The Contribution of Groundwater to the Salinization of Reservoir-Based Irrigation Systems

Round 1

Reviewer 1 Report

Authors did a significant work with extensive water quality analysis well supported by different plots to elucidate the processes water quality evolution in the irrigation system.   Scientifically, it is sound work, however before it can be published it must address following points:

1. Both abstract and introduction section is ill written and need to be  thoroughly revised
2. Several figure and tables need to be rewritten and redrawn for better presentation of your result
3. Conclusion need to be revised 
4. Please find attached reviewed file for more comments.

Comments for author File: Comments.pdf

Author Response

Response to Reviewers

Reviewer 1

1.1 General comment:

1. Both abstract and introduction section is ill written and need to be thoroughly revise.

Response: Comment is accepted. Accordingly, both abstract and introduction parts are revised. 

2. Several figure and tables need to be rewritten and redrawn for better presentation of your result.

Response: Comment is accepted. Figures and tables are redrawn and rewritten as per the comment.

3. Conclusion needs to be revised.

 Response: Comment is accepted and it is revised as per the comment. 

1.2 Editorial Comments given in the text/body of the manuscript.

Abstract

Page 1:

1. Line numbers 11-13: Rephrased as per the comment.
2. Line number 15: “water chemical” is replaced by “hydrochemical analyses”.
3. Line numbers 26 – 30. Rephrased as per the comment.
4. Introduction

1.1 General

1. Line number 42: “arises in every climatic condition” is replaced by “occurs in nearly all climatic regions”.
2. Line numbers 43 – 69. Rephrased by including the suggestion of the other reviewers too as per the comment.
3. Line numbers 102 – 104. Rephrased as per the comment.

1.2.2 Geology

1. Line numbers 127 - 128: References are included.

3.3.5 pH

1. Line numbers 384 – 392. Deleted as per the comment.
2. Line number 393. As per the comment Table 2 is inserted again.
3. Discussions

4.1. Sources of Salinity

1. Line numbers 437 – 451. As per the comment I checked it again and found it that 41.2 % of the total samples favoring incongruent dissolution of silicate minerals as it was stated.
2. Line number 455. Redrawn as per the comment.
3. Line number 466. Redrawn as per the comment.
4. Conclusion
5. Line numbers 508 – 515. Rephrased as per the suggestion.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper "The Contribution of Groundwater to the Salinization of Reservoir-Based Irrigation Systems" provides a case-study on the observed salinzation of the shallow groundwater system in the Tigray region of Ethiopia.  The paper applies preexisting methods and techniques to establish why the system is observing higher TDS and salinity values.  The findings that the groundwater is serving as the source of the ions in supported but not surprising.  More insight into the flow region would be helpful to establish this area as a groundwater discharge zone .  An underlying question is did the the building of the dam alter the flow region, thus creating the discharge zone or is this the natural discharge zone for the groundwater path? 

Additional comments and observations are provided in the annotated paper, which is attached.

Comments for author File: Comments.pdf

Author Response

Response to Reviewers

Reviewer 2

1.1 General comment:

An underlying question is did the building of the dam alter the flow region, thus creating the discharge zone or is this the natural discharge zone for the groundwater path? 

Response: One of the impacts of the construction of the dam in the hydrologic environment of the catchment is on its groundwater potential. The construction of the dam did not alter the flow region rather enhanced the groundwater potential of the area by increasing the groundwater recharge.  Yes it is the natural discharge zone for the groundwater flow.

1.2 Editorial Comments given in the text/body of the manuscript.

Abstract

Page 1:

1. Line numbers 19-21: Comment accepted and acted according to the suggestion.
2. Introduction

1.1 General

1. Line number 39: clarification is done by including the suggestion of the other reviewers too as per the comment.
2. Line number 58. “both” is replaced by “all” as per the comment.
3. Line numbers 79. “is’ is replaced by ‘are’ as per the comment.
4. Line numbers 90. “,’ is inserted as per the comment.

1.2 The Study Area

1.2.1 Location

1. Line numbers 115-119: “For clarity, the irrigation water comes from the reservoir, there is no groundwater that is extracted for irrigation purpose?”

Response: There is no groundwater extraction for irrigation purpose. The dam water is the only source for the irrigation.

2. Line number 120: The figure is redrawn and modified as per the comment.
3. Line numbers 123-124: The figure was removed.

1.2.2 Geology

1. Line numbers 127 - 128: References are included.
2. Line number 142. Yes it is.
3. Line numbers 160-161: Yes disseminated pyrite is reported to be found in the limestone.
4. Line number 168. “Somewhere else” is replaced by “Elsewhere”.
5. Methods

Line numbers 195 – 196: Commented noted.

