Determination of Groundwater Recharge Mechanism Based on Environmental Isotopes in Chahannur Basin
Round 1
Reviewer 1 Report (Previous Reviewer 1)
line 12 - is this sentence necessary? if this is the cause of isotope research done, it should be better justified. We don't know here what is the relation of Tsakhanaur Basin to Chhannur Basin in the title.
line 42- dot in the middle of the sentence
line 43 - add space in theHebei
line 53-54 - this type of description should be based on literature, I believe some researches were done if You mentioned about it?
line 81, 83 - effectively de-tine the age ? strontium four isotopes - I believe this is the mistake, therefore You should check the whole text to eliminate small mistakes or others like spaces, commas, dots, etc.
line 86 - a basis for the study of area reduction control measures? - Sorry but I don't understand that
line 93 -"and the ecological environment is fragile" - how it was estimated?
line 89-98 - the entire description must be organized, the information provided should be specific, e.g. environment is fragile, anti-interference ability is poor, The large-scale development of irrigated agriculture - they do not provide any data on the pressure on groundwater and the environment
title, chapter 1 i 2 - Chhannur Basin or Chaghannur basin and Chahannao, Chahannaoer and Chahannauer Basin with Chahannauer Lake - I don't know what You are describing at the moment, and also Chahannur Lake in fig. 1 (is not clearly marked in fig., also the quality of the images still isn't very good)
line 121, 126 - these sentences have no continuation, after adding the new information it is worth to read all.
line 180 - Hloroflourocarbon...
line 225 - significantly correlates - how strong is the correlation (Pearson's)?
table 2 - different font types, there is 49 samples not 51
line 257 - age no has
line 262 - The lower reaches of the vadose zone have lower groundwater level, and the retention time is shorter, about 30-50a - another sentence in which I do not know what the author's message is
table 4 - small delta for 2H
fig.6 - no legend for the trend lines, the central part of the chart has to many information to read, maybe change points to smaller or create zoom for that part
chapter 3.2.2.1. - previously I mentioned the need for the Sr2 + diagram and strontium isotopes, it is a pity that the authors did not make it because the whole results would be clearer and easier to interpret (maybe there would be groups related to the circulation system, as for oxygen and hydrogen isotopes)
line 421 -does not circulate southward but flows southward - ??
line 483 - diving water - ??
line 493 - rather do not than did not
conclusions - for me, there is no conclusion summarizing the complexity of recharge, circulation and drainage of groundwater, which could suggest what actions should be taken to avoid water resources shrinking, maybe indicate areas where recharge is crucial for the entire circulation area
Author Response
Sincerely thank you for your valuable comments on this paper. Your comments are helpful to further improve the manuscript. Thank you very much! Here are my responses to your comments one by one:
line 12 - is this sentence necessary? if this is the cause of isotope research done, it should be better justified. We don't know here what is the relation of Tsakhanaur Basin to Chhannur Basin in the title.
In the manuscript, the first sentence of 12 lines was changed to "In recent years, the area of Chahannauer Lake has gradually decreased due to the decline of groundwater level".
line 42- dot in the middle of the sentence
A period has been changed to a comma in the manuscript.
line 43 - add space in theHebei
Spaces have been added in Hebei Province on line 43.
line 53-54 - this type of description should be based on literature, I believe some researches were done if You mentioned about it?
Documents have been added to the manuscript.”[1]Chen Moyu, Li Yancang, Lei Xiaohui, Li Naqing, Gao Qi, Wang Chenchen. Quantitative assessment of spatio-temporal evolution characteristics and driving factors of groundwater level in Chahannaoer basin [J]. Resources and Environment in Arid Areas, 2022,36 (11): 105-111. DOI: 10.13448/j.cnki.jalre.2022.282(in China).”
line 81, 83 - effectively de-tine the age ? strontium four isotopes - I believe this is the mistake, therefore You should check the whole text to eliminate small mistakes or others like spaces, commas, dots, etc.
The words in lines 81 and 83 have been revised as "In a word, the main purpose of this study is to trace the sources of tritium, freon, hydrogen and 82 oxygen and strontium isotopes. It mainly solves the following problems: using isotopes to determine the recharge and discharge characteristics and hydrochemical characteristics of groundwater in the Chaganur Basin". See lines 83-84 for details.
line 86 - a basis for the study of area reduction control measures? - Sorry but I don't understand that
The surface water in the Chahannauer Lake area is mainly supplied by rainfall and groundwater, and the discharge is mainly evaporation. Therefore, the study of groundwater recharge runoff discharge is helpful to study the reasons for the reduction of the lake area in the Chahannauer Basin. Therefore, the last sentence in the manuscript is changed to "provide a reference basis for the reasons for the reduction of the lake area in the Chahannauer Lake area by analyzing the source of groundwater and the supply and discharge conditions".
line 93 -"and the ecological environment is fragile" - how it was estimated?
According to literature [1] and relevant domestic reports, it is clear that the area of Chahannur Lake is decreasing year by year, groundwater level is decreasing, and soil desertification is serious. It is concluded from literature that the ecological environment is fragile.
line 89-98 - the entire description must be organized, the information provided should be specific, e.g. environment is fragile, anti-interference ability is poor, The large-scale development of irrigated agriculture - they do not provide any data on the pressure on groundwater and the environment
In the manuscript, the person in line 89-98 has been revised as "The total area of Chahannor basin is 6757km2, and the altitude is between 1270-1561m. The surrounding terrain is high, and the central terrain is low (Figure 1). There are many valleys. The natural geographical environment of the basin is simple, the lakes in this area are shrinking or completely dry, and the serious land desertification problem is prominent [1] 。 From 1990 to 2020, the annual average rainfall and annual average temperature of the Chanur basin are 364.1mm and 3.7 ℃ respectively. "
title, chapter 1 i 2 - Chhannur Basin or Chaghannur basin and Chahannao, Chahannaoer and Chahannauer Basin with Chahannauer Lake - I don't know what You are describing at the moment, and also Chahannur Lake in fig. 1 (is not clearly marked in fig., also the quality of the images still isn't very good)
The study area of this article is the whole Chahannauer basin, which includes many lake areas, the most important of which is the Chahannauer lake area. In recent years, the area of Chahannauer lake area has gradually decreased. Based on this situation, the groundwater recharge mechanism of the Chahannauer basin is studied by investigating the groundwater isotopes characteristics of the whole Chahannauer basin. At the same time, The research results can provide a certain reference basis for explaining the area reduction of Chahannaoer Lake area. The scale of Chahannauer Lake area in Figure 1 has been enlarged.line 121, 126 - these sentences have no continuation, after adding the new information it is worth to read all.
line 180 - Hloroflourocarbon...
