Evaluation of Seasonal Groundwater Quality Changes Associated with Groundwater Pumping and Level Fluctuations in an Agricultural Area, Korea

Round 1

Reviewer 1 Report

The article entitled "Evaluation of seasonal groundwater quality changes associated with groundwater pumping and level fluctuations in an agricultural area, Korea" presents the waterlevel  and water quality fluctuation in an agricultural area. Even though the paper doesnt include any innovative parts, it is interesting due to the high quality, density and frequency of the data presented.

Comments for author File: Comments.pdf

Author Response

The article entitled "Evaluation of seasonal groundwater quality changes associated with groundwater pumping and level fluctuations in an agricultural area, Korea" presents the waterlevel and water quality fluctuation in an agricultural area. Even though the paper doesn’t include any innovative parts, it is interesting due to the high quality, density and frequency of the data presented.

The introduction needs improvement. The authors state that ". However, few studies have considered both groundwater 69 level fluctuations and quality at the same time" , I think there are plenty of publications and the authors should read and mention some of them in the introduction and use some of them to compare their result with the result of the published material. Please read the work of “ Troudi, N. Hamzaoui,F., Zammouri, M. Tzoraki, O. 2020, Assessment of groundwater quality for drinking purpose with special emphasis on salinity and nitrate contamination in the shallow aquifer of Guenniche (Northern Tunisia). Environmental Monitoring and Assessment Journal. 192(10)”

Re: Thank you for your comments and suggestions. Of course, the papers to deal with the groundwater quality changes are so many. The papers you recommended have been carefully read, and it was added to the references (line 68). Consequently, the reference numbers were modified from line 567 to 589. The sentence was modified as the followings to avoid confusion from line 68 to line 70.

“Although many papers have been published on the change in groundwater quality, there are not many that have been dealt with on the change in groundwater quality based on level fluctuations caused by groundwater pumping.”

4.2 pump permit. According your results is it a good idea to keep the pump permit high or is it better to keep the gw quality to decrease the pump permit threshold? “There are a total of 25 wells for agricultural use in the area and the pump permit of those wells is 1,918 m³/day , which is 700,070 m³/year?”

Re: We agree with the reviewer's opinion to set up pump permit to conserve groundwater quality. However, the pump permit in the study is the amount allocated for administrative approval when the well was developed. It is beyond the scope of the study to set the threshold of the pump permit to preserve water quality.

Do you have any explanation for the change of water e.g. from CaHCO₃ (II) to mixed CaMgCl (III); Figure 4. Which parameter of each well you compare in figure 8?

Re: Wells whose groundwater quality type changed from CaHCO₃ (II) to mixed CaMgCl (III) are B-11 and D-04 (Table 4). In Figure 8, the first survey results are marked as B1-11 and D1-04, and the second results as B2-11 and D2-04. The water quality change can be inferred from the figure 8. In figure 8, PC1 confirms that DO, EC, Ca, Mg, Na, K, Cl, SO₄, and Br are the main contributors, while PC2 is affected by pH, SiO(aq), and HCO₃, and PC3 is affected by NO₃ as represented from line 430 to line 435.

The B-11 and D-04 were confirmed and corrected in Figure 1, and Table 3 were rearranged in alphabetical order of well ID to find the wells and quality data easily.

And, figure 9 is added in the manuscript for better understanding to explain the groundwater quality change during the pumping in the rice-paddy irrigation. PC1, PC2, PC3 and outer water source (seawater influence) are represented from line 464 to line 485.

Additionally, we carefully reviewed and corrected the English. The revised part is marked in red.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and suggestions for Authors in te attachment.

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions

Evaluation of seasonal groundwater quality changes associated with groundwater pumping and level fluctuations in an agricultural area, Korea. The subject of this paper is suitable for publication profile of Water. The Authors should clearly specify the original aspects of her study in view of already published papers.

Re: Thank you for your comments. We presented the studies on the groundwater quality changes so far in the introduction from line 49 to line 66, and the purposes of this study were elaborated from line 67 to line 76.

