The Impact of Lake Water Quality on the Performance of Mature Artificial Recharge Ponds
Round 1
Reviewer 1 Report
The paper is generally well written, while the novelty of this work is not clear. The authors should reconstruct the Introduction to remove very general (“textbook-like”) paragraphs and to explain what this work can add to the decades of research history on microcystin in drinking water. Overall, the Introduction is very lengthy.
The scientific impact of their findings, especially on microcystin analysis, may be minor because a semi-quantitative method with high cross-reactivity was used for microcystin analysis (I suggest the authors use "microcystins" instead of "microcystin LR" for this reason), which limits scientific discussion based on their results.
Below are my specific comments.
At the bottom of p. 4, the authors state “It took two months (in June) to have a stable system before taking samples from both inlets of the pond and it took four months (in August) to have enough standing water in the both half ponds to take pond water samples.” Do you mean the pond was empty when you started the experiment in April?
Delete “the” in first line of 2.4 to read “every other week”.
In 2.5, please provide how you conducted the resampling (e.g. how you obtained random samples, how many resampling was made) here. The current sentences only explain what “bootstrapping” is. For which parameter(s) did you apply the resampling?
If you want to cite Fig. 5 at the end of p. 6, the figure should be placed after the paragraph as Fig. 3.
In 3.3, how did you calculate the 8 times difference based on the categorical data in Supplementary Table 2 or Supplementary Figure 5? In my understanding, volumes (cell biomass) cannot be estimated based on areas (cell coverage or “biomass scale”). We usually evaluate cell biomass by counting cells, sometimes after washing or sonication to disperse flocked cells.
The Results and Discussion are not well separated. For example, the third and forth paragraphs in 3.3 should be moved to Discussion.
Second paragraph of 3.4: It seems you do not have winter and spring samples as samples were collected from June to October.
The first sentence of 4.: It should be either “on-site” or “in-situ”.
I could not get the point of the latter half of the third paragraph in 4.3. It seems you are discussing something that you did not observe (i.e. your observation denied such “potential” threats).
The first paragraph of 4.5: It is not meaningful to discuss on other ponds, as the readers do not know the variation in size, etc. In addition, it seems that the microcystin concentration after the pre-treatment and in the pond are similar, which shows that the lake water quality is not affected by the size of the lake.
The last paragraph of the Conclusion is general and is not well supported by this work (e.g. you did not observe anatoxin and saxitoxins). I suggest you delete this.
Author Response
Dear Reviewer
Thank you for your kindness and efforts. Your comments are accepted and the Corrections and improvements are attached.
Thank you and all the best
Jing Li
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Very good paper dealing with a very important subject. I appreciated very much this work. The subject is well presented, with competency and enough details and references. It is written in good easily readable English language. The methodology used for the research is highly appropriate and compares two different water pre-treatment, introducing new data in the water recharge technology. The obtained results can be very useful for others similar applications and contribute positively for a safer water supply.
Author Response
Thank you so much for your comments and I have resubmitted a new version!
All the best regards
Jing
Reviewer 3 Report
General: Cyanobacteria and their toxins are a serious problem so that people should not drink surface waters without treatment (in spite it is and has been done and sometimes travel agencies etc. tell that so specific lakes are so clean that you could drink their water). Possibly the fertilization with phosphorus during the last some 70 years in Sweden and other industrial countries has increased the risks of cyanobacteria. Today some responsible water supply companies may have noticed that they must improve their water treatment process to be able to produce water with very limited amount of cyanobacteria, organic matter, phosphorus etc.). Filtration and contact filtration are methods that can be studied in order to reduce efficiently.
In this case contact filtration using PACl + flocculation was much more effective than only sand filtration. The result of turbidity, TOC and phosphorus are much lower in water after contact filter than after filtration. Similarly, the densities of cyanobacteria were reduced. The concentration of water soluble nitrate was similar.
Paper is mainly well written and you refer the literature as needed. There are some small errors.
Use italics for all scientific names. In the page 3 you try to present 10 to 5 (one hundred thousand) and 10 to 6 (one million) but no the exponent is lacking. Correct! In Fig 1 you use white text and blue background. When reading this on laptop screen in a rainy it is very difficult to see the text. You have also very small numbers (?) on red background. I cannot see those numbers, but I must guess them only. Please, use colors which are visible (black in white etc.). In Figs 2, 3, and 4 you present important results. I would present also numbers of determinations which you have in supplementary data. N in this case gives more value for your results.
