Study on the Sources of Salinity of Groundwater in Holocene and Late Pleistocene Sediments Based on Hydrochemical and Isotopic Methods in Southern Laizhou Bay

Round 1

Reviewer 1 Report

The manuscript  water-1884351 presents chemical and isotopic data of groundwater from the Laizhou Bay area. The manuscript is substantially well written, but needs some improvements especially in the analytical methods section. In particular: 1) it seems that the ICP-MS technique was used to measure the concentration of major cations, which is quite unusual given the salinity of the water and the problems that can arise with this technique (see in detail the comments enclosed in the pdf file); 2) the method of water isotopes analysis is not described in detail; 3) neither precision nor accuracy of the MC-ICP-MS method used for the Sr isotope ratio is described. In the latter case, it would be necessary to explain the type of standards used, how the isobaric interferences -for example due to ⁸⁴Kr, ⁸⁵Rb, ⁸⁶Kr- were solved and if normalization to ⁸⁶Sr/⁸⁸Sr = 0.1194 was used.

I have enclosed other comments in the attached pdf.

Hope this helps

Comments for author File: Comments.pdf

Author Response

Cover Letter

Manuscript Number: water-1884351

Dear editor and Reviewer,

Thank you for your letter and for reviewer’s comments concerning our manuscript entitled “Study on the sources of salinity of groundwater in Holocene and Late Pleistocene sediments based on hydrochemical and isotopic methods in southern Laizhou Bay”. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The amendments are marked up using the “Track Changes” function in the revised manuscript. Point by point responses to the reviewers’ comments are listed below this letter.

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The manuscript water-1884351 presents chemical and isotopic data of groundwater from the Laizhou Bay area. The manuscript is substantially well written, but needs some improvements especially in the analytical methods section. In particular: 1) it seems that the ICP-MS technique was used to measure the concentration of major cations, which is quite unusual given the salinity of the water and the problems that can arise with this technique (see in detail the comments enclosed in the pdf file); 2) the method of water isotopes analysis is not described in detail; 3) neither precision nor accuracy of the MC-ICP-MS method used for the Sr isotope ratio is described. In the latter case, it would be necessary to explain the type of standards used, how the isobaric interferences -for example due to ⁸⁴Kr, ⁸⁵Rb, ⁸⁶Kr were solved and if normalization to ⁸⁶Sr/⁸⁸Sr = 0.1194 was used.

Authors response:

The indoor detection indicators were sent to the Groundwater Mineral Water and Environmental Monitoring Center of the Ministry of Land and Resources for measuring. Through consulting the staff of the monitoring center, we learned about the measuring instruments and methods, and wrote them in the article.

According to the expert's suggestion, we consulted the staff of the monitoring center again on the relevant instruments and methods, and found that the measuring instruments and methods in this reply were different from the previous reply. After our repeated consultation, and the confirmation of monitoring center, the real measuring instruments and methods are the modified content in the article.

（1）it seems that the ICP-MS technique was used to measure the concentration of major cations, which is quite unusual given the salinity of the water and the problems that can arise with this technique (see in detail the comments enclosed in the pdf file).

①The comments enclosed in the pdf file:

It is unusual to determine major cations by ICP-MS. Rather, these elements are usually determined by ICP-OES. This is particuarly true for brackish and brine water samples. Indeed, due to high TDS, salt deposition could occludes the sampler cone of the ICP-MS. Therefore, the authors should specify this analytical choice, and explain what trick they used to face and solve that problem. Moreover, please also specify the MS brand and model.

Authors response:

After our repeated consultation, and the confirmation of monitoring center, cations (K⁺, Na⁺, Ca²⁺, and Mg²⁺) and Sr were determined using inductively coupled plasma optical emission spectrometer (ICP-OES). The brand was Optima and the model was 8000. Please see Page 6, lines198-199.

②The comments enclosed in the pdf file:

At line 179, it seems that all samples were 0.45 microm-filtered. So, why specificate this only for Sr?

Authors response:

All samples were 0.45 microm-filtered, we should not specificate this only for Sr. The article has been revised.

③The comments enclosed in the pdf file: Chloride have an high concentration and high and wide peak in chromatography. Please explain how this problem was faced and solved. Moreover, please also specify the brand and model of IC and of the columns used.

Authors response:

After our repeated consultation, and the confirmation of monitoring center, F^-, Cl^-, Br^-, NO₃^-, SO₄^2- were determined by ICS-1500 ion chromatograph from Thermo Fisher, USA. The chromatographic column used was an AS14 analytical column, and the data system was the Thermo Fisher chameleon chromatographic data system. The chromatographic analysis method can completely separate F^-, Cl^-, Br^-, NO₃^-, SO₄^2- according to this peak sequence, and the high concentration chloride peak shape did not affect the subsequent Br^-, NO₃^-, SO₄^2- peaks.

I^- was measured by CIC-D160 type ion chromatograph, and the brand of the instrument was Qingdao Shenghan. The characteristic of the measurement was the use of amperometric detector, and the chromatographic column was SH-AC-4 type chromatographic column. Please see Page 6, lines 204-211.

（2）the method of water isotopes analysis is not described in detail.

①The comments enclosed in the pdf file:What kind of "water isotope analyser"? In particular, ther to brand and model of the instrument, the analytical method should be specified: it was a Cavity ring-down spectroscopy? A water-gas equilibration method? A TC-EA analyzer coupled with MS? Please specify in detail.

Authors response:

After our repeated consultation, and the confirmation of monitoring center, "water isotope analyser" specifically called “laser spectroscopic water isotope analyzer”. The brand of the instrument was Picrro, and the model of the instrument was 2130i. The analytical method was optical cavity ring down principle. Please see Page 7, lines 214-216.

（3）neither precision nor accuracy of the MC-ICP-MS method used for the Sr isotope ratio is described. In the latter case, it would be necessary to explain the type of standards used, how the isobaric interferences -for example due to ⁸⁴Kr, ⁸⁵Rb, ⁸⁶Kr^- were solved and if normalization to ⁸⁶Sr/⁸⁸Sr = 0.1194 was used.

①The comments enclosed in the pdf file: Please specify brand and model. Moreover, what is the accuray of this measurement and how it was achieved (standards used for calibration and correction methods)?

Authors response:

The certified reference was NBS987. The precisions for ⁸⁷Sr/⁸⁶Sr was 0.014‰. The ⁸⁷Sr/⁸⁶Sr ratio was exponential normalization correction using ⁸⁸Sr/⁸⁶Sr = 8.375209. The natural isotope ratio of krypton (⁸³Kr/⁸⁴Kr =0.20175, ⁸³Kr/⁸⁶Kr=0.66474) was used to deduct the interferences of krypton. The fractionation behaviors of rubidium and strontium were considered to be consistent, and the natural ratio of ⁸⁵Rb/⁸⁷Rb (⁸⁵Rb/⁸⁷Rb=2.5926) was used to deduct the interference of ⁸⁷Rb on ⁸⁷Sr by measuring ⁸⁵Rb. As long as Rb /Sr was less than 0.01, the interference of rubidium can be completely deducted. Please see Page 7, lines 220-227.

（4）The comments enclosed in the pdf file: I suggest to use the Köppen-Geiger climate classification, using the proper code for the study area according to the published map:

http://koeppen-geiger.vu-wien.ac.at/present.htm

https://www.researchgate.net/publication/281132710_Linking_human-biometeorological_thermal_conditions_with_the_Koppen Geiger_climate_classification_updated_-_The_Example_of_China

Authors response:

We have revised to use the Köppen-Geiger climate classification, using the proper code for the study area according to the published map. Please see Page 2, lines 76-78.

（5）According to the reviewer's suggestion, we have added relevant references. Please see Page 3-4.

（6）The comments enclosed in the pdf file: Why only 2 significant numbers? Please increase till to 6th significant digit according to values described in section 4.3.2. Moreover, the analytical accuracy and precision should be detailed in the method section.

Authors response: We have increased till to 6th significant digit according to values described in section 4.3.2. Moreover, we have added detailed instructions about the analytical accuracy and precision in the method section. Please see Table1.

（7）The comments enclosed in the pdf file: I suggest to use only one anion and only one cation (i.e., the highest in the considered sample), for example: HCO₃-Na. The same for all chemical classification used throughout the manuscript, including abstract. Authors can do this converting concentrations as meq/l and then looking to the highest anion and cation. In this manner, chemical faies will be more clear for the reader.

