Variation of Diatoms and Silicon in a Tributary of the Three Gorges Reservoir: Evidence of Interaction
Round 1
Reviewer 1 Report
The authors took in consideration our concerns from the last two rounds of reviews. In particular, since the last round:
- figure 4 is now legible
- the captions of tables 1 and 2 are now complete
- the language overall has been improved
- the references have been corrected.
I do not have any additional issues with this paper which, as far as I m concerned, is ready for publication.
Author Response
Response to Reviewers
Dear editor and reviewers:
We appreciated editor and reviewers for your comments and constructive suggestions on our manuscript. We have considered these comments carefully and made corrections, hope the revision meet with approval. We are looking forward to your consideration. The main corrections in the manuscript and the responds to the reviewer’s comments are explained in the following:
Response to Reviewer 1 Comments
The authors took in consideration our concerns from the last two rounds of reviews. In particular, since the last round:
- figure 4 is now legible
- the captions of tables 1 and 2 are now complete
- the language overall has been improved
- the references have been corrected.
I do not have any additional issues with this paper which, as far as I m concerned, is ready for publication
Response: Thank you for your positive comments.
Response to Reviewer 2 Comments
Major concern:
1. In both the result and the discussion sections, give us more specific on diatom community at genus level. Right now, only community structure at family level is discussed. This is insufficient when the authors are trying to connect the diatom composition with environmental variables. This is a major concern and I do believe it takes the authors' a quite bit of time to revise.
Response: Thanks for your suggestion. This manuscript was reworked according to your advice. Figure 4 provides the diatom cell density and composition at different sites. There were mainly 15 kinds of diatoms detected from the Xiangxi River (Fig.4B), Cyclotella, Melosira, Amphiprora and Synedra were the most common genus, and the discussion section was modified according to your suggestion.
2 Minor concerns
1. The similarity and difference between dissolved silicon and biogenic silicon is not introduced very clearly here. Try to convey them in a more logic way. The similarities and the differences are including the source, the destination, the range of absolute amount in the water, the conversion between each other, etc. And clarify in the introduction that if these two silicon pools are the main sources of silicon in the water.
Response: We agree with your opinion. All these information have been provided in the revision. The information on the similarity and difference between dissolved silicon and biogenic silicon was added. The absolute numbers of diatoms and composition at each site were provided in the revision.
2. Separate the content between Line 128-143 to another subsection as they're not discussing the study site per se but something on sample collection.
Response: Thank you for pointing this out. This manuscript was reworked according to your advice.
3. Please add necessary legend to every panel of figure 4.
Response: Thanks for your suggestion. It was modified.
4. Upload all data into a public-access data repository and give the link in the paper.
Response: Thanks for your suggestion. Considering that the experimental projects we have carried out have not been fully completed, according to the project requirements, the experimental data is not yet publicly available. We will disclose the data when the trial project is over. But if you need it now, we can send it to you separately.
We appreciated Editors/Reviewers’ work earnestly, and hope that the corrections will meet with your approvals.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Major concern:
1 In both the result and the discussion sections, give us more specific
on diatom community at genus level. Right now, only community structure
at family level is discussed. This is insufficient when the authors are
trying to connect the diatom composition with environmental variables.
This is a major concern and I do believe it takes the authors' a quite
bit of time to revise.
2 Minor concerns
1 The similarity and difference between dissolved silicon and biogenic silicon is not introduced very clearly here. Try to convey them in a more logic way. The similarities and the differences are including the source, the destination, the range of absolute amount in the water, the conversion between each other, etc. And clarify in the introduction that if these two silicon pools are the main sources of silicon in the water.
2 Separate the content between Line 128-143 to another subsection as they're not discussing the study site per se but something on sample collection.
3 Please add necessary legend to every panel of figure 4.
4 Upload all data into a public-access data repository and give the link in the paper.
Author Response
Response to Reviewers
Dear editor and reviewers:
We appreciated editor and reviewers for your comments and constructive suggestions on our manuscript. We have considered these comments carefully and made corrections, hope the revision meet with approval. We are looking forward to your consideration. The main corrections in the manuscript and the responds to the reviewer’s comments are explained in the following:
Response to Reviewer 1 Comments
The authors took in consideration our concerns from the last two rounds of reviews. In particular, since the last round:
- figure 4 is now legible
- the captions of tables 1 and 2 are now complete
- the language overall has been improved
- the references have been corrected.
I do not have any additional issues with this paper which, as far as I m concerned, is ready for publication
Response: Thank you for your positive comments.
Response to Reviewer 2 Comments
Major concern:
1. In both the result and the discussion sections, give us more specific on diatom community at genus level. Right now, only community structure at family level is discussed. This is insufficient when the authors are trying to connect the diatom composition with environmental variables. This is a major concern and I do believe it takes the authors' a quite bit of time to revise.
Response: Thanks for your suggestion. This manuscript was reworked according to your advice. Figure 4 provides the diatom cell density and composition at different sites. There were mainly 15 kinds of diatoms detected from the Xiangxi River (Fig.4B), Cyclotella, Melosira, Amphiprora and Synedra were the most common genus, and the discussion section was modified according to your suggestion.
2 Minor concerns
1. The similarity and difference between dissolved silicon and biogenic silicon is not introduced very clearly here. Try to convey them in a more logic way. The similarities and the differences are including the source, the destination, the range of absolute amount in the water, the conversion between each other, etc. And clarify in the introduction that if these two silicon pools are the main sources of silicon in the water.
Response: We agree with your opinion. All these information have been provided in the revision. The information on the similarity and difference between dissolved silicon and biogenic silicon was added. The absolute numbers of diatoms and composition at each site were provided in the revision.
2. Separate the content between Line 128-143 to another subsection as they're not discussing the study site per se but something on sample collection.
Response: Thank you for pointing this out. This manuscript was reworked according to your advice.
3. Please add necessary legend to every panel of figure 4.
Response: Thanks for your suggestion. It was modified.
4. Upload all data into a public-access data repository and give the link in the paper.
Response: Thanks for your suggestion. Considering that the experimental projects we have carried out have not been fully completed, according to the project requirements, the experimental data is not yet publicly available. We will disclose the data when the trial project is over. But if you need it now, we can send it to you separately.
We appreciated Editors/Reviewers’ work earnestly, and hope that the corrections will meet with your approvals.
Author Response File: Author Response.docx
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
In order to investigate which environmental factors determine the distribution of different diatoms, these authors conducted an annual study on diatom communities from several sites in the upstream of Three Gorges Dam. By comparing the dominant diatom group with different silicon sources, the argument was made that the water velocity determines the diatom distribution and several other conclusions. Though in face of a few tiny flaws that require some minor revisions, the overall quality looks pretty good and the main findings have been clearly stated.
Here are my detailed comments:
1 The primary science question that the authors were motivated by to conduct this study, ought to be better clearly and logically stated in the introduction section.
2 More background information on the conversion between Bsi and Dsi should be introduced, as Dsi and Bsi are not two independent variations and have their own intrinsic association in the water. Considering Dsi requires more time to be converted to biological available, is it possible that in riverine areas, by larger water velocity, the conversion yield from Dsi is Bsi is low in a certain time course because most Dsi has been run off by the water? Rather in lacustrine area Dsi has more time to convert to Bsi?
3 A map of Dsi and Bsi at different collection sites ought to be given for better visualization.
3 In summary, there are three pairs of variations involved in this study determining the diatom groups: Dsi (low and high), Bsi (low and high), water character (riverine and lacustrine areas), thus if the authors could make a table to summarize these variations with diatom group character, this findings of the paper should look particularly clear and easy to grasp.
Author Response
Response to Reviewer 1 Comments
In order to investigate which environmental factors determine the distribution of different diatoms, these authors conducted an annual study on diatom communities from several sites in the upstream of Three Gorges Dam. By comparing the dominant diatom group with different silicon sources, the argument was made that the water velocity determines the diatom distribution and several other conclusions. Though in face of a few tiny flaws that require some minor revisions, the overall quality looks pretty good and the main findings have been clearly stated.
Response: Thank you for your positive comments. This manuscript was reworked according to your advice.
Here are my detailed comments:
Point 1 The primary science question that the authors were motivated by to conduct this study, ought to be better clearly and logically stated in the introduction section.
Response 1: Thanks for your suggestion. The primary science question in the introduction section was modified to make it clearly and logically.
Point 2 More background information on the conversion between Bsi and Dsi should be introduced, as Dsi and Bsi are not two independent variations and have their own intrinsic association in the water. Considering Dsi requires more time to be converted to biological available, is it possible that in riverine areas, by larger water velocity, the conversion yield from Dsi is Bsi is low in a certain time course because most Dsi has been run off by the water? Rather in lacustrine area Dsi has more time to convert to Bsi?
Response 2: We agree with your opinion. The information on the conversion between BSi and DSi was added. Dsi and Bsi are not two independent variations in the water and the process of DSi converted to biological available silicon needs time. When water velocity is high, the hydraulic retention time is short and can’t meet the need of converting procedure. When water velocity is low, the hydraulic retention time is long and the converting procedure would be finished in the Xiangxi River. On the other side, water temperature is also a very important factor in this procedure. Compared to the riverine areas, the lacustrine area would be easier to finish this procedure. So, in the lacustrine area, diatom could deplete DSi and produce BS in a stable environment.
Point 3 A map of Dsi and Bsi at different collection sites ought to be given for better visualization.
Response 3 : The map of DSi and BSi at different collection sites was given.
Point 4 In summary, there are three pairs of variations involved in this study determining the diatom groups: Dsi (low and high), Bsi (low and high), water character (riverine and lacustrine areas), thus if the authors could make a table to summarize these variations with diatom group character, this findings of the paper should look particularly clear and easy to grasp.
Response 4: Thank you for your advice. The table was added in the revision according to your suggestion. Diatom group character was added in Figure 3.
Author Response File: Author Response.docx
Reviewer 2 Report
Overall the authors of this paper have collected an interesting data set regarding diatons and their relationship with environemntal parameters in the Three Gorges Reservoir. However, the data could be presented ina more comprehensive and informative fashion, and this would improve the paper greatly.
Methods
There is not enough information on the methods used. For example, how were diatoms and water samples collected? Were samples taken from each site in triplicate?
