An Integrated Statistical, Geostatistical and Hydrogeological Approach for Assessing and Modelling Groundwater Salinity and Quality in Nile Delta Aquifer

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall this is great study employing various statistical and geostatistical methods to investigate the salinization patterns in Nile delta aquifer. My main suggestion would be consolidating the data and presenting the various statistical test results in more coherent story. Some of figures can be consolidated as subfigures for better comparison and results and discussion could go beyond visual interpretation of each graph. 

I enjoyed reading the discussion part as it was concise and well-structured report of the trends observed in the data. The results section was very long with a lot of data in tables and graphs to process. For better reader comprehensions perhaps some of the data can be moved to Supplementary Information.

While the study limitations are mentioned, it would be good to add some discussion along the data set having 10 year interval. How did this affect the data analysis and results. Would conclusions and trends be different if similar study would be done on datasets collected over consequent years or on different temporal scales (e.g, seasonal changes)

It would be good to add a discussion on how combination of different methods enrich the study findings and provided better insights for groundwater management. 

Some specific suggestions:

Linear model of Coregionalization and geostatistical results tables can be moved to Supplementary Information.

Figure 4: what does red circle means. Provide more descriptive figure captions and label subplots.

In 2007, zone with higher Cl concentrations is wider than that of EC, what could be the potential reasons of higher Cl in those areas. In 2018, EC and Cl profile match pretty consistent from Figures 5 and 6.

Na zone with higher concentration is decreasing with time, while Cl and EC increasing. Did you make correlation between Cl, Na and EC. Are they correlated?

Rather than plotting the Figures 5-8 separately suggest making one Figure (maybe on full page with subplots representing geochemical species and date) for easier comparison. 

Overall, rather than providing descriptive analysis of the results (description of each figure), it would be beneficial to see critical analysis of the observed patterns and how the geochemical data unfolds the overall story.

QQ plots: While the results of hydraulic head, EC and Cl changes between 1996 vs 2007 are impressive, the other trends are not as clear and there was very limited explanation on the potential causes of the observed relationships. 

Author Response

Dear Reviewer, 

Please find below the author's reply to your comments

• Overall this is great study employing various statistical and geostatistical methods to investigate the salinization patterns in Nile delta aquifer. My main suggestion would be consolidating the data and presenting the various statistical test results in more coherent story. Some of figures can be consolidated as subfigures for better comparison and results and discussion could go beyond visual interpretation of each graph. 

Authors: In the “discussions” and in the “conclusions” there is now a comparative and consequential analysis of the data and results. See also the response to observation 6 of the reviewer’s specific suggestions

 

 

• I enjoyed reading the discussion part as it was concise and well-structured report of the trends observed in the data. The results section was very long with a lot of data in tables and graphs to process. For better reader comprehensions perhaps some of the data can be moved to Supplementary Information.

Authors: This is done by moving LMC tables of the three years to supplementary materials

 

 

 

 

• While the study limitations are mentioned, it would be good to add some discussion along the data set having 10 year interval. How did this affect the data analysis and results. Would conclusions and trends be different if similar study would be done on datasets collected over consequent years or on different temporal scales (e.g, seasonal changes).

Authors: The trends of this work are mainly controlled by the chemical composition of the studied data sets. Wherever there are changes in the chemical composition, there will be different trends.

 

 

 

 

• It would be good to add a discussion on how combination of different methods enrich the study findings and provided better insights for groundwater management. 

Authors: La combinazione dei differenti metodi e la consequenzialità dei risultati ottenuti è descritta nel capitolo “Discussion”. In questo abbiamo aggiunto dei contenuti all’inizio ed alla fine del capitolo che arricchiscono la discussione.

 

 

 

Some specific suggestions:

• Linear model of Coregionalization and geostatistical results tables can be moved to Supplementary Information.

 

Authors: Done

 

 

 

• Figure 4: what does red circle means. Provide more descriptive figure captions and label subplots.

 

Authors: The red circle indicates rise to a lobed shape of the piezometric surface in the central area, lines 363 -365

 

 

 

• In 2007, zone with higher Cl concentrations is wider than that of EC, what could be the potential reasons of higher Cl in those areas. In 2018, EC and Cl profile match pretty consistent from Figures 5 and 6.

Author’s response: The studied aquifer varies from semi-confined to unconfine where the response to anthropogenic impact is a potential reason for increase in Cl content. Additionally, the reuse of irrigation water, the season, pumping rate are potential factors. There is no sharp regulation on pumping rates and land uses for cultivation, this also contribute to the variability.

 

 

 

• Na zone with higher concentration is decreasing with time, while Cl and EC increasing. Did you make correlation between Cl, Na and EC. Are they correlated?

Authors: The decrease in the content of Na with time and with increased EC confirm the progressive salinization of the coastal groundwater due to seawater intrusion where reverse ion exchange is prominent (i.e., Na is captured on the aquifer matrix and Ca and Mg were released to the groundwater.

 

• Rather than plotting the Figures 5-8 separately suggest making one Figure (maybe on full page with subplots representing geochemical species and date) for easier comparison. 

