Review Reports - Control of Nuisance Cyanobacteria in Drinking Water Resources Using Alternative Algae-Blocking Mats

Round 1

Reviewer 1 Report

The article concerns a very important problem related to the safety of drinking water intakes. It refers to the risk of cyanobacterial blooms occurring in reservoirs providing drinking water to the public. The results of the study show the effectiveness of special mats in removing excessive numbers of cyanobacteria in the water intake.

Detailed comments below:

Abstract

Explain the abbreviation 2-MIB - it is later explained in the text but should also be in the abstract

Materials and Methods

No morphometric data of the analyzed reservoir constituting the water intake. Morphometric data, information on the use of the catchment and existing sources of pollution should be included.

A map with the location of the reservoir and water intake would also be a good illustration.

Apart from the ABM scheme, it would be helpful to include a picture of such a mat.

There is no information on whether these mats were rinsed, suspended solids or periphyton development during the study.

In what months was daily monitoring carried out?

Was the water transparency measured in the reservoir?

In this chapter the authors state that such indicators as: dissolved oxygen, conductivity, turbidity and pH were measured. However, there are no results of these measurements in the text of the article. A table with ranges and averages should be presented, for example

Results

This chapter should actually be called Results and Discussion, because it contains not only the results of research but also their discussion.

Figure 2. - Do the presented results refer to the surface layer or is it the average from the vertical profile? The marking of the X-axis requires more detail. It is not clear what the individual columns mean.

Page 5 line 7 - " This increase was due to increased total phosphorus" - on what basis was this statement made? What were the phosphorus concentrations?

Page 6 line 8 – I don’t understand „ The ARE ranged from -98 to 65%” What does it mean „-98”?

Figure 5 - does the absence of one of the columns mean that the sample was not taken? The caption of the figure says "monthly variation" which would suggest monthly averages and in the description of the X axis there are 2 dates for the same months.

Figure 6 - what does a single column mean ? Not clear description of the X axis.

Page 9 line 4 - does 35% mean average value from vertical profile or other value?

The discussion should be enriched with literature on the use of materials to reduce the inflow of cyanobacteria to water intakes. How effective is ABM compared to other methods?

Specific recommendations on the use of these mats should also be given in order to make them as effective as possible.

Author Response

Point-by-point responses to Reviewers’ Comments

reviewer#1

Response: Thank you very much for your positive understanding on our works. We have carefully revised the old version of manuscript according to the reviewer’s comments.

Detailed comments below:

Abstract

Explain the abbreviation 2-MIB - it is later explained in the text but should also be in the abstract

Response: We have inserted the full name of 2-MIB in abstract, defined as 2-methylisoborneol.

Materials and Methods

No morphometric data of the analyzed reservoir constituting the water intake. Morphometric data, information on the use of the catchment and existing sources of pollution should be included. A map with the location of the reservoir and water intake would also be a good illustration.

Response: According to the reviewer’s recommendation, we have added a map of the studying reservoir (Figure 1) and inserted a water intake with the simple explanation (Figure 2).

Apart from the ABM scheme, it would be helpful to include a picture of such a mat.

Response: According to the reviewer’s recommendation, we inserted a picture of mat structure of both SBM (simple blocking mat) and AFM (algal filtering mat) into Table 1.

There is no information on whether these mats were rinsed, suspended solids or periphyton development during the study.

Response: According to the reviewer’s recommendation, we have added that “and rinsed with a strong water pressure using field water to remove suspended solids or periphyton development during the study”.

In what months was daily monitoring carried out?

Response: We have conducted the daily monitoring in August (Aug 24 and 25), due to the algal blooming period of cyanobacteria with high water temperature in Korea-wide.

Was the water transparency measured in the reservoir?

Response: We have measured the water transparency both IN (water passed through AFM) and OUT (reservoir), but did not measure Secchi disc depth. We have used the underwater light intensity photometer between surface and bottom, and HOBO photometer settled at 1 m depth. In this study, both photometers were used to measure the fluctuation of light intensity for the determination of washing time and/or periods of SBM and AFM.

Response: We acknowledge the reviewer’s comment that we have prepared Table 3 showing the mean and standard deviation of dissolved oxygen, pH, electrical conductivity, and turbidity.

Results

This chapter should actually be called Results and Discussion, because it contains not only the results of research but also their discussion.

Response: Thank you very much. According to the reviewer’s recommendation, we revised as Results and Discussion.

Response: Thank you for your kind comments. Actually, Figure 2 showed average cell abundance from the vertical water column. Using average data, we wanted to show the overall change of biomass and dominant species. In the early days of the experiment, low cell abundance of Bacillariophyceae (diatom) was appeared at low temperatures. Later, harmful blue green algae were increased explosively due to the increase in temperature.

Page 5 line 7 - "This increase was due to increased total phosphorus" - on what basis was this statement made? What were the phosphorus concentrations?

Response: According to the reviewer’s comments, we have made a new graph presenting the relationship between total phosphorus and precipitation. As you can see, the total phosphorus concentration tends to increase after the rainfall on July 25. The graph is based on data from the Korea Meteorological Administration and the Ministry of Environment.

Page 6 line 8 – I don’t understand „ The ARE ranged from -98 to 65%” What does it mean „-98”?

Response: We acknowledge the reviewer’s comment. We revised that sentence as “The ARE largely varied from –98 to 65%, minus means more increase of phytoplankton density in IN passed through ABM than reservoir”.

Response: According to the reviewer’s comments, we removed a term “Monthly” from the old title.

Figure 6 - what does a single column mean? Not clear description of the X axis.

Response: Thank you very much. A single column (dotted line) that show not algal removal efficiency, the same algal density in both IN and OUT. We added a related sentence to the captions of Figure 7.

Page 9 line 4 - does 35% mean average value from vertical profile or other value?

Response: Thank you very much. We calculated the average value using vertical profile, a difference in light intensity at 1-m water depth between IN and OUT of ABM.

The discussion should be enriched with literature on the use of materials to reduce the inflow of cyanobacteria to water intakes.

How effective is ABM compared to other methods? Specific recommendations on the use of these mats should also be given in order to make them as effective as possible.

Response: Thank you very much for your kind comments. According to the reviewer’s comments, we added the new sentence to compare to other methods, in the highlight of the effective advantages and operational necessity of ABM methods documented in this study.

Reviewer 2 Report

The manuscript entitled "Control of nuisance cyanobacteria in drinking water resources using alternative algal-blocking mats" refers to very important aspect of cyanobacterial harmful blooms occurrence and the possibility to control them. There are some uncertain sentences and inconsistencies which require to be checked and corrected. Generally, the results are poorly discussed. The section of “Discussion” is missed. Only a few sentences in the section “Results” refer to partial discussion. Thus, this manuscript requires a major revision. After careful revision, it can be re-submitted to WATER.

Detailed main comments

Cyanobacteria is more common used name instead of “blue-green algae”.
Nowadays, CyanoHABs refer to cyanobacterial harmful algal blooms.
The aim of the study should be clarified.
Please verified the pore size in Table 1 (µm) and the values given in the text below this table: “…a simple blocking mat (SBM), which can block small particulate matter (<9 mm).” and “A permeable algal filtering mat (AFM, pores ≤100 mm, porosity: 92%, thickness: 2 cm)”.
Please correct the sentence: “To measure the biomass of phytoplankton, water samples were collected at each depth, fixed with 1% Lugol’s solution, and transferred to the lab.” In real, there was measured only density of phytoplankton expressed as abundance in cells/mL. What was counted? Single cells or colonies?
What does mean “standing crop”? Please explain.
Please use a proper time expression throughout the whole manuscript, e.g. “11:30 am - 1:30 pm” – instead “11:30-13:30”.
The section of “Results” should be “Results and Discussion”.
Discussion should be improved and markedly broaden.
Please revise in the sentence “… diatom species Cyclotella, Fragilaria, and Aulacoseira …” – there are genera not species. Please check throughout the whole manuscript.
Please check the sentence: “The ARE ranged from –98 to 65%.” When did the value of -98% happen? Are you sure? In 10-June in middle layer?
Please revise the taxonomic names of species. For example: instead of Anabaena crassa (Lemmermann) Komárková-Legnová & Cronberg should be Dolichospermum crassum (Lemmermann) P.Wacklin, L.Hoffmann & J.Komárek. Please check the currently accepted taxonomically names according to AlgaeBase (https://www.algaebase.org/).

