Assessment of Water Quality in a Coastal Region of Sea Dike Construction in Korea and the Impact of Low Dissolved Oxygen Concentrations on pH Changes

Round 1

Reviewer 1 Report

The impact of man-made structures such as dikes on water quality is an important research area, but, as the authors mention (line 57), data are still scarce. This paper presents the temporal variations of basic water quality parameters from 2015 to 2020 at a shallow site outside a dike built for wetland generation in South Korea west coast. For the study region, this work provides data which were previously unavailable. The findings are also useful to researchers in other regions with potentially the same concerns. The quality of the measured data in this work seems acceptable, the statistical analyses are adequate, and the paper is generally well written. I support the publication of this paper in JMSE after a revision. 

 

Major comments

 

This work is only an effort to analyze already-collected monitoring data, it is not a well-designed, hypothesis-based research. Data needed to answer critical questions (such as the major causes of DO variation) were not collected; most discussions are therefore literature-based speculations. For example, the existence and the upward swell of hypoxic conditions cannot be evidenced because measurement was made at only one depth (1 m) thus it is impossible to know the vertical trends of DO. Also, the influence of the dike cannot be confidently defined, because no “control site”, where (or when) there is no impact of the dike, was sampled to contrast the study site. Additionally, it would be very helpful if the redox potential (ORP) were measured. PCA analysis showed that only 65% was counted for by components 1 to 3 together, suggesting important influencing factors were not identified. 

 

There is no explanation on why the depth of 1 m was chosen. What is the mixing depth at the site, and how the mixing depth varies with time? The mixing depth was certainly very different before and after the dike was built. Line 325-6 mentions equilibrium with the atmosphere, which may not be the case if the air-water interface is stagnant without disturbance. Also, the saturation level of DO in water (via Henry’s Law constant) is a strong function of the ambient temperature. For this reason, I would suggest using % saturation in discussions, where appropriate, rather than the absolute DO levels in mg/L. 

 

I also suggest improving brevity. Lengthy discussion may be shortened, especially the speculative ones. The number of references cited is >70, which is a lot for this paper.

 

Minor comments

 

Title: Suggest deleting “using statistical analyses”, as the words are not needed and sound redundant.

 

L112: Should the “6” in both numbers be superscripts?

 

L154: Delete one of the two periods at the end of the Table 1 title.

 

Table 1: Why are monthly data presented for 1999 and 2000 only? Unless the data in Table 1 are more fully utilized for discussion in the paper, this complicated table may be expanded, re-organized, and moved to Supplemental Materials.

 

L171-176: Suggest moving and merging this paragraph to the last paragraph in Introduction. It is redundant here.

 

L378-380: Why does Table 1 appear again?

 

L429: “2” in CO2 should be subscript.

 

Figure 8: Suggest adding a sentence in the caption to describe which method was used for AOU estimation.

 

 

 

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

First, I would like to thank the authors for their contribution. 

 

The paper presents the statistical analyses in a coastal region of sea-dike construction in Korea to assess the water quality, low dissolved oxygen concentrations and its impact on pH changes. 

 

-          The novelty of the paper is not clear to me.  I think it would be helpful if the authors explain the objectives of the research and its novelty in Introduction more clear and highlight it.

-          Paper is too long specially when it comes to statistical analysis, and it is difficult to follow the flow or paper. I suggest to reduce it, if possible. 

-          In general, the paper has a new idea which can be recommended for publication with some revision. 

-          The paper results and conclusion are very much focused on the case study. However, in a research paper, it is better to draw more general conclusions which could be applicable in a more general way.  In this way, the international reader would lose the interest because it is only for a specific region.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic of the paper is interesting and suitable for the journal. The authors investigate water quality from surface water outside a sea-dike for six years from 2015 to 2020 in the Saemangeum region of Korea. The data and results are interesting as studies on water quality associated with artificial constructions (massive harbours, sea-dikes,…) are scarce, particularly for waters outside of the artificial constructions.

 

Overall the paper is well-written, reasonably justified and explained, thus, minor revision is recommended.

 

Please find below a list of issues to be addressed before publication:

 

[1.] Explain the data pre-treatment applied to the data before PCA calculation. Was the raw data transformed, centred, normalized or auto-scaled?

 

[2.] Based on the PCA results the authors conclude that the water quality in this system was predominantly governed by natural processes followed by pollutant inputs as the secondary influencing factor. However, a pollutant with low variability among the different samples could heavily contaminate the water, and this would not be seen either in the first compoment (or latent variable) of a PCA. PCA focus on data variability not on water quality, and those variables with higher variability will contribute most to the new components (or latent variables) from the PCA. Do the authors have some other compelling reason to conclude that water quality in this system was predominantly governed by natural processes?

 

[3.] A PCA decomposition yields the relationship among variables, which are shown and explained in the manuscript, but also the relationship among observations (samples) which are not mentioned in the paper (not even in the supplementary information). Please add and explain the score plot of the PCA, to understand how the observations(samples) are projected on the PCA.

 

[4.] In Figure 1, the word “Sea-dyke” appears twice, while in the manuscript “Sea-dike” is used. Please correct it.

 

[5.] In Figure 2, the units of two variables are missing: DO and salinity. Please add the units of these variables.

 

[6.] Page 10, lines 249 – 250. 1968). Figure 4 shows the results of the time-series forecasting….  This sentence is not clear. Which period is predicted? Clarify what do you refer with times-series forecasting because it is not seen any prediction in Figure 4.

 

[7.] Figure 6, Figure 7 and Figure 8, use the same units for the DO variable as in the rest of the manuscript (in the tables and most figures the units used is mg/L). This change would affect the fitting equations shown In the titles of these figures.

Overall the quality of English is adequate.

 

[4.] In Figure 1, the word “Sea-dyke” appears twice, while in the manuscript “Sea-dike” is used. Please correct it.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf