #2, 14 Aug 2019
- AC2: 'Response to comments by Anonymous Referee #2', Adeline Cojean, 30 Aug 2019

Peer-review completion

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

ED: Reconsider after major revisions (06 Sep 2019) by Perran Cook

AR by Adeline Cojean on behalf of the Authors (25 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Oct 2019) by Perran Cook

RR by Anonymous Referee #1 (22 Oct 2019)

Suggestions for revision or reasons for rejection

The authors have done a good job incorporating new information and clarifying aspects of the paper.

I only have a couple of corrections/suggestions.

L109. If procedures from Line 106-109 were made in anaerobic glove box as you mention in the reply, this should be included in the text.

L115. I did not argue tha purging will affect the DOC pool. Purging can potentially affect the balance of gases (CO2, H2, CH4) and anaerobic processes in the sediment. Pre-incubation may affect the availability of labile DOC (even without purging).

L121. Please mention that you filtered the samples in the glove box before freezing.

L173. In my previous comment "The profiles do indeed indicate that the surface sediment of the Figino is less at the surface than further below. Any reason why? However, the profiles of nitrate do not indicate directly that the sediment acts as a sink given that nitrate and nitrite microprofiles occur same as for oxygen at a mm scale." I did not express myself correctly.

Your profiles of NO3 are in cm, not mm as you mention in your answer.

With a resolution of 1 cm slices, the authors would not be able to notice the nitrification/denitrification zone which can be as little as 1-2mm to 1 cm. So it may be that by integrating porewater profiles at such coarse resolution can indicate the wrong conclusion. What would happen if I make a porewater profile of oxygen in a highly productive sediment at a 1 cm resolution? I would see a decrease from 200 to 0 and I would assume that it is consuming oxygen whereas in reality it will be releasing O2 across the sediment water interface. Same here. Without core incubations, you cannot really know if the sediment is a net sink or source.

My other question was, why do the authors think it might be that the sediment at Figino seems less reactive near the surface than further below? Changes in porosity? changes in OC?

L224 now 230.
I can easily argue that with the bottom oxygen values they have, the porosity of your sediment and the water temperature, OC data, the authors can make a pretty good estimate of the potential oxygen concentrations in the sediment. My point here was to try to show the potential importance of their finding on the N cycling of the lake since, as the authors admit themselves, the effect of partitioning will only occur in the first 1-2 mm of the sediment (oxygen penetration). It was a suggestion and will not insist any further.

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ED: Publish subject to minor revisions (review by editor) (22 Oct 2019) by Perran Cook

AR by Adeline Cojean on behalf of the Authors (28 Oct 2019) Author's response Manuscript

ED: Publish as is (29 Oct 2019) by Perran Cook

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Short summary

Our results demonstrate the importance of oxygen in regulating the fate of nitrogen (N) in the sediments of Lake Lugano south basin, Switzerland. Hence, our study suggests that, by changing oxygen concentration in bottom waters, the seasonal water column turnover may significantly regulate the partitioning between N removal and N recycling in surface sediments, and it is likely that a similar pattern can be expected in a wide range of environments.

Direct O2 control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

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Direct O₂ control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments