Multivariate Statistical Analysis and Structural Sovereignty for Geochemical Assessment and Groundwater Prevalence in Bahariya Oasis, Western Desert, Egypt

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The purpose of the manuscript “sustainability-1707871” is to study the geochemistry of Groundwater in Bahariya Oasis emphasizing the roles of geologic structures in monitoring groundwater flow regimes and hydrogeochemistry

 

The paper appears well-structured; however, some sections must be improved.  Therefore, I believe

the manuscript should be published only after major revision.

 

Comments

 

The introduction does not take into account many general factors responsible for water mineralization. Read and add the following books and work in the references:

 

Langmuir, D., 1997. Aqueous environmental geochemistry (No. 551.48 L3.).

 

Apollaro, C., Marini, L. and De Rosa, R., 2007. Use of reaction path modeling to predict the chemistry of stream water and groundwater: a case study from the Fiume Grande valley (Calabria, Italy). Environmental geology, 51(7), pp.1133-1145.

 

Fuoco, I., et al. "Use of reaction path modelling to investigate the evolution of water chemistry in shallow to deep crystalline aquifers with a special focus on fluoride." Science of The Total Environment 830 (2022): 154566.

 

no measurement of the redox potential (Eh) is reported, why?

 

It is not reported any data regarding analysis accuracy and precision. It is recommended to add this information

 

To evaluate the chemical composition of the water it is not enough to use the Piper diagram because it does not take into account (as proposed by the authors) salinity, I suggest using a TIS salinity diagram, as proposed by:

 

Apollaro, C.; Vespasiano, G.; De Rosa, R.: Marini L. Use of mean residence time and flowrate of thermal waters to evaluate the volume of reservoir water contributing to the natural discharge and the related geothermal reservoir volume. Application to Northern Thailand hot springs. Geothermics 2015, 58, 62-74

 

in the calculation of the satration with dolomite, which dolomite was used, the ordered one or the disordered one?

 

In the sentence (row 637): The second factor (F2) of the shallow groundwater samples accounting for 13.6 % of the total variance is associated with high negative loading of Fe2+ (-0.7) and Mn2+ (-0.65)  while a strong positive loading value for pH (0.78). Accordingly, F2 is assumed to be in dicative of the natural processes and water-rock interaction (geogenic sources), because  the presence of Mn2+and Fe2+ in the groundwater is a direct result of the reductive dissolution of the mineral which typically exists….. the authors cannot hypothesize this without a measure of the redox potential (Eh).

 

In the sentence (row 646): Factor 3 contributes 7.4% of the total variance and 0.96 of the eigenvalues, is marked by significant negative loadings with HCO3- (-0.77), which reflects the mixing of freshwater from the underlying deep aquifers with water of shallow aquifer….. the reason for this statement is not clear!

 

Discussions and conclusions need to be rewritten taking into account previous comments

 

Recommended works must be added in the bibliography

 

• Langmuir, D., 1997. Aqueous environmental geochemistry (No. 551.48 L3.).

 

• Apollaro, C., Marini, L. and De Rosa, R., 2007. Use of reaction path modeling to predict the chemistry of stream water and groundwater: a case study from the Fiume Grande valley (Calabria, Italy). Environmental geology, 51(7), pp.1133-1145.

 

• Fuoco, I., et al. "Use of reaction path modelling to investigate the evolution of water chemistry in shallow to deep crystalline aquifers with a special focus on fluoride." Science of The Total Environment 830 (2022): 154566.

 

• Apollaro, C.; Vespasiano, G.; De Rosa, R.: Marini L. Use of mean residence time and flowrate of thermal waters to evaluate the volume of reservoir water contributing to the natural discharge and the related geothermal reservoir volume. Application to Northern Thailand hot springs. Geothermics 2015, 58, 62-74

 

Author Response

Reviwer1_Comments

• The introduction does not take into account many general factors responsible for water mineralization. Read and add the following books and work in the references:

The comment is followed, the introduction section was adequately changed, and the references were inserted correctly, Page 2, lines 56-65.

• no measurement of the redox potential (Eh) is reported, why?

During the field trip in 2019, the instrument concerning the redox potential (Eh) malfunctioned.

• It is not reported any data regarding analysis accuracy and precision. It is recommended to add this information.

The comment is followed, and the analysis accuracy and precision were inserted correctly, page 8, lines 409-412.

• To evaluate the chemical composition of the water it is not enough to use the Piper diagram because it does not take into account (as proposed by the authors) salinity, I suggest using a TIS salinity diagram, as proposed by:

The comment is followed, and the TIS diagram and its interpretation were inserted correctly, page 11, lines 548-552 and figure 9.

• In the calculation of the saturation with dolomite, which dolomite was used, the ordered one or the disordered one?

The disordered dolomite was used

• In the sentence (row 637): The second factor (F2) of the shallow groundwater samples accounting for 13.6 % of the total variance is associated with high negative loading of Fe2+ (-0.7) and Mn2+ (-0.65) while a strong positive loading value for pH (0.78). Accordingly, F2 is assumed to be indicative of the natural processes and water-rock interaction (geogenic sources), because the presence of Mn2+and Fe2+ in the groundwater is a direct result of the reductive dissolution of the mineral which typically exists….. the authors cannot hypothesize this without a measure of the redox potential (Eh).

I suppose this hypothesize based on the previously mentioned information on the same area, and the related research was inserted correctly, (Sharaky and Abdoun 2020)(Page 14, line 684)

• In the sentence (row 646): Factor 3 contributes 7.4% of the total variance and 0.96 of the eigenvalues, is marked by significant negative loadings with HCO3- (-0.77), which reflects the mixing of freshwater from the underlying deep aquifers with water of shallow aquifer….. the reason for this statement is not clear!

The comment is followed, and the reason is revealed correctly.

 

• Discussions and conclusions need to be rewritten taking into account previous comments

The comment is followed, these sections were adequately changed

• Recommended works must be added in the bibliography

The comment is followed, and all the recommended works were added to the bibliography.

Author Response File: Author Response.pdf

Reviewer 2 Report

Ms. Ref. No.: sustainability-1707871
Title: Multivariate Statistical Analysis and Structural Sovereignty for Geochemical Assessment and Groundwater Prevalence in Bahariya Oasis, Western Desert, Egypt
Mohamed Abd El-Wahed, Mohamed El Horiny , Mahmoud Ashmawy , Samar Abdelkereem

General recommendation:
The manuscript submitted by Abd El-Wahed et al. fits very well with the aims and scope of Sustainability. The authors present a valuable hydrogeochemical assessment to evaluate the groundwater in Bahariya Oasis. However, the manuscript in its current state precludes the acceptance for publication. After significant improvements, I really encourage the authors to resubmit this manuscript.

Some points  to work on are marked following:

1.  Line 64-77: It seems to be part of the methodology section
2.  Line 78-91: Re-write this section to clarify the objectives of this research and its benefit.
3. Line 110: maintain the units across the manuscript; please use the SI units
4.  Section 2.1 and 2.2 are too long. Please reduce it, or move to supplementary material if the authors consider this part important.
5. Line 370. Is the sample time of purging for shallow and deep groundwater sampling? Why?
6. Line 375. The physicochemical parameters were not measured in the same time as the sampling campaign?
7. Please show the accuracy of the analysis in table 2 and put the number of samples for each type of water in the table.
8. Section 3.3 Do you perform any data-transformation previous the multivariate statistical analysis? If not, why?
9. Section 4.1 What is the relation between groundwater flow patterns and the hydrochemical characteristics? If there is no linkage between both, remove that section
10. In the shallow aquifer, there are significant standard deviations across the variables. Why not create a cluster analysis to perform a better interpretation.
11. TDS and EC are redundant variables. Remove one of them in the multivariate analysis
12. The conclusion is not a summary. Please rework this section.
13. Figure 2. Units are not shown in the scale bar.
14. Move figures 3, 4, 5, and 6 to a supplementary material section. 
15. Figure 9. Be consistent across the manuscript. Use the same symbols as the rest of the figures (shallow and deep aquifers)
16. Fig. 12a) separate in two figures to be clear between shallow and deep aquifer samples.