Line number 209. Calcite and gypsum.

3. Results
4. Line number 249: It is done as per the comment.
5. Line number 255. “,’ is inserted as per the comment.
6. Line numbers 258. “,’ is inserted as per the comment.
7. Line numbers 393. The table is inserted again and the samples are located in the geological map of the area.
8. Line numbers 466. Figure 11 is done to show the actual facts with regard to the concentration of Ca²⁺ over SO₄^2- and HCO₃^-, respectively, in the analyzed water samples. Eq. 11 is presented here just as an example to show how silicate mineral, anorthite, give rise to dissolved constituents (Ca²⁺ and HCO₃^-) to the water when it is affected by hydrolysis process . It is not presented here to show how Figure 11 is supported in terms of chemical reaction.
9. Conclusion

This part is corrected by including the suggestions of the other reviewers too.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript has numerous drawbacks. Although the topic of the paper is interesting for the readers of the journal Agriculture, this manuscript does not meet the high standards of this journal, neither methodologically nor in terms of presentation, which is clear from remarks below.

1. Line 21 – the term „command area“. What does it mean?
2. Line 23 – SO to SO₄ in Ca-Na-HCO₃-SO type of water!
3. Lines 28 to 30 – the sentence is vague: “The increment of the availability of groundwater due to the existing dam supplemented by dissolution of carbonate minerals (calcite, dolomite, gypsum), silicate weathering and cation exchange are the main causes of salinity in the irrigated land.” It follows from it that “the increment of the availability of groundwater due to the existing dam”….is the cause of solubility…?
4. In the introduction, the authors often refer to numerous references, without clearly explaining the link between each individual reference and the topic of this article.
5. All figures are of very poor quality.
6. Chapter 1.2.2. “Geology” is written referring to only one literature reference.
7. The geological map is too simple, since one of the goals of the paper is to determine the geological causes of salinization. Authors had to show at least two transverse geological profiles (NW-SE and W-E) in order to show geological relationships by depth. Names of the rivers mentioned in the text are not visible on the geological map. Hydrogeology map and profiles are missing!
8. Chapter 2.1. is poorly written. It is not clear what geological research the authors conducted and for what purpose. The authors took the calculation of the water balance from the existing literature, so their contribution is not clear. It is also not clear how groundwater level measurements were carried out (manually or automatically using a logger), and it is not clear whether groundwater samples for chemical analysis were taken at high, medium or low water levels.
9. The main results are not clearly presented throughout the text. It is very difficult to systematically monitor and control these results, as they are not adequately displayed on maps and profiles.
10. Table 1 is taken from the literature cited in the text. The positions of the effective watersheds from Table 1 are not shown on the (hydrogeology) map. It is not clear what this data refers to. Part of the data (names of water balance parameters) is not even visible due to a poorly designed table. This is evident also in the Table 2.
11. Locations from which samples were taken for chemical analysis are not shown on the hydrogeological map.
12. The authors did not show the main water types using some of the standard graphical methods like Piper diagram, Stiff diagram etc.
13. Line 309: “category I of Ayers and Westcot [30] classification“. What does it mean exactly?
14. Lines 310-312 – literature references are missing!
15. In the discussion chapter, the authors tried to define the geochemical characteristics of groundwater and conclude on the main causes of salinization. They used very simple graphical representations of the ratios of individual ions, which is fine, but they neither tried to connect or confirm their results with the results of similar studies nor did they link the results to geological facies in the observed area. Conclusions about the dominance of calcium ions over sulphates and bicarbonates are inconclusive and are more a reflection of qualitative estimates than realistic quantitative indicators.

…….

Author Response

Response to Reviewers

Reviewer 3

Comment 1. Line 21 – the term „command area“. What does it mean?

Response: It used to refer to the current irrigated land

Comment 2. Line 23 – SO to SO₄ in Ca-Na-HCO₃-SO type of water!

Response: It is corrected as per the comment.

Comment 3. Lines 28 to 30 – the sentence is vague: “The increment of the availability of groundwater due to the existing dam supplemented by dissolution of carbonate minerals (calcite, dolomite, gypsum), silicate weathering and cation exchange are the main causes of salinity in the irrigated land.” It follows from it that “the increment of the availability of groundwater due to the existing dam”….is the cause of solubility…?

Response: No it is not. The construction of the dam enhanced the groundwater potential of the area. This increment in the availability of the groundwater in the catchment enhanced dissolution of carbonate minerals (calcite, dolomite, gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated area.  