Authors: We prefer to leave them as they are to be related to the text of each figure.

 

 

 

 

• Overall, rather than providing descriptive analysis of the results (description of each figure), it would be beneficial to see critical analysis of the observed patterns and how the geochemical data unfolds the overall story.

Authors: We believe that what is reported in the chapters “results” and “discussion” is significant for the understanding of the overall story. Furthermore, we believe that the description of the figures is not a mere descriptive analysis but contains and synthesizes in itself a complex and articulated succession of operations that go from the survey, to the cataloging, to the processing, to the representation, to the interpretation and finally to the description of the results. In any case, to take into account the reviewer’s advice, the comparative and consequential analysis of the different methods has been implemented in the chapter “discussion”.

 

 

 

• QQ plots: While the results of hydraulic head, EC and Cl changes between 1996 vs 2007 are impressive, the other trends are not as clear and there was very limited explanation on the potential causes of the observed relationships. 

 

Authors: We believe that in the analysis of SWI phenomena it is of primary importance to analyze the evolution of the intrusion marker ions, which are Na and Cl and total salinity. We agree that the variation over time of the other ions would have been interesting but the treatment would have been burdened and the contribution to the problem would have been of little benefit. Furthermore, as described in chapter 3.2, the ions that make the difference between the two main groups of waters are Na, Cl and Ca. All three ions have been better characterized through QQplots.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Paper Structure and Clarity

• Paragraph Structure: Some paragraphs are too long. Suggest breaking them into smaller sections, especially the discussions in Section 4, to focus on one core theme per paragraph for better readability.
• Figure Description: Ensure consistency between figure numbers and descriptions. For example, Figure 3 mentioned on page 5 should clearly explain its content and its connection to the text to avoid confusion when readers refer to the figure.

2. Data Description and Methodology

• Data Year Inconsistency: In the "Data Collection" section, Table 1 lists different years for sample points and depth ranges, but there is inconsistency with the year mentioned in the discussion. For example, the data for 2018 shows 60 sample points in the text but lists 67 in Table 1. It’s recommended to verify and standardize the data.

3. Result Analysis

• Salt Change Cause Analysis: The section on salt concentration changes mentions pumping from Lake Manzala, but fails to analyze other potential factors such as hydrological and climatic impacts on saltwater intrusion. It's suggested to explore these factors and their interactions more deeply, and attempt to quantify their influence.

4. Statistical Methods and Explanation

• Kriging Method: The paper uses Kriging and Factorial Kriging analysis methods, but lacks detailed explanation of their theoretical foundation and practical application. Adding a brief overview of these methods, including why they were chosen and their strengths and limitations, would be beneficial.
• 5. Language and Terminology

• Terminology Consistency: The paper uses multiple geological and hydrological terms (e.g., “hydraulic head,” “pore water surface,” “saltwater intrusion”) that should be consistent throughout the text. Avoid different expressions for the same term to reduce potential confusion.
• 6. Conclusion Section

• Further Research Contributions: The conclusion should more clearly highlight the contributions of the research, such as introducing the relationship between saltwater and freshwater distances. Emphasize how the method improves the precision of saltwater intrusion monitoring.
• Future Research Directions: Add suggestions for future research, like more detailed model validation or validation of data from different regions to guide future studies.

7. Figures and Formatting

• Figure Clarity:
  • Lines 1-73: Text on Figures 1, 3, 4-8 is unclear. Please revise the text in the images.
  • Line 114: Figures 2 should be placed alongside the text for better clarity.
  • Lines 112-113: Clarify what "asl" means.
  • Lines 160-167: Check formatting; there seems to be an issue with layout and alignment. Please ensure the paper follows the journal's formatting guidelines.
  • Figures 11-13: These figures could be combined into a single figure or moved to the appendix to reduce redundancy in the main body of the paper.

Author Response

Dear Reviewer, 

Please find below the author's reply to your comment 

Paper Structure and Clarity

• Paragraph Structure: Some paragraphs are too long. Suggest breaking them into smaller sections, especially the discussions in Section 4, to focus on one core theme per paragraph for better readability.

Authors: The observation is in contradiction with what was requested by reviewer 1 who asked for a more extensive description. However, we have tried to optimize the description

 

• Figure Description: Ensure consistency between figure numbers and descriptions. For example, Figure 3 mentioned on page 5 should clearly explain its content and its connection to the text to avoid confusion when readers refer to the figure.

Authors: Done

 

2. Data Description and Methodology

• Data Year Inconsistency: In the "Data Collection" section, Table 1 lists different years for sample points and depth ranges, but there is inconsistency with the year mentioned in the discussion. For example, the data for 2018 shows 60 sample points in the text but lists 67 in Table 1. It’s recommended to verify and standardize the data.

Authors: Done

3. Result Analysis

• Salt Change Cause Analysis: The section on salt concentration changes mentions pumping from Lake Manzala, but fails to analyze other potential factors such as hydrological and climatic impacts on saltwater intrusion. It's suggested to explore these factors and their interactions more deeply, and attempt to quantify their influence.

