Seasonal Development of Phytoplankton in South Bohemian Fishponds (Czechia)
, Jan Potužák 3, Ján Regenda 1 and Otakar Strunecký 1
Round 1
Reviewer 1 Report
Review for the paper "Seasonal development of phytoplankton in South Bohemian fishponds" by Anna Ivanova, Jaroslav Vrba, Jan Potužák, Ján Regenda, Otakar Strunecký submitted to "Water".
General comment.
Due to the diverse role that phytoplankton play in the aquatic environments, much research has been devoted to fluctuations in the density, biomass and community composition of these organisms. Current work concerning long-term variability in phytoplankton populations has predominantly focused on the abundance and biomass of the entire phytoplankton population or large functional groups within it, such as diatoms and dinoflagellates. The physical environment has also been implicated as the dominant factor driving population fluctuations over interannual time scales. The variability of phytoplankton on long time scales is less studied, especially in regard to shifts in community composition. The authors aimed to study the phytoplankton succession processes in fishponds with different trophic status based on data obtained during an 8-year period. They revealed differences in the composition of microalgae between various types of water bodies. We authors used standard methods to collect the samples and to process the data. Data set to be analyzed is comprehensive and allowed the authors to provide a detailed temporal pattern of the phytoplankton composition and density. The main results are confirmed byh statistics and illustrated with relevant Figures and Tables. Discussion is concerned with main results. In general, the paper is well written and structured. The results of the study may be interesting for ecologists dealing with the phenology of plankton assemblages. However, the paper can be improved according to my suggestions.
Specific remarks.
L59, 64. "Daphnia" should be italicized.
L68. '–1' must be formatted as the upper index.
L75. Consider replacing "behavior" with "fluctuations".
L82. Consider replacing "1.3 to 5.9×103 m3" with "1.3×103 to 5.9×103 m3". '3' at '10' and 'm' must be formatted as the upper index.
L91. Consider replacing "the Spring part of the season" with "the spring".
L94. Consider replacing "The Autumn" with "The autumn".
Table 1. Volume (103 m3). '3' at '10' and 'm' must be formatted as the upper index.
L130. Consider replacing "from the layer0–1 m depth layer" with "from the 0–1 m layer".
L135. Please, provide reference number after Komárková and Cronberg (1994).
Also, note that this reference is not in the Reference list.
L136. Please, specify the units for phytoplankton biomass (wet mass, dry mass, carbon mass).
L138. Delete full stop after ('Table 2)'.
L138-138. Consider replacing "and determined" with "and zooplankton organisms were determined".
L150. Consider replacing "consicted of 90% Common" with "consisted of 90% common".
L150 and hereafter. Latin names of the species and genera must be italicized according to international zoological nomenclature.
L155-156, 355, 363-370. '-1' must be formatted as the upper index.
Fig. 2. The upper part of the figure seems to be damaged. Please, correct.
L150. Consider replacing "Biplots" with "Biplot".
Section 3. The authors should carefully describe their data. There are many cases such as 'had minimum values in summer 0.1 m and maximum in April 2 m' (L193), 'in this group was found in October 0.4 mg L -1' (L230), 'TB of algae was in HK 109 mg L -1 ' (L242) etc. I suggest to present the data as follows: 'had minimum values in summer (0.1 m) and maximum in April (2 m)' (L193), 'in this group was found in October (0.4 mg L -1)' (L230), 'TB of algae was in HK (109 mg L -1) ' (L242) etc.
In other words, the corresponding values must be in parentheses.
Section 3. The authors decided to include figures showing variations in environmental variables in the main ms (Figures 3 and 4) but the Figures indicating the core results they presented as Supplementary Data. Because the paper was focused on plankton dynamics, I strongly recommend placing Figures S1-S4 in the main ms while Fig. 3-4 may be moved to Supplementary Data.
L244-247. Names of the families must be formatted as the Capital letter.
L303. Delete '(57.96)'.
L324. Delete 'were used'.
L327. Consider replacing "biomass" with "dry biomass".
L333. Consider replacing "indicate" with "occurred".
L347. Delete "concentration of ".
L381. Delete "generic".
L384. Consider replacing "season didn't show the spring maxima" with "season showed no spring maxima".
L389-390. Unclear sentence. Please, rephrase.
L420. "Dinobryon" should be italicized.
L429. Consider replacing "has been" with "was".
L435. Delete "interestingly".
L459. Replace ')' with ','.
L467. Consider replacing "conform" with "correspond".
L479-480. The verb seems to be missing here. It is unclear sentence. Correct.
L480. Consider replacing "Autumn" with "autumn".
Author Response
Reviewer 1
General comment.
