Hydrochemical Characteristics and Genetic Analysis of Groundwater in Zhanjiang City, Guangdong Province, South China
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. Some terminology usded in the manucript is incorrect, and the english needs to be polished. e.g., the expression of the water type is wrong; "volcanic rock pore fissure water", "loose rock pore water", "evaporation concentration" are mistranslations.
2. Were there any analysis of the rock samples from the aquifer? Or the mineral compositions were infered from SI calculation, if so, the mineral compositon of the aquifer is doubtful.
3. In fig.1, the flow line in the hydrogeologyical profile is inaccurate. In addition, some legends of the rocks are missing.
4. Which mineral does the "SI" reffer to in Fig.7?
5. The orgin of SO4 is contradictory.
6.No specific formula of CAL-I and CAL-II were given.
7. Aqueous SiO2 is a indicator you have to measure, it do not have to be exacted in the field.
8. The measurement precison of the chemical indices should be eluciated.
9. What does “**” mean in talbe 2？
10. “Spearman’s rank correlation” should be “Pearson Correlation”.
11. Maps should be used to illustrate the spatial variation of the major ions in the groundwater.
Comments on the Quality of English Language
Some terminology usded in the manucript is incorrect, and the english needs to be polished.
Author Response
Comments 1: Some terminology usded in the manucript is incorrect, and the english needs to be polished. e.g., the expression of the water type is wrong; "volcanic rock pore fissure water", "loose rock pore water", "evaporation concentration" are mistranslations.
Response 1: We are very grateful for your valuable comments. After careful review, we have made the following corrections: "Volcanic rock pore fissure water" has been revised to "fracture water in volcanic rocks". "Loose rock pore water" has been revised to "pore water in unconsolidated rocks". "Evaporation concentration" has been revised to "evaporative concentration".
Comments 2: Were there any analysis of the rock samples from the aquifer? Or the mineral compositions were infered from SI calculation, if so, the mineral compositon of the aquifer is doubtful.
Response 2: We did not conduct direct analysis of rock samples from the aquifer in this study. The mineral compositions were primarily inferred from the saturation index (SI) calculations and the geological background of the study area. While we acknowledge that this approach may introduce some uncertainties, we believe that the SI calculations, combined with the known geological information, provide a reasonable estimation of the potential minerals influencing the groundwater chemistry.
Comments 3: In fig.1, the flow line in the hydrogeologyical profile is inaccurate. In addition, some legends of the rocks are missing.
Response 3: We have carefully reviewed and revised the hydrogeological profile to ensure the accuracy of the flow lines. Additionally, we have added the missing legends for the rock types to provide a clearer representation of the geological setting.
Comments 4: Which mineral does the "SI" reffer to in Fig.7?
Response 4: In Figure 7, the "SI" refers to the saturation index of calcite. We have added a clear label and explanation in the figure caption to avoid any confusion. The SI of calcite is used to assess the dissolution and precipitation states of calcite in the groundwater, which is an important indicator of the water–rock interaction processes in the aquifer.
Comments 5: The orgin of SO4 is contradictory.
Response 5: After re-examining our data and analysis, we have revised the relevant sections to provide a more consistent and accurate interpretation. The primary sources of SO4 in the groundwater are the dissolution of evaporite minerals (such as gypsum) and, to a lesser extent, the weathering of sulfate minerals in the aquifer and human activities.
Comments 6: No specific formula of CAL-I and CAL-II were given.
Response 6: We appreciate the reviewer's comment on the missing formulas for CAI-â… and CAI-â…¡. We have now included the specific formulas for these indices in the manuscript.
Comments 7: Aqueous SiO2 is a indicator you have to measure, it do not have to be exacted in the field.
Response 7: We agree with the reviewer that aqueous SiO2 is an important indicator that should be measured. In our study, we did not measure SiO2 in the field due to logistical constraints. However, we have now added a discussion on the potential impact of this omission on our analysis and conclusions.