In the manuscript, "Hloroflourocarbon" has been changed to "CFCs", see line 178 for details.
line 225 - significantly correlates - how strong is the correlation (Pearson's)?
According to the data, we can only qualitatively analyze the relationship between the tritium content in the groundwater and the groundwater burial depth, and cannot quantitatively explain the correlation, Therefore, the text in line 222-226 is revised as "The attribute isotope content in shadow groundwater in the study area ranges from<1.3 to 11.9TU, with little difference in spatial distribution. In general, the attribute content in groundwater is regular with the depth of groundwater level, and the attribute content in shadow groundwater is relatively high"
table 2 - different font types, there is 49 samples not 51
There are 51 groundwater sampling points in total, of which 49 are selected to detect tritium isotpes and 51 are selected to detect CFCs. Therefore, Table 2 contains 49 detection data and Table 3 contains 51 detection data.
line 257 - age no has
“The regional groundwater age no has clear rules it follows”has been deleted from the manuscript
line 262 - The lower reaches of the vadose zone have lower groundwater level, and the retention time is shorter, about 30-50a - another sentence in which I do not know what the author's message is
The 253-262 lines have been modified to“In the Territorial River Basin - Yannao Groundwater System, groundwater age ranges from ~31~52a. The groundwater age distribution presents a dumbbell shape, with both sides high and intermediate low. The middle reaches of the first line of the Tonglingdi River are high age groundwater areas, mostly older than 50 years, with a short retention time of about 30-50 years.”
table 4 - small delta for 2H
It has been revised in the manuscript, see Table 4 for details
fig.6 - no legend for the trend lines, the central part of the chart has to many information to read, maybe change points to smaller or create zoom for that part
Figure 6 has been modified according to expert opinions.
chapter 3.2.2.1. - previously I mentioned the need for the Sr2 + diagram and strontium isotopes, it is a pity that the authors did not make it because the whole results would be clearer and easier to interpret (maybe there would be groups related to the circulation system, as for oxygen and hydrogen isotopes)
line 421 -does not circulate southward but flows southward - ??
Relevant expressions have been modified, see line 420 for details.“The Sr2+content in the groundwater of Qiannaobuzi Village and Laozhangjia Village in Dengyoufang Town is 0.72mg/L and 0.93mg/L respectively, indicating that the groundwater in Changdi Village flows southward along Erhaoba Township, Shaojiying Village and Xiabenhong Village, and finally flows into Yannao River.”
line 483 - diving water - ??
Modified "diving water" to "phreatic watcr"
line 493 - rather do not than did not
conclusions - for me, there is no conclusion summarizing the complexity of recharge, circulation and drainage of groundwater, which could suggest what actions should be taken to avoid water resources shrinking, maybe indicate areas where recharge is crucial for the entire circulation area
The conclusion of this article has been re-condensed.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (Previous Reviewer 2)
Review of ‘Determination of groundwater recharge mechanism based on environmental isotopes in Chhannur Basin’ by Tian Xizhao, Gong Zhiqiang, Fu Lulu , You Di , Li Fan , Wang Yahui , Chen Zhi and Zhou Yahong
The objective of the study is to use tritium, freon, hydrogen and oxygen, strontium four isotopes traceability methods to determine the age, recharge, discharge and hydrochemical characteristics of groundwater in Chaghannur basin. This study determined groundwater characteristics in the Chhannur Basin, including the age and structure, identifying the groundwater and surface water supply source and supply mode, and created a groundwater flow model, which included recharge mechanisms, connectivity between aquifers and directions of flow.
I believe the paper makes a useful contribution to the understanding of groundwater in the study region and should be published. However, a major revision is recommended to address the many issues raised below.
Introduction: Since I had read the paper, there have been some improvements. In particular, the introduction now contains some useful context and setting up an intriguing problem. However, there are several problems with the grammar in the Introduction, with several sentences not actually being sentences. The paper then cites a few random papers on isotopes. Given that there are whole books written on isotope hydrology, it isn’t clear what the purpose these papers serve. To make it even more confusing, the whole introduction runs on on in the same paragraph, rather than separating concepts. Even the sentence containing the aims of the paper is not grammatically correct. The aim appears to be to use isotopes to define a groundwater model for the Chaghannur Basin and all that it means (recharge, discharge, age) from isotopes. This is an extremely broad objective for the paper. The results should ‘provide a basis for the study of area reduction control measures in Chaghannur watershed’, whatever that means.
Spelling of Chaghannur: The first sentence of the abstract reads: ‘In recent years, the area of the Tsakhanaur Basin has been decreasing’. Apart from not knowing how a basin is decreasing, the name of the basin appears to be different from the title ‘Chhannur Basin’, or third line of abstract: ‘Chahanzur Basin’ or sixth line of abstract: ‘Chahanzaur Basin’ or later ‘Chakhanzaur’ or ‘Chaghannur’ in first line of Introduction. And back to ‘Chhannur Basin’ in the Study area and then ‘Chahannaoer’. I’m not sure whether these refer to different things or the problems of anglicising a Chinese name.
Material and methods: After the very broad aims of the Introduction, I had hoped that something more specific aims/ hypothesis would develop in this section; but this is not the case. The second sentence: ‘The natural geographical environment of the basin is simple, the anti-interference ability is poor, also it is worth mentioning if recently annual precipitation sum is on the same level than earlier, and the ecological environment is fragile.’ This is a very complex sentence and I am unsure what anti-interference means in this situation, or what earlier refers to. ‘The groundwater system of the Chahannauer Basin (another spelling) is artificially divided into two parts, the groundwater system of the Chahannauer Lake area and other saline groundwater systems.’ I thought that finding the Lake on the map was difficult (and seems to have been altered in Fig. 2b) and realised that I was unsure of where exactly the Chahannauer Basin was and what ‘artificially divided’ meant. I wasn’t sure what ‘water- resisting property is excellent’ ; presumably a low hydraulic conductivity. There are elements of a conceptual groundwater flow model here, but not pulled together and certainly not to make objectives more specific, hypotheses to be tested or differentiating between potential alternative conceptual models. Without some specific objectives the isotopes section tends to read as though we knew nothing about the catchment and we used all the isotopes every where to see what emerged rather than using a scientific strategy.
Data collection: This lack of a strategy seems to be borne out by the first few sentences in Data collection. Apart from the first sentence not being a sentence, it suggests the broad aim to ‘understand age, discharge, hydrochemical characteristics’. There does not appear to be any details on depth of water sampling except that ‘All the samples used in this study were collected within the depth range of 0 to 50 m.’ This would appear to make interpretation difficult. I am unsure what the difference between the two maps is or why there is mention of groundwater contamination in caption.