How were the sites classified into Lacustrine and Riverine. On what basis was this done - was it water velocity?
There seems to be just 2 sites for riverine samples, and 10 for lacustrine. Are all of the lacustrine sites similar in water quality? Were they all grouped together in the subsequent analysis?
More infomration is needed on how the DSi adn BSi was measured - not just a reference [29]. More detail also needed on waht wavelengths were CHl-a measured at. How were algal species quanitfied - what sort of counting chamber, how many cells were counted?
Why was COD measured? What relevance does COD have in the system under study?
In summary, for the methods more detail is required, more infomration on replication, and and more justification for the sites selection and grouping.
Results
The paper refers to diatom community structure and diatom species, however no data is presented on species composition. The closest to this is Figure 3 which has cell density, but does not give an indication of the types of diatoms present. Fig 6 shows a proportion of pennates, but only as a percentage. It would be good to see absolute numenrs of diatoms at each site and how they varied.
There are 10 lacustrine sites, yet they are grouped together. Was there no varation in these lacustrine sites?
There is also no data on the environmental parameters measured at each site. For example, what was velocity at each site.
DSi and BSi are in units of umol/L, it is much more common in freshwater ecology to use mg/l. Using mg/l will make it much easier for the reader to compare your findings to other studies.
In summary, there is lots of data available that is not shown. For example, cell counts, environmental analysis, species composition lists, but these are not shown. In addition it would be very interesting to see how the parameters varied between the different sites studies. Water velocity seems very important but no data is given on this (and the description of how it was measured in the methods does not privide enoguh information)
The authors refer to a paper (Bahnwart et al., 1998) that also looked at longitudinal changes in diatoms, and that paper does procide information on water velocity, and changes in algal community sturcture at each site, and I feel the current paper would benefit form this approach to data presentation.
Discussion
It is difficult to determine if the discussion and conclusions are justified by the data presented due to the large amo9unt of data that is not shown, and the way many sites have been grouped together.
I am a little worried that in the manuscript centric diatoms are refered to as a species however they are not a species. They are also referred to earlier as a genus (line 183) and they are not a genus either.
Line 225 states that 'centric diatoms had a postive realtionship with water velocty' yet line 192 refers to 'centric is negatively correlated with water velocity'. This is confused.
The discussion referes to parameters such as light penetration, water transparancy but no data is provided on this.
Other points.
Line 33: This sentence seems to be incorrect - 371 tons of dissolved silicon and 8835 tons of particulate is very small indeed - I think tyou mean Million tons?
Line 42: 'a silicon decrease is observed in many rivers and lakes worldwide' - over what time scale does this statement apply. There is a decrease annually during the growth season but are you saying that there is a decrease in silicon in waters over longer time scales?
Author Response
Overall the authors of this paper have collected an interesting data set regarding diatons and their relationship with environemntal parameters in the Three Gorges Reservoir. However, the data could be presented in a more comprehensive and informative fashion, and this would improve the paper greatly.
Response: Thank you for your comments. This manuscript was reworked according to your advice.
Methods
There is not enough information on the methods used. For example, how were diatoms and water samples collected? Were samples taken from each site in triplicate?
Response: Surface water samples (0.5m) were collected with a Van Dorn sampler at each site, all samples were run in triplicate. Samples for quantitative phytoplankton analyses sere fixed with neutral Lugol’s solution, and concentrated after 48h sedimentation. All these information was provided in the revision.
How were the sites classified into Lacustrine and Riverine. On what basis was this done - was it water velocity?
Response: Yes, it’s based on water velocity to classify study sites into lacustrine and riverine zone. It was added in the materials and methods section.
There seems to be just 2 sites for riverine samples, and 10 for lacustrine. Are all of the lacustrine sites similar in water quality? Were they all grouped together in the subsequent analysis?
Response: Yes, only two sites was the delegates from the riverine area and 10 for lacustrine. A table was given in the revision to show the physic-chemical parameter of each site. And all of the lacustrine sites are similar in water quality, so they are grouped together in the subsequent analysis.
More infomration is needed on how the DSi adn BSi was measured - not just a reference [29]. More detail also needed on waht wavelengths were CHl-a measured at. How were algal species quanitfied - what sort of counting chamber, how many cells were counted?
Response: The measurement methods of DSi and BSi were added in detail. The wavelengths and other information on chl a and algal species quantified were provided.
Why was COD measured? What relevance does COD have in the system under study?
Response: COD was used as an environmental parameter and related with diatom in this study,.
In summary, for the methods more detail is required, more infomration on replication, and more justification for the sites selection and grouping.
Response: All the information had been added in the revision.
Results
The paper refers to diatom community structure and diatom species, however no data is presented on species composition. The closest to this is Figure 3 which has cell density, but does not give an indication of the types of diatoms present. Fig 6 shows a proportion of pennates, but only as a percentage. It would be good to see absolute numenrs of diatoms at each site and how they varied.
Response: The absolute numbers of diatoms and composition at each site were provided in the revision.
There are 10 lacustrine sites, yet they are grouped together. Was there no varation in these lacustrine sites?