Throughout the manuscript, the charges at the cations and anions are missing, eg lines 155, 157, 167-168, table 3 and table 4. Please correct.

Re: Thank you for your comments. We did correct and modify the charges at the cations and anions as the reviewer suggested. All corrected sentences to include the charged were shown in red colored letters in the revised manuscript.

Was a change in groundwater pH depending on the seasons found during the research? If so, what was the reason?

Re: In table 3 and figure 5, the pH changes are represented, and the pH changes occurred under the context of PC2 from the PCA results. We think that it reflect the water-rock interaction under groundwater flow control.

And, figure 9 is added in the manuscript for better understanding to explain the groundwater quality change during the pumping in the rice-paddy irrigation. PC1, PC2, PC3 and outer water source (seawater influence) are represented from line 464 to line 485 .

Was the content of organic substances, eg TOC or DOC, determined in the groundwater samples?

Re: Unfortunately, TOC and DOC were not determined in this study. As recommended by the reviewer, we will try to have an opportunity to analyze the water quality items in the future.

Additionally, we carefully reviewed and corrected the English. The revised part is marked in red.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The explanation given by the authors and the corrections are adequate

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

The topic is of high scientific importance and worth of investigation. However, authors must address following points before it can be accepted for the publication:

1. Abstract and conclusion is very weak and need to be rewritten with key findings from this study.
2. In Study area, population should be 120000 instead of 120? Please check.
3. For figure 2, I do not see any discussion about pumping wells in the text. You have just mentioned about monitoring wells. Please add few lines in section 3.1 to mention it clearly.  
4. Please rewrite sentences from line number 192-194, 241-243 as they are pretty confusing.
5.  For figure 3, legends especially well IDs are too small to read anything. Please increase the font size. 
6. For showing the relation between groundwater level and precipitation in line 253-254, better to draw the hydro-graph. 
7. Sentence 271-272 is very confusing. What do you mean to say here? Is this use recorded from years different than 2018-2019? Or this value is from some report? However the 54625 m3 is the observed value, hence this is a critical issue to manage?
8. For table 3, please write all cations and anions in ionic form with their charges. Also add well depth and location from sea?
9. As section 4.3.1 is currently very superficial to give any insight about hydrological processes, it must be elaborated.
10. For figure 5, please add depth of sampling wells in x-axis of the figure as discussed in the text.
11. For paragraph between line number 351-362, please explain why do you consider Br? 
12. Revise sentence for the line number 390-392 as the information is not true. in this case, samples are far placed from summer LMWL. please check.
13. Throughout the manuscript, you have just shown the results but you need to also discuss the reasoning behind this occurrence. This section is really weak.
14. Please check the reviewed manuscript for other minor comments

Author Response

The topic is of high scientific importance and worth of investigation. However, authors must address following points before it can be accepted for the publication:

Re: Thank you for your valuable comments and suggestions. We have considered all comments and suggestions and revised our manuscript to justify our works.

1. Abstract and conclusion is very weak and need to be rewritten with key findings from this study.

Re: As a result of previous literature surveys, there are many references to changes in water quality in agricultural areas, but little understanding of recharge and water level changes to the aquifer of irrigation water due to groundwater pumping has been achieved.

The purposes of the study was represented in lines 66-74. We think that this paper is meaningful in that for the first time, water quality changes in agricultural areas were analyzed by comparing groundwater level data and usage data, and water quality changes were quantitatively identified using multivariate statistical techniques. We added the following sentence in the Abstract.  

(line 32-34)

“These results provide a qualitative and quantitative basis for groundwater quality change in agricultural areas, particularly, rice paddies areas, along with groundwater level and usage.”

2. In Study area, population should be 120000 instead of 120? Please check.

Re: Thank you for detailed review and comments. The study area is a small rural village with a population of 120.

3. For figure 2, I do not see any discussion about pumping wells in the text. You have just mentioned about monitoring wells. Please add few lines in section 3.1 to mention it clearly.

Re: Thank you for detailed review and comments. The pumping wells and monitoring wells are mentioned in Table 1 and caption of Figure 2, but as requested by the reviewer, they have been added to section 3.1 as follows.