Groundwater age: It is good to see what is meant to be ‘groundwater age’ in this paper defined at the top of p5, because groundwater does not have an age, but a residence time in the saturated zone. Groundwater mixes in the aquifer and any sample across a wide screen depth will have a mean residence time that represents a mix of different residence times. As the paper is not specific about screen depth, it is difficult to assess how much of an issue this is. One of the common mis-understandings is that ‘the half-life of radioactive isotopes, which is usually fixed, so the method is relatively reliable’. It actually needs to be shown to be reliable for the situation. An assumption is made here that ‘The vertical recharge condition of groundwater is well-conditioned … It is assumed that the transfer time of isotopes on different streamlines in the same section is equal. There is no hydrodynamic dispersion or molecular diffusion’. Apart from ‘condition being specified twice, it is not clear how recharge is well-conditioned. Transfer times for different depths of the same section are highly likely to be different (e.g. Vogel model) because of lateral movement. Of course, dispersion and diffusion exist everywhere but may in some situations not be important to interpret isotopes. Piston flow does not exist anywhere but may be a reasonable assumption in some places and the assumption should be tested, if possible. Equation (4) is derived by ‘substituting Formula (2) into Formula (1)’ actually (3) into (2) ‘Tt is the tritium age of groundwater (a).’ Not sure what this means.
Title of 2.3.2 spelt incorrectly. Some of 3.1.1 (tritium input concentrations) should be in methods. Table 1 seems a sensible basis for interpreting TU in groundwater. Where is Yannur (can’t find on map). The overall groundwater age is a mixture of old and new water.’ The word ‘fresh’ appears to refer to young water, whereas it normally means water of low salinity. This is transferred to the conclusions. I really have difficulty with Table 2 and wonder whether this should be a histogram or a plot of ‘apparent age’ against depth to water table. Bore numbers are used but there is no map showing this. I believe the ‘age’ here is wrong, as it will almost certainly be a mixture, especially for deeper water tables. Some term such as ‘apparent age’ would illustrate that this. Using four significant figures is inappropriate, given all the assumptions. Why the interpretation in Table 1 is ignored is unclear. It recognises (a) mixtures; (b) that Figure 4b is not monotonic and hence not a 1:1 relationship between TU and ‘age’; and (c) uncertainty in the interpretation of TU. For Table 3, unclear whether this should be plotted as a histogram but using uncertainty bar to illustrate different ‘apparent ages’. This is a good test of ‘piston flow’ and shows it may be a reasonable approximation as values are not too widespread. I’m not sure why tritium ‘age’ is not compared to CFC age on bores such as KBB46 and 47, again a test of piston flow assumption.
The stable isotope discussion appears to be good. Some of the results in 3.2. 1.2 could be in a table. In caption of Fig. 7 ,’oxygen’ is not required. For strontium isotopes, a range of 0.709222-0.711418 would suggest that a delta notation may be useful and avoids the stupidity of having up to six significant figures. Line 415, isotopes in superscript.
Conclusions: The first paragraph is correct in saying that a groundwater flow model has been developed, but ‘thorough’ would be an overstatement given many attributes have not been studied. The statement ‘provides a basis for future groundwater and surface water cycle studies and conversions in arid areas’ has not been justified anywhere in the paper. For conclusion (2), no need for ‘obvious’. Conclusion (3) ‘new’ and ‘old’ water not defined. Ages of 60 years not really ‘old’. Also, please note previous comment on ‘fresh’. Conclusion (4), not sure what ‘diving’ water is. Many of the conclusions are ‘results’ rather than conclusions, comparing isotopes rather than a physical interpretation of groundwater system. Conclusion (6) salt flow seems to be mentioned for first time.
Author Response
Dear Editor and Reviewers,
Sincerely thank you for your valuable comments on this paper. Your comments are helpful to further improve the manuscript. Thank you very much! Here are my responses to your comments one by one:
Introduction: Since I had read the paper, there have been some improvements. In particular, the introduction now contains some useful context and setting up an intriguing problem. However, there are several problems with the grammar in the Introduction, with several sentences not actually being sentences. The paper then cites a few random papers on isotopes. Given that there are whole books written on isotope hydrology, it isn’t clear what the purpose these papers serve. To make it even more confusing, the whole introduction runs on on in the same paragraph, rather than separating concepts. Even the sentence containing the aims of the paper is not grammatically correct. The aim appears to be to use isotopes to define a groundwater model for the Chaghannur Basin and all that it means (recharge, discharge, age) from isotopes. This is an extremely broad objective for the paper. The results should ‘provide a basis for the study of area reduction control measures in Chaghannur watershed’, whatever that means.
Thank you very much for your advice. According to your advice, I have refined the key issues, key objectives and tasks, reduced the excessive introduction of the research area, and refined the research results of different scholars on this research direction. At the same time, I put forward that the ultimate significance of the research is to provide reference basis for the reduction of the area of Chhannur Lake and the risk reduction of soil desertification.Please refer to the introduction for details.
Spelling of Chaghannur: The first sentence of the abstract reads: ‘In recent years, the area of the Tsakhanaur Basin has been decreasing’. Apart from not knowing how a basin is decreasing, the name of the basin appears to be different from the title ‘Chhannur Basin’, or third line of abstract: ‘Chahanzur Basin’ or sixth line of abstract: ‘Chahanzaur Basin’ or later ‘Chakhanzaur’ or ‘Chaghannur’ in first line of Introduction. And back to ‘Chhannur Basin’ in the Study area and then ‘Chahannaoer’. I’m not sure whether these refer to different things or the problems of anglicising a Chinese name.
Thank you very much for your reminding. "Chhannur Basin, Chahannaoer, Chahanzaur Basin" refers to the same meaning. In order to facilitate reading, I have changed the whole text to the unified name instead of "Chhannur Basin".The study area of this article is the whole Chhannur Basin, which includes many lake areas, the most important of which is the Chhannur lake area. In recent years, the area of Chhannur lake area has gradually decreased. Based on this situation, the groundwater recharge mechanism of the Chhannur basin is studied by investigating the groundwater isotopes characteristics of the whole Chhannur basin. At the same time, The research results can provide a certain reference basis for explaining the area reduction of Chhannur Basin Lake area.