Response: Yes, there were 10 site in the lacustrine area. Due to they showed similar the physio-chemical characteristics and similar diatom communities, so they were grouped together. No obvious variation in these sites could be found.
There is also no data on the environmental parameters measured at each site. For example, what was velocity at each site.
Response: The environmental conditions at each site were showed in a table in the revision.
DSi and BSi are in units of umol/L, it is much more common in freshwater ecology to use mg/l. Using mg/l will make it much easier for the reader to compare your findings to other studies.
Response: Since BSi concentration is low, it’s common to useμmol/L instead of mg/L.
In summary, there is lots of data available that is not shown. For example, cell counts, environmental analysis, species composition lists, but these are not shown. In addition it would be very interesting to see how the parameters varied between the different sites studies. Water velocity seems very important but no data is given on this (and the description of how it was measured in the methods does not privide enoguh information)
The authors refer to a paper (Bahnwart et al., 1998) that also looked at longitudinal changes in diatoms, and that paper does procide information on water velocity, and changes in algal community sturcture at each site, and I feel the current paper would benefit form this approach to data presentation.
Response: All information has been provided in the revision. The reference has been checked carefully.
Discussion
It is difficult to determine if the discussion and conclusions are justified by the data presented due to the large amount of data that is not shown, and the way many sites have been grouped together.
I am a little worried that in the manuscript centric diatoms are refered to as a species however they are not a species. They are also referred to earlier as a genus (line 183) and they are not a genus either.
Response: Centric diatom was not a species and there were 28 species observed in this manuscript and they were grouped together as centric diatom.
Line 225 states that 'centric diatoms had a postive realtionship with water velocty' yet line 192 refers to 'centric is negatively correlated with water velocity'. This is confused.
The discussion referes to parameters such as light penetration, water transparancy but no data is provided on this.
Response: Thank you for your comments. This is a mistake in writing. The sentence was corrected as “centric diatoms had a negative relationship with water velocity”.
Other points.
Line 33: This sentence seems to be incorrect - 371 tons of dissolved silicon and 8835 tons of particulate is very small indeed - I think you mean Million tons?
Response: This is a mistake in writing. Yes, it should be million tons. We have modified it in the revision.
Line 42: 'a silicon decrease is observed in many rivers and lakes worldwide' - over what time scale does this statement apply. There is a decrease annually during the growth season but are you saying that there is a decrease in silicon in waters over longer time scales?
Response: We have modified this sentence. Silicon concentration deceased over one or more decades, not annually during the growth season.
Author Response File: Author Response.docx
Reviewer 3 Report
The article tries to analyse the relationship between diatom concentration, silica concentration and hydrography in a tributary in the Three Gorge Reservoir. The data acquired are valuable. The discussion and conclusions make sense given the results. However, there are a certain number of (major) issues that needs to be addressed before considering this article for publication:
- The method section is problematically incomplete: in particular, no details are given as to how the diatom data was collected (were the samples sieved, decanted, other? was a specific area [if dried]/volume [if not] counted? etc.). Without this information the results are irreproducible.
- The way the introduction is written is confusing at best: the use of past tense coupled with the lack of transition between sentences/paragraph makes the whole lot difficult to understand.
- Several references are either missing or incorrect (see below for details).
- Although the statistics shown are relevant to the study, some additional statistics should be also shown: the data in question in the study are time-series, yet no stats specifics to time-series are used. In particular, seasonality seems to be important here but is not accounted for by any of the statistical tool used. Also, given the Three Gorges Reservoir was set up during the timeframe of the study, a comparison of the community before and after this set-up seems necessary (given the authors draw conclusions on that point, see lines 218-219). Additionally and importantly, the fact that it was set up during the timeframe of the study is not mentioned anywhere in the article: this seems like a relevant bit of information that change drastically the context of the article.
- I assume the “conflict of interest” section will only be added after review, but given the subject and who the authors funder is, it seems important to be stated clearly.
- I do believe the underlying data should thus be given as supplementary material given how important they are to the paper. Given the conflict of interest, it is in the interest of the authors to provide them as well as a clear methodology (see above), to alleviate any worries about a potential bias.
Follow line-by-line comments:
Line 41: is "precipitates" the right word here?
Line 41-42: "DSi can hardly be compensated by anthropogenic activities" why would the author expect it to?
"Since BSi precipitates to the sediment and DSi can hardly be compensated by anthropogenic activities, a silicon decrease is observed in many rivers and lakes worldwide [4-6]." I'm quite confused by that sentence, please rephrase.
Line 43: "were related". are related? Or are you talking about a specific time/area/study?
Lines 43-56: feels honestly like a random collection of facts having to do with what impact diatom growth. Need to be rewritten in my opinion.
Line 48: Skeletonema costatum should be in italics.
Line 109: What does SVR stands for?
Line 110: Is there a scientific publication explaining how this system works?
Line 111: Acronym COD should be spelled out on its first occurrence, do the author mean DOC=Dissolved Organic Carbon? Also Gilcreas 1966 is the reference of an editorial introducing the "Standard methods" not the reference to the "Standard Methods" itself, as far as I can tell.
Line 116: Olympus
Line 116: How were the diatom quantified specifically? Was a specific slide area considered, as specific tally of diatoms, ...? How were the diatom samples prepared, collected? More explanations are needed as this is the main measurement considered in this article.
