Hydrochemical Characterisation of High-Fluoride Groundwater and Development of a Conceptual Groundwater Flow Model Using a Combined Hydrogeological and Hydrochemical Approach on an Active Volcano: Mount Meru, Northern Tanzania
, Jill Van Reybrouck 1, Ceven Shemsanga 3, Mary Kisaka 3,4, Ines Tomašek 4,5,6,7, Karen Fontijn 8, Matthieu Kervyn 4 and Kristine Walraevens 1Round 1
Reviewer 1 Report
This paper uses a statistical method to present the hydrochemical characterization of high-fluoride groundwater on an active volcano, Mount Meru, Northern Tanzania. It did not represent siginificant findings on assessment. I suggest that the authors analyze the impact of high-fluoride groundwater on an active volcano on the studied area's natural and usable water resources in detail and present it in a section.
Author Response
Response to Reviewer 1 Comments
Point 1: This paper uses a statistical method to present the hydrochemical characterization of high-fluoride groundwater on an active volcano, Mount Meru, Northern Tanzania. It did not represent significant findings on assessment. I suggest that the authors analyze the impact of high-fluoride groundwater on an active volcano on the studied area's natural and usable water resources in detail and present it in a section.
Response 1: The suggestion has been accepted and implemented. The discussion of the usable groundwater resources has been added: Line 738 to 747. “Table 9 summarises the overview of the usable groundwater sources from the sampled inventoried groundwater points in reference to their F⁻ concentrations. From the 122 sampled inventoried groundwater points, 93% (n=114) of the points provide usable groundwater sources for different purposes; drinking, other domestic use, irrigation and livestock. From the 114 usable groundwater points, 59% (n=67) of the points are used to provide drinking water to the local community despite of their high F⁻ values which exceed both WHO and Tanzanian limits, as most local people do not have any alternative for drinking water. Only 7% (n=8) of the usable points are not used for drinking purpose due to their high F⁻ values which exceed the limits of the two standards.” Also, a table summarising the usable resources has been added: Line 753 to 755.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article presents a hydrogeochemical study and uses mineralization (namely F-) to explain a complex conceptual model, with different flow lines, residence times, and passing through different geological formations of variable weatherability. So, I think the title does not reflect the whole article content and should be revised.
Line 272 to 292: I suggest that the information given in section 2.3 “Sampling” is given in the format of a table
Line 314: “and NH4+” should be removed since it is not an anion
Line 370 on: Table 1 is not easy to read. Maybe a decrease of letter size (similar to Table 2) or change to microg/L for Mn2+, NH4+ and NO2- could help saving some space
Line 733: what is said is very clear and interesting. Do you have an explanation for EC higher values of S22 compared to the other two springs? I was expecting lower EC values for S22.
Line 744: “the springs show lower concentrations of the different hydrogeochemical parameters followed by” should be “the higher springs show lower concentrations of the different hydrogeochemical parameters compared to lower springs, followed by”
Section 3 headers are not clear and I suggest the authors to revise them. When reading the sections titles it seems that the issue was already written before, e.g. “Major and minor ions” are also “physicochemical parameters”. Here are my suggestions:
Line 348: Delete “3.1. Groundwater properties”
Line 375: replace “3.1.1. Physicochemical parameters” by “3.1. Physicochemical characteristics and conceptual flow model”
Line 473: replace “3.1.2. Major and minor ions” by “3.2. Major and minor ions origin” (please be aware of subsections numbering accordingly to the changes)
Line 694: replace “3.1.3 Temporal variability of fluoride concentrations” by “3.3 Temporal variability of fluoride concentrations and precipitation/recharge values”
Author Response
Response to Reviewer 2 Comments
Point 1: The article presents a hydrogeochemical study and uses mineralization (namely F-) to explain a complex conceptual model, with different flow lines, residence times, and passing through different geological formations of variable weatherability. So, I think the title does not reflect the whole article content and should be revised.
Response 1: The title has been revised to “Hydrochemical characterisation of high-fluoride groundwater and development of a conceptual groundwater flow model using a combined hydrogeological and hydrochemical approach on an active volcano: Mount Meru, Northern Tanzania”: Line 2 to 5.
Point 2: Line 272 to 292: I suggest that the information given in section 2.3 “Sampling” is given in the format of a table
Response 2: The suggestion has been accepted and implemented; the information has been summarised: Line 289 to 332, and the details have been given in the format of a table: Line 323 to 324.
Point 3: Line 314: “and NH4+” should be removed since it is not an anion
Response 3: “and NH4+” it has been removed, and corrections have been made: Line 345 to 348.
Point 4: Line 370 on: Table 1 is not easy to read. Maybe a decrease of letter size (similar to Table 2) or change to microg/L for Mn2+, NH4+ and NO2- could help saving some space
Response 4: The letter size in Table 1 (now is Table 2) has been decreased (similar to other tables), and the Mn2+, NH4+ and NO2- have been changed to µg/l: Line 405 to 411.
Point 5: Line 733: what is said is very clear and interesting. Do you have an explanation for EC higher values of S22 compared to the other two springs? I was expecting lower EC values for S22.
Response 5: Explanations have been given: Line 800 to 809. “But, the high EC values of S22 compared to S3 and S5 are attributed to the influence of the mantling ash deposits. The S22 is located in the pyroclastics with subordinate nephelinitic and phonolitic lavas covered with mantling ash. Here the area is surrounded by mantling ash deposits. Ash deposits are very loose and fine-grained, these characteristics make them highly weatherable and readily dissolve in water. The S3 and S5 are located in the Lemurge DAD, and their recharge area is located in pyroclastics with subordinate nephelinitic and phonolitic lavas. There are no ash deposits in these areas. Therefore, the lower EC values of S3 and S5 compared to S22 are attributed to slow weathering of lavas. The lavas deposits are more compact and less weatherable as compared to the DADs and mantling ash deposits”
Point 6: Line 744: “the springs show lower concentrations of the different hydrogeochemical parameters followed by” should be “the higher springs show lower concentrations of the different hydrogeochemical parameters compared to lower springs, followed by”
Response 6: The suggestion has been accepted and changes have been made as proposed: Line 820 to 821.
Point 7: Section 3 headers are not clear and I suggest the authors to revise them. When reading the sections titles it seems that the issue was already written before, e.g. “Major and minor ions” are also “physicochemical parameters”. Here are my suggestions:
Point 7a: Line 348: Delete “3.1. Groundwater properties”
Response 7a: The suggestion has been accepted, and the title “Groundwater properties” has been deleted: Line 381.
Point 7b: Line 375: replace “3.1.1. Physicochemical parameters” by “3.1. Physicochemical characteristics and conceptual flow model”
Response 7b: The suggestion has been accepted and implemented as proposed: Line 413.
Point 7c: Line 473: replace “3.1.2. Major and minor ions” by “3.2. Major and minor ions origin” (please be aware of subsections numbering accordingly to the changes)
Response 7c: The suggestion has been accepted and implemented as proposed: Line 515. Also, the subsections have been numbered accordingly to the changes: 3.2.1 - Line 541; 3.2.2 - Line 632; 3.2.3 - Line 653; 3.2.4 - Line 683.
Point 7d: Line 694: replace “3.1.3 Temporal variability of fluoride concentrations” by “3.3 Temporal variability of fluoride concentrations and precipitation/recharge values”
Response 7d: The suggestion has been accepted and implemented as proposed: Line 760.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
No additional comment.