Material and methods: After the very broad aims of the Introduction, I had hoped that something more specific aims/ hypothesis would develop in this section; but this is not the case. The second sentence: ‘The natural geographical environment of the basin is simple, the anti-interference ability is poor, also it is worth mentioning if recently annual precipitation sum is on the same level than earlier, and the ecological environment is fragile.’ This is a very complex sentence and I am unsure what anti-interference means in this situation, or what earlier refers to. ‘The groundwater system of the Chahannauer Basin (another spelling) is artificially divided into two parts, the groundwater system of the Chahannauer Lake area and other saline groundwater systems.’ I thought that finding the Lake on the map was difficult (and seems to have been altered in Fig. 2b) and realised that I was unsure of where exactly the Chahannauer Basin was and what ‘artificially divided’ meant. I wasn’t sure what ‘water- resisting property is excellent’ ; presumably a low hydraulic conductivity. There are elements of a conceptual groundwater flow model here, but not pulled together and certainly not to make objectives more specific, hypotheses to be tested or differentiating between potential alternative conceptual models. Without some specific objectives the isotopes section tends to read as though we knew nothing about the catchment and we used all the isotopes every where to see what emerged rather than using a scientific strategy.
Thank you very much for your reminding. It is true that the expression was not very accurate or clear before. I have revised the whole paragraph again, please refer to the section 2.1.
Data collection: This lack of a strategy seems to be borne out by the first few sentences in Data collection. Apart from the first sentence not being a sentence, it suggests the broad aim to ‘understand age, discharge, hydrochemical characteristics’. There does not appear to be any details on depth of water sampling except that ‘All the samples used in this study were collected within the depth range of 0 to 50 m.’ This would appear to make interpretation difficult. I am unsure what the difference between the two maps is or why there is mention of groundwater contamination in caption.
Thank you very much for your reminding. It is true that the expression was not very accurate or clear before. I have revised the whole paragraph again, please refer to the section 2.1.
Groundwater age: It is good to see what is meant to be ‘groundwater age’ in this paper defined at the top of p5, because groundwater does not have an age, but a residence time in the saturated zone. Groundwater mixes in the aquifer and any sample across a wide screen depth will have a mean residence time that represents a mix of different residence times. As the paper is not specific about screen depth, it is difficult to assess how much of an issue this is. One of the common mis-understandings is that ‘the half-life of radioactive isotopes, which is usually fixed, so the method is relatively reliable’. It actually needs to be shown to be reliable for the situation. An assumption is made here that ‘The vertical recharge condition of groundwater is well-conditioned … It is assumed that the transfer time of isotopes on different streamlines in the same section is equal. There is no hydrodynamic dispersion or molecular diffusion’. Apart from ‘condition being specified twice, it is not clear how recharge is well-conditioned. Transfer times for different depths of the same section are highly likely to be different (e.g. Vogel model) because of lateral movement. Of course, dispersion and diffusion exist everywhere but may in some situations not be important to interpret isotopes. Piston flow does not exist anywhere but may be a reasonable assumption in some places and the assumption should be tested, if possible. Equation (4) is derived by ‘substituting Formula (2) into Formula (1)’ actually (3) into (2) ‘Tt is the tritium age of groundwater (a).’ Not sure what this means.
Thanks for your suggestion. After re-thinking, the reference to mixed water has been removed and some incorrect expressions have been deleted.
Title of 2.3.2 spelt incorrectly. Some of 3.1.1 (tritium input concentrations) should be in methods. Table 1 seems a sensible basis for interpreting TU in groundwater. Where is Yannur (can’t find on map). The overall groundwater age is a mixture of old and new water.’ The word ‘fresh’ appears to refer to young water, whereas it normally means water of low salinity. This is transferred to the conclusions. I really have difficulty with Table 2 and wonder whether this should be a histogram or a plot of ‘apparent age’ against depth to water table. Bore numbers are used but there is no map showing this. I believe the ‘age’ here is wrong, as it will almost certainly be a mixture, especially for deeper water tables. Some term such as ‘apparent age’ would illustrate that this. Using four significant figures is inappropriate, given all the assumptions. Why the interpretation in Table 1 is ignored is unclear. It recognises (a) mixtures; (b) that Figure 4b is not monotonic and hence not a 1:1 relationship between TU and ‘age’; and (c) uncertainty in the interpretation of TU. For Table 3, unclear whether this should be plotted as a histogram but using uncertainty bar to illustrate different ‘apparent ages’. This is a good test of ‘piston flow’ and shows it may be a reasonable approximation as values are not too widespread. I’m not sure why tritium ‘age’ is not compared to CFC age on bores such as KBB46 and 47, again a test of piston flow assumption.
According to your question, I added the well depth information of the monitoring point wells. At the same time, because some expressions were not very accurate and clear before, the whole paragraph was completely revised. At the same time, the groundwater age distribution map is drawn to better understand the description.The results of tritium "age" and CFC age determination were compared and analyzed subsequently.See lines 271-273.
The stable isotope discussion appears to be good. Some of the results in 3.2. 1.2 could be in a table. In caption of Fig. 7 ,’oxygen’ is not required. For strontium isotopes, a range of 0.709222-0.711418 would suggest that a delta notation may be useful and avoids the stupidity of having up to six significant figures. Line 415, isotopes in superscript.
The word oxygen has been deleted. Some results in 3.2.1.2 are put in the table, see Table 5 for details. Modified the superscript and subscript of isotopes. The problem of 6 significant figures has been modified, see3.2.2.1. Spatial distribution characteristics of strontium isotopes
Conclusions: The first paragraph is correct in saying that a groundwater flow model has been developed, but ‘thorough’ would be an overstatement given many attributes have not been studied. The statement ‘provides a basis for future groundwater and surface water cycle studies and conversions in arid areas’ has not been justified anywhere in the paper. For conclusion (2), no need for ‘obvious’. Conclusion (3) ‘new’ and ‘old’ water not defined. Ages of 60 years not really ‘old’. Also, please note previous comment on ‘fresh’. Conclusion (4), not sure what ‘diving’ water is. Many of the conclusions are ‘results’ rather than conclusions, comparing isotopes rather than a physical interpretation of groundwater system. Conclusion (6) salt flow seems to be mentioned for first time.
Thank you very much for your opinion. I have revised and improved the conclusion according to your suggestion. Please refer to the final conclusion for details.
Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
This paper by Zhao et al. reports an interesting case study based on field investigation and multi-isotope measurements in Chhannur Basin area. In this paper, the water age, groundwater flowpath and resource sources were revealed by tracing method. Overall, it is well written. However, there's some mistakes in language, contents and format. Please consider the comments and suggestions below before submitting the revised version.
Line 15: "estimate" instead of "estimated".
The introduction should focus on the key research question, main goal and specific objectives of this paper. Now it reports too much on the characteristics of study area.
Line 40: delete the word "however".
Lines 42-43: Please check the grammar.
You should provide references for the risks brought by the shrinking and degradation of Chaghannur.
Lines 77-80: you cannot just list the name of authors and introduce what they did in a short sentence. It is suggested to summarize the main findings briefly.
Lines 79-80: where is the citation numbers for these references (may be 10-14?)
The details for the measurements of tracers should be mentioned. For example, information about laboratory, instrument, instrumental accuracy.