Lines 118-129. References are missing for Origin 9.1, SPSS, T-test, Spearman analysis, Redundancy analysis, CANOCO, etc.
Line 142: Language: the detection limit of 4.51µmol/L
Line 145: "significantly" but p.value>0.05. Everywhere else in the MS "significance" is defined as being at least <0.05.
Line 186: "environmental variables were standardized by normalization" can the authors be more precise?
Line 218-219: "Therefore, TGR’s operation enhanced the diatom cell density and prolonged diatom growth period in the lacustrine zone of the tributary."
Nowhere in the article is it mentioned that the TGR operation started during the studied timeframe. This seems like an important information that is lacking. Also, given this fact, some analysis are lacking: how about comparing explicitely before and after?
Line 259: Can't it be just that BSi is more recycled in riverine zone? If not, what does that means: are diatom cell bigger in the riverine zone, or more heavily-silicified? This seems like something the authors might have been able to observed while collecting their diatom data.
Line 261: "provided the further evidence that diatom was the main contributor to BSi" True. Which raise the question: what about synurophytes in the Xiangxi River?
Line 267: "It could be speculated that when cell density increase by an order of magnitude, DSi concentration would decrease by 6.45 μmol/L" This sentence only make sense if "by an order of magnitude" is replaced by an actual number.
Line 269: "However, no correlation was found between DSi and diatom cell density in the riverine zone (Figure 4B)."
Actually this is precisely not shown on that figure. Even if there is no correlation, the result of the linear regression should be shown (with its R2, equation, etc.)
Line 282: Language: On the other side, centric diatom flourishing would promote silicon cycling efficiency in the reservoir while exerting negative influence on the downstream rivers and its adjacent estuary.
Line 289 "Considering diatom contributes approximately 40% of the global marine primary productivity" the correct citation for that statement is Nelson et al. 1995:
Nelson, D.M., Treguer, P., Brzezinski, M.A., Leynaert, A., Queguiner, B., 1995. Production and dissolution of biogenic silica in the ocean: revised global estimates, comparison with regional data and relationship to biogenic sedimentation. Glob. Biogeochem. Cycles 9, 359-372.
Also, this is an estimate for "marine" diatom productivity, not freshwater, so I fail to see the relevance here.
Reference 12: this paper was written by two persons. The correct citation is:
Egge, J.K, Aksnes, D.L. Silicate as regulating nutrient in phytoplankton competition. Mar. Ecol. Prog. Ser 1992, 83, 281-289.
Reference 36: format issue.
Author Response
The article tries to analyse the relationship between diatom concentration, silica concentration and hydrography in a tributary in the Three Gorge Reservoir. The data acquired are valuable. The discussion and conclusions make sense given the results. However, there are a certain number of (major) issues that needs to be addressed before considering this article for publication:
Response: Thank you for your comments. This manuscript was reworked according to your advice.
- The method section is problematically incomplete: in particular, no details are given as to how the diatom data was collected (were the samples sieved, decanted, other? was a specific area [if dried]/volume [if not] counted? etc.). Without this information the results are irreproducible.
Response: All these information have been provided in the revision.
- The way the introduction is written is confusing at best: the use of past tense coupled with the lack of transition between sentences/paragraph makes the whole lot difficult to understand.
Response: We have corrected the tense and the sentence structure.
- Several references are either missing or incorrect (see below for details).
- Although the statistics shown are relevant to the study, some additional statistics should be also shown: the data in question in the study are time-series, yet no stats specifics to time-series are used. In particular, seasonality seems to be important here but is not accounted for by any of the statistical tool used. Also, given the Three Gorges Reservoir was set up during the timeframe of the study, a comparison of the community before and after this set-up seems necessary (given the authors draw conclusions on that point, see lines 218-219). Additionally and importantly, the fact that it was set up during the timeframe of the study is not mentioned anywhere in the article: this seems like a relevant bit of information that change drastically the context of the article.
- I assume the “conflict of interest” section will only be added after review, but given the subject and who the authors funder is, it seems important to be stated clearly.
- I do believe the underlying data should thus be given as supplementary material given how important they are to the paper. Given the conflict of interest, it is in the interest of the authors to provide them as well as a clear methodology (see above), to alleviate any worries about a potential bias.
Response: All you’re concerned were be treated seriously and the information in detail was provided in the revision, including the TGR operation process in the study site section.
Follow line-by-line comments:
Line 41: is "precipitates" the right word here?
Response: it was replaced by “deposite”.
Line 41-42: "DSi can hardly be compensated by anthropogenic activities" why would the author expect it to?
Response: Because DSi cannot be added much to the water through fertilizing or sewage like other nutrients like nitrogen and phosphorus by anthropogenic activities. Compared to this, weathering is the only way for DSi compensation. We think it is hard to be compensated.
"Since BSi precipitates to the sediment and DSi can hardly be compensated by anthropogenic activities, a silicon decrease is observed in many rivers and lakes worldwide [4-6]." I'm quite confused by that sentence, please rephrase.
Response: This sentence was modified and made it clearly in the revision.