Due to the diverse role that phytoplankton play in the aquatic environments, much research has been devoted to fluctuations in the density, biomass and community composition of these organisms. Current work concerning long-term variability in phytoplankton populations has predominantly focused on the abundance and biomass of the entire phytoplankton population or large functional groups within it, such as diatoms and dinoflagellates. The physical environment has also been implicated as the dominant factor driving population fluctuations over interannual time scales. The variability of phytoplankton on long time scales is less studied, especially in regard to shifts in community composition. The authors aimed to study the phytoplankton succession processes in fishponds with different trophic status based on data obtained during an 8-year period. They revealed differences in the composition of microalgae between various types of water bodies. We authors used standard methods to collect the samples and to process the data. Data set to be analyzed is comprehensive and allowed the authors to provide a detailed temporal pattern of the phytoplankton composition and density. The main results are confirmed byh statistics and illustrated with relevant Figures and Tables. Discussion is concerned with main results. In general, the paper is well written and structured. The results of the study may be interesting for ecologists dealing with the phenology of plankton assemblages. However, the paper can be improved according to my suggestions.
We would like to thank the Reviewer 1 for the evaluation. We would like to thank as well for addressing the typos and suggested formatting changes to make the text clearer. The text underwent a language correction by native speaker. We corrected all noted lapses and hopefully even more.
Specific remarks.
L59, 64. "Daphnia" should be italicized.
Thank you, it was corrected
L68. '–1' must be formatted as the upper index.
The upper index was corrected
L75. Consider replacing "behavior" with "fluctuations".
The word "behavior" was changed to "fluctuations".
L82. Consider replacing "1.3 to 5.9×103 m3" with "1.3×103 to 5.9×103 m3". '3' at '10' and 'm' must be formatted as the upper index.
Thank you, it was replaced
L91. Consider replacing "the Spring part of the season" with "the spring".
All seasons were replaced according to reviewers suggestions and "parts" were deleted.
L94. Consider replacing "The Autumn" with "The autumn".
The capitals in all seasons were replaced according to reviewers suggestions .
Table 1. Volume (103 m3). '3' at '10' and 'm' must be formatted as the upper index.
The upper indexes in Table 1 were corrected.
L130. Consider replacing "from the layer0–1 m depth layer" with "from the 0–1 m layer".
The corrected the sentence according the suggestion.
L135. Please, provide reference number after Komárková and Cronberg (1994).
Also, note that this reference is not in the Reference list.
We included references Komárková and Cronberg (1994) in the revised version of MS.
L136. Please, specify the units for phytoplankton biomass (wet mass, dry mass, carbon mass).
We specified the biomass type biomass as wet biomass in the text.
L138. Delete full stop after ('Table 2)'.
The full stop was deleted.
L138-138. Consider replacing "and determined" with "and zooplankton organisms were determined".
We replaced phrase according to reviewer 1.
L150. Consider replacing "consicted of 90% Common" with "consisted of 90% common".
We changed the wording as suggested.
L150 and hereafter. Latin names of the species and genera must be italicized according to international zoological nomenclature.
The Latin names of fish species were italicized according to international zoological nomenclature.
L155-156, 355, 363-370. '-1' must be formatted as the upper index.
The upper indexes were fixed.
Fig. 2. The upper part of the figure seems to be damaged. Please, correct.
Sorry for that, this issue was fixed.
L150. Consider replacing "Biplots" with "Biplot".
The word "Biplots" was changed by "Biplot".
Section 3. The authors should carefully describe their data. There are many cases such as 'had minimum values in summer 0.1 m and maximum in April 2 m' (L193), 'in this group was found in October 0.4 mg L -1' (L230), 'TB of algae was in HK 109 mg L -1 ' (L242) etc. I suggest to present the data as follows: 'had minimum values in summer (0.1 m) and maximum in April (2 m)' (L193), 'in this group was found in October (0.4 mg L -1)' (L230), 'TB of algae was in HK (109 mg L -1) ' (L242) etc.
In other words, the corresponding values must be in parentheses.
We modified results as suggested, the vast majority of data values were positioned in parentheses and wording was corrected by a native speaker.
Section 3. The authors decided to include figures showing variations in environmental variables in the main ms (Figures 3 and 4) but the Figures indicating the core results they presented as Supplementary Data. Because the paper was focused on plankton dynamics, I strongly recommend placing Figures S1-S4 in the main ms while Fig. 3-4 may be moved to Supplementary Data.
Thank for this remark, we shifted the figures as it was logically recommended.
L244-247. Names of the families must be formatted as the Capital letter.
Names of the families were formatted as the capital letter.
L303. Delete '(57.96)'.
These numbers were deleted.
L324. Delete 'were used'.
It was deleted.
L327. Consider replacing "biomass" with "dry biomass".
We replaced "biomass" with "dry biomass".
L333. Consider replacing "indicate" with "occurred".
We replaced "indicate" with "occurred".
L347. Delete "concentration of ".
The "concentration of " was deleted.
L381. Delete "generic".
The word "generic" was deleted
L384. Consider replacing "season didn't show the spring maxima" with "season showed no spring maxima".
We replaced "season didn't show the spring maxima" with "season showed no spring maxima".
L389-390. Unclear sentence. Please, rephrase.
We tried to make the sentence understandable on the first go by simplifying it and grouping it into the previous sentence.
L420. "Dinobryon" should be italicized.
We italicized the name of the Dinobryon.
L429. Consider replacing "has been" with "was".
We replaced "has been" with "was".
L435. Delete "interestingly".
The word "interestingly" was deleted .
L459. Replace ')' with ','.