Table 4: δ2H instead of Δ2H.
Lines 294-299: You cannot identify the water vapor source and the monsoon only based on 1 or 2 isotopic data.
Line 300: What kind of water are these ranges for?
Fig. 6: the δ2H-δ18O relationships in global and local precipitation should be named as "global meteoric water line (GMWL) and "local meteoric water line (LMWL). In this figure, you should make it clear about the correspondence between water types and lines.
Why do the R2 values for δ2H-δ18O regressions differ so greatly between waters?
The conclusion should be more concise, only including the main findings. Avoid emphasizing the importance and repeating the results.
Author Response
Dear Editor and Reviewers,
Sincerely thank you for your valuable comments on this paper. Your comments are helpful to further improve the manuscript. Thank you very much! Here are my responses to your comments one by one:
Line 15: "estimate" instead of "estimated".
Revised in manuscript
The introduction should focus on the key research question, main goal and specific objectives of this paper. Now it reports too much on the characteristics of study area.
The key issues, tasks and objectives have been described in detail according to expert opinions, and the description of the research area has been reduced. See lines 38-45 for details.
Line 40: delete the word "however".
The key issues, tasks and objectives have been described in detail according to expert opinions, and the description of the research area has been reduced. See lines 38-45 for details.
Lines 42-43: Please check the grammar.
The key issues, tasks and objectives have been described in detail according to expert opinions, and the description of the research area has been reduced. See lines 38-45 for details.
You should provide references for the risks brought by the shrinking and degradation of Chaghannur.
“The research results can provide reference for the risk caused by the reduction and degradation of the lake area in Sahannur.”been added to the manuscript
Lines 77-80: you cannot just list the name of authors and introduce what they did in a short sentence. It is suggested to summarize the main findings briefly.
The research methods and findings of relevant experts have been detailed, as shown in lines 57-84.
Lines 79-80: where is the citation numbers for these references (may be 10-14?)
The research methods and findings of relevant experts have been detailed, as shown in lines 57-84.
The details for the measurements of tracers should be mentioned. For example, information about laboratory, instrument, instrumental accuracy.
Additional laboratory and equipment methods and accuracy for isotope tests are shown in lines 115-131
Table 4: δ2H instead of Δ2H.
It has been modified
Lines 294-299: You cannot identify the water vapor source and the monsoon only based on 1 or 2 isotopic data.
Thank you very much for your reminding. After careful consideration, no relevant conclusions can be drawn, so relevant descriptions have been removed from the manuscript.
Line 300: What kind of water are these ranges for?
phreatic watcr
Fig. 6: the δ2H-δ18O relationships in global and local precipitation should be named as "global meteoric water line (GMWL) and "local meteoric water line (LMWL). In this figure, you should make it clear about the correspondence between water types and lines.
The drawing name has been modified according to expert advice.
Why do the R2 values for δ2H-δ18O regressions differ so greatly between waters?
Thank you for your reminding. I have corresponded the data again and found some calculation errors. Now I have corrected and redrawn the map
The conclusion should be more concise, only including the main findings. Avoid emphasizing the importance and repeating the results.
Thank you very much for your opinion. I have revised and improved the conclusion according to your suggestion. Please refer to the final conclusion for details.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report (Previous Reviewer 2)
The manuscript has improved considerably over the previous versions.
Reviewer 3 Report (New Reviewer)
The authors have given good response to my comments. I would like to recommend this paper to be published.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
1. line 36 - Excessive drainage - can You add the information about objects and amount of water taken from surface/groundwater?
2. line 61 - Jianfei Yuan? remove or change the sentence
3. line 68 - Error! Reference source not found. - correct please
4. line 87 - add reference to this, also it is worth mentioning if recently annual precipitation sum is on the same level than earlier in 90s.
5. fig.1 - figure is too small, there are no details from the text e.g. main river's name, blurry descriptions of the cities, no selection of the Chhannur lake, no grid lines and grid bottom description is cut; if the gray color is the elevation it should be also legend for the range
6. fig.2 - also too small, there are more than 52 sampling points selected on the map, show Your sampling points
7. line 161 - correct misspell
8. fig.3 - no legend to the chart
9. line 208 - deeper depths - rather: greater depth, also it would be good to add to the Table 2 groundwater depth to have support for the results described in the lines 205-208, and also the numbers of the sample holes should be pointed at the documentation map (fig.1?), in the table 2 there are 51 samples only (and SYC75 is two times)
10. line 217-227 - in this description one cannot refer to any fig. because there are no described rivers on it (look at comment no.5)
11. fig.5 - Why do you need a map that extends beyond the research area? for all figures, you should narrow the presented area, remove the thick frame that overwhelms, use a higher resolution, indicate on the map elements that are part of the descriptive results (e.g. rivers), format the font in the legend and add a figure with tritium interpolation indicating in the text the interpolation method
12. fig.6 - too small, it would be good to use some colors
13. line 322 and 341 - groundwater systems, earlier in the text there is no mention of these systems, whether they are previously defined systems (add citation if so) or distinguished by the Authors based on the results of their own research (add introductory sentence), in this part of the text there are also references to river names that are not found on any map, city names are legible but it is not clear to which point on the map they refer (fig. 7). In Fig. 7, I propose to select only the names that appear in the text.
14. line 363 - again: no sampling point location!
15. different ranges of Sr2+ concentration in the line 364 and 368, which is correct?
16. line 370-371 - I don't understand this sentence
17. line 376 - 0.416-0.318mg/L, why in this order? and why then characterize values above 1 mg/ l?
18. line 363-388 and fig.8: fig.8b contradicts the 87Sr/86Sr range given on line 365 (min value 0.710942 vs 0.709222), Sr2+ also different. this piece of text needs to be sorted out: the number of samples representing the aquifer types, the range of the entire population, the ranges in each group.
19. line 392 - chapter 3.2.2.2 - the interpretation of circulation based on the strontium results is easier when the described groups are separated on the chart: X - Sr2 + concentrations; Y - 87Sr / 86Sr (standard interpretation), in fact, there is no interpretation of isotope results, but only the concentrations
20. line 425 - No. 1-12 villages???
21. fig.9 - what is cyclic characteristics? you can omit this figure and put the directions of water flow in the system on the earlier maps of strontium, deuterium and oxygen isotopes
22. line 440 - it is rather conceptual groundwater flow model
23. line 449 -conclusion 1 - from what I can see, the age of the water obtained by two methods differs significantly, e.g. sample SYC75 age by 3H is 17, by CFC is 33 years, it is worth explaining it if you can or indicate the differences.