Line 43: "were related". are related? Or are you talking about a specific time/area/study?
Response: It should be “were related”, and it’s talking about the specific study.
Lines 43-56: feels honestly like a random collection of facts having to do with what impact diatom growth. Need to be rewritten in my opinion.
Response: The paragraph to emphasize the importance of silicate availability on diatom growth was rewritten to make it clear.
Line 48: Skeletonema costatum should be in italics.
Response: Thank you for your advice. It was modified.
Line 109: What does SVR stands for?
Response: SVRTM is a hand-held electronic wave water velocity detector made by Decatur Electronics, Inc, USA.
Line 110: Is there a scientific publication explaining how this system works?
Response: Yes, some information was added.
Line 111: Acronym COD should be spelled out on its first occurrence, do the author mean DOC=Dissolved Organic Carbon? Also Gilcreas 1966 is the reference of an editorial introducing the "Standard methods" not the reference to the "Standard Methods" itself, as far as I can tell.
Response: COD = Chemical oxygen demand. The reference “APHA”(American Public Health Association) was corrected.
Line 116: Olympus
Response: Yes, it was modified.
Line 116: How were the diatom quantified specifically? Was a specific slide area considered, as specific tally of diatoms, ? How were the diatom samples prepared, collected? More explanations are needed as this is the main measurement considered in this article.
Response: These information was added in the method section.
Lines 118-129. References are missing for Origin 9.1, SPSS, T-test, Spearman analysis, Redundancy analysis, CANOCO, etc.
Response: We have added the reference required.
Line 142: Language: the detection limit of 4.51µmol/L
Response: From the detection limit to 4.51μmol/L
Line 145: "significantly" but p.value>0.05. Everywhere else in the MS "significance" is defined as being at least <0.05.
Response: It’s not significant. We have corrected it.
Line 186: "environmental variables were standardized by normalization" can the authors be more precise?
Response: We have added the details.
Line 218-219: "Therefore, TGR’s operation enhanced the diatom cell density and prolonged diatom growth period in the lacustrine zone of the tributary."
Nowhere in the article is it mentioned that the TGR operation started during the studied timeframe. This seems like an important information that is lacking. Also, given this fact, some analysis are lacking: how about comparing explicitely before and after?
Response: We have added the information about TGR operation process in the study site section.
Line 259: Can't it be just that BSi is more recycled in riverine zone? If not, what does that means: are diatom cell bigger in the riverine zone, or more heavily-silicified? This seems like something the authors might have been able to observed while collecting their diatom data.
Response: One of the reasons is that BSi is more recycled in the riverine zone due to strong hydrodynamics especially in the flood season. Another reason is that there is more proportion of pennate diatom in the riverine zone, and pennate diatom is usually larger than centric diatom.
Line 261: "provided the further evidence that diatom was the main contributor to BSi" True. Which raise the question: what about synurophytes in the Xiangxi River?
Response: We admit that synurophytes may contribute to BSi. But the significant relationship between BSi and phytoplankton biomass (chla) demonstrates that the main contributor is diatom.
Line 267: "It could be speculated that when cell density increase by an order of magnitude, DSi concentration would decrease by 6.45 μmol/L" This sentence only make sense if "by an order of magnitude" is replaced by an actual number.
Response: We have replaced it by “expand ten fold”
Line 269: "However, no correlation was found between DSi and diatom cell density in the riverine zone (Figure 4B)."
Actually this is precisely not shown on that figure. Even if there is no correlation, the result of the linear regression should be shown (with its R2, equation, etc.)
Response: We have plot Figure 4B again
Line 282: Language: On the other side, centric diatom flourishing would promote silicon cycling efficiency in the reservoir while exerting negative influence on the downstream rivers and its adjacent estuary.
Response: We have correct the “exerting” into “exert”
Line 289 "Considering diatom contributes approximately 40% of the global marine primary productivity" the correct citation for that statement is Nelson et al. 1995:
Nelson, D.M., Treguer, P., Brzezinski, M.A., Leynaert, A., Queguiner, B., 1995. Production and dissolution of biogenic silica in the ocean: revised global estimates, comparison with regional data and relationship to biogenic sedimentation. Glob. Biogeochem. Cycles 9, 359-372.
Also, this is an estimate for "marine" diatom productivity, not freshwater, so I fail to see the relevance here.
Response: The correct citation was added in this revision. Diatom flourish and sediment in the riverine reservoir would reduce the silicate transport to the ocean in the long term, thus reduce the marine diatom growth.
Reference 12: this paper was written by two persons. The correct citation is:
Egge, J.K, Aksnes, D.L. Silicate as regulating nutrient in phytoplankton competition. Mar. Ecol. Prog. Ser 1992, 83, 281-289.
Reference 36: format issue.
Response: Both the two problems have been corrected.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
This manuscript is now improved.
INTRODUCTION
Quality of the English is poor in places, and this can lead to confusion. I have not marked every example of this, but a few examples are:
Line 71 ' and diatom species is different' - do you mean the effect of the environment varies depending on species?
Line 74 - ' More further researches'
Line 81 ' has worsen the eutrophication' instead of 'has worsened'
Line 82 'Biogeochemistry cycle' should be 'biogeochemical cycling'
Line 89 'the lower water water velocity' should be 'lower water velocity'
These are just a few examples - there are many other examples. The manuscript needs careful attention to the quality of the written English.
