Multivariate Statistical Analysis of the Spatial Variability of Hydrochemical Evolution during Riverbank Infiltration
Round 1
Reviewer 1 Report
This manuscript deals with the study of a river bank filtration system to treat river water infiltrating into aquifers before pumping. The subject is interesting since river water is generally more polluted than groundwater. The river bank filtration system thus authorizes their use. However, the manuscript requires significant improvements and corrections.
The authors present a study which is just one-off and covers only one riverside wellfield. No information is provided about the functioning of the groundwater/surface water system. This is obviously necessary to assess the sustainability of the river bank filtration operation. A fairly exhaustive description of the groundwater/surface water system must be given, at both local and regional scales, to understand the functioning of this hydraulic system in time and space. A conceptual model can be useful.
The title does not correspond to the text since temporal variability is not addressed.
Detailed comments.
1. Give a complete description of the geological and hydrogeological setting. In particular, piezometric maps, at high and low water levels, are necessary to analyze groundwater-river relations, since water level variations are significant (L104-106).
2. At the local scale, cross-sections should be drawn between the 2 arms of the Songhua River (Fig2a) since the study site is located between these 2 arms. If infiltration to the wellfield is from the right arm of the river, what is the relationship of the wellfield to the left arm? Are the water levels in these 2 arms located at the same altitude?
3. Figure 2 is difficult to read, almost illegible
4. L46-53. Statements about hydrogeochemical methods are wrong. Please refer to the following basic references for right statements:
· Frezze R.A. & Cherry J.A., 1979. Groundwater. Prentice Hall Ed.
· Clark I., & Fritz P., 1997. Environmental isotopes in Hydrogeology. CRCPress.
· Clark I., 2015. Groundwater geochemistry and isotopes. CRCPress.
5. L78. What are the activities which impact the groundwater quality?
6. L99. Average annual rainfall is 425mm. Is the study site located in semi-arid context?
7. L101-102. Check the figures of depth and width of the river. 450m is not usual as river depth !
8. L104, L105 and throughout the text. Avoid excessive number of decimal digits.
9. L108-112. See comment above on hydrogeological setting. Cross-sections would be helpful.
10. L113-119. Piezometric maps are necessary to describe the groundwater flow pattern.
11. L120-124. Location of water samples should be shown, with respect to the wellfield. Evolution of chemical types should be commented.
12. L128. As far as I understand, the data matrix is composed of 20 variables collected on 12 wells arranged in NS and FS wells. Other wells shown in Fig.2 are not included in data matrix. Right ? Data were collected only in september 2018. Thus there is no any temporal variation analysis. Right ?
13. L128. Was the ionic balance checked to validate the hydrochemical analyses ?
14. L136. What’s the purpose of these ‘Groundwater detection’ wells O18 and O20 ? In addition they are separated from the other NS and FS wells by the left arm of river Songhua. Are they hydraulically connected to these NS and FS wells ? That’s why a clear description of the hydrogeological setting is necessary (see comments above).
15. L168. Please provide meaning of the acronyms.
16. Section 2.3.1. F.A. What difference with PCA ?
17. L207-209. Given the annual average rainfall (425 mm), the area would be in semi-arid context. In such climatic condition, rivers would not recharge groundwater throughout the year. Clarifications are required in this respects.
18. L209-211. The groundwater level are given in relation to what ?
19. L215. What’s the interest of these gradients values (with 2 decimal digits !) ?
20. L205-215. Hydrodynamics of the river-groundwater is quite poorly discribed. Is there any estimation of the river bed hydraulic conductivity ? Any pumping tests to analyze river-groundwater interaction ?
21. L217-223. Number and locations of the samples in the river and in the groundwater ?
22. L217. This is not clear. Do the authors consider local recharge (around the wellfield) or regional recharge ? No recharge from rainfall infiltration ?
23. No rainfall water isotopes data ? Anyway, refer to the basic references provided above, for an indepth analysis of the isotopes data.
24. L237. Locations of samples from the regional groundwater should be shown.
25. L258-264. It is mentioned in the text that river is recharching groundwater. In this paragraph, it is mentioned that concentrations of Mn and Fe are very high in the river, but very low in the groundwater. Please clarify.
26. L265-271. Are the average concentrations of SO4 for the river and the regional groundwater actually representative? How many samples? Where are their locations? As far as I understand, there are significant variations along NS and FS wells. what do they correspond to?
27. L292-294. Very unclear. There seems to be confusion between PC explained variance and variable loadings.
28. L295-307. Again very unclear. It is unclear whether the authors comment on the raw data or interpret the PCA results. Their conclusion ‘Therefore, F1 represents the effect of mineral leaching’ is not founded.
29. L308-319. Again there seems to be confusion between PC explained variance and variable loadings. Scores of PCs should be shown. Again, the distinction is not very clear between raw data and PCA results. The conclusion is unfounded.
30. L324-327. What are the links with the field? Have these conditions been verified?
31. L333-370. There are a lot of generalities in these lines about geochemical processes. But we find no demonstration of the conclusion mentioned in lines 368-370. One can also wonder what the PCA results were used for.
32. Section 3.5. One wonders on which data matrix was the C.A. conducted? Raw data or other data? This must be clarified so that the development of the C.A. could be followed. Figure 3 for example is quite unclear.
33. Figures 4 and 5 are illegible.
34. The discussion given in section 4 is not convincing, insofar as the hydrogeological functioning of this system has not been precisely described. This is an essential prerequisite for analyzing chemical processes in a realistic way and not being content with generalities and uncontrollet assumptions.
In conclusion, this manuscript requires a rather thorough revision as much on the scientific aspect as on the form. The entire manuscript is quite confusing. The methodology adopted by the authors is not presented clearly so that readers can follow their approach easily.
The analysis of the aquifer-river system in space and time is an essential prerequisite for the study of the evolution of iron and manganese contents. The hydrodynamic relationships between the groundwater and the river remain preponderant on the dynamics of these metals. Multivariate statistical analyzes are commonly used. In this manuscript their use is not very clear. It is necessary to show the raw data used and the results obtained (numerical and graphical), and to clearly highlight the contribution of these methods in understanding the functioning of the system.
Author Response
Dear reviewer:
Thank you for your insightful and valuable comments, which are helpful for improving the quality of this manuscript. According to your indication, we have carefully revised the manuscript. Please see the details below. We have finished the correction according to the reviewers’ suggestions. Reviewers’ comments are in black font; our responses below are in blue font, and any changes and references to them are in red font. All the corrections are clearly highlighted in red font in the manuscript as well. All the comments from the reviewer have been replied point by point. If you have any queries, please contact us.
Thank you and best regards.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The main concern of the study is the age of the data set. In the opinion of the reviewer, a data set that is four years old is of limited use by decision-makers and water managers.
Line 157 – should be “The” and in line 158 should be “spectrometer”
Paragraph 2.3.1 should be carefully revised since Factor Analysis and Principal Component Analysis have slightly different backgrounds. The authors write about FA, however, I assume they think about FA where one of the options for the generation of the factors is an algorithm of the principal components. This should be clarified in detail since the authors further use the abbreviation PC (Principal Components) instead of F (Factors).
Line 191: the term “closeness” is inadequate in this place. Especially when the authors write about samples. The correct description of CA should be prepared using the term “similarity” in the multidimensional space of variables. Also, it is not correct if the difference in Euclidean distance is a measure of similarity since the CA allows to use of a variety of distance measures, and Euclidean distance is only one of them.
The name of the company which delivers SPSS and its version should be indicated.
Author Response
Dear reviewer:
Thank you for your insightful and valuable comments, which are helpful for improving the quality of this manuscript. According to your indication, we have carefully revised the manuscript. Please see the details below. We have finished the correction according to the reviewers’ suggestions. Reviewers’ comments are in black font; our responses below are in blue font, and any changes and references to them are in red font. All the corrections are clearly highlighted in red font in the manuscript as well. All the comments from the reviewer have been replied point by point. If you have any queries, please contact us.
Thank you and best regards.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors, thank you for submitting the manuscript to the journal of Water. Its topic is very interesting. However, the current version of the paper suffers from a number of weaknesses related to the empirical strategy used. I have the following comments/questions for the authors:
Abstract
· The abstract could be more specific. I suggest the authors should organize the abstract as well as main text in four sections, namely: scope, objectives, methods, results, conclusions. Also, abstract section should be completed with the results of the study. Don’t use abbreviation on the first time. Define full form for the first time than after use abbreviation only (Please check in the entire manuscript).
· The abstract section needs a lot of improvement in scientific writing. There are many sentences which are not properly presented.
· Add important results in the abstract section.
· The authors ought to re-write the abstract so that it briefly presents the problem at hand, objectives of the study, methods used to achieve the objectives in logical order. Also, abstract section should be completed with the results of the study.
Introduction
· The introduction section is need to improvement. It was suggested to make it concise as much as possible. Rather than addressing this comment, authors further enhance the length of introduction by adding, so many necessary information. It must be made better. Try to highlight the regional or national significance of this study.
· Add some facts and figures of surface and groundwater quality around the globe in your introduction.
· Add some recent article to make your introduction more attractive and strong. I propose to add this survey method in the overview section of the introduction section, based on the latest literature. Please add citations of newest literature.
https://0-doi-org.brum.beds.ac.uk/ 10.1007/s12517-020-05882-x
https://0-doi-org.brum.beds.ac.uk/ 10.3390/w14071131
Materials and Methods
Site Description
· Describe all the features of the study area in brief including topography, geology, and hydrogeology?
· From Line 120 to Line 124 (Are these results obtained?). Please move it to the results section.
Sampling and Analysis
· Please give detailed information on water samplers (e.g., accuracy, manufacturer).
· Sampling locations were selected carefully within the groundwater to have a good representation of the spatial variability of quality indicators across-section of water quality monitoring. What criteria where analyzed to select this locations?
· What criteria where analyzed to select this locations?
· Please provide detailed detection methods and quality control results?
· Please support your methods by providing appropriate references or give the guidelines used to analyze the water quality parameters.
· How did you do quality control (QC) and quality assurance (QA) on the obtained data to validate the conclusions?
Discussion
· The authors have presented some of the results of this study under the discussion section (Please move the results of the study under the results section)
· Figures 6, 7, and 8 (Please move these figures into the Results section)
· The discussion section was not supported with any relevant references. Add some relevant cited references such as https://0-doi-org.brum.beds.ac.uk/ 10.1016/j.nrjag.2016.04.003
· You should think how transformational the research is likely to be should be made so that the outcome of the work will have an impact on the community/society facing given sustainability related challenges?
· Write the practical applications of your work in a separate section, before the conclusions and provide your good perspectives.
· Why do you believe your research to be important? What long-term impacts will it have on environmental protection and the wider public or the field following the completion of the research?
· The authors ought to re-write the discussion section.
I recommend the authors to combining between results and discussion under section "Results and Discussion"
Conclusion
· Concise the text in conclusion and add future work in order to recommend your work. Shorten the length of each and every paragraph by adding only relevant and major findings in your study.
Please respond to all of those comments in the revised manuscript by pointing out precisely and concisely on which page and in which line you have incorporated your response one by one.
Comments for author File: Comments.pdf
Author Response
Dear reviewer:
Thank you for your insightful and valuable comments, which are helpful for improving the quality of this manuscript. According to your indication, we have carefully revised the manuscript. Please see the details below. We have finished the correction according to the reviewers’ suggestions. Reviewers’ comments are in black font; our responses below are in blue font, and any changes and references to them are in red font. All the corrections are clearly highlighted in red font in the manuscript as well. All the comments from the reviewer have been replied point by point. If you have any queries, please contact us.
Thank you and best regards.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
This paper is an interesting study and authors have studied the spatio-temporal variability of hydrogeochemical evolution during riverbank infiltration through multivariate statistical analysis.
The article is written correctly, includes a discussion of the research findings, and a good review of the literature. The results are presented in a clearly structured manner. The paper has a logical structure and clearly describes the methodology. The manuscript has been significantly improved and can now be accepted in current form.