Comments 8: The measurement precison of the chemical indices should be eluciated.
Response 8: We have added a detailed section on the measurement precision of the chemical indices used in our study. The precision of each analytical method is as follows: Temperature: ±0.1°C, Total Dissolved Solids (TDS): ±5 mg/L, Dissolved Oxygen: ±0.1 mg/L, Chloride: ±0.5 mg/L, Sulfate: ±1.0 mg/L, Nitrate: ±0.5 mg/L, Potassium: ±0.1 mg/L, Sodium: ±0.5 mg/L, Calcium: ±0.5 mg/L, Magnesium: ±0.5 mg/L, Bicarbonate: ±5 mg/L. These precision values are based on the instrument specifications and the laboratory's quality control procedures.
Comments 9: What does “**” mean in talbe 2？
Response 9: In Table 2, the symbol " ** " indicates a statistically significant correlation at the 0.01 level (two-tailed). We have added a clear footnote to the table to explain the meaning of this symbol.
Comments 10: “Spearman’s rank correlation” should be “Pearson Correlation”.
Response 10: We thank the reviewer for pointing out this error. We have revised "Spearman’s rank correlation" to "Pearson Correlation" throughout the manuscript.
Comments 11: Maps should be used to illustrate the spatial variation of the major ions in the groundwater.
Response 11: We have added maps to illustrate the spatial variation of the major ions in the groundwater. These maps provide a visual representation of the distribution patterns of the ions across the study area.
We appreciate the reviewer's valuable feedback and look forward to the opportunity to further improve our work. We have carefully addressed each of the reviewer's comments and made the necessary revisions to improve the quality and accuracy of our manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I do have som serious concerns about your manuscript as reported in the attached file.
Comments for author File: Comments.pdf
Although I am not a mother tongue, I have to say that the language needs to be remarkedly improved.
Best regards.
Author Response
Comments 1: The geological and hydrogeological setting is rather scarce. More information is needed to better understand the study area. Mining activity is mentioned in the text but not in the geological setting. Low pH values and their relation to acid drainage are not discussed. Figure 1 should provide the location of Zhanjiang. The hydrogeological profile is not deeply discussed in the text. Springs were not sampled, and the terminology for aquifers is inconsistent.
Response 1: We are very grateful for your valuable comments. We have engaged a professional academic editor with expertise in hydrogeochemistry to thoroughly review and polish the manuscript. This process has included correcting grammatical errors, improving sentence structure, and enhancing the overall clarity and readability of the text. We have expanded the geological and hydrogeological description of the study area to provide a more comprehensive background. Additionally, we have clarified the terminology for the aquifers, consistently referring to them as shallow (0-30 m), middle (50-200 m), and deep (>200 m) aquifers. The hydrogeological profile has been further discussed in the text to explain the groundwater flow paths and interactions between different aquifers. We have also addressed the potential impact of acid drainage on groundwater pH and included relevant data and discussion.
Comments 2: The whole chemical dataset for the 35 samples has not been included. The data must be available at least in Supplementary Material. Table 1 reports incorrect statistics (min and max values are inverted). Some samples have pH values >8.3, but no carbonate data are available.
Response 2: We have included the complete chemical dataset for all 35 samples in the Supplementary Material to ensure transparency and accessibility of the data. We have also corrected the statistical values in Table 1, ensuring that the minimum and maximum values are accurately reported. Additionally, we have provided carbonate data for samples with pH values >8.3, explaining the potential sources of carbonate ions in these samples.
Comments 3: The Gibbs diagram and Gaillardet diagrams are typically used for surface waters. The authors did not explain why these diagrams were used, and some samples' ratios are not clearly accounted for (Figure 6).
Response 3: We have revised the manuscript to provide a detailed explanation of why these diagrams were chosen and how they are applicable to groundwater systems. We have clarified that while these diagrams are commonly used for surface waters, they can also provide valuable insights into groundwater geochemical processes, particularly in areas where water–rock interactions are significant. We have also added a detailed discussion of the ratios used in Figure 6, explaining the geochemical processes that influence these ratios in the groundwater samples.
Comments 4: There is confusion between the summatory of the main species in mg/L and the Fixed Residue.
Response 4: We have clarified the analytical methods used to measure the main species in mg/L and distinguished them from the Fixed Residue.
We appreciate the reviewer's valuable feedback and look forward to the opportunity to further improve our work. We have carefully addressed each of the reviewer's comments and made the necessary revisions to improve the quality and accuracy of our manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsBrief summary
The paper focuses on the chemical analysis outcomes of 35 groundwater samples collected in Zhangjiang City. For each sample, ten parameters have been analysed: pH, TDS, four major cations and four major anions. Next, a number of graphical and statistical techniques was used to define and show the hydrochemical characteristics (hydrochemical facies or water types) of the samples, as well as their degree of similarity or diversity. Several of the graphical techniques gave also clues regarding important genetic processes that have influenced the groundwater quality. For the graphical analysis, the 35 groundwater samples were divide into three subgroups: those taken from the shallow aquifer (17), the middle-deep aquifer (16) and the deep aquifer (2). The content of the paper corresponds very well to what from its title may be expected, although it fails to inform the reader on the horizontal variations in hydrochemical characteristics. The paper claims also that the results of the study provide insights for the development, utilization and management of the local groundwater resources, but it does not elaborate on this aspect.
General concept comments
· The paper follows a well-designed methodology and makes use of a variety of useful analysis techniques. For several of these techniques, the analysis data are subdivided according to three vertically distinct aquifer domains: shallow, medium deep and deep.
· Nevertheless, no attention is paid to showing and analysing hydrochemical variations in horizontal directions. Similarly, the horizontal distribution and variation of local environmental conditions (geology, hydrology, agriculture, mining activities, etc) across the study area are not shown (except for surface geology in Figure 1).
· As a result, the genetic analysis and interpretation are mainly based on the hydro-chemical data (in some cases speculative, subject to considerable uncertainty) and lack clear links of the chemistry of samples with nearby local environmental conditions. In other words: opportunities are missed to demonstrate the plausibility of the interpretations by linking mechanisms such as dissolution by rock weathering, concentration by evaporation, pollution by human activities, etc with local contextual features.
· Another major weakness is that although the paper mentions repeatedly that knowledge of groundwater chemistry is highly important for effective groundwater development and management, it fails to identify the risks of groundwater quality degradation (what and where?) and to suggest steps how to use the acquired knowledge for this purpose. Hence, no guidance is provided to groundwater managers on how to make use of the outcomes of this study.
· Suggestions to remove or reduce the weaknesses mentioned above: (1) adding a number of small maps, such as a land use map (urban residential zones, agricultural land, industrial zones, mining sites/areas, etc); a groundwater vulnerability map; a map showing zones where evaporation from a shallow water-table is likely to occur; maps showing relevant hydro-chemical patterns for each of the three aquifer domains; (2) linking the hydro-chemical patterns to the contextual maps; (3) adding a brief diagnostic section, outlining the perceived threats to groundwater quality, indicating where in the area each of the threats are most critical, and proposing measures for control and mitigation.
Specific comments
General
· The file ‘water-3392890-peer-review-v1-comments’ contains detailed comments written during reading and reading the paper. The main comments and suggestions are summarized below.
Weaknesses caused by lacking definitions of terms, inappropriate terminology or poor formulation of sentences
· The 35 groundwater samples are subdivided in two ways: (1) according to depth (shallow, medium deep and deep); and (2) according to type of interstices (pores, pore fissures, pore and fissures). The first subdivision is used in table 1 and the graphs, but in parts of the text the second grouping is followed. However, the reader is not informed on the spatial distribution of these different types of interstices, nor on how these categories are related to the depth categories. Furthermore, it is not clear whether the category ‘pore and fissure’ is identical with ‘pore fissures’. Do both refer to so-called ‘dual porosity’?