In line 42 I am confused about the biogenic silicon being an important 'component of the DSi', yet you measure DSi on 0.45 filtered water, and measure the BSi on the material retained by the filter paper. This would suggest to me that DSi and BSI are separate, and are defined by the cutoff of a 0.45 um filter paper, and that the BSI is actually particulate silicon?
METHODS
I do not understand why Figure 1 is in the results. It should be in the methods alongside the description of the study sites. There are no results in Figure 1, so it should not be in the results section.
Line 130 - It says samples were run in triplicate. Does this mean that 1 sample was taken at each site on each sampling occasion, and the single sample ran three times? Or were 3 samples taken from each site on each sampling occasion? This information needs to be included.
There is no information on what keys were used to identify the diatoms - how were they identified?
Why were cells measured (line 157)?
RESULTS
There is data presented in table 1 that is not in the methods section - for example SD, Turb, ORP, Fv.
There is also methods presented - for example COD that is not in Table 4 (or presented anywhere.
The legend for Table 1 is inadequate. What do the values represent? Is it a mean, what is the number of samples? Is the error an SE or SD. All this information should be in a clear legend.
Figure 2 again lacks information in the legend. Are these mean values? Where are there no error bars? What is the n numbers?
Figure 3 and 4 - again where is information about the data? The key to graphs 1 and 2 is missing the right hand side. Again are these means? Where are error bars? Are they averages over the full sampling period?
In summary the methods and results don't fully relate to each other. If the results are presented and used than the methods needs to describe how they were obtained.
There is obviously more data collected than described in the methods. It is therefore unclear which results were used in the RDA analysis. All of them?
FIGURE 7: I am confused by this as it shows pennate diatoms in the river to be up to 90% but this does not agree with Figure 4A where the pennate in the river sites is less than 50%. It may be that figure 4A is seasonal averages, while figure 7 is monthly values. If this is the case then it suggests that there is a lot of seasonal variation in the proportion of pennates/centrics, in which case (a) what is the points of grouping you data all together as an average over the whole sampling period as it masks the interesting seasonal variations and (b) why group all diatoms together in Figure 4C at the lacustrine and riverine sites, when it would be more interesting to show pennates and centrics separately?
Author Response
Response to Reviewer 2 Comments
May. 1th 2019
Dear editor and reviewer:
We appreciated editor and reviewers for your positive comments and constructive suggestions on our manuscript.We have considered these comments carefully and have made corrections that we hope the revision meet with approval. We are looking forward to your consideration. The main corrections in the manuscript and the responds to the reviewer’s comments are explained in the following:
INTRODUCTION
Quality of the English is poor in places, and this can lead to confusion. I have not marked every example of this, but a few examples are:
Line 71 ' and diatom species is different' - do you mean the effect of the environment varies depending on species?
Response: We rewrote this sentence. It was changed as “diatom species varied depending on the environmental conditions”.
Line 74 - ' More further researches'
Response: It was modified.
Line 81 ' has worsen the eutrophication' instead of 'has worsened'
Response: It was modified.
Line 82 'Biogeochemistry cycle' should be 'biogeochemical cycling'
Response: It was corrected.
Line 89 'the lower water water velocity' should be 'lower water velocity'
Response: It was corrected.
These are just a few examples - there are many other examples. The manuscript needs careful attention to the quality of the written English.
In line 42 I am confused about the biogenic silicon being an important 'component of the DSi', yet you measure DSi on 0.45 filtered water, and measure the BSi on the material retained by the filter paper. This would suggest to me that DSi and BSI are separate, and are defined by the cutoff of a 0.45 um filter paper, and that the BSI is actually particulate silicon?
Response: BSi is particulate silicon actually and a source of DSi. When BSi was decomposed, it would be transfer as DSi. DSi was measured with the water samples after the treatment of 0.45 μm filter and the residues on the filter was used to measure the BSi.
METHODS
I do not understand why Figure 1 is in the results. It should be in the methods alongside the description of the study sites. There are no results in Figure 1, so it should not be in the results section.
Response: The position of Figure 1 has been changed.
Line 130 - It says samples were run in triplicate. Does this mean that 1 sample was taken at each site on each sampling occasion, and the single sample ran three times? Or were 3 samples taken from each site on each sampling occasion? This information needs to be included.
Response: Single sample ran three times. This information was provided in the revision.
There is no information on what keys were used to identify the diatoms - how were they identified?
Response: The information has been submitted.
Why were cells measured (line 157)?
Response: Algal cell measuring was used to count the cell density and algal abundance.
RESULTS
There is data presented in table 1 that is not in the methods section - for example SD, Turb, ORP, Fv.
Response: Information was added in the revision.
There is also methods presented - for example COD that is not in Table 4 (or presented anywhere.
Response: COD was presented in Table 2 and Figure 8.
The legend for Table 1 is inadequate. What do the values represent? Is it a mean, what is the number of samples? Is the error an SE or SD. All this information should be in a clear legend.
Response: The information was added below the table.
