Temporary and net sinks of atmospheric CO<sub>2</sub> due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

Cao, Yingjie; Xuan, Yingxue; Tang, Changyuan; Guan, Shuai; Peng, Yisheng

doi:https://doi.org/10.5194/bg-17-3875-2020

Articles | Volume 17, issue 14

https://doi.org/10.5194/bg-17-3875-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-3875-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 14

Research article

|

31 Jul 2020

Research article |

| 31 Jul 2020

Temporary and net sinks of atmospheric CO₂ due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

Yingjie Cao, Yingxue Xuan, Changyuan Tang, Shuai Guan, and Yisheng Peng

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Final revised paper (published on 31 Jul 2020)
Supplement to the final revised paper
Preprint (discussion started on 13 Nov 2019)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'comments', Anonymous Referee #1, 10 Dec 2019
- AC1: 'Responses to Anonymous Referee #1:', Changyuan Tang, 10 Feb 2020
RC2: 'Comments on Cao et al.', Anonymous Referee #2, 10 Jan 2020
- AC2: 'Responses to Anonymous Referee #2', Changyuan Tang, 10 Feb 2020

Peer-review completion

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

ED: Reconsider after major revisions (13 Feb 2020) by Nobuhito Ohte

AR by Changyuan Tang on behalf of the Authors (14 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (31 Mar 2020) by Nobuhito Ohte

RR by Anonymous Referee #2 (09 Apr 2020)

Suggestions for revision or reasons for rejection

The manuscript by Cao et al. has been improved by this revision. However, there are still some concerns to publish it in Biogeosciences.

* alkalinity, DIC and [HCO3-]
I understood the calculation method of alkalinity, DIC and [HCO3-] and that these values are similar at pH 7.5–8.5 in this river. However, this explanation is only shown in the response letter. I think concurrent use of these three parameters without special meanings or explanations in the manuscript makes readers confused. For example, equation (26) can be simply described as [HCO3-]CCW = αCCW × [HCO3-]riv.

* analytical errors
Thank you for showing the analytical errors of each ion (5%). I think these errors can propagate to the following calculations such as CCW or CCR. In the current manuscript, significant digits of these parameters (as well as ions in Table 1) seem to be too large.

L. 35-37
In the first, second, third, and fourth paragraph in the introduction section, the authors describes the mechanisms of silicate/carbonate weathering, human impact on the chemical weathering, problems in the previous studies in various global rivers, and study area and objectives of this study, respectively. The lines 35-37 are about areas, and should be noted in the third or fourth paragraph.

L. 139-140
The chemical compositions of the rain water should be noted in the result section.

L. 141
“expert for” reads as “except for”.

L. 151
“Fig. 11” reads as “Fig. 2”. This figure about stoichiometric analysis is the second figure referred in the manuscript. Please also correct numbers of the following figures.

L. 202/208
There are still two equations numbered as (23). Please correct numbers of the following equations.

L. 517-520
I think these lines and Fig. 12 added in this revision are very important to suggest human impact on the chemical weathering and net sink of CO2. However, the relationship between [SO42-]riv and net sink of CO2 seems to be statistically insignificant. Furthermore, I have no idea why the authors use [SO42-]riv in this figure. To check the human impact, I think [SO42-]scw and [SO42-]ssw should be compared.

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ED: Reconsider after major revisions (17 Apr 2020) by Nobuhito Ohte

AR by Changyuan Tang on behalf of the Authors (21 May 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Jun 2020) by Nobuhito Ohte

RR by Anonymous Referee #2 (05 Jun 2020)

ED: Publish subject to technical corrections (13 Jun 2020) by Nobuhito Ohte

AR by Changyuan Tang on behalf of the Authors (17 Jun 2020) Author's response Manuscript

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Short summary

About half of the global CO₂ sequestration due to chemical weathering occurs in warm and high-runoff regions. To evaluate the temporary and net sinks of atmospheric CO₂ due to chemical weathering, we selected a typical subtropical catchment as our study area and did fieldwork to sample surface water along the main channel and major tributaries in 1 hydrological year. The result of mass balance calculation showed that human activities dramatically decreased the CO₂ net sink.

Temporary and net sinks of atmospheric CO2 due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

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Interactive discussion

Peer-review completion

Temporary and net sinks of atmospheric CO₂ due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology