The impacts of runoff decrease and shoreline change on the salinity distribution in the wetlands of Liao River estuary, China

Zhang, Mingliang; Xu, Tianping; Jiang, Hengzhi

doi:https://doi.org/10.5194/os-17-187-2021

Articles | Volume 17, issue 1

https://doi.org/10.5194/os-17-187-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-17-187-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 1

Research article

|

27 Jan 2021

Research article |

| 27 Jan 2021

The impacts of runoff decrease and shoreline change on the salinity distribution in the wetlands of Liao River estuary, China

Mingliang Zhang, Tianping Xu, and Hengzhi Jiang

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Final revised paper (published on 27 Jan 2021)
Preprint (discussion started on 10 Jul 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee comment to authors', William Pringle, 12 Sep 2020
- AC1: 'Response to Referee 1', Mingliang Zhang, 13 Oct 2020
RC2: 'Comments on “The impact of shoreline change on the salinity distribution in the wetlands of Liao River Estuary, China” by Mingliang Zhang et al.', Anonymous Referee #2, 15 Sep 2020
- AC2: 'Response to Referee #2', Mingliang Zhang, 13 Oct 2020
RC3: 'Review of manuscript "The impact of shoreline change on the salinity distribution in the wetlands of Liao River Estuary, China"', Anonymous Referee #3, 24 Sep 2020
- AC3: 'Response to Referee #3', Mingliang Zhang, 13 Oct 2020

Peer-review completion

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

AR by Mingliang Zhang on behalf of the Authors (13 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Oct 2020) by Anne Marie Treguier

RR by William Pringle (04 Nov 2020)

RR by Anonymous Referee #3 (04 Nov 2020)

Suggestions for revision or reasons for rejection

The authors have improved the manuscript following comments from myself and the other reviewers. The model setup in particular is much better described. Broadly the manuscript makes sense, it is focused on a few experiments. It is publishable with minor edits.

A couple comments remain:

1/ On the salinity boundary condition: 34 PSU at surface at 32 PSU at depth? I would have expected the opposite -- estuarine flow is usually characterised by salty flow at depth and fresher flow at the surface -- so 32 at surface at 34 at depth. Given the constant temperature, does the higher-salinity above lower-salinity water lead to unstable stratification?

2/ On the river discharges. The authors present two discharge scenarios (high flow season and low flow season) for both pre-port and post-port domains. To me, the 1995 version represents a baseline salinity regime that the vegetation is compatible with -- it survives both seasons, perhaps thriving in one and tolerating the other. The suite of experiments does not take into account the decrease in freshwater discharge due to recent diversions for use by the population. That is, there should be a low flow 1995 scenario contrasted with a low-flow 2019 scenario where the low-flows are adjusted for the diversions. The manuscript would benefit from drawing attention to the fact that this comparison was not done (perhaps saving it for future work to be done alongside adding surface forcing). Meanwhile, the speculation in section 4.1 about higher salinity as a consequence of increased water use seems to have been promoted to become part of the conclusions in section 5 ("Once the port was constructed, its obstruction of the port area strengthened the tidal current mixing, and the partial runoff from the Daliao River was diverted. As a result, the fresh water dilution effect further weakened, thus increasing the salinity of the sea water in the lower reaches of the Pink Beach Wetland."). The latter part wasn't shown, so the conclusions needs to be adjusted here.

2b/ Also regarding Table 1: are the high/low flow season discharges from 1995 (pre-port and pre-diversions) or from 2019 (post-port and post-diversions)?

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RR by Anonymous Referee #2 (06 Nov 2020)

Suggestions for revision or reasons for rejection

Second review of the manuscript “The impact of shoreline change on the salinity distribution in the wetlands of Liao River Estuary, China” by Mingliang Zhang et al.

I would like to highlight the authors’ efforts in improving the manuscript and especially the figures. The paper is now much easier to read. However, a few points still require consideration and I did not find answers to all of my questions. I would therefore recommend that the points raised in this second review be addressed prior to final publication.

Introduction
Question 2
The authors answered “We applied FVCOM instead MIKE 21 model because we want to investigate the three-dimensional distribution of salinity in the LRE.” I do not understand: do thay mean that MIKE21 does not enable 3D studies? The authors add “In mike model, Qiao et al. discussed the influence of runoff decrease on salt intrusion”, so I am a little confused.

Model description
Question 1
I am still frustrated with the model description, and I do not find any mention of the use of primitive equations. I suggest the author consider the following description:
Page 8 Line 12.
“It is a three-dimensional ocean model (Chen et al. 2003, http://fvcom.smast.umassd.edu/fvcom) based on primitive equation and using the finite volume method with the capability to deal with horizontal unstructured triangular cells, which is well fitted to irregular coastline.”

Model configuration
Question 1
The authors partially answered the question. They tackled the issue of initial and boundary variables values but they did not add the description of open boundary conditions. FVCOM offers the choice between different OBC schemes. For the elevation, did the authors use Orlansky conditions? Radiative GWI? What about the heat and momentum OBC?
Question 5
Your answer mentions some additional explanations. I was not able to find them in the text, nothing was added in that paragraph. Please help the reviewer in finding them.

Results and discussion
Question2
Figure 14 is a zoom of Figure 15, it represents a great improvement but it is still not easy to handle. You should definitely put less arrows but enlarge them.
Question 4
If your focus is mainly on residual flow, then you should not put a summary on salinity results.

Figures
Figure 6 looks the same than before

Minor corrections and typos:

Page 8 Line 4: Split this long sentence into two sentences, replace with “semidiurnal tide. In addition,…”.
Page 8 Line 19. Split into two sentences, replace with “(Chen et al., 2006). The application…”
Page 9 Line 14: replace with “of the LRE that we measured”.
Page 9 Line 22: remove “Model”, and replace “zero velocity” with “ocean at rest, zero velocity”.
Page 20 Line 17: the doi link does not work for Chen et al. (2003), replace with a valid one.
Page 12 Line 6: there is a problem with the sentence beginning with “Where”. Please correct.
Page 19 Line 11: “differs”

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ED: Reconsider after major revisions (22 Nov 2020) by Anne Marie Treguier

AR by Mingliang Zhang on behalf of the Authors (01 Dec 2020) Author's response Manuscript

ED: Publish as is (04 Dec 2020) by Anne Marie Treguier

Short summary

In this paper, we applied FVCOM to perform the numerical simulation of salinity in Liao River estuary waters, with consideration of the effects of river discharge cutoff and shoreline variation. Decrease in runoff was demonstrated to significantly increase the mean salinity values of the estuary. The shoreline change caused by the port construction was observed to have an obvious influence on salinity distribution patterns, with the mean salinity value increased in wetland waters near the port.