· Lacking definitions of some terms used causes also at several other locations in the paper that the text is difficult to understand. Example: ‘evaluation indicator’ in lines 107-109.
· At several locations, sentences or parts of these are not clearly formulated and therefore difficult to understand. Examples: lines 222-223; 344; 394-396
· At some other locations, sentences are incorrectly formulated, although most readers could guess what the authors intend to say. Examples: lines 273-274; 352-353.
· Apparently the term ‘runoff’ (commonly used in relation to surface water) is used in this paper to indicate ‘groundwater flow’ or ‘groundwater outflow’ (see e.g. lines 184 and 188). Correction is needed to avoid confusion.
· The uncommon term ‘depression funnel’ (lines 356 and 359) should be replaced by ‘depression cone’.
· Another uncommon term that may be difficult to understand is ‘burial depth’ (see e.g. lines 172 and 313-314) What is this, and can a more common term be used?
Figures and tables
· Figure 1: by using three colours (green, blue and red) the sampling points can simply be differentiated into shallow, medium-deep and deep. Furthermore, a scale stick should be added to give the reader an impression of the areal extent.
· Table 1: the labels ‘max’ and ‘min’ are incorrectly placed; they should be swapped.
· Table 1 and line 146 state that all TDS values are below 1000 mg/L, but this is contradicted by one data point in Figure 7.
· Figure 7: three graphs, but is it not shown for which mineral each of these are valid. Even after this information is added, it will be difficult for most readers to understand the lines 269-273.
· Figure 10: I did not find any text that refers to this figure.
Conclusions
· Given the generally low TDS of groundwater in the area, the macro-substances covered in this study are only of limited relevance for groundwater quality management, with exception of the NO3 content (which is closely related to human activities). The last few sentences of the paper should not omit mentioning that several other water quality parameters (related to the specific human activities in the area) should be measured and monitored in order to guide effective groundwater quality management.
15 January 2025
Comments for author File: Comments.pdf
Author Response
Comments 1: No attention is paid to showing and analysing hydrochemical variations in horizontal directions. Similarly, the horizontal distribution and variation of local environmental conditions (geology, hydrology, agriculture, mining activities, etc) across the study area are not shown (except for surface geology in Figure 1). The genetic analysis and interpretation are mainly based on the hydro-chemical data (in some cases speculative, subject to considerable uncertainty) and lack clear links of the chemistry of samples with nearby local environmental conditions.
Response 1: We appreciate the recognition of our methodology and the use of various analysis techniques. We have added maps to illustrate the horizontal variations in hydrochemical characteristics and local environmental conditions. We have revised the manuscript to link the hydro-chemical patterns to the contextual maps. This section, added to Section 3.4, connects the discussion of rock weathering, dissolution, evaporation, concentration, and human activity pollution to the current context.
Comments 2: Another major weakness is that although the paper mentions repeatedly that knowledge of groundwater chemistry is highly important for effective groundwater development and management, it fails to identify the risks of groundwater quality degradation (what and where?) and to suggest steps how to use the acquired knowledge for this purpose.
Response 2: We have added a brief diagnostic section in “4. conclusions” outlining the perceived threats to groundwater quality, indicating where in the area each of the threats are most critical, and proposing measures for control and mitigation. This section provides specific recommendations for groundwater managers on how to utilize the study outcomes for effective groundwater quality management.
Comments 3: The 35 groundwater samples are subdivided in two ways: (1) according to depth (shallow, medium deep and deep); and (2) according to type of interstices (pores, pore fissures, pore and fissures). The first subdivision is used in table 1 and the graphs, but in parts of the text the second grouping is followed. However, the reader is not informed on the spatial distribution of these different types of interstices, nor on how these categories are related to the depth categories. Furthermore, it is not clear whether the category ‘pore and fissure’ is identical with ‘pore fissures’. Do both refer to so-called ‘dual porosity’?