(The line numbers have been modified due to some sentence insertion)

(line 177-179)

“In Figure 2a, the pumping wells are D-08 and D-11, and D-09 and D-11 in Figure 2b. And, in Figure 3c, there is no pumping well, and in Figure 2d, D-03 and D-05 are pumping wells. Except for the pumping well, the wells shown in Figure 2 are all monitoring wells.”

4. Please rewrite sentences from line number 192-194, 241-243 as they are pretty confusing.

Re: Thank you for detailed review and comments. As pointed out by the Reviewer, the sentence has been modified as follows to avoid unit confusion.

(The line numbers have been modified due to some sentence insertion)

(line 204-206)

“The groundwater levels at C-09 fluctuated between 13.68 and 15.6 m in mean sea level elevation, showing about a 1.2 m drop from 14.9 m on 12 May to 13.7 m on 7 June.”

(line 254-256)

“The groundwater levels in mean sea level elevation were 2.38 m to 32.75 m (average 15.18 m) in July and 7.02 m to 32.80 m (average 15.71 m) in October.”

5. For figure 3, legends especially well IDs are too small to read anything. Please increase the font size.

Re: As pointed out by the Reviewer, the figure 3 has been modified.

6. For showing the relation between groundwater level and precipitation in line 253-254, better to draw the hydro-graph.

Re: As suggested by the Reviewer, the figure 2 has been modified to include precipitation into each graph of Figure 2 hydrograph.

7. Sentence 271-272 is very confusing. What do you mean to say here? Is this use recorded from years different than 2018-2019? Or this value is from some report? However the 54625 m3 is the observed value, hence this is a critical issue to manage?

Re: We wanted to show that the amount reported to the administration and the amount of groundwater actually used is very different. To clarify the sentence, we modified it as the following sentence. And, in Table 2 and the some sentences, a comma is inserted to indicate the thousands.

(The line numbers have been modified due to some sentence insertion)

(line 284-286)

“There are a total of 25 wells for agricultural use in the area and the pump permit of those wells is 1,918 m³/day, which is 700,070 m³/year. However, the actual amount used for one year is reported as 28,414 m³, so this amount is only about 4% of the pump permit.”

8. For table 3, please write all cations and anions in ionic form with their charges. Also add well depth and location from sea?

Re: As suggested by the Reviewer, we write all cations and anions in ionic form with their charges, but, the well depth of each well and locations has been included in Table 1. And, the study area is too small, and the wells in study area are considered to be generally at a same distance from the sea. And then, well depth and distance from the sea are are not included in Table 3. In addition, the text was also modified and marked in ionic form.

9. As section 4.3.1 is currently very superficial to give any insight about hydrological processes, it must be elaborated.

Re: As pointed out by the reviewer, we add the sentence in section 4.3.1 to give any insight about hydrological processes in the study area.

 (The line numbers have been modified due to some sentence insertion)

 (line 294-297)

“The main causes of water quality change in the study area are various such as precipitation, groundwater pumping, and pollution from agricultural activities. In particular, when the drought in the summer of 2018 was severe, the temporary supply of salty water from Hongseongho Lake as irrigation water is also expected to affect water quality changes.”

10. For figure 5, please add depth of sampling wells in x-axis of the figure as discussed in the text.

Re: C and B/D are divided into wells according to well depth. Because each well depth cannot be displayed in the box plots. Alternatively, we add the following sentence in the caption of Figure 5.

(line 342-344)

“Group C wells are installed mainly at shallow depths in alluvial aquifer, and group B/D wells are installed deep in bedrock.”

11. For paragraph between line number 351-362, please explain why do you consider Br?

Re: Among the factors that influenced the groundwater quality in the study area, saltwater was supplied as irrigation water from Hongseongho Lake during the summer drought in 2018. Hongseongho Lake is an artificial lake by blocking the water flowing out to the shore, and its salinity is not low enough to be used as irrigation water. Therefore, it is believed that the origin of salty water is caused by seawater. Among the items analyzed in this study, it was used to find out whether the effect of seawater remains due to the relationship between Na, Cl, and Br.