24. line 454-460 - no noticeable difference but nevertheless you have distinguished different trend lines on the D / 18O chart so maybe it is worth mentioning it, and also that there are places where: line 353 - "and river water recharges the groundwater near these locations" as an example of local circulation identification
25. conclusions - the presented conclusions refer only to the local aspect, while reading such an article I would like to have indicated general and methodological conclusions that can be applied to another area. There is nothing in the conclusions (and abstract) about the results of the CFC method, the differences between the methods should be indicated and conclusions should also be provided for them.
26. Overall:
A. The graphics page needs significant improvement to be compatible with the text and allow the reader to visualize the basic characteristics of the area and the results.
B. Some results could be enriched graphically, e.g. conceptual system of water circulation as a schematic cross-section with marked values of 18O, Sr2 + etc.
e.g. fig.8 from https://doi.org/10.3390/w14060951
C. line 14 (abstract) "the Chhannur basin lake area has decreased..." there is no data support in the text for this, as long as there has been a decrease (how much? any data documentation?), if it was the main reason for the work, then one should refer to whether the obtained results are able to improve the current state and what are the proposals for this goal
Author Response
Dear expert, I have revised the corresponding text and pictures according to your suggestions. Thank you very much for your valuable suggestions, which greatly improved the quality and level of the article. I have also gained a lot, and my personal level has been significantly improved under your guidance. Thank you again.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Review ‘Estimating groundwater recharge mechanism based on environmental isotopes in Chhannur Basin in Hebei province China‘ by Gong Zhiqiang, Fu Lulu, Wang Yahui, Yin Hanling, Chen Zhi and Zhou Yahong .
In this paper, isotopes are used to study the age and recharge flow pattern of groundwater and surface water and explore the interaction and transformation process of groundwater and surface water. The conclusions are:
1. Groundwater levels are lower around Chhannur and Yannao, and the overall groundwater age tends to be a mixture of old and new water. Groundwater ages between 4-23a are widely distributed throughout the study area, mainly concentrated in the Chhannur Lake area in the study area, where the groundwater renewal rate is relatively fast.
2. The investigation shows no noticeable difference in the distribution range of hydrogen and oxygen isotopes between unconfined and confined water, and there is a close hydraulic relationship between the two. Both surface water and groundwater in the basin come from atmospheric precipitation in the region, and river (reservoir) water is strongly affected by evaporative fractionation, mainly because of evaporation accompanied by the precipitation process. Surface water itself is also directly affected by evaporation.
3. The groundwater circulation process reflected by hydrogen and oxygen isotopes and strontium isotopes is consistent. The fractured pore water and bedrock fissure water of clastic rock in the northern part of the study area, the groundwater in the first line of Changdi Village - Wanglide Village of ErhaoBu xiang does not flow south, but flows to Yannao, along the area of No. 2 Buxiang - Shaojiaying Village - Xiaojiahong Village. Quaternary pore water north of Liujiabu Village – Yugouliang Village - Sujiliang Village flows to Yannao in a southwest direction. The groundwater in the southeast of the study area does not run through the front line of Dayingpan Town Wetland Park - Mengguying Village, and is not discharged to Chhannur. The groundwater flow direction from upstream to the middle reaches of the Daqinggou River flows along the river.
The science in this paper appears to be solid, but the presentation of the results and interpretation needs to be improved. I would recommend that the paper is accepted, but major revisions are required.
1. Rationale: the dwindling lake is used to justify the study, but it is not clear how the study links to this rationale, or how the results may be used. Abstract Lines 14-15 is an example, leads to objective of the study (lines 15-16) without appropriate link. The final statement lines 28-30 tries to link back to rationale, but is so wishy-washy, it says nothing. The first paragraph of Introduction lines 34-39 also gives an outline of paper, but without explanation. The objective of the paper is restated in lines 76-78 without link to rationale; and does not explain what aspects of recharge will provide answers. The first paragraph of the study area implies that shrinking lake is due to groundwater development for irrigation, while lines 34-39 implies that it is excessive drainage. The discussion and conclusion provide no link back to the rationale or how this information may be used to improve management. The time scale over which the reduction of lake area has occurred, the time scale over which groundwater development has occurred or area of groundwater development. For a paer on recharge mechanisms, there does not appear to be a context given for climate and land use.
2. Clear objective: Groundwater age is often used in an ill-defined manner, which leads to untidiness in thinking. It is defined for this context on lines 116-117, but has been used several times before then. In particular, it is used in the abstract and introduction well before being defined. In conclusion 1, ‘groundwater age tends to be a mixture of old and new water. Groundwater ages between 4-23a are widely distributed.’ Age is age and can not be a mixture of water of any description. Also, as soon as water mixes, one can not attribute an age to that water. Solutes in that water may indicate that a component of water must have recharged within some time frame. The objective talks of a recharge flow patterns, but I don’t believe there is such as recharge flow; perhaps groundwater flow; but also do not know what a recharge flow pattern of surface water is; perhaps groundwater discharge to streams or recharge from streams. I am not sure what ‘transformation’ means in the context of different water bodies, presumably exchange or transfer. The title talks of estimating… mechanisms. Mechanisms can be identified or determined, but not estimated. Similarly for sources of groundwater recharge (line 17).
3. Groundwater ‘ages’: In lines 116-122, the separation between ‘dating’ techniques and history matching is not distinct, usually a combination of both is required. In equation (1), an integral is missing. This integral has been converted to a summation in Equation(2) but maximum of τ should be t. In Equation (3), g should be h. In Table1, 1-3TU refers to a mixture, which is inconsistent with piston flow and 10-20TU to nuclear explosion, which is pattern-matching. Table 2 gives no information on screen depth and hence of any mixing, nor gives location of bores. The precise nature of the age is inconsistent with using Table 1 for interpretation and is inconsistent with the values in Figure 4(b) (too low). For example, an age of 51 years would equate to the peak in Figure 4(b). A further ssumption must have been made, but this is not described. It is difficult to see that the ‘age’ can be given to the nearest year, as implied by Table 2 or the inferences about the ‘age’ in the following paragraphs. These paragraphs refer to ‘age’ being correlated to renewal rates, rather than renewal rates being inferred from the ‘age’. Line 161 ‘C’ missing from title. Line 174, ‘atomosphere’ should be ‘atmosphere’ line 238, ‘no’ should be ‘number’. Line 243, ‘reaches’ should be ‘depths’. Some of the bores in Tables 2 and 3 are the same, yet there appears to be no direct comparison between the numbers nor why the age distribution appears to be different. I’m not sure what the plume distribution of groundwater pollution in Figure 2 refers to. Is the spatial distribution as shown in Figure 5 actually meaningful by going from 30 to 55 years. Surely, what is required here is not age, but a recharge flux derived from the ages.
