Coastal Aquifer Salinization in Semi-Arid Regions: The Case of Grombalia (Tunisia)

Round 1

Reviewer 1 Report

The manuscript although decently written, includes some flaws which could be potentially serious as affect the overall assessments. For example, co-processing and assessing the analytical results over a 12 years timespan (2005 -2014 – 2017) cannot be accepted, as salinization is a dynamic phenomenon (even though slower than others).  Even though the authors clearly state in the materials and methods part, that the use data with chemical analyses from 2014 and 2017 (and only isotope data from 2005), subsequently in the text (e.g. figure 5) it seems like they use chemical data from 2005 as well, which poses serious concerns about the validity of the research and the uncertainty of the assessments.  

To my suggestion, the authors shall distinguish these analyses and re-perform data processing with 2014-2017 values only (again, this may also include uncertainties) and use 2005 data for temporal comparison only, as using data from some long timespans is dubious.

In its current state, the paper cannot be revised, as the assessments are potentially reflecting an erroneous interpretation. I would therefore recommend that authors should re-work data and re-submit the paper with the above amendments. Below, are some minor comment which should also taken into account.

• It is not clear whether there is a hydraulic connection between the upper semi-confined and the deep confined aquifer.
• Can you please explain why you chose kriging instead of other interpolation method? Was that arbitrary or did you consider any geostatistical approach?

L171-172: The undersaturated state of evaporites, does not indicate their presence. On the contrary, that should be indicated if supersaturated.

L204: Any references to the ration you mention?

L206-207: The term “contamination” is erroneous, as probably the excessive amount of calcium is attributed to geogenic factors (ion exchange, thus, called natural enrichment)

L217-L219: The Ca-Cl water types does not indicate “reverse ion exchange”. It is widely accepted (e.g. see in Appelo and Postma 2005, Geochemistry and Groundwater Pollution, p. 243) that Ca-Cl indicates direct ion exchange, where saline water turns into brackish.  On the contrary, the Na-HCO3 water type indicates “reverse ion exchange”, where fresh water flushes the brackish water. Please amend.

L226-L227: Salinization is a dynamic phenomenon (although slow, in comparison with other processes). Thereby, process together samples collected and analyzed in along timespan (2005 – 2014 - 2017) is a serious flaw that may lead you to erroneous assessments. Data processing regarding salinization shall be distinguished and processed individually. You may only use jointly this samples for comparison in terms of temporal variation and evolution of the phenomenon through time.

L232: Again, in the methodological section, you state that you collected (and presumably processed) data from 53 samples, from the years 2014-2017 and used only the isotope data from the samples of 2005. In that case, how could it be possible to construct the diagram of Figure5c????

Discussion part: The paper used variable methods and techniques; however, the need for a discussion paragraph where all these methods shall be combined towards project goals is missing. To this aim, I strongly suggest authors to add a paragraph, addressing how do they combined these methods, especially in relation to the title of the paper (which is not fully supported).

Author Response

Dear Reviewer,

Thank you very much for your review.

Your comments and suggestions were greatly important and made our paper better. We hope that you will consider our paper ready for publication at this time.

Please find in attached file our detailed response. All comments were taken into account and specific changes were made in the manuscript. All revisions are clearly highlighted in the manuscript using the "Track Changes" function in Microsoft Word.

Best regards,

Author Response File: Author Response.pdf

Reviewer 2 Report

The results presented in the manuscript are of both scientific and especially practical interest. The work is well written and structured. I have only a small number of suggestions for improving its content, viz:

1. You hypothesize about the potential impact of the Mediterranean Sea on mineralization and groundwater chemistry (especially the shallow aquifer) in the coastal zone, in the north of the region that you studied. The age of groundwater, given by you, based on different sources, is estimated from modern to several thousand years, i.e., this is historical time. This means that there must be some historical or archaeological evidence of the flooding of the coastal plain by the sea, which one way or another was recorded in this long-inhabited region of the Mediterranean. If fluctuations in sea level took place at this time, then they should also have left geomorphological traces. Please give more information about it to more reliably present this hypothesis.
2. In the Discussion, you point out that the most likely cause of water pollution in the upper aquifer you studied is the filtration of contaminated waters, including as a result of the use of fertilizers. This is a quite probable hypothesis, but it requires more confirmation (first of all, the volumes and structure of fertilizers used in recent decades in comparison with previous decades, etc.). Please provide this information so that the reader can have more confidence in this leading hypothesis. More facts!
3. Lines 495-496. “For the deep aquifer, it reveals the existence of two recharge periods: pre-nuclear and post-nuclear tests in 1952.” However, you did not consider this issue in detail in your work. Then, please, explain how useful it will be to use technogenic isotopes (for example, cesium) that have appeared in the environment since the beginning of nuclear weapons tests and in technogenic accidents.
4. For a better understanding of the study area, in Figure 1, please provide a map of the distribution of heights (elevation map).
5. Line 44-46. “Understanding the processes and factors controlling the temporal evolution of the chemical composition is therefore essential to guide decision-makers towards a rational and sustainable management of these resources.” Why the temporal evolution? Why is this not a temporal dynamic? Evolution is a much more complex phenomenon.
6. Table 1. Age – in years? What is Actuel? Actual (Current)?

Author Response

Dear Reviewer,

Thank you very much for your review.

Your comments and suggestions were greatly important and made our paper better. We hope that you will consider our paper ready for publication at this time.

Please find in attached file our detailed response. All comments were taken into account and specific changes were made in the manuscript. All revisions are clearly highlighted in the manuscript using the "Track Changes" function in Microsoft Word.

Best regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have applied all suggested revisions. The manuscript is improved and I thereby recommended for publication in its current form.

Reviewer 2 Report

I have no more comments on the content of the manuscript.