Author Response

Point-by-point responses to Reviewers’ Comments

reviewer#2

The manuscript entitled "Control of nuisance cyanobacteria in drinking water resources using alternative algal-blocking mats" refers to very important aspect of cyanobacterial harmful blooms occurrence and the possibility to control them. There are some uncertain sentences and inconsistencies which require to be checked and corrected. Generally, the results are poorly discussed.

The section of “Discussion” is missed. Only a few sentences in the section “Results” refer to partial discussion. Thus, this manuscript requires a major revision. After careful revision, it can be re-submitted to WATER.

Response: Thank you very much for your kind comments. We carefully revised the old version of manuscript according to the reviewer’s comment.

Detailed main comments

Cyanobacteria is more common used name instead of “blue-green algae”.

Nowadays, CyanoHABs refer to cyanobacterial harmful algal blooms.

Response: According to the reviewer’s comment, all of the term “blue-green algae” used over the text was revised as cyanobacteria or cyanobacterial harmful algal blooms.

The aim of the study should be clarified.

Response: According to the reviewer’s comment, the old version of manuscript was revised, to add the aim of study to the last part of introduction.

Please verified the pore size in Table 1 (µm) and the values given in the text below this table: “…a simple blocking mat (SBM), which can block small particulate matter (<9 mm).” and “A permeable algal filtering mat (AFM, pores ≤100 mm, porosity: 92%, thickness: 2 cm)”.

Response: According to the reviewer’s comment. The unit over the text was revised as the same unit (µm).

Please correct the sentence: “To measure the biomass of phytoplankton, water samples were collected at each depth, fixed with 1% Lugol’s solution, and transferred to the lab.” In real, there was measured only density of phytoplankton expressed as abundance in cells/mL. What was counted? Single cells or colonies?

Response: According to the reviewer’s comment, we revised the sentence as “To measure the phytoplankton density, water samples were collected at each depth, fixed with 1% Lugol’s solution, and transferred to the lab. After precipitation of samples in a laboratory, the phytoplankton were identified, and their abundance (cells/mL) was enumerated using a Sedgwick-Rafter chamber under an inverted microscope (Olympus CKX41, Olympus, Japan).

What does mean “standing crop”? Please explain.

Response: We acknowledge the reviewer’s comment. The term “ standing crop” can be explained as various meaning of organism. In this study, we used the meaning of the phytoplankton density defined at the special time and space.

Please use a proper time expression throughout the whole manuscript, e.g. “11:30 am - 1:30 pm” – instead “11:30-13:30”.

Response: According to the reviewer’s comment, the unit 11:30 am - 1:30 pm were changed as 11:30-13:30.

The section of “Results” should be “Results and Discussion”.

Response: According to the reviewer’s comment, we made a section “Results and Discussion”

Discussion should be improved and markedly broaden.

Response: According to the reviewer’s comment, we added the new sentence to compare to other methods, in the highlight of the effective advantages and operational necessity of ABM methods documented in the last part of Discussion.

Please revise in the sentence “… diatom species Cyclotella, Fragilaria, and Aulacoseira …” – there are genera not species. Please check throughout the whole manuscript.

Response: According to the reviewer’s comment, the exact name of diatom species was inserted over the text.

Please check the sentence: “The ARE ranged from –98 to 65%.” When did the value of -98% happen? Are you sure? In 10-June in middle layer?