Comment 4. In the introduction, the authors often refer to numerous references, without clearly explaining the link between each individual reference and the topic of this article.

Response: Corrected as per the comment.

Comment 5. All figures are of very poor quality.

Response: Improved as per the comment.

Comment 6. Chapter 1.2.2. “Geology” is written referring to only one literature reference.

Response: More references are included and improved as per the comment.

Comment 7A. The geological map is too simple, since one of the goals of the paper is to determine the geological causes of salinization. Authors had to show at least two transverse geological profiles (NW-SE and W-E) in order to show geological relationships by depth.

Response: The geological work was not done in detail to enable us to show at least two transverse geological profiles (NW-SE and W-E) as it was suggested. However, we feel that what is presented here is sufficient to support our findings. Mineralogical description, surface geological information’s and sub-surface information’s from the open pits and existing hand dug wells enable us to explain the geology of the area and relate it to groundwater chemistry.   

Comment 7B.  Names of the rivers mentioned in the text are not visible on the geological map.

Response: Improved as per the comment.

Comment 7C. Hydrogeology map and profiles are missing!

Response: This was not part of our investigation. Because of this, this comment is not addressed in the paper.

Comment 8A. The authors took the calculation of the water balance from the existing literature, so their contribution is not clear.

Response: Reference is given regarding this part of the paper. The reference by itself clearly show who conducted this research.

Comment 8B. It is also not clear how groundwater level measurements were carried out (manually or automatically using a logger), and it is not clear whether groundwater samples for chemical analysis were taken at high, medium or low water levels.

Response: Improved as per the comment.

Comment 9. The main results are not clearly presented throughout the text. It is very difficult to systematically monitor and control these results, as they are not adequately displayed on maps and profiles.

Response: Improved as per the comment.

Comment 10. Table 1 is taken from the literature cited in the text. The positions of the effective watersheds from Table 1 are not shown on the (hydrogeology) map. It is not clear what this data refers to. Part of the data (names of water balance parameters) is not even visible due to a poorly designed table. This is evident also in the Table 2.

Response: Improved as per the comment.

Comment 11. Locations from which samples were taken for chemical analysis are not shown on the hydrogeological map.

Response: Improved as per the comment.

Comment 12. The authors did not show the main water types using some of the standard graphical methods like Piper diagram, Stiff diagram etc.

Response: Improved as per the comment (Figure 7).

Comment 13. Line 309: “category I of Ayers and Westcot [30] classification“. What does it mean exactly?

Response: Corrected as per the comment.

Comment 14. Lines 310-312 – literature references are missing!

Response: Corrected as per the comment.

Comment 15. In the discussion chapter, the authors tried to define the geochemical characteristics of groundwater and conclude on the main causes of salinization. They used very simple graphical representations of the ratios of individual ions, which is fine, but they neither tried to connect or confirm their results with the results of similar studies nor did they link the results to geological facies in the observed area.

Response: Almost all the literature that we got and referred about the study area regarding to source of salinization it is hardly difficult to find a single literature that link the causes of salinization to the underlain geological material and the hydrochemical nature of the groundwater. However, most researchers recommend this to be done. This is the reason why did not show any comparison of our results with the results of similar studies in the investigated area. However, the result we obtained is linked with the geology of the area (please refer Lines 485 – 497 in the conclusion part).

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors have addressed my comments in the revised version, so I recommend for its acceptance.

Author Response

Response to Reviewers

Reviewer 2 Report

The paper is hampered by a lack of clarity/coherence.  Knowing how the waters are used and from where the samples were collected would help a reader to better understand the results and interpretation.  The authors state that “This research was done with the objective to identify the cause of salinity in the Gumselasa irrigation scheme by considering the underlain geological units and the hydrochemical nature of the groundwater of the area.”  To decipher the cause, the source of irrigation water needs to be identified.  While waters from the reservoir, the river, and groundwaters from two areas are sampled, the use of these waters (or what they represent) is not clear.  Without knowing, I would assume that the reservoir waters are the source of irrigation, but if that assumption is wrong, my interpretations would be wrong.  The authors need to clarify this aspect.  The groundwaters that are sampled, are they shallow or deep? The results of Nata et al. (2018) highlight the water balance and the potential pathways.  The Piper diagram could help to see the evolution of the waters, but the same symbol is used for all sample type.  The authors suggest the CA waters are rising groundwater, which seems possible, but these are in the area that is irrigated (as I infer). 