Author Response
Dear Reviewer,
Thank you so much for your review comments! Really appreciate your highlight of the importance of the study and kindness to point places to improve.
I have given all scientific names italics format.
In page 3, I have changed it back the number 5 and 6 to exponent: Cylindrospermospsis raciborskii (105–106 cells/mL)
I have changed Figure 1 by using your suggestion. Now it is very clear! ?
I moved the nitrate and ammonia figures to the results part from the supplementary section. I changed the description as below.
‘’To monitor nitrogen level is important for final drinking water quality and controlling cyanobacteria favourable growth condition. The nitrate concentration in these two different processes is significant difference both in the pond water and in the well water (Fig.6). The nitrate level in the control pond has around 25% lower than the contact filter pond and the value in the control well is almost doubled of the value in the contact filter well. The nitrogen concentration in the form of Ammonium is almost the same in these two treatment processes (Fig. 7). ‘’
And I have also added discussion below in the discussion section, regarding the nutrient removal.
‘’
Continuous contact filtration has been known for its high removal of phosphorus and it was also observed in our case study. This brought a positive impact on preventing the cyanobacteria regrowth in the pond water. The difference between the nitrate concentration level in the pond water and the well water for these two treatment processes might be due to the difference of the cyanobacteria biomass and the species. The difference might influence the nitrogen cycle in the pond. More cyanobacterial biomass in the control pond and regrowth of cyanobacteria might consume more nitrate than the contact filter pond. The higher nitrate level in the control well might be contributed by the decay of cyanobacteria. As the ammonia condition didn’t vary, this might also indicate that some extra nitrogen from the air was fixed by cyanobacteria into the pond and ended in the infiltration system.
‘’
All the best regards
Jing LI
Round 2
Reviewer 1 Report
The authors made reasonable responses to my comments and revised the manuscript accordingly. I do not have additional issues to point out.
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 study is presenting the benefit of installing a coagulation/flocculation followed by sand filtration pretreatment of lake water before groundwater recharge. The study is overall well designed, the manuscript well structured, clearly presented and definitely of interest as case study for such schemes. Therefore I would definitely recommend its publication. Still, I have some comments that I believe can be considered before publication:
Few comments on the methodology/discussion:
· I do not see much of the added value of the bootstrapping resampling since the results are quite clear…but maybe I missed something
· Also, can you clarify if the 2 compared lines control vs. contact treatment were fully separated/independent or if to some extend some flows could go from one to the other line? Especially during filtration before reaching wells.
· Any idea of kinetic/ time before noticeable changes were observed in the ponds and in the wells? Is there a way to highlight that?
· Fig 2 and sup fig 2 and 3: quite clear effect of the pre-treatement on the water quality in the ponds but nothing ‘’significant’’ o the wells. Typically I would not insist too much especially on TOC reduction since within interval of uncertainty…
I have also quite some ‘’cosmetic’’comments:
· Referencing is a bit weird: instead of [1], [2]….. it should be [1,2…]
· To my knowledge, picture are considered as figures as well…but maybe I am wrong
· I would keep most supplementary figure in the core document since they are of significant interest for the discussion. Maybe make them bit smaller to fit 2 figures in one row.
· At the beginning of section 3.3., you mean Fig1 or pic 1?
· Figure design could be generally improved, those excel basics design sometimes does not look super professional/scientific…but up to you…
· Do not have scale below 0 in figures
· In sup figure 6 I would use similar scale to better show the difference in-between treatments…
Author Response
Dear reviewer
Thank you so much for your comments and constructive feedback and I accepted them and did improvement as below (my answers are below your comments):
The study is presenting the benefit of installing a coagulation/flocculation followed by sand filtration pretreatment of lake water before groundwater recharge. The study is overall well designed, the manuscript well structured, clearly presented and definitely of interest as case study for such schemes. Therefore, I would definitely recommend its publication. Still, I have some comments that I believe can be considered before publication:
1. I do not see much of the added value of the bootstrapping resampling since the results are quite clear…but maybe I missed something
Regarding bootstrapping, I scaled down with a focus on the likely blooming season (June to October) as it is clear seasonal pattern that I don’t need to include other seasons. I used it, on one hand, it is because of the limited data set (13 sets) and the concentrations are very low especially in the well water. On the other hand, I want to give more statistical options for water operators to use for water quality analysis. I will discuss with my co-authors, if we will keep it or not. It is as you say, it is clear to see the difference and a simple t-test can give a direct answer for the comparison.