4. Stable isotopes of water: Usually 2H rather than D is the standard. Line 71 , what type of sample do these refer to. Deuterium surplus on line 310 probably needs to be defined. Line 323, these towns are not apparent on map in Figure 7. Same for some of the towns mentioned later. Groundwater flow directions are mentioned but there has not yet been any maps of groundwater flow lines. Deuterium and oxygen-18 values are highly correlated, in Figure 7, so perhaps deuterium surplus may be more sensitive, highlighting differences between the two isotopes. Defining the local meteoric water line based on one day’s rainfall appears to be extremely ambitious. Trying to match surface water run-off as measured at one time to the groundwater also seems to be extremely ambitious. Line 357, ‘dilution’ appears twice. I’m not sure why atmospheric precipitation is used rather than just precipitation.
5. Strontium isotopes: Line 365, too many significant figures. Same for lines 372 and 378. Line 396, 87 and 86 should be superscripts. Again, I am having trouble finding the mentioned villages on Figure 8. Spatial maps do not help the matching of groundwater values to surface water values. Groundwater circulation patterns would be helped by having hydrological transects both N-S and E-W and groundwater levels.
6. Conclusions: First sentence, not clear what structure of groundwater means. Line 449 first conclusion: not sure if I saw the evidence of lower groundwater levels. There did not appear to be any groundwater level map or decent topography map. Lines 456-457: where else apart from precipitation would surface run-off and groundwater come from? Lines 458-460:Evaporative fractionation may not mean much outside isotopic circles. What does this mean for hydrology in the basin. Lines 461-466 many of the names do not appear to be on map. I’m not sure what first line refers to or frontline.
Author Response
Dear expert, thank you for your valuable advice. Under your guidance, the quality of the article has been greatly improved, and my personal level has also been significantly improved. Thank you again for your guidance
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors appear to have addressed many of the critical comments and the manuscript has improved. However, I do believe more revisions are required before it can be published. These revisions are minor as the conclusions appear to be solid and supported by strong evidence.
1. A need to respond to all previous comments: I note that many of the original review comments have no response. I believe that is a need to respond to all original comments. I am happy for the authors to disagree with most of these, and respond as appropriate; but would like to think that they have thought about the issues in revising the manuscript. The following two comments relate to issues of particular mention.
2. ‘Groundwater age and uncertainty’: While I have no difficulty with the conclusions of the study, I do have difficulty with the presentation of the results and the discussion of groundwater age and uncertainty. Any scientific study needs to be conscious of the real uncertainty of results and present accordingly. There are four types of uncertainty in reporting 'ages':
a. Analysis uncertainty of a sample. This is the simplest, but should be reported.
b. Uncertainty in translating concentration or isotope value into a ‘pseudo-age’, using the half-life or matching the pattern. The uncertainty in the analysis, the initial concentration or that of the pattern can amplify into a larger uncertainty in age depending on the sensitivity of ‘age’ to isotope value/concentration. This uncertainty can be readily estimated but will vary greatly between samples .
c. Uncertainty associated with mixing processes: The sampled water and associated solutes will have undergone mixing processes. The ‘pseudo-age’ represents the weighted mean residence time of water/solutes since recharge, assuming other fractionation processes are unimportant. While piston flow or exponential mixing assumptions may be invoked, these do not occur in practice. Estimating the uncertainty associated with such an assumption is difficult in practice. Comparison of estimates using different tracers (e.g. different hydrofluorocarbons and tritium)can give a sense of this uncertainty.
d. Uncertainty due to the spatial heterogeneity of processes: This will occur at all scales but reporting of values for samples from different bores gives some sense at the appropriate scale.
Of these four uncertainties, only the last is considered in the paper e.g. by reporting 4-23 years. However, it is highly unlikely that the first three uncertainties will be less than one year. It is important that these other uncertainties are discussed and results are reported in a way that is appropriate. Perhaps, a more accurate reporting would be the mean residence time being less than thirty years rather than 4-23 years. This would not change the conclusion but would be more justifiable. p of the groundwater system
3. Mapping values of the stable isotopes of water: The isotope values of 2H are often highly correlated with 18O; and so the plotting or mapping of both often shows the same patterns, as shown in Figure 6. There is little value in mapping both of these. If there is an important difference, it will be difficult to detect. Another approach is to plot/map the residual of the linear correlation. If the residuals are small and random, this would indicate no significant difference in the processes. However, if the residual has a distinct spatial pattern and/or is significant, this may be attributable to a process. I had originally suggested using the isotope discriminant for this purpose, but as the authors suggested, this may not be physically significant.
Author Response
I am very happy that the experts can give such valuable suggestions, I very much agree with your suggestions, your expert advice so that the whole article has a great improvement. It has been revised completely according to the expert opinion, and has replied to the expert opinion one by one, please check with the expert. Amend the statement to read as follows:
The science in this paper appears to be solid, but the presentation of the results and interpretation needs to be improved. I would recommend that the paper is accepted, but major revisions are required.
Rule Number One:
（1）Rationale: the dwindling lake is used to justify the study, but it is not clear how the study links to this rationale, or how the results may be used.
Reply: lines 42 ~ 47 in the preface show that the area of the lake is decreasing gradually. It is suggested that the groundwater recharge mechanism around the lake should be deeply studied to provide the basis for the reason of the decrease of the lake area.
- Abstract Lines 14-15 is an example, leads to objective of the study (lines 15-16) without appropriate link. The final statement lines 28-30 tries to link back to rationale, but is so wishy-washy, it says nothing. The first paragraph of Introduction lines 34-39 also gives an outline of paper, but without explanation. The objective of the paper is restated in lines 76-78 without link to rationale; and does not explain what aspects of recharge will provide answers.
Reply: in the preface line 85 ~ 89, the paper describes the method to study the groundwater recharge mechanism in Chahannuoer basin.
- The first paragraph of the study area implies that shrinking lake is due to groundwater development for irrigation, while lines 34-39 implies that it is excessive drainage. The discussion and conclusion provide no link back to the rationale or how this information may be used to improve management.
Reply: the source of groundwater recharge in the Chahannur Basin has been re-verified and revised, as detailed in lines 42-47.
- The time scale over which the reduction of lake area has occurred, the time scale over which groundwater development has occurred or area of groundwater development. For a paer on recharge mechanisms, there does not appear to be a context given for climate and land use.
Reply: A description of land use and climate background has been added in lines 36-42 of the preface.
Rule Number Two:
- Clear objective: Groundwater age is often used in an ill-defined manner, which leads to untidiness in thinking. It is defined for this context on lines 116-117, but has been used several times before then. In particular, it is used in the abstract and introduction well before being defined.
Reply: 1) definitions of the time of residence of groundwater bodies in the ground have been included for the first time in the summary section (see line 54 for details) .