Response: We acknowledge the reviewer’s comment. We revised that sentence as “The ARE largely varied from –98 to 65%, minus means more increase of phytoplankton density in the water of IN passed through ABM than reservoir”.

Please revise the taxonomic names of species. For example: instead of Anabaena crassa (Lemmermann) Komárková-Legnová & Cronberg should be Dolichospermum crassum (Lemmermann) P.Wacklin, L.Hoffmann & J.Komárek. Please check the currently accepted taxonomically names according to AlgaeBase (https://www.algaebase.org/).

Response: We acknowledge the reviewer’s comment. We revised the name of Anabaena crassa as Dolichospermum crissum.

Reviewer 3 Report

The title: Control of nuisance cyanobacteria in drinking water resources using alternative algal-blocking mats

Procs: Distribution of species of phytoplankton analysis

Cons: There is no scientific discussion or data analysis.

Although it is hard to discuss and make a conclusion from field result, this MS is not suitable to be published due to no logic and scientific approach.

As mentioned in MS, algal-blocking mats are a kind of filter which can remove bio-contaminant by physical and biological reaction. However, the authors did not mentioned the physical effect. Instead, there is only reported for removal efficiency between out and in water quality.

Author Response

Point-by-point responses to Reviewers’ Comments

reviewer#3

The title: Control of nuisance cyanobacteria in drinking water resources using alternative algal-blocking mats

Procs: Distribution of species of phytoplankton analysis

Cons: There is no scientific discussion or data analysis.

Response: We acknowledge the reviewer’s comment. Actually, we first introduced and installed the ABM considering cyanobacterial biomass varying vertical migration depending a water depth, seasonal variation too. Therefore, our data wholly focused on the effect of ABM with SBM and AFM to block the phytoplankton biomass. In this study, we did not explain the exact function of both mats, because of heavy changeable flow (direction and strength) of lake water. This part would be a new challenge of our research team, although there is some difficulties to express the phenomenon in the laboratory until now. On the effective advantage and operational condition of ABM, we added the new sentence to compare to other methods, in the highlight of the effective advantages and operational necessity of ABM methods documented in the last part of Discussion.

Although it is hard to discuss and make a conclusion from field result, this MS is not suitable to be published due to no logic and scientific approach.

Response: We acknowledge the reviewer’s comment. Above all, we have tried out to maximize the blocking effect of ABM against cyanobacteria in reservoir. Actually, the PIF management organ have been used the simple blocking mat for 20 years. Unfortunately, they did not escape the physical damage due to the typhoon and heavy rainfall. This study is the first challenge to support the previous SBM, for the stabilization of the device structure. In sum, the scientific approach of ABM in the field is after the multiple laboratory experiment and model approaching. Again thank you for valuable comments.

Response: We acknowledge the reviewer’s comment. We added the new sentence to compare to other previous methods, in the highlight of the effective advantages of ABM methods documented in the last part of Discussion. Thank you.

Round 2

Reviewer 1 Report

I think that the manuscript has been significantly improved and now
warrants publication in Water.

Kind regards,

Author Response

Thanks very much for your help.

Reviewer 2 Report

Dear Authors ,

The original title of manuscript was: "Control of nuisance cyanobacteria in drinking water resources using alternative algal-blocking mats". Now, after improving the title is: "Control of harmful blue-green algae in drinking water resources using alternative algal-blocking mats".

Why you decided to use term "blue-green algae" in the title and in some parts of manuscript, if your response is: "Response: According to the reviewer’s comment, all of the term "blue-green algae" used over the text was revised as cyanobacteria or cyanobacterial harmful algal blooms."?

Why you use both terms: "blue-green algae" and "cyanobacteria"?

Detailed main comments

Dolichospermum crissum should be changed into Dolichospermum crassum in Table 2 and in the text.

Author Response

Response: Thank you so much. According to the reviewer’s comment, the title of manuscript was return to the original title including “nuisance”

Why you decided to use term "blue-green algae" in the title and in some parts of manuscript, if your response is: "Response: According to the reviewer’s comment, all of the term "blue-green algae" used over the text was revised as cyanobacteria or cyanobacterial harmful algal blooms."? Why you use both terms: "blue-green algae" and "cyanobacteria"?