2. Also, can you clarify if the 2 compared lines control vs. contact treatment were fully separated/independent or if to some extend some flows could go from one to the other line? Especially during filtration before reaching wells.
Thank you so much for reminding me with this question and I rearranged the graph to make it clearer that we had the concern to avoid mixing to the maximum, the inlets to the pond were located at the furthest side at each pond (the distance between the inlets equals to the pond length 100 meters and the distance between the wells and the inlets is 2 meters ). And I have also already mentioned in the design part that there is a deep wall in the middle to separate them. Many thanks for this comment!
3. Any idea of kinetic/ time before noticeable changes were observed in the ponds and in the wells? Is there a way to highlight that?
Based on the flow rate 10.2 L/s and the area 3000 m2, it is around 0.4 m/day infiltrate to the ground and it is estimated to take around 7 days to 14 days to reach the ground level. As our project started in the April and we adjusted the system to be stable to be able to take samples in the June, there is no opportunity to see the noticeable changes in the well water. While in the ponds water, we see obvious changes after running the project for 4 months, by the end of Auguest, the whole bottom in the control pond was covered by water, while only 2/3 of the contact filter pond was covered by water. I added thoese content in the article too.
4. Fig 2 and sup fig 2 and 3: quite clear effect of the pre-treatement on the water quality in the ponds but nothing ‘’significant’’ o the wells. Typically I would not insist too much especially on TOC reduction since within interval of uncertainty…
Yes. I agree with you and we discussed how important for drinking water quality to improve in regards of TOC removal from 3.5 mg/L to 2.4 mg/L. We ended with a conclusion that it is a big improvement for water quality as organic matter content in the following processes such as disinfection and bacteria growth in the distribution system are of great concerns. It matters more regarding to the actual factions that are removed and stayed.
I have also quite some ‘’cosmetic’’comments:
· Referencing is a bit weird: instead of [1], [2]….. it should be [1,2…]
Changed.
· To my knowledge, picture are considered as figures as well…but maybe I am wrong
Thank you! I made it as a figure!
· I would keep most supplementary figure in the core document since they are of significant interest for the discussion. Maybe make them bit smaller to fit 2 figures in one row.
It is good recommendation. I did it for the first version and I got comments to move them down as supplementary figures. I will bring it up again and discuss with my co-authors.
· At the beginning of section 3.3., you mean Fig1 or pic 1?
Good observation! Thanks! I have changed it!
· Figure design could be generally improved, those excel basics design sometimes does not look super professional/scientific…but up to you…
Yes. I have changed, including increase the size and put vertical titles and units.
· Do not have scale below 0 in figures
Changed it too
· In sup figure 6 I would use similar scale to better show the difference in-between treatments…
Excellent! Thank you and did it!
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper evaluated the effect of pre-treatment using coagulation-filtration on water quality of ponds that are used for artificial groundwater recharge. The topic itself falls within the
scope of the journal. The methodology and results were presented, although it requires some modification.
One of the issues is that the quality of water after groundwater recharge was good without the pre-treatment, in terms of the parameters they measured, hence the effect of pre-treatment on the water quality after recharge was not observed (i.e. the treatment was not needed). I could not find why they selected this pond system as the study site. Thus the scientific significance of this research is relatively minor and limited to show the treatment efficiency of the pre-treatment. But the technology (coagulation-filtration) has been investigated for a long time, so this work could not add new knowledge with this regards. The parameters they evaluated were common in water
quality management, which also reduced the significance of this study.