Response 3: We have clarified the terminology and ensured consistency throughout the manuscript. Both intermediate and deep waters include ‘pore water’ and ‘fissure water’. The terms ‘pore and fissure’ refers to the same concept of ‘pore water and fissure water’. The term ‘pore fissure water’ refers to ‘fissure water’.
Comments 4: Lacking definitions of some terms used causes also at several other locations in the paper that the text is difficult to understand. Example: ‘evaluation indicator’ in lines 107-109. At several locations, sentences or parts of these are not clearly formulated and therefore difficult to understand. Examples: lines 222-223; 344; 394-396.
Response 4: In a multi-indicator evaluation system, each ‘evaluation indicator’ often has different magnitudes and units due to their unique nature. An ‘evaluation indicator’ refers to a measurable parameter used to assess the characteristics of groundwater samples. In this study, these indicators include pH, TDS, major cations (Na+, Ca2+, Mg2+, K+), and major anions (Cl-, SO42-, HCO3-, NO3-). We have revised the sentences at the specified locations to improve clarity and readability.
Comments 5: At some other locations, sentences are incorrectly formulated, although most readers could guess what the authors intend to say. Examples: lines 273-274; 352-353. Apparently the term ‘runoff’ (commonly used in relation to surface water) is used in this paper to indicate ‘groundwater flow’ or ‘groundwater outflow’ (see e.g. lines 184 and 188). Correction is needed to avoid confusion.
Response 5: We have corrected the formulations of the sentences at the specified locations to ensure they are grammatically correct and convey the intended meaning. We have replaced the term "runoff" with "groundwater flow" or "groundwater outflow" where appropriate to avoid confusion.
Comments 6: The uncommon term ‘depression funnel’ (lines 356 and 359) should be replaced by ‘depression cone’. Another uncommon term that may be difficult to understand is ‘burial depth’ (see e.g. lines 172 and 313-314) What is this, and can a more common term be used?
Response 6: We have replaced "depression funnel" with "depression cone" to use the more common term. We have clarified that "burial depth" refers to the depth at which the groundwater is found，and have made the corresponding modification in the text.
Comments 7: by using three colours (green, blue and red) the sampling points can simply be differentiated into shallow, medium-deep and deep. Furthermore, a scale stick should be added to give the reader an impression of the areal extent.
Response 7: We have updated Figure 1 to use three colors to differentiate the sampling points by depth and added a scale stick to provide a better understanding of the areal extent.
Comments 8: the labels ‘max’ and ‘min’ are incorrectly placed; they should be swapped. Table 1 and line 146 state that all TDS values are below 1000 mg/L, but this is contradicted by one data point in Figure 7. Figure 7: three graphs, but it is not shown for which mineral each of these are valid. Even after this information is added, it will be difficult for most readers to understand the lines 269-273. Figure 10: I did not find any text that refers to this figure.
Response 8: We have corrected the labels in Table 1 to accurately reflect the maximum and minimum values. We have reviewed the data and corrected any inconsistencies in Table 1 and Figure 7 to ensure accuracy. We have added labels to Figure 7 to indicate which minerals each graph represents. We have also revised the text at lines 269-273 to provide a clearer explanation. We have added a reference to Figure 10 in the text to ensure it is properly discussed and understood.
Comments 9: Given the generally low TDS of groundwater in the area, the macro-substances covered in this study are only of limited relevance for groundwater quality management, with exception of the NO3 content (which is closely related to human activities). The last few sentences of the paper should not omit mentioning that several other water quality parameters (related to the specific human activities in the area) should be measured and monitored in order to guide effective groundwater quality management.
Response 9: We have revised the conclusions to emphasize the importance of monitoring additional water quality parameters related to specific human activities in the area. We have also highlighted the need for further research and monitoring to guide effective groundwater quality management.
We appreciate the reviewer's valuable feedback and look forward to the opportunity to further improve our work. We have carefully addressed each of the reviewer's comments and made the necessary revisions to improve the quality and accuracy of our manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsNo more comments