12. Revise sentence for the line number 390-392 as the information is not true. in this case, samples are far placed from summer LMWL. please check.

Re: Thank you for your comments. We checked the sentences that you pointed out, and confirmed that the sentence is correct. In Figure 7, the oxygen and hydrogen isotope composition of groundwater is distributed in parallel with the summer precipitation line (rainy season) (LMWL). In this LMWL, mainly Group C wells and some D group wells show a pattern of departure from the LMWL due to the effect of evaporation.

13. Throughout the manuscript, you have just shown the results but you need to also discuss the reasoning behind this occurrence. This section is really weak.

Re: Thank you for your comments. As pointed out as the reviewer, we reinforced the conclusions in the text. The added sentences and modifications were marked as red colored letters.

14. Please check the reviewed manuscript for other minor comments

Re: Thank you for your comments. We have considered all comments valuable to improve our manuscript and checked thoroughly again.

Author Response File: Author Response.pdf

Reviewer 2 Report

I have read the water-996768 paper submitted by Ha K. et al.

Unfortunately, I cannot suggest a publication in the current state of the paper. Then, I would not make very detailed suggestions, but here is my general feeling.

The geological structure of the site is not described.The presentation of the study area shows reliefs, but are they permeable or not?  In other words, we don't know whether the water flows only in the alluvial valleys, or whether it can circulate under the reliefs. Is it permeable sandstone or other porous rock?

An error of justification appeared to me.The authors justify that the microelements are not taken into account because the values are very low, but during the treatment by PCA, being based on the matrix of correlations, the fact of having low values is not an obstacle.

The depth of the wells is mentioned, and these are below sea level. But there is no indication of the depth of the strainer of these wells.

No analysis is given as to the significance of the factorial axes (PCs).  The first axis is an axis of minerality, this seems to be clear. But what is the meaning of the other axes? What are the associated processes? Rock alteration? Redox? The absence of this analysis greatly limits the interest in monitoring the evolution of the factor axes between the two periods.

To conclude, the scope of the study is too small. One indicator is that the introduction starts with "In Korea..." instead of placing the study in a broader scientific framework. We don't see what this study brings to the community, apart from very local knowledge.

Author Response

I have read the water-996768 paper submitted by Ha K. et al. Unfortunately, I cannot suggest a publication in the current state of the paper. Then, I would not make very detailed suggestions, but here is my general feeling. The geological structure of the site is not described. The presentation of the study area shows reliefs, but are they permeable or not? In other words, we don't know whether the water flows only in the alluvial valleys, or whether it can circulate under the reliefs. Is it permeable sandstone or other porous rock?

Re: We added the sentences to explain the geology and aquifer constitutions in the area additionally in line 85-88 as follows.

(line 85-88)

“The upper layer is an alluvial layer mainly composed of porous media, and the lower layer is composed of bedrock. Therefore, the upper porous media constitutes an alluvial aquifer, and the lower fractured bedrock constitutes a bedrock aquifer.”

An error of justification appeared to me. The authors justify that the microelements are not taken into account because the values are very low, but during the treatment by PCA, being based on the matrix of correlations, the fact of having low values is not an obstacle.

Re: As pointed out by the reviewer, the PCA analysis was conducted by focusing on the overall trend rather than putting significance on the subtle changes in water quality. If you look at the relationship between PC1 and PC2 and PC2 and PC3 for the groundwater quality in July and October, it can be seen that each well has a direction in Figure 8.

The depth of the wells is mentioned, and these are below sea level. But there is no indication of the depth of the strainer of these wells.

Re: It is difficult to determine the correct well structure, but it is assumed that the screen was installed in the main aquifer section. We added a column to represent main aquifer in Table 1, and the screen installation are mentioned in line 117-118

No analysis is given as to the significance of the factorial axes (PCs). The first axis is an axis of minerality, this seems to be clear. But what is the meaning of the other axes? What are the associated processes? Rock alteration? Redox? The absence of this analysis greatly limits the interest in monitoring the evolution of the factor axes between the two periods.