Below are my specific comments
p. 1, l. 13 of Introduction: Remove “2018”.
p. 1, l. 3 from the bottom: remove the comma after “generally”.
p. 2, ll. 13-15: Show the reference of the study at Lake Chaohu.
p. 2, l. 42: Move section 2.1 to Materials and Methods.
p. 3, ll. 8-9: What do you mean by “renewable water resources”?
p. 3, section 2.1: What was the concentration of PACl, depth of the sand filter, composition (e.g. diameter) of the sand filter?
p. 3, section 2.2: When did you start the pre-treatment? I assume it takes time until the pond water quality after contact filter treatment was stabilized and ready for investigation.
p. 4, section 2.3: Show the location and country of the manufacturer of Hach turbidimeter, pH meter, microcystin test kit, etc. What kind of microcystin (e.g. LR, RR) can be detected using the kit? What is the standard or guideline value for microcystin in Sweden?
p. 6, Picture 1: When did you take these pictures?
p. 7, section 3.3: There is no data on cyanobacteria biomass.
p. 7, second paragraph of section 3.3: Explain which group has larger/smaller in cell size. Does the cell size explain the difference in removal rates of each group?
p. 8: I don’t think the bootstrap analysis gives a better idea on treatment efficiency because the microcystin concentration apparently showed seasonal trends. There is no meaning in comparing microcystin concentration before and after treatment observed at different time.
p. 9, section 3.5: Are the guideline or standard values for source water to be treated at water treatment plants or finished water (i.e. tap water)? If they are for finished water, it is not meant to
apply the values to the source water quality.
Figures: The fonts are too small. Explain the vertical axis with units. What do the plots, bars, etc. represent?
Author Response
Dear reviewer
Thank you so much for your general comment above and all the specific comments below! I really appreciate your time and efforts to improve my manuscript. I answer your comments and suggestions below:
This paper evaluated the effect of pre-treatment using coagulation-filtration on water quality of ponds that are used for artificial groundwater recharge. The topic itself falls within the scope of the journal. The methodology and results were presented, although it requires some modification.
One of the issues is that the quality of water after groundwater recharge was good without the pre-treatment, in terms of the parameters they measured, hence the effect of pre-treatment on the water quality after recharge was not observed (i.e. the treatment was not needed). I could not find why they selected this pond system as the study site. Thus the scientific significance of this research is relatively minor and limited to show the treatment efficiency of the pre-treatment. But the technology (coagulation-filtration) has been investigated for a long time, so this work could not add new knowledge with this regards. The parameters they evaluated were common in water quality management, which also reduced the significance of this study
Thank you! I feel positive that our current system is actually working well as you also mentioned. That is one of the purposes of testing. The necessity for introducing more effective pre-treatment might be very good reference for the future water which might be browner and greener. In my opinion, contact filtration is known as removing phosphorus and suspended solids. In my study, I would like to focus on the impact on preventing secondary algal blooms in the artificial recharge ponds and the cyanotoxin removal. And I would like to bring concerns for likely stricter regulations in regards to cyanotoxin in drinking water in this article. In my other articles, I will also discuss how to manage another type of cyanotoxin monitoring in drinking water under strict regulation (saxitoxin) while not well-developed monitoring tools are available. Those are not well discussed in the current drinking water supply.
Below are my specific comments
I accept all your constructive feedback and did the corrections and improvement accordingly.
p. 1, l. 13 of Introduction: Remove “2018”.
Did
p. 1, l. 3 from the bottom: remove the comma after “generally”.
Did
p. 2, ll. 13-15: Show the reference of the study at Lake Chaohu.
Did
p. 2, l. 42: Move section 2.1 to Materials and Methods.
Did
p. 3, ll. 8-9: What do you mean by “renewable water resources”?
Groundwater recharge. We have annual precipitation over the catchment area. To average the water volume coming to this catchment to a second, there is around 10 m3/s water into this catchment, we just assume that around half of them are infiltrated into the ground. I formulated it into at least 5m3/s water are infiltrated to the groundwater aquifer.
p. 3, section 2.1: What was the concentration of PACl, depth of the sand filter, composition (e.g. diameter) of the sand filter?
The Sand grain size is around 1.2 to 2.0 mm, area of 3 m2 with the filter bed height about 1.5 m. And the optimized adjusted conditions were also added: The control of the dosage of Aluminium is the key factor for the removal of fine suspended solids and phosphate. It is tested at the beginning of the project. At the end, 195µl/l Pax 15 (KEMIRA, Sweden) was used for this pilot test. To guarantee a good efficiency, the following condition was adjusted: the maximum flow is 10.5L/s; sand movement average speed is 9,79 mm/min; pH level around 6.4. The consumption of Pax 15 is 177 L/ day. A week consumption of Pax 15 is around 1240L.
p. 3, section 2.2: When did you start the pre-treatment? I assume it takes time until the pond water quality after contact filter treatment was stabilized and ready for investigation.
