Model Test of the Effect of River Sinuosity on Nitrogen Purification Efficiency
Round 1
Reviewer 1 Report
Although the scientific quality of the paper is average I recommend it for publication because of extremely important conclusions which may be a voice for saving rivers as natural as possible and for rivers restoration. I encourage authors to further studies on advantages and environmental benefits of naturally flowing rivers.
I suggest to add more information about similar studies in the introduction part. This, I believe, will positively influence also the discussion part.
I suggest to complete the method section with information about sand preparation. There are information about physical parameters and about bacteria and pollutant added to the sand, but what was the purity of the sand before? Was it pure, sterile, germ-free quartz?
Author Response
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Author Response File: 
Author Response.doc
Reviewer 2 Report
GENERAL COMMENTS
Overall, this manuscript fits into an important context about a river's ability to withstand the rejection of significant polluting loads. In this case, the influence of a river's sinuosity on the reduction of the Total Nitrogen (TN) concentration rejected in an upstream section is investigated. Spatiotemporal distribution of TN in pore water is also addressed. For several reasons, including human actions and ongoing climate change, the issue of pollution of water resources, in particular surface water pollution, is already dramatic in many parts of the world. Therefore, all research in this area must be understood as a contribution to the sustainability of our planet. Accordingly, and from a very wide perspective, the research covered in this manuscript, although not very deep and ambitious, is on the agenda and can be valued. Of course, there are aspects to be improved, some of which I point out below in a more specific context.
SPECIFIC REMARKS
First of all, the topic must be framed in a broader context. It is worth mentioning that several aspects related to water quality are not covered, nor are they mentioned in this analysis and need to be addressed at least in the Introduction and, preferably, with data. Among them, the mean velocities and depths must be provided in the same sections for all sinuosities, at least between measuring points 5-6 and 9-10. The turbulence effects are critical to improving water quality and must also be addressed. Other channel slopes with slower and faster flows should also be addressed and/or taken into account in future research.
Also of note are the erosion-deposition effects, as they influence the water quality in natural systems. This is related to the eventual protection needs of the bottom and banks.
Other "minor" flaws/corrections are:
- When the first author of a reference with several co-authors is identified, the name of the first author must be followed by "et al."; just a few examples: line 48: Elósegui [7] must be Elósegui et al. [7]; line 50: Kumar [8] must be Kumar et al. [8], etc.
- Line 75 reads "...channel simulation models with sinuosities of 1.0, 1.4, 1.8 and 2.2, ...". For a reader to understand these values, the concept of sinuosity adopted must be provided in advance.
- Line 112: what is intended by "curvature coefficient Cc = 0.9273"?
- Line 117, equation (1): this concept of sinuosity is not enough. In fact, it does not reflect the existence of more or fewer bends, depending on the radius of the bend. Something more must be added.
- Line 122: "...with a sinuosity of 1.0, 1.4 and 1.8, 2.2..." must be "...with a sinuosity of 1.0, 1.4, 1.8 and 2.2...".
- Line 183 reads "each set of tests were the same to ensure that all variables except river sinuosity remained unchanged". It should be noted that a single test for each sinuosity doesn't assure unchanged variables. Repeating a test, certainly, differences would appear in all parameters, notably flow patterns, water depths, mean velocities, TN concentrations, etc.
- Figure 2: an additional explanation is needed for the strong decrease in TN concentrations around 15-16h, especially in the cases of sinuosities 1.0 and 1.4, and also for the different behavior of sinuosity 1.8.
- Line 230 reads "tests with sinuosities of 2.4, 1.8, and 1.4". Is it not "tests with sinuosities of 2.2, 1.8, and 1.4"?
- Some repetitions throughout the text and in the Discussion section should be avoided.
- Other guidelines for future research should be considered in the Conclusions, namely:
. other river slopes;
. turbulence effects;
. degree of sinuosity [more or fewer bends with identical river sinuosity, according to equation (1)].
The above comments and specific remarks are intended to contribute to the improvement of the manuscript and its possible resubmission. However, they do not exhaust all corrections to be made.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
I find this manuscript useful for readers of the WATER journal. There is only one point I would like to see improved: English, as it is not always fine. Just two examples added in the review process, among others: "The mean flow velocity and depth of each test channel is shown in Table 1" (sic) (lines 198-199). "It is noteworthy that after 15h, the TN concentration of sinuosity 1.0 and 1.4 showed a relatively strong decrease" (sic) (lines 218-219).
Therefore, I recommend proofreading the text, preferably by a native English speaker.
Author Response
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Author Response File: Author Response.docx