- In conclusion 1, ‘groundwater age tends to be a mixture of old and new water. Groundwater ages between 4-23a are widely distributed.’ Age is age and can not be a mixture of water of any description. Also, as soon as water mixes, one can not attribute an age to that water. Solutes in that water may indicate that a component of water must have recharged within some time frame.The objective talks of a recharge flow patterns, but I don’t believe there is such as recharge flow; perhaps groundwater flow;
Reply: I agree with the experts, the age of groundwater is not mixed, the age of groundwater can only indicate the groundwater is new water, Old Water and new old mixed water. So change the term“Groundwater age mixing” to“Groundwater age mixing”
（3）but also do not know what a recharge flow pattern of surface water is; perhaps groundwater discharge to streams or recharge from streams.
Reply: I very much agree with the expert. It is considered that the recharge mode of surface water is the mutual recharge between groundwater and surface water, as well as the recharge by atmospheric precipitation.
（4）I am not sure what ‘transformation’ means in the context of different water bodies, presumably exchange or transfer. The title talks of estimating… mechanisms. Mechanisms can be identified or determined, but not estimated. Similarly for sources of groundwater recharge (line 17).
Reply: I agree with you and have revised the title according to the expert opinion. The relevant contents of groundwater recharge sources have been revised, as detailed in lines 33-42.
Rule Number Three:
- Groundwater ‘ages’: In lines 116-122, the separation between ‘dating’ techniques and history matching is not distinct, usually a combination of both is required. In equation (1), an integral is missing. This integral has been converted to a summation in Equation(2) but maximum of τ should be t. In Equation (3), g should be h.
Reply: 1) the formula has been modified, see formula (1) , Formula (2) and formula (3) , lines 152,171.
- In Table1, 1-3TU refers to a mixture, which is inconsistent with piston flow and 10-20TU to nuclear explosion, which is pattern-matching. Table 2 gives no information on screen depth and hence of any mixing, nor gives location of bores. The precise nature of the age is inconsistent with using Table 1 for interpretation and is inconsistent with the values in Figure 4(b) (too low). For example, an age of 51 years would equate to the peak in Figure 4(b). A further ssumption must have been made, but this is not described. It is difficult to see that the ‘age’ can be given to the nearest year, as implied by Table 2 or the inferences about the ‘age’ in the following paragraphs. These paragraphs refer to ‘age’ being correlated to renewal rates, rather than renewal rates being inferred from the ‘age’. Line 161 ‘C’ missing from title.
Reply: the contents of Tables 1 and 2 have been revised and reformulated in accordance with expert advice. See lines 218 and 230 for details. A“C” has been added to the title.
（3）Line 174, ‘atomosphere’ should be ‘atmosphere’ line 238, ‘no’ should be ‘number’. Line 243, ‘reaches’ should be ‘depths’.
Reply: related spelling mistakes have been corrected.
（4） Some of the bores in Tables 2 and 3 are the same, yet there appears to be no direct comparison between the numbers nor why the age distribution appears to be different. I’m not sure what the plume distribution of groundwater pollution in Figure 2 refers to. Is the spatial distribution as shown in Figure 5 actually meaningful by going from 30 to 55 years. Surely, what is required here is not age, but a recharge flux derived from the ages.
Reply: the relevant content has been revised according to the expert's suggestion. See the full text for details. Also, figure 5 has been modified to qualitatively express a groundwater circulation path and recharge source in response to figure 5.
Rule Number Four:
（1）Stable isotopes of water: Usually 2H rather than D is the standard.
Reply: we simultaneously detect 2H and D, 2H effect is not ideal, so only analyzed D.
- Line 71 , what type of sample do these refer to. Deuterium surplus on line 310 probably needs to be defined. Line 323, these towns are not apparent on map in Figure 7.Same for some of the towns mentioned later.
Reply: 1) line 71 is a sample of groundwater distributed in the vicinity of the Chahannur Basin; 2) the definitions proposed by the experts have been revised; 3) the corresponding villages and towns have been marked in Figure 7, as detailed in line 380.
- Groundwater flow directions are mentioned but there has not yet been any maps of groundwater flow lines. Deuterium and oxygen-18 values are highly correlated, in Figure 7, so perhaps deuterium surplus may be more sensitive, highlighting differences between the two isotopes.
Reply: Based on the results of isotope analysis of groundwater samples, the approximate flow direction of groundwater is plotted, but the more accurate flow line can not be drawn due to less data. See Line 459, figure 9.
- Defining the local meteoric water line based on one day’s rainfall appears to be extremely ambitious. Trying to match surface water run-off as measured at one time to the groundwater also seems to be extremely ambitious. Line 357, ‘dilution’ appears twice. I’m not sure why atmospheric precipitation is used rather than just precipitation.
Reply: in accordance with your expert opinion has been revised to the multi-year average rainfall to determine the atmospheric water line; “Atmospheric rainfall” has been amended to“Rainfall.
Rule Number Five:
Strontium isotopes: Line 365, too many significant figures. Same for lines 372 and 378. Line 396, 87 and 86 should be superscripts. Again, I am having trouble finding the mentioned villages on Figure 8. Spatial maps do not help the matching of groundwater values to surface water values. Groundwater circulation patterns would be helped by having hydrological transects both N-S and E-W and groundwater levels.
Reply: I agree with your suggestion. I have rechecked the figures, revised the superscript and subscript, and added the relevant village locations as shown in Figures 1 to 9. The locations of surface water are also indicated, make groundwater and surface water match more obvious.
Rule Number Six:
（1）Conclusions: First sentence, not clear what structure of groundwater means. Line 449 first conclusion: not sure if I saw the evidence of lower groundwater levels. There did not appear to be any groundwater level map or decent topography map.
Reply: This study is mainly aimed at the shallow water of Chahannur basin, the water level is buried in 1 ~ 10m. Since 2000, the lake area has gradually decreased, and the surface water of the lake is mainly supplied by groundwater, therefore, the decrease of Lake area is a proof of the decline of groundwater level. Conclusion 1 has been reformulated and refined in accordance with your expert opinion to make it more meaningful and persuasive.
（2）Lines 456-457: where else apart from precipitation would surface run-off and groundwater come from? Lines 458-460:Evaporative fractionation may not mean much outside isotopic circles. What does this mean for hydrology in the basin. Lines 461-466 many of the names do not appear to be on map. I’m not sure what first line refers to or frontline.
Reply: 1) regional groundwater recharge only atmospheric rainfall, runoff and surface water and groundwater conversion. 2) I very much agree with you that evaporative fractionation does not make any sense for watershed hydrology, the article simply states that there is evaporative fractionation in the conversion between groundwater. 3) the village equivalents have been added to the map.
Author Response File: Author Response.docx