Thank you. Yes. It took 2 months to build a stable system for sampling. Have added in the Study Design part.
p. 4, section 2.3: Show the location and country of the manufacturer of Hach turbidimeter, pH meter, microcystin test kit, etc. What kind of microcystin (e.g. LR, RR) can be detected using the kit? What is the standard or guideline value for microcystin in Sweden?
Thanks for your suggestion. Did!
p. 6, Picture 1: When did you take these pictures?
Have added August 2014
p. 7, section 3.3: There is no data on cyanobacteria biomass.
I have included a subjective evaluation of the biomass of cyanobacteria by using a guide book and microscope in to the result.
p. 7, second paragraph of section 3.3: Explain which group has larger/smaller in cell size. Does the cell size explain the difference in removal rates of each group?
Thanks. Yes. And did.
p. 8: I don’t think the bootstrap analysis gives a better idea on treatment efficiency because the microcystin concentration apparently showed seasonal trends. There is no meaning in comparing microcystin concentration before and after treatment observed at different time.
Thanks for your thoughts! I added the seasonal trends in the result and I also reconsidered this and did it again by only including the likely bloom season (From June to October). As there is limited number of samples, I should use bootstrap advantage to show the significant mean difference. I can also just make a simple t-test, and it works too. Just want to test more available statistical methods for water quality analysis. So that our drinking water operators have more options. And I recommended in the conclusion as well.
p. 9, section 3.5: Are the guideline or standard values for source water to be treated at water treatment plants or finished water (i.e. tap water)? If they are for finished water, it is not meant to
apply the values to the source water quality.
Yes, I agree with you. The guidelines are for the finished water and I also mentioned in the article that I focus on the risk reduction during the treatment process. I also added if 0.1 would be used in Swedish water, one August sample in the reference well which above 0.1 µg/l might be a concern. Under current data and low concentration, I try my best to discuss different perspectives as possible.
Figures: The fonts are too small. Explain the vertical axis with units. What do the plots, bars, etc. represent?
Thanks! Done!
Thank you again and look forward to your new comments!
Best regards
Jing
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors responded to some of my comments, while some of my concerns, including the major ones, remain.
> In my study, I would like to focus on the impact on preventing secondary algal blooms in the artificial recharge ponds and the cyanotoxin removal.
Then you can construct your work to focus on algal concentrations and microcystins. I cannot find such statements in the last paragraph of the Introduction (“understanding of challenges of cyanobacteria and their toxins” is very general and vague). In addition, the analysis in this aspect is quite primitive (e.g. Hach kits for microcystin analysis, non-quantitative analysis for algal concentration).
It is not meaningful to assume that the water quality standards will be stricter, without mentioning that there is such discussion in the national or local government or related agencies. You can create any scenarios that favor your statements.
> p. 3, ll. 8-9: What do you mean by “renewable water resources”?
> Groundwater recharge. We have annual precipitation over the catchment area. To average the water volume coming to this catchment to a second, there is around 10 m3/s water into this catchment, we just assume that around half of them are infiltrated into the ground. I formulated it into at least 5m3/s water are infiltrated to the groundwater aquifer.
The assumption is very arbitrary and can be misleading. Reference(s) must be shown.
> p. 7, section 3.3: There is no data on cyanobacteria biomass.
> I have included a subjective evaluation of the biomass of cyanobacteria by using a guide book and microscope into the result.
What do you mean by “subjective evaluation”? What is the “biomass scale” in Supplementary Figure 5 and how did you calculate the “8 times difference” based on the qualitative data in Supplementary Table 2?
> p. 9, section 3.5: Are the guideline or standard values for source water to be treated at water treatment plants or finished water (i.e. tap water)? If they are for finished water, it is not meant to apply the values to the source water quality.
> Yes, I agree with you. The guidelines are for the finished water and I also mentioned in the article that I focus on the risk reduction during the treatment process. I also added if 0.1 would be used in Swedish water, one August sample in the reference well which above 0.1 µg/l might be a concern. Under current data and low concentration, I try my best to discuss different perspectives as possible.