The conclusions are not well supported or fully derived from the results/discussion presented.  The first two paragraphs of the conclusion were drawn from data not presented in the paper – there are no new data in this papers the lead to these conclusions.  The insight can be provided in the discussion with the reference to Nata et al. (2018) but they should not be in the conclusions – it is misleading.  The conclusion made in the fourth paragraph (Lines 578-580) cannot be evaluated with the data as presented.  The conclusion is an interpretation of spatial data, but the data are not presented in a spatial way that allows for verification.   

Comments for author File: Comments.pdf

Author Response

Response to Reviewers

Reviewer 2 – Round 2

1.1 General comment:

The paper is hampered by a lack of clarity/coherence.  Knowing how the waters are used and from where the samples were collected would help a reader to better understand the results and interpretation.  The authors state that “This research was done with the objective to identify the cause of salinity in the Gumselasa irrigation scheme by considering the underlain geological units and the hydrochemical nature of the groundwater of the area.”  To decipher the cause, the source of irrigation water needs to be identified.  While waters from the reservoir, the river, and groundwaters from two areas are sampled, the use of these waters (or what they represent) is not clear.  Without knowing, I would assume that the reservoir waters are the source of irrigation, but if that assumption is wrong, my interpretations would be wrong.  The authors need to clarify this aspect.

 Response: Comment is accepted. The source of irrigation water is clearly mentioned in subtopic 1.2.1 paragraph 3, line 167. The use of the waters is also mentioned by introducing a new subtopic, subtopic 1.2.3 Water uses

1.2 General comment: The groundwater’s that are sampled, are they shallow or deep? 

Response: All the groundwater samples are shallow groundwater and were collected at low water levels manually. This is clearly indicated in the subtopic 2.1 Data collection paragraph 5.

1.3 General comment: The Piper diagram could help to see the evolution of the waters, but the same symbol is used for all sample type. 

Response: The diagram is corrected as per the comment and is shown in Figure 8.

1.4 General comment: The conclusions are not well supported or fully derived from the results/discussion presented. 

Response: Comment is accepted and modified accordingly.

1.5 General comment: The first two paragraphs of the conclusion were drawn from data not presented in the paper – there are no new data in this papers the lead to these conclusions.  The insight can be provided in the discussion with the reference to Nata et al. (2018) but they should not be in the conclusions – it is misleading. 

Response: Comment is accepted. The first two paragraphs were removed from the conclusion parts.

 1.6 General comment: The conclusion made in the fourth paragraph (Lines 578-580) cannot be evaluated with the data as presented.  The conclusion is an interpretation of spatial data, but the data are not presented in a spatial way that allows for verification.

Response: Comment is accepted. The data are labeled as per the comment in the geology map (Figure 4).

1.2 Editorial Comments given in the text/body of the manuscript.

1. Introduction

1.2.1 Location

Page 4:

Comment: Lines numbers 167-171: Comment accepted and the source of irrigation water is mentioned.

Comment:  Line 175: Figure 1. It is modified and corrected as per the comment.

1.2.2 Geology

3. Figure 4. Comment is accepted and the samples are labeled. The samples are representatives of the water resources of the study area. River water and dam water represents the surface water resource of the catchment. Groundwater is the other water resource of the area. However, this groundwater has two different chemical natures: fresh and alkaline and brackish and alkaline. These two different hydrochemical natures of the groundwater are represented by samples from the upstream and downstream sides of the dam based on their occurrences.
4. Results

3.1 Water balance

Comment: Lines number 327 - 340: What is the importance of the command waters?  Having read the paper I am not sure what they are used for or their importance.

Response: The groundwater in the command area can be used for different purposes and has a great importance. However, this is not the objective of this study. This part of the paper is all about estimation of groundwater recharge: to reveal the available groundwater potential in this part of the catchment. Because of this, this comment is not addressed in the paper. Any application of water to the command area should take into consideration the availability of this amount of groundwater in the command area and its quality nature.

3.2 Hydrochemical Analyses

Comment on the Piper diagram: Given the different types of waters, the Piper diagram would be more effective if the types of waters were delineated/differentiated.

Response: The diagram is corrected as per the comment and is shown in Figure 8.

3.3 Irrigation Water Quality

3.3.1. Salinity of Water

Comment: Lines 387 -390: comment accepted and correction is made accordingly.

5. Conclusion

Comment: Lines number 554 – 564. Comment accepted and the two paragraphs are removed from this part.

Comment: Lines number 578 – 580. This conclusion cannot be evaluated with the data as p[resented.  There is no spatial distribution of the data presented nor is there a layout of the sampling locations (labeled).

Response: Comment is accepted and the data are labeled (Figure 4).