Response: This is mistake. According to the reviewer’s comment, we replaced the “blue-green algae” by “cyanobacteria” over the text. All authors confirmed the use of this terminology, because our works did not appeal the toxic or harmful of cyanobacteria through the text.

Detailed main comments

Dolichospermum crissum should be changed into Dolichospermum crassum in Table 2 and in the text.

>> Response: Thank you so much. According to the reviewer’s comment, all of the term “Dolichospermum crissum” used over the text was revised as Dolichospermum crassum.

Reviewer 3 Report

Dear Authors

Thank you for kind and specific response.

As I said at the first review, I totally agree with you that it is hard to analyze results obtained from field study.

However, the modified MS still do not have scientific discussion and satisfy the standard to be published.

Author Response

As I said at the first review, I totally agree with you that it is hard to analyze results obtained from field study.

Response: Thank you very much for positive comments.

However, the modified MS still do not have scientific discussion and satisfy the standard to be published.

Response: According to the reviewer’s comment, we added some sentences and improved Discussion.

Round 3

Reviewer 2 Report

The corrections were made according to previous comments. However, a small verification of sentences should be done.

Please check and change the sentences in lines 310-312, 329-330 which are unclear and misleading: (1) “In this study, we did not confirm the occurrence of algae or algae colonies caused by ABM, especially Microcystis destruction and destruction. The SBM layer of ABM can effectively blocks the surface cyanobacteria or phytoplankton, but there is a possibility that the AFM can produce layer cyanotoxins like microcystin via a destruction of cyanobacteria or Microcystis colony, then enter PIF." (2) "The introduction of the ABM model to block cyanobacteria and Microcystis colony in the water purification plant like PIF should be considered several insights and application conditions."

Cyanobacteria is one of the component in phytoplankton and Microcystis is cyanobacterium as you mentioned in lines 32, 169, 203, 215, 232, 250-251.

Please explain why the author list was extended in the manuscript version 3. Hyuk Lee was joined as one of the authors.

Author Response

The corrections were made according to previous comments. However, a small verification of sentences should be done.

Response: I carefully revised the manuscript over the text according to the reviewer's comments

Please check and change the sentences in lines 310-312, 329-330 which are unclear and misleading:

1) “In this study, we did not confirm the occurrence of algae or algae colonies caused by ABM, especially Microcystis destruction and destruction. The SBM layer of ABM can effectively blocks the surface cyanobacteria or phytoplankton, but there is a possibility that the AFM can produce layer cyanotoxins like microcystin via a destruction of cyanobacteria or Microcystis colony, then enter PIF."

Response: I revised as " In this study, the incidence of destroyed cyanobacterium Microcystis and colonies by ABM was not confirmed. Within the ABM, the SBM layer can effectively block the surface cyanobacteria, but AFM can also destroy Microcystis and colonies and introduce microcystin into the PIF. Therefore, to confirm this, in vitro testing of the destruction of Microcystis and colonies, and the production and penetration of microcystin using AFM is required

2) "The introduction of the ABM model to block cyanobacteria and Microcystis colony in the water purification plant like PIF should be considered several insights and application conditions."

Response: According to the reviewer's recommendations, I revised as " In order to block nuisance cyanobacterium Microcystis and its colonies in water purification plant like PIF, the application of the ABM model should be considered the following several points:

Cyanobacteria is one of the component in phytoplankton and Microcystis is cyanobacterium as you mentioned in lines 32, 169, 203, 215, 232, 250-251.

Response: According to the reviewer's recommendations, the term Microcystis was replace by cyanobacterium Microcystis over the text.

Please explain why the author list was extended in the manuscript version 3. Hyuk Lee was joined as one of the authors.

Response: Dr. Hyuk Lee was added by all co-authors, due to the contribution of validation and draft preparation.