As I mentioned in my previous response, the drinking water quality standard can be applied only to the finished water (the well water in this survey may be acceptable). Thus, the last paragraph of section 3.5 comparing all results with the standard is inappropriate.
I could not find the reference for the 0.1 µm/L standard of Minnesota, which seems very strict. The Minnesota Department of Health states “Community water systems in Minnesota are required to provide drinking water that meets the federal Safe Drinking Water Act (SDWA) standards. The MDH Drinking Water Protection Program is responsible for assuring that Minnesota's public water supply systems comply with the SDWA.”, which implies that they do not have the State standards. I appreciate if you could add a reference here. Is the standard for the average concentration or the maximum concentration?
Source: https://data.web.health.state.mn.us/drinkingwater
English editing by professionals is necessary. Below are some points I found in the Abstract.
ll. 1-3: Two “and” in one sentence.
l. 5: Replace “evaluate” with “evaluated”.
l. 5: Replace “impact” with “effect (or treatment efficiency)”.
l. 10: Revise to read “reduced phosphorus by 95%”.
l. 11: Revise to read “corresponding to the reduction in the average concentration from…”.
ll. 12-13: Delete the second “reduced”.
Author Response
Thank you, dear reviewer, for your valuable comments. I try my best to clarify the project in blue.
The authors responded to some of my comments, while some of my concerns, including the major ones, remain.
> In my study, I would like to focus on the impact on preventing secondary algal blooms in the artificial recharge ponds and the cyanotoxin removal.
Then you can construct your work to focus on algal concentrations and microcystins. I cannot find such statements in the last paragraph of the Introduction (“understanding of challenges of cyanobacteria and their toxins” is very general and vague). In addition, the analysis in this aspect is quite primitive (e.g. Hach kits for microcystin analysis, non-quantitative analysis for algal concentration).
It is not meaningful to assume that the water quality standards will be stricter, without mentioning that there is such discussion in the national or local government or related agencies. You can create any scenarios that favor your statements.
I try my best to make it clear. I can rephrase in this way. It is true that contact filtration has been used for many years and there is no innovation about it. They are known for high treatment efficiency of phosphorus and organic matter. While in our case, we have a hypereutrophic lake and we have more challenges beyond phosphorus removal and organic removal and we have concerns about the water quality in the whole process. How the pre-treatment influences the following process and the final water quality? We designed the project following the whole process to see how our artificial recharge retention ponds are influenced by the pre-treatment and check if it can make the water quality in the treatment system more stable and produce higher quality drinking water.
I have not found studies about contact infiltration’s function as a barrier for algae and cyanotoxin removal. We would like to involve harmful algae and microcystin issue into discussion. It is a big concern for our drinking water treatment plant. As the removal of nutrients as a first step will influence the growing condition in the pond. It is valuable to see the difference of the pond water quality as regrowth of cyanobacteria is a potential risk for drinking water safety. I would consider our work as a treatment system rather than a certain technology.
Yes. The microcystin test kit is semi-quantitative analysis. It has a calibration curve with a standard solution and the concentration can be calculated. Why it is semi-quantitative is because it can also detect other variants besides microcystin-LR as I described in the method section. We don’t have advanced analytical technology at the water treatment plant to use. One of my research interests is to find practical tools that are suitable for water treatment plants to use as in most cases, advanced analytical tools are not available. They are only sitting in specialized institutes and used for further confirmation. The microcystin test kit was suggested by Swedish food agency to use for practical monitoring of microcystin-LR and other microcystin variants at waterworks.
Regards to the water quality standard, I believe research is responsible to bring different perspectives and considerations before policies happen. I have the links and documents to prove (in p. 9, section 3.5:) that I didn’t create future scenarios by myself and it is happening in those two states in the USA. European parliament might pass a proposal to change the parametric value 1 µg/L to include detectable microcystin variants: https://ec.europa.eu/info/law/better-regulation/feedback/11022/attachment/090166e5b9a1ecd7en
> p. 3, ll. 8-9: What do you mean by “renewable water resources”?
> Groundwater recharge. We have annual precipitation over the catchment area. To average the water volume coming to this catchment to a second, there is around 10 m3/s water into this catchment, we just assume that around half of them are infiltrated into the ground. I formulated it into at least 5m3/s water are infiltrated to the groundwater aquifer.