Author Response File: Author Response.docx

Reviewer 3 Report

The authors did not significantly correct the remarks I made in the previous version of the article, neither methodological nor presentation. Images are not corrected according to the instructions. The authors made major changes only in the introductory part of the article, but the rest of the paper has not been changed, which is not enough to significantly improve the quality of the article.

Author Response

Response to Reviewers

Reviewer 3 - Round 2

Comment 1. Line 21 – the term „command area“. What does it mean?

Response: It used to refer to the current irrigated land

Comment 2. Line 23 – SO to SO₄ in Ca-Na-HCO₃-SO type of water!

Response: It is corrected as per the comment.

Comment 3. Lines 28 to 30 – the sentence is vague: “The increment of the availability of groundwater due to the existing dam supplemented by dissolution of carbonate minerals (calcite, dolomite, gypsum), silicate weathering and cation exchange are the main causes of salinity in the irrigated land.” It follows from it that “the increment of the availability of groundwater due to the existing dam”….is the cause of solubility…?

Response: No it is not. The construction of the dam enhanced the groundwater potential of the area. This increment in the availability of the groundwater in the catchment enhanced dissolution of carbonate minerals (calcite, dolomite, gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated area.  

Comment 4. In the introduction, the authors often refer to numerous references, without clearly explaining the link between each individual reference and the topic of this article.

Response: Corrected as per the comment.

Comment 5. All figures are of very poor quality.

Response: Improved as per the comment.

Comment 6. Chapter 1.2.2. “Geology” is written referring to only one literature reference.

Response: More references are included and improved as per the comment.

Comment 7A. The geological map is too simple, since one of the goals of the paper is to determine the geological causes of salinization. Authors had to show at least two transverse geological profiles (NW-SE and W-E) in order to show geological relationships by depth.

Response: The geological work was not done in detail to enable us to show at least two transverse geological profiles (NW-SE and W-E) as it was suggested. However, we feel that what is presented here is sufficient to support our findings. Mineralogical description, surface geological information’s and sub-surface information’s from the open pits and existing hand dug wells enable us to explain the geology of the area and relate it to groundwater chemistry.   

Comment 7B.  Names of the rivers mentioned in the text are not visible on the geological map.

Response: Improved as per the comment.

Comment 7C. Hydrogeology map and profiles are missing!

Response: This was not part of our investigation. Because of this, this comment is not addressed in the paper.

Comment 8A. The authors took the calculation of the water balance from the existing literature, so their contribution is not clear.

Response: Reference is given regarding this part of the paper. The reference by itself clearly show who conducted this research.

Comment 8B. It is also not clear how groundwater level measurements were carried out (manually or automatically using a logger), and it is not clear whether groundwater samples for chemical analysis were taken at high, medium or low water levels.

Response: Corrected as per the comment.

Comment 9. The main results are not clearly presented throughout the text. It is very difficult to systematically monitor and control these results, as they are not adequately displayed on maps and profiles.

Response: Corrected as per the comment.

Comment 10. Table 1 is taken from the literature cited in the text. The positions of the effective watersheds from Table 1 are not shown on the (hydrogeology) map. It is not clear what this data refers to. Part of the data (names of water balance parameters) is not even visible due to a poorly designed table. This is evident also in the Table 2.

Response: Corrected as as per the comment.

Comment 11. Locations from which samples were taken for chemical analysis are not shown on the hydrogeological map.

Response: Shown in the geological map.

Comment 12. The authors did not show the main water types using some of the standard graphical methods like Piper diagram, Stiff diagram etc.

Response: Corrected as per the comment (Figure 8).

Comment 13. Line 309: “category I of Ayers and Westcot [30] classification“. What does it mean exactly?

Response: Corrected as per the comment.

Comment 14. Lines 310-312 – literature references are missing!

Response: Corrected as per the comment.

Comment 15. In the discussion chapter, the authors tried to define the geochemical characteristics of groundwater and conclude on the main causes of salinization. They used very simple graphical representations of the ratios of individual ions, which is fine, but they neither tried to connect or confirm their results with the results of similar studies nor did they link the results to geological facies in the observed area.

Response: Almost all the literature that we got and referred about the study area regarding to source of salinization it is hardly difficult to find a single literature that link the causes of salinization to the underlain geological material and the hydrochemical nature of the groundwater. However, most researchers recommend this to be done. This is the reason why did not show any comparison of our results with the results of similar studies in the investigated area. However, the result we obtained is linked with the geology of the area (please refer Lines 485 – 497 in the conclusion part).

Author Response File: Author Response.docx