 

Author Response

Reviwer2_Comments

General recommendation:

The manuscript submitted by Abd El-Wahed et al. fits very well with the aims and scope of Sustainability. The authors present a valuable hydrogeochemical assessment to evaluate the groundwater in Bahariya Oasis. However, the manuscript in its current state precludes the acceptance for publication. After significant improvements, I really encourage the authors to resubmit this manuscript.

Some points to work on are marked following:

1. Line 64-77: It seems to be part of the methodology section

The comment is followed, and these lines are transferred to the methodology part (page 9 lines 450-457)

2. Line 78-91: Re-write this section to clarify the objectives of this research and its benefit.

The comment is followed, and this section is adjusted and inserted correctly (Page3 lines 102-117).

3. Line 110: maintain the units across the manuscript; please use the SI units

The comment is followed, and the unit is converted to Km² (Page3, line137).

4. Section 2.1 and 2.2 are too long. Please reduce it or move to supplementary material if the authors consider this part important.

The comment is followed, and both sections were adjusted and reduced as much as possible without causing any defect in the scientific content.

5. Line 370. Is the sample time of purging for shallow and deep groundwater sampling? Why?

The average purging time is relative, depending on obtaining a pure and representative sample of both aquifers (shallow and deep)

6. Line 375. The physicochemical parameters were not measured in the same time as the sampling campaign?

The comment is followed, and it was mentioned that the key physicochemical parameters comprising temperature (T oC), electric conductivity (EC), and total dissolved solids (TDS) were measured in situ using portable meters (Page 8, lines 403-405).

7. Please show the accuracy of the analysis in table 2 and put the number of samples for each type of water in the table.

The comment is followed, and a number of samples for each aquifer is inserted in Table 1 and the accuracy of the analysis is mentioned in the text (page 8 lines 409-412).

8. Section 3.3 Do you perform any data-transformation previous to the multivariate statistical analysis. If not, why?

No data-transformation previous to the multivariate statistical analysis was performed because there is some controversy regarding the desirability of performing such transformations since often, they cause more problems than they solve. Sometimes a transformation can be considered simply as another way of looking at the data. One thing that is very important is that transformations be applied uniformly, e.g., when comparing three groups of data, it would not be appropriate to apply a log transformation to one group but not to the other two.

9. Section 4.1 What is the relation between groundwater flow patterns and the hydrochemical characteristics? If there is no linkage between both, remove that section

This section exhibits the status of piezometric levels over the 17 years and shows the relation between the structural control on the groundwater flow patterns. I followed your comment and try to focus on the important results and discussion.

10. In the shallow aquifer, there are significant standard deviations across the variables. Why not create a cluster analysis to perform a better interpretation.

According to the availability of these shallow sampling, their collection is very limited and not distributed throughout the whole area very well. As a result, in my point of view, I think the application of cluster analysis is not well represented.

 

11. TDS and EC are redundant variables. Remove one of them in the multivariate analysis

The comment is followed, the EC as variables is removed and the multivariate analysis was executed and the changes in values in both text and tables were adjusted.

12. The conclusion is not a summary. Please rework this section.

The comment is followed, this section was adequately changed

13. Figure 2. Units are not shown in the scale bar.

The comment is followed, and the unit was placed.

14. Move figures 3, 4, 5, and 6 to a supplementary material section. 

These figures are important because they reveal the structural setting of the area in different sites and how it controls the topographic features and subsequently the groundwater flow.

15. Figure 9. Be consistent across the manuscript. Use the same symbols as the rest of the figures (shallow and deep aquifers)

The comment is followed, and the symbols were uniformed

16. 12a) separate in two figures to be clear between shallow and deep aquifer samples.

The comment is followed, and the separation between two aquifer samples was identified in the same figure.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

 

Remarks from  reviewers have been correctly addressed, and the paper is now more focuse on his core topic
In my opinion it is now acceptable.
Best regards

Reviewer 2 Report

The authors take into consideration the suggestions of the previous revision, so at this moment, the manuscript could be accepted