Blue carbon stocks in Baltic Sea eelgrass (<i>Zostera marina</i>) meadows

Röhr, Maria Emilia; Boström, Christoffer; Canal-Vergés, Paula; Holmer, Marianne

doi:https://doi.org/10.5194/bg-13-6139-2016

Articles | Volume 13, issue 22

https://doi.org/10.5194/bg-13-6139-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-13-6139-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 22

Research article

|

14 Nov 2016

Research article |

| 14 Nov 2016

Blue carbon stocks in Baltic Sea eelgrass (Zostera marina) meadows

Maria Emilia Röhr, Christoffer Boström, Paula Canal-Vergés, and Marianne Holmer

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Final revised paper (published on 14 Nov 2016)
Preprint (discussion started on 27 Apr 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Röhr et al.', Anonymous Referee #1, 08 Jun 2016
AC1: 'Reply to Anonymous Referee #1', Maria Emilia Röhr, 22 Jun 2016
RC2: 'Blue carbon stocks in baltic Sea eelgrass', Anonymous Referee #2, 14 Jul 2016

Peer-review completion

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

ED: Reconsider after major revisions (03 Aug 2016) by Gerhard Herndl

AR by Maria Emilia Röhr on behalf of the Authors (06 Sep 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Sep 2016) by Gerhard Herndl

RR by Anonymous Referee #1 (20 Sep 2016)

Suggestions for revision or reasons for rejection

The authors have addressed many of the issues raised during the first reviews, but a number of issues remain problematic
1. The fact that samples were not acidified prior to analysis remains not well discussed. In the original version, the authors stated that “The inorganic carbon content in our samples was low (0.003 to 0.3 %DW, n= 10 per region) and therefore carbonates were not removed from the sediment samples prior to the analysis”. Given that %OC varies from 0.1 to 5.78 % (average values) for the different sites, this implies that inorganic carbon can contribute at least 5.2 % of the total carbon (assuming the highest %IC was found in the sample with the highest %OC), but it could be more if %IC and %OC are not related. Hence, I feel the data should be presented so that readers can make their own judgement on how problematic this is.
Assuming the carbonate fraction has a d13C of around 0 per mil and the organic fraction somewhere between -15 and -20 per mil, a 5% contribution of carbonate to in the measured sample can correspond to a bias of about 1 per mil, which is large. This should at least be acknowledged and discussed.

Line 334 and further in the revised verison: this still does not make sense. The total organic C stock is measured and should be derived from your bulk density and %OC data, the OC accumulation rates are irrelevant here. The same applies to the section on line 223 and further in the revised version (see also my original comments). The same goes for their reply to my original comment (12) that yo use a rate to calculate the OC stock.
My original comment concerning the relationship observed between %OC and bulk density; the authors mention they don’t understand this comment and mention their data show exactly this. Yes, they do, but the point is that this is not a causal relationship but a logical inverse relationship reflecting different contributions of organic matter (low density) and the mineral fraction (which has a high density). Thus, statements that %OC is determined partially by density are not appropriate.
Earlier comment regarding extremely low OC contents (<0.001 mg cm-3), I still do not see these low numbers on Figure 3. These are incredibly low
Minor comments:
Table 1: use “.” as the decimal separator throughout, not comma’s
Table 1: use 1 decimal only to report d13C data given the analytical uncertainty.

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ED: Publish subject to minor revisions (Editor review) (26 Sep 2016) by Gerhard Herndl

AR by Maria Emilia Röhr on behalf of the Authors (09 Oct 2016) Author's response Manuscript

ED: Publish as is (15 Oct 2016) by Gerhard Herndl

Short summary

Our results show that Finnish eelgrass meadows are minor carbon sinks compared to the Danish meadows, and that majority of the Corg produced in the Finnish meadows is exported. Similarly, the estimates for Corg accumulation in Finnish meadows were over 1 magnitude lower compared to Denmark. Our results further showed that > 40 % of the variation in the Corg stocks was explained by sediment characteristics. To clarify the role of seagrasses in global carbon budget, more studies are in urgent need.