Re: Three main components were derived from the result of principal component analysis, and dilution was judged as the biggest factor as PC1. Dilution is caused by a mixture of precipitation, river water, and groundwater, and this effect can be inferred from the phenomenon that the groundwater level rises during the period of continuous pumping from the groundwater level data. The second factor as PC2 is not clear, but it is presumed to be water-rock interaction, which is composed of mainly pH, HCO₃^-, and Si⁴⁺ concentration. The third factor as PC3 may have been associated with anthropogenic contamination is due to nitrate nitrogen. The significance and indications of each components are explained in line 432-466.

To conclude, the scope of the study is too small. One indicator is that the introduction starts with "In Korea..." instead of placing the study in a broader scientific framework. We don't see what this study brings to the community, apart from very local knowledge.

Re: Thank you for our comments, and we reinforced the abstract and conclusions. The added and modifications are marked as red colored letters.

Reviewer 3 Report

The manuscript "Evaluation of seasonal groundwater quality changes associated with groundwater pumping and level fluctuations in an agricultural area, Korea" describes a local monitoring case study in Hongseong County. The manuscript is well written, with clear and well-described assumptions, methodology and thorough results description and analysis. I find no flaws in the manuscript, exception made for its general relevance.  The case study description is very specific and it looks more like an internal report than a scientific paper. My concerns are about the interest of this case study on readership, and hence its added value to knowledge advancement. Reported conclusions have very limited significance and cannot be applied to other similar situations. In this sense, I doubt whether it merits publication.

Author Response

The manuscript "Evaluation of seasonal groundwater quality changes associated with groundwater pumping and level fluctuations in an agricultural area, Korea" describes a local monitoring case study in Hongseong County. The manuscript is well written, with clear and well-described assumptions, methodology and thorough results description and analysis. I find no flaws in the manuscript, exception made for its general relevance. The case study description is very specific and it looks more like an internal report than a scientific paper.

Re: We appreciate on your comments and affectionate advices.

My concerns are about the interest of this case study on readership, and hence its added value to knowledge advancement. Reported conclusions have very limited significance and cannot be applied to other similar situations. In this sense, I doubt whether it merits publication.

Re: Thank you for your valuable comments and affectionate advices. We think that this paper is meaningful in that it quantitatively evaluated the change of groundwater quality in relation with irrigation water by groundwater pumping, precipitation and other possible factors (saline water supply during summer drought in previous year in this study) in rice farming areas for the first time.

Round 2

Reviewer 1 Report

As authors have addressed all the comments raised during revision of the manuscript, I recommend for its publication in its current form.

Reviewer 2 Report

The second version of the article is slightly improved compared to the previous version. However, many gaps, weaknesses and questions remain.
The meaning of the first factorial axis is classical (water minerality), but the meaning of the second factorial axis, probably reflecting the arrival of water from the high areas of the sector, is evaded. Under these conditions, it is difficult to interpret the evolution of the points in the first factorial plane.
Is the silica dosed by inductively coupled plasma-optical emission spectrometry really in the Si4+ form as indicated in the whole article? This would be an important discovery... it is very unlikely that the silica is in this form and nothing in the article demonstrates this. It is very likely that it is in the form of dissolved silica and not ionised silicon.
At the isotopic level, the evaporated water points (in particular C3) show that the salted drillings do not come from a simple mixture with sea water but from evaporation as indicated by the authors. The Br/Cl relations confirm this but are only poorly valued by the authors. The explanation of the origin of water evaporated at depth is eluded.

Many other weaknesses persist in this work.
In general, the article has serious scientific weaknesses and does not provide innovative input on techniques or processes. As a result, this study only deals with a local case, with no input that can be extrapolated to other regions of the world.
The quality of the work, the presence of many weaknesses, the absence of really innovative input, the regional character make this draft article weaker than what is generally published in the journal Water.
For these reasons, I do not recommend the publication of this work in the journal Water.

Reviewer 3 Report

The manuscript was improved with the introduction of new information and discussion. In my opinion it could be accepted for publication in this revised version.