Figure 2 again lacks information in the legend. Are these mean values? Where are there no error bars? What is the n numbers?
Response: They are the mean values during the study period. Since the variation range was large within the period, the error bars were not shown.
Figure 3 and 4 - again where is information about the data? The key to graphs 1 and 2 is missing the right hand side. Again are these means? Where are error bars? Are they averages over the full sampling period?
Response: They are mean values over the full sampling period (23 months). Since the variation range was large, the error bars were not shown.
In summary the methods and results don't fully relate to each other. If the results are presented and used than the methods needs to describe how they were obtained.
There is obviously more data collected than described in the methods. It is therefore unclear which results were used in the RDA analysis. All of them?
Response: All of environmental variables were used in the RDA, and a forward-selection was conducted in the RDA. Therefore only the significant environmental variables that remained in the figure.
FIGURE 7: I am confused by this as it shows pennate diatoms in the river to be up to 90% but this does not agree with Figure 4A where the pennate in the river sites is less than 50%. It may be that figure 4A is seasonal averages, while figure 7 is monthly values. If this is the case then it suggests that there is a lot of seasonal variation in the proportion of pennates/centrics, in which case (a) what is the points of grouping you data all together as an average over the whole sampling period as it masks the interesting seasonal variations and (b) why group all diatoms together in Figure 4C at the lacustrine and riverine sites, when it would be more interesting to show pennates and centrics separately?
Response: Figure 4A showed the pennate at each site over the full sampling period while figure 7 is monthly values. (a) Grouping the data all together as an average was to show the specific date at each site rather than two different zones. (b) Grouping all diatoms together in Figure 4C was to show the different diatom at each month in two different zones. Pennate and centric are not shown separately because pennate diatom density was always low at both zones from October to next March.
We appreciated Editors/Reviewers’ work earnestly, and hope that the corrections will meet with your approvals.
Yours sincerely,
Prof.Dr.Yonghong Bi
Author Response File: Author Response.docx
Reviewer 3 Report
@page { margin: 0.79in } p { margin-bottom: 0.1in; line-height: 115% }In my opinion, the authors adequately answered our most major concerns: in particular the material & methods section, which was critically incomplete, was significantly improved and expanded.
Remains a few minor issues:
Figure 4 is a wonderful addition to the manuscript but it should probably be redone as Panel B covers part of Panel A and Panel C part of Panel B. The three panels are also not aligned vertically, and the borders of panel B are showing. In my opinion the size and resolution of that figure should also be expanded as it contains a lot of details that are currently difficult to read: maybe the authors should redo it as a column, i. e. A over B over C, instead of side-by-side? Also, in Panel B the choice of colour is a bit unfortunate: is the main red that covers most of the plot Cyclotella or Cymatopleura?
Reference 48: In the author's reply to my comments, the authors claimed that citation 48 was corrected but it wasn't. The current citation (Hendry & Brzezinski 2014) did not come up with the estimate of 40%, they merely cite Nelson et al. 1995 who did.
The abbreviation used as column headers in the tables should be spelled out in the captions. Also, there are currently two "Table 1".
Line 263: spaces missing in front of parentheses.
Line 93: Language: This study aims at understanding
Author Response
Response to Reviewer 3 Comments
May. 1th 2019
Dear editor and reviewer:
We appreciated editor and reviewers for your positive comments and constructive suggestions on our manuscript.We have considered these comments carefully and have made corrections that we hope the revision meet with approval. We are looking forward to your consideration. The main corrections in the manuscript and the responds to the reviewer’s comments are explained in the following:
In my opinion, the authors adequately answered our most major concerns: in particular the material & methods section, which was critically incomplete, was significantly improved and expanded.
Response: Thank you for your positive comments. This manuscript was reworked according to your advice.
Remains a few minor issues:
Figure 4 is a wonderful addition to the manuscript but it should probably be redone as Panel B covers part of Panel A and Panel C part of Panel B. The three panels are also not aligned vertically, and the borders of panel B are showing. In my opinion the size and resolution of that figure should also be expanded as it contains a lot of details that are currently difficult to read: maybe the authors should redo it as a column, i. e. A over B over C, instead of side-by-side? Also, in Panel B the choice of colour is a bit unfortunate: is the main red that covers most of the plot Cyclotella or Cymatopleura?
Response: The figure was modified, expanded the size and resolution as a column according to your suggestion. In Pannel B I changed the colour and it showed that red covered plot Cyclotella and yellow covered the Cymatopleura.
Reference 48: In the author's reply to my comments, the authors claimed that citation 48 was corrected but it wasn't. The current citation (Hendry & Brzezinski 2014) did not come up with the estimate of 40%, they merely cite Nelson et al. 1995 who did.
Response: Sorry for this mistake. We have modified this.
The abbreviation used as column headers in the tables should be spelled out in the captions. Also, there are currently two "Table 1".
Response: The captions and the table number was corrected.
Line 263: spaces missing in front of parentheses.
Response: It was modified.
Line 93: Language: This study aims at understanding
Response: It was reworked.
We appreciated Editors/Reviewers’ work earnestly, and hope that the corrections will meet with your approvals.
Yours sincerely,
Prof.Dr.Yonghong Bi
Author Response File: Author Response.docx