The assumption is very arbitrary and can be misleading. Reference(s) must be shown.
Thank you. I agree. I made a change and deleted the renewable water resources and I just simply described the situation as it is. I have listed the below reference and the text you can see, and it is written as renewable water resources which might be misleading. Therefore, I have changed it.
https://books.google.se/books?id=_XWFcntCZ8EC&pg=PA144&lpg=PA144&dq=vombsj%C3%B6n+renewable+water&source=bl&ots=DJrU_CQmVm&sig=ACfU3U1G5BWXUh7D5TBNHBLavx7q6LM8rg&hl=sv&sa=X&ved=2ahUKEwjY6qDn9p_jAhULpYsKHeHrAyIQ6AEwAnoECAkQAQ#v=onepage&q=vombsj%C3%B6n%20renewable%20water&f=false
> p. 7, section 3.3: There is no data on cyanobacteria biomass.
> I have included a subjective evaluation of the biomass of cyanobacteria by using a guide book and microscope into the result.
What do you mean by “subjective evaluation”? What is the “biomass scale” in Supplementary Figure 5 and how did you calculate the “8 times difference” based on the qualitative data in Supplementary Table 2?
There is no standard definition of bloom to follow. Subjective evaluation is that if we see clear blooms, we use a dark color, if it is not that much, we use less color, if it is clear water, there is no color. The purpose was to compare the difference, not the actual number. As it is not that scientific as you mentioned, I have removed it from the article. I used the same figures for the cyanobacteria species instead. I have checked and made it clear with our definition of the biomass scale. It is the coverage of the algae out of the chamber area. 1 equals 10% 2 equals 20% and so on. I have written into the text.
> p. 9, section 3.5: Are the guideline or standard values for source water to be treated at water treatment plants or finished water (i.e. tap water)? If they are for finished water, it is not meant to apply the values to the source water quality.
> Yes, I agree with you. The guidelines are for the finished water and I also mentioned in the article that I focus on the risk reduction during the treatment process. I also added if 0.1 would be used in Swedish water, one August sample in the reference well which above 0.1 µg/l might be a concern. Under current data and low concentration, I try my best to discuss different perspectives as possible.
As I mentioned in my previous response, the drinking water quality standard can be applied only to the finished water (the well water in this survey may be acceptable). Thus, the last paragraph of section 3.5 comparing all results with the standard is inappropriate.
I agree. The purpose to compare is to understand the raw water situation and how much we need to treat to be able to meet the standard. There is no standard for raw water to follow.
I could not find the reference for the 0.1 µm/L standard of Minnesota, which seems very strict. The Minnesota Department of Health states “Community water systems in Minnesota are required to provide drinking water that meets the federal Safe Drinking Water Act (SDWA) standards. The MDH Drinking Water Protection Program is responsible for assuring that Minnesota's public water supply systems comply with the SDWA.”, which implies that they do not have the State standards. I appreciate if you could add a reference here. Is the standard for the average concentration or the maximum concentration?
Source: https://data.web.health.state.mn.us/drinkingwater
Answer:
If you search Microsystin in the link you put above, you can find the below document:
https://www.health.state.mn.us/communities/environment/risk/docs/guidance/gw/mclrinfo.pdf
¨Based on available data, MDH has derived a guidance value of 0.1 ppb for microcystin-LR in drinking water. A person drinking water at or below this level, whether briefly, occasionally, or daily for a lifetime, would have little or no risk of any health effects from microcystin-LR. MDH currently recommends that this guidance for microcystin-LR be used for total microcystins.¨
This is the calculation: https://www.health.state.mn.us/communities/environment/risk/docs/guidance/gw/microcystin.pdf
English editing by professionals is necessary. Below are some points I found in the Abstract.
ll. 1-3: Two “and” in one sentence.
l. 5: Replace “evaluate” with “evaluated”.
l. 5: Replace “impact” with “effect (or treatment efficiency)”.
l. 10: Revise to read “reduced phosphorus by 95%”.
l. 11: Revise to read “corresponding to the reduction in the average concentration from…”.
ll. 12-13: Delete the second “reduced”.
Thank you for kindness. Language can always be improved. Have tried many times to rewrite and get a native speaker to go through it.
Thank you for your continuous support and discussion!
All the best
Jing Li