Authors response: We have modified the water chemistry type to only one anion and only one cation (i.e., the highest in the considered sample). The same for all chemical classification used throughout the manuscript, including abstract and conclusion. Please see Page10-11, lines 268-277; Page1, lines 21-23; Page20, lines 520-522.

（8）The comments enclosed in the pdf file: why "obviously"? I suggest to delete the word (Page 11 lines 277).

Authors response: We have deleted "obviously". Please see Page 11, line 277.

（9）The comments enclosed in the pdf file: The constituents described in the following sections are not usually "major ions". I suggest to use a different title, e.g.: "Other significant constituents and ratios." (Page 13, lines 340 ).

Authors response: We have revised “major ions” to "Other significant constituents and ratios." Please see Page 13, line 340.

（10）The comments enclosed in the pdf file: So why brine are not close to evaporation line but shifted towards seawater or sampled meteoric water? Moreover, why you rainwater sample is different from long term mean of Yantai station? Please explain.

Authors response: 1) Since there were only two brine samples, there was a large randomness, and it was difficult to summarize the variation law. Therefore，we have deleted this passage (The δ¹⁸O and δ²H of fresh water in groundwater were relatively depleted. From fresh water to brine, with an increase in salinity, the δ¹⁸O and δ²H in groundwater tended to increase gradually, but they did not show a trend of changing towards standard seawater. Instead, these values gradually approached the evaporation line, which indicated that the study area was mainly dominated by salt water and brine intrusion. Additionally, evaporation played an important role in groundwater salinization ). Please see Page 18, lines 456-461.

2) Rain sample was taken from Weifang City (Liu Sen et al.,2017), so it was different from long term mean of Yantai station.

（11）The comments enclosed in the pdf file: I suggest to add also the three seawater samples of Han et al. (2011), Table 1 of that work.

Authors response: We have added also the three seawater samples of Han et al. (2011), Table 1 of that work. Please see Fig.9.

（12）The comments enclosed in the pdf file: I suggest to insert the long-term mean value, including error bar, of the precipitation Yantai station from IAEA-Wiser dataset (https://nucleus.iaea.org/wiser/index.aspx). These are -7.18 ± 0.68 ‰ for oxygen and -51.0 ± 4.6 ‰ for hydrogen.

Authors response: We have inserted the long-term mean value, including error bar, of the precipitation Yantai station from IAEA-Wiser dataset. Please see Fig.9.

Author Response File: Author Response.docx

Reviewer 2 Report

The work presented is interesting. It tries to evaluate the situation of marine intrusion in a multilayer coastal aquifer of Quaternary age, with hydrochemical and isotopic methods. However, it has some drawbacks, which must be resolved before publication.

The most debatable aspect is related to the qualification of "Holocene" and "Upper Pleistocene" groundwater. Actually, what is shown in the work is that there is an aquifer in Holocene sediments and another in Pleistocene sediments, with waters of different characteristics. But not waters of different age.

I think they should explain this more clearly in the paper, included in the title itself. In addition, there are some small modifications that must be carried out, such as:

1. In Figure 1, it should be indicated in the key that line A-A' is the hydrogeological section of Figure 2.

2. In figure 2, meters of altitude should be indicated as m a.s.l.

3. line 135: what does "metamorphism of seawater" mean? please explain.

4. I think that when referring to the roof of a geological formation it should be top.

5. A piezometric map of the aquifers should be included.

6. Some bibliographic citations are necessary for some statements (for example, lines 137-138; lines 145-146).

7. Attention when writing the Cl/Br ratio, sometimes the "l" is changed to a "1" or to an "I"...

Author Response

Cover Letter

Manuscript Number: water-1884351

Dear editor and Reviewer,

Thank you for your letter and for the reviewer’s comments concerning our manuscript entitled “Study on the sources of salinity of groundwater in Holocene and Late Pleistocene sediments based on hydrochemical and isotopic methods in southern Laizhou Bay”. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The amendments are marked up using the “Track Changes” function in the revised manuscript. Point by point responses to the reviewers’ comments are listed below this letter.

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The work presented is interesting. It tries to evaluate the situation of marine intrusion in a multilayer coastal aquifer of Quaternary age, with hydrochemical and isotopic methods. However, it has some drawbacks, which must be resolved before publication.

