Evidence for Groundwater Salinity Origin Based on Hydrogeochemical and Isotopic (²H, ¹⁸O, ³⁷Cl, ³H, ¹³C, ¹⁴C) Approaches: Sousse, Eastern Tunisia

Round 1

Reviewer 1 Report

It is of great academic significance that this manuscript used geochemical and isotope methods to identify the source of groundwater salinization in coastal areas. However, there are some issues that need to be addressed as below.

（1）Due to the limitation of hydro-geochemical and isotopic approaches for identifying the groundwater salinity, the manuscript is better to add some information of  hydrogeological investigation and give some discussion.

(2)Carefully check that if the  EC value of groundwater samples in Table 1  is consistent with the size of the circle in Figure 5. For example, the EC values of sample 10 and sample 16 are 1.87 and 1.58, while those shown in the figure are 5.0-7.7 and 7.5-10.0 respectively.

(3) The values of chemical parameters such as Cl concentration in Table 1 are better expressed in mg/L, and the groundwater age is better expressed in numerical value, which is also convenient for comparison with the EC value of the groundwater samples.

(4) Generally speaking for geochemical and isotope analysis, the ancient saline groundwater, modern seawater, rainwater and surface fresh water would show their different characteristics. If the cluster analysis and mapping are carried out, it will be found whether the groundwater in the study region is affected by seawater intrusion or by the ancient saline water. The evidence of groundwater salinity in the region would be more clear if adding some  value dots in the related figures.

Author Response

Dear Reviewer, 

Please find attached the reply to your comments.

Best regards

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript is presenting an impressive set of data as given in Table 1. Also a set of chlorine isotope data are insert, data which are hard to aquire.

Beside paragraphs which are well written, many of the phrases are incomprehensible.

Also the authors have all the data in order to plot  Piper diagrams for the given anionic and cationic composition. 

Electrical Conductivity is not included in the Methods.

Results and Discussions should be split.

The authors have to check carefully the text with an english native speaker. There are 58 comments insert directly on the manuscript which should be considered.

For the present version of the manuscript I suggest reject.

After considering carefully the points above, I suggest resubmission of the manuscript.

 

 

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer, 

Please find attached the reply to your comments.

Best regards

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,

the paper is interesting but it needs some work before publications.

First of all authors need to check the font character and size. 

They have to check if all the references are cited in the text and integrate in some cases.

Pay attention to the quality of the figures and, when it is possible, the authors colud use the same symbols for the same samples in all the figures when they are reported. In all the figures please use the same font for the legends and the axis.

Other comments and suggestions are reported in the attached file.

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer, 

Please find attached the reply to your comments.

Best regards

Author Response File: Author Response.docx

Reviewer 4 Report

Water

Manuscript Number: water- 2207085

 Title: Evidence for groundwater salinity origin based on hydrogeochemical and isotopic (²H, ¹⁸O, ³⁷Cl, ³H, ¹³C, ¹⁴C) approaches: Sousse, Eastern Tunisia

 

Article Type: Research Paper

 

Keywords: Geochemistry; salinization; coastal aquifers; isotopes; Tunisia

 

The authors provide a multidisciplinary approach, based on the use of geochemical, stable (²H, ¹³C, ¹⁸O and ³⁷Cl) and radioactive (³H and ¹⁴C) isotope methods, to identify the key processes responsible for the rise of groundwater salinization in the Mio-Pliocene aquifer system of Sousse (Tunisia, eastern coastline).

The manuscript water- 2207085 is well written and represents a valuable contribution to the literature and I believe this manuscript could be published but only after a major revision.

 

Comments (MP = manuscript page#/R = row#):

 

MP11/R28-34 - Introduction: for a more complete collection of available studies, please include the following works in the references:

 

Vespasiano G., Cianflone G., Romanazzi A., Apollaro C., Dominici R., Polemio M., De Rosa R. (2019). A multidisciplinary approach for sustainable management of a complex coastal plain: The case of Sibari Plain (Southern Italy). Marine and Petroleum Geology. https://doi.org/10.1016/j.marpetgeo.2019.06.031

 

Vespasiano, G., Cianflone, G., Marini, L., De Rosa, R., Polemio, M., Walraevens, K., Vaselli, O., Pizzino, L., Cinti, D., Capecchiacci, F., Barca, D., Dominici, R. & Apollaro, C. (2023). Hydrogeochemical and isotopic characterization of the Gioia Tauro coastal Plain (Calabria-southern Italy): A multidisciplinary approach for a focused management of vulnerable strategic systems. Science of The Total Environment, 160694

 

MP2/Figure 1: Please improve the legend with the units of measurement of the digital elevation model.

 

MP3/R100: What do you mean by “ETP”? Please, not only the acronym should be reported.

 

MP4/Figure 2: The geological map of Tunisia (1:500.000) is not very clear. The Geology is well shown in the figure on the right. I would suggest simplifying the upper left figure by reporting only structures and place names. In addition, I would suggest that the caption include a description of the acronyms of the geological units given in the legend. All unit and formation names in the legend should be well explained in the text.

 

MP5/Figure 3: Where is the trace of the section?

 

MP6/R165-166: I cannot locate the sampling points in Figure 1

 

MP6/Material and Methods: The section should be improved. It should be reported a deep description of multiparameter probes with relative precision, accuracy, and calibration technics.

 

MP7/Table1: What are “PL” and “NA”? Please, improve the caption by adding coordinates for each sample and reference standard for each isotope ratio.

 

MP8/Results and discussion: To which aquifer are sampled wells attributable?

 

MP11/Saturation Indices: How were the saturation indices calculated?

 

MP11/Figure 8: in the caption, Saturation index of what?

 

Hydrochemical characteristics: For a better comprehension of the geochemical groups and the processes in act characterizing the studied area, it could be useful to add Piper and TIS diagrams to get an immediate idea of the composition and salinity of each individual source.

 

Recharge estimation: To determine residence times and recharge areas why don't you use water isotopes? (³H, d¹⁸O and d²H)

see also:

 

Apollaro C., Vespasiano G., De Rosa R. & Marini L. (2015): 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 58 (2015) 62–74

 

Vespasiano G., Apollaro C., De Rosa R., Muto F., Larosa S., Fiebig J., Mulch A., Marini L. (2015): The Small Spring Method (SSM) for the definition of stable isotope - elevation relationships in Northern Calabria (Southern Italy). Applied Geochemistry. 63, 333-346.

 

Apollaro C., Vespasiano G., Muto F., De Rosa R., Barca D. & Marini L. (2016): Use of mean residence time of water, flowrate, and equilibrium temperature indicated by water geothermometers to rank geothermal resources. Application to the thermal water circuits of Northern Calabria. Journal of Volcanology and Geothermal Research.  328, 147–158

 

Conclusions:

From a general point of view, the conclusion should be improved with a final consideration of the importance of the research.

 

 

Author Response

Dear Reviewer, 

Please find attached the reply to your comments.

Best regards

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

It is not clear why you state that the salinity is related to input and dissolution form the geological formations surrounding the aquifer and not from input of marine water related to overexploatation.

Which are the arguments against overexploatation of aquifers? How it is possible to prove it with the used methodology?

English needs also a serious consideration over the entire text.

 

Author Response

Dear reviewer,

Please find attached the reply to your comments

Best regards

Author Response File: Author Response.docx