 

Authors: The hydrogeological and climatic impacts play significant roles in saltwater intrusion. In the Nile Delta coastal aquifer, the primary factor contributing to this phenomenon is the over-pumping process. The aquifer is considered renewable as it is recharged by the River Nile's distributed branches in the delta region. Normally, groundwater flows from the south to the northern parts. However, continuous over-pumping has led to an increase in seawater intrusion, particularly in the northern areas.

4. Statistical Methods and Explanation

• Kriging Method: The paper uses Kriging and Factorial Kriging analysis methods, but lacks detailed explanation of their theoretical foundation and practical application. Adding a brief overview of these methods, including why they were chosen and their strengths and limitations, would be beneficial.

Authors: this has been mentioned in lines 213 – 215  and lines 245 – 256

 

5. Language and Terminology

• Terminology Consistency: The paper uses multiple geological and hydrological terms (e.g., “hydraulic head,” “pore water surface,” “saltwater intrusion”) that should be consistent throughout the text. Avoid different expressions for the same term to reduce potential confusion.

Authors: Done, Lines 26, 184, 187, 228, 346, 350, 355, 357, 359, 364, 382, 408, 410, 415, 417, 431, 525, 551, 558, 564, 571

 

6. Conclusion Section

• Further Research Contributions: The conclusion should more clearly highlight the contributions of the research, such as introducing the relationship between saltwater and freshwater distances. Emphasize how the method improves the precision of saltwater intrusion monitoring.

Authors: We understand the reviewer's request, but we believe that what has already been summarized in the conclusions and what is reported in the previous chapter "discussion" clearly highlights the contribution of the research. Any other clarification would therefore be redundant given what is described in the chapter immediately preceding the conclusions.

 

• Future Research Directions: Add suggestions for future research, like more detailed model validation or validation of data from different regions to guide future studies.

Authors: We do not understand the reviewer's suggestion. We have emphasized the need to have more data in space and time to better apply the proposed methodology. Applying other methods would certainly contribute to water resources management, but it would be out of the scope of this work.

 

 

 

7. Figures and Formatting

• Figure Clarity:
• Lines 1-73: Text on Figures 1, 3, 4-8 is unclear. Please revise the text in the images.

Authors: Figures has been improved

 

• Line 114: Figures 2 should be placed alongside the text for better clarity.

Authors: Done

 

 

• Lines 112-113: Clarify what "asl" means.

Authors: It stands for “above sea level”.

• Lines 160-167: Check formatting; there seems to be an issue with layout and alignment. Please ensure the paper follows the journal's formatting guidelines.

               Authors: Done

 

• Figures 11-13: These figures could be combined into a single figure or moved to the appendix to reduce redundancy in the main body of the paper.

Authors: Figures 11-13 are combined in one figure (Fig. 10).

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The study on " An integrated statistical, geostatistical and hydrogeological approach for assessing and modelling groundwater salinity and  quality in Nile Delta aquifer " is interesting, however, the manuscript can be improved by addressing the following observations:

 

Improve the quality of Figure 1, the map legends are not visible.

The environmental conditions of the site, such as precipitation, average temperature, existing vegetation, are not described in the materials and methods section.

Line 269 - Line 272 write adequately the chemical formula of the compounds and ions.

Re-do figure 3 does not appreciate well the information provided and the color of the lines.

Improve the quality of Figure 4, 5, 6, 7, and 8. The map legends are not visible.

In the discussion section on line 226, support with similar studies on the effects of saline intrusion and in the generation section, the discussion should be supported with other similar research.

In the conclusion section, mention the impact that the Nile River would have due to the effect of saline intrusion on agriculture.

Author Response

Dear Reviewer, 

Please find below the author's reply to your comments 

The study on " An integrated statistical, geostatistical and hydrogeological approach for assessing and modelling groundwater salinity and quality in Nile Delta aquifer " is interesting, however, the manuscript can be improved by addressing the following observations:

 

• Improve the quality of Figure 1, the map legends are not visible.

Authors: Done, the figure quality has been improved

 

 

 

• The environmental conditions of the site, such as precipitation, average temperature, existing vegetation, are not described in the materials and methods section.

Authors: Done, Lines 95 – 99

 

 

 

• Line 269 - Line 272 write adequately the chemical formula of the compounds and ions.

Authors: Done, Lines 303 and 305

 

 

 

 

• Re-do figure 3 does not appreciate well the information provided and the color of the lines.

 

Authors: Done

 

 

• Improve the quality of Figure 4, 5, 6, 7, and 8. The map legends are not visible.

Authors: Figures quality has been improved

 

 

• In the discussion section on line 226, support with similar studies on the effects of saline intrusion and in the generation section, the discussion should be supported with other similar research.

Authors: A comparison with similar research in the study area was added in the discussion section with citations.

 

 

• In the conclusion section, mention the impact that the Nile River would have due to the effect of saline intrusion on agriculture.

 

Authors: done

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed and improved the manuscript with the recommendations made.