The most debatable aspect is related to the qualification of "Holocene" and "Upper Pleistocene" groundwater. Actually, what is shown in the work is that there is an aquifer in Holocene sediments and another in Pleistocene sediments, with waters of different characteristics. But not waters of different age.

I think they should explain this more clearly in the paper, included in the title itself.

Authors response: Yes, what is shown in the work is that there is an aquifer in Holocene sediments and another in Pleistocene sediments, with waters of different characteristics. We have revised "Holocene" and "Upper Pleistocene" groundwater to “groundwater in Holocene and Late Pleistocene sediments”. Similar revisions have been made to relevant statements throughout the article.

In addition, there are some small modifications that must be carried out, such as:

1.In Figure 1, it should be indicated in the key that line A-A' is the hydrogeological section of Figure 2.

Authors response: We have indicated in the key that line A-A' is the hydrogeological section of Figure 2. Please see Page 3 Figure 1.

2.In figure 2, meters of altitude should be indicated as m a.s.l.

Authors response: We have indicated meters of altitude as m a.s.l. in Figure 2. Please see Page 5 Figure 2.

3.line 135: what does "metamorphism of seawater" mean? please explain.

Authors response: In the article "metamorphism of seawater" means “burial diagenesis of seawater”. Please see Page 4, line 142.

4.I think that when referring to the roof of a geological formation it should be top.

Authors response: Yes, when referring to the roof of a geological formation it should be top. We have revised the corresponding sentence to that the top of the Late Pleistocene groundwater (deep groundwater) is buried at a depth of 25-30 m, and a cohesive soil aquifer with a relatively stable distribution and thickness of 5-10 m developed between the top of the Late Pleistocene groundwater and overlying shallow aquifer. Please see Page 4 Lines 125-128.

5.A piezometric map of the aquifers should be included.

Authors response:  We have added the piezometric map of the aquifers (March 1, 2021). Please see Page 5, Fig.2.

6.Some bibliographic citations are necessary for some statements (for example, lines 137-138; lines 145-146).

Authors response: We have added some bibliographic citations for some statements. Please see Page 3-4.

7.Attention when writing the Cl/Br ratio, sometimes the "l" is changed to a "1" or to an "I"...

Authors response: We have revised “C1” and “CI” to “Cl” in the full article.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The Authors have addressed all of my concerns with the original manuscript.

My last comment: the word "Piccro" al line 207 of the revised version (section 3.2 Sampling) should be changed to "Picarro".

Hope this helps.

Best Regards

Author Response

Cover Letter

Manuscript Number: water-1884351

Dear editor and Reviewer,

Thank you for your letter and for reviewer’s comments concerning our manuscript entitled “Study on the sources of salinity of groundwater in Holocene and Late Pleistocene sediments based on hydrochemical and isotopic methods in southern Laizhou Bay”. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The amendments are marked up using the “Track Changes” function in the revised manuscript. Point by point responses to the reviewers’ comments are listed below this letter.

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The Authors have addressed all of my concerns with the original manuscript.

My last comment: the word "Piccro" al line 207 of the revised version (section 3.2 Sampling) should be changed to "Picarro".

Authors response: We have revised "Piccro" to "Picarro", Please see line 215.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors, thank you for accepting all suggestions and improving the original manuscript. Just a small additional correction: in the key of figure 2 it is indicated "piezometric map", when in fact it is a "piezometric profile" or the "piezometric level situation". Please change.

Author Response

Cover Letter

Manuscript Number: water-1884351

Dear editor and Reviewer,

Thank you for your letter and for reviewer’s comments concerning our manuscript entitled “Study on the sources of salinity of groundwater in Holocene and Late Pleistocene sediments based on hydrochemical and isotopic methods in southern Laizhou Bay”. This comment is valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The amendments are marked up using the “Track Changes” function in the revised manuscript. Point by point responses to the reviewers’ comments are listed below this letter.

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

Dear authors, thank you for accepting all suggestions and improving the original manuscript. Just a small additional correction: in the key of figure 2 it is indicated "piezometric map", when in fact it is a "piezometric profile" or the "piezometric level situation". Please change.

Authors response: We have revised " piezometric map " to " piezometric profile ", Please see figure 2.

Author Response File: Author Response.docx