The ) on line 459 was replaced by ,.
L467. Consider replacing "conform" with "correspond".
We replaced it according to reviewer 1.
L479-480. The verb seems to be missing here. It is unclear sentence. Correct.
We corrected the sentence.
L480. Consider replacing "Autumn" with "autumn".
The seasons' capitals were corrected throughout the text.
Reviewer 2 Report
I have reviewed manuscript water-1727070 by Ivanova et al. The authors propose to test several hypotheses (lines 72–78):
- The concentrations of nitrogen and phosphorus are positively correlated with the biomass of phytoplankton in fishponds in the Czech Republic
- Zooplankton preferentially consume algae versus cyanobacteria, and high concentrations of zooplankton in the same fishponds therefore lead to high concentrations of cyanobacteria
The studies were carried out in nine fishponds from April to October of each year from 2008 through 2016. The ponds were characterized as hypereutrophic (3 ponds), eutrophic (4 ponds), or mesotrophic (2 ponds). The two mesotrophic ponds were not managed for fish production; they were used only for recreational fishing. The other 7 ponds were managed for fish production (mainly common carp) and were provided with supplemental feed (mainly wheat and barley).
What seems very odd about this paper is that the two hypotheses that the authors proposed to test in lines 72–78 are never mentioned in the Discussion. They seem to have been totally forgotten by the authors. The results of the study indicate that denitrification removes much of the nitrogen that would otherwise have been available to algae. The result is that the autotrophic community becomes dominated by nitrogen-fixing cyanobacteria. The great abundance of cyanobacteria seems to underscore arguments made by Schindler et al. (first article listed in References) that eutrophication cannot be controlled by reducing inputs of nitrogen. The great abundance of fish reduced the zooplankton population to the point that grazing by zooplankton had little impact on the relative abundance of eukaryotic and prokaryotic autotrophs. The Results section includes a long discussion of the relative abundances of different kinds of eukaryotic autotrophs. This discussion has nothing to do with the two hypotheses that the authors supposedly set out to test. There is mention of the PEG model or the revised PEG model in several places, and the authors conclude that the plankton dynamics in the eutrophic and mesotrophic fishponds were not consistent with the revised PEG model, but there is no mention of the PEG model in the hypotheses to be tested.
My conclusion is that the authors need to go back to square one and decide what this manuscript is all about. What hypotheses are they really going to test and/or what questions are they going to ask. They should clearly pose those hypotheses and/or ask those questions in the Introduction. The presentation of the results should be consistent with the hypotheses/questions, and the discussion of the results should address whether the hypotheses should be accepted or rejected and/or what the answers were to the questions.
The manuscript suffers from some inconsistencies. I would assume, for example, that the average depth of a lake equals the volume divided by the area. However, the volume/area ratio of DH is 2.1 m, not 2.4 m, and the volume/area ratio of SV is 1.6 m, not 2.0 m. It is unclear to me why the average depth of BZ is listed as NA. The volume/area ratio for that lake is 1.5 m.
In line 150, consicted should be consisted.
In line 211, bellow should be below.
Author Response
I have reviewed manuscript water-1727070 by Ivanova et al. The authors propose to test several hypotheses (lines 72–78):
The concentrations of nitrogen and phosphorus are positively correlated with the biomass of phytoplankton in fishponds in the Czech Republic
Zooplankton preferentially consume algae versus cyanobacteria, and high concentrations of zooplankton in the same fishponds therefore lead to high concentrations of cyanobacteria
The studies were carried out in nine fishponds from April to October of each year from 2008 through 2016. The ponds were characterized as hypereutrophic (3 ponds), eutrophic (4 ponds), or mesotrophic (2 ponds). The two mesotrophic ponds were not managed for fish production; they were used only for recreational fishing. The other 7 ponds were managed for fish production (mainly common carp) and were provided with supplemental feed (mainly wheat and barley).
What seems very odd about this paper is that the two hypotheses that the authors proposed to test in lines 72–78 are never mentioned in the Discussion. They seem to have been totally forgotten by the authors. The results of the study indicate that denitrification removes much of the nitrogen that would otherwise have been available to algae. The result is that the autotrophic community becomes dominated by nitrogen-fixing cyanobacteria. The great abundance of cyanobacteria seems to underscore arguments made by Schindler et al. (first article listed in References) that eutrophication cannot be controlled by reducing inputs of nitrogen. The great abundance of fish reduced the zooplankton population to the point that grazing by zooplankton had little impact on the relative abundance of eukaryotic and prokaryotic autotrophs. The Results section includes a long discussion of the relative abundances of different kinds of eukaryotic autotrophs. This discussion has nothing to do with the two hypotheses that the authors supposedly set out to test. There is mention of the PEG model or the revised PEG model in several places, and the authors conclude that the plankton dynamics in the eutrophic and mesotrophic fishponds were not consistent with the revised PEG model, but there is no mention of the PEG model in the hypotheses to be tested.
We absolutely agree with the reviewer that eutrophication cannot be controlled by reducing nitrogen inputs, as stated in Shindler's paper. However, this matter is still discussed again and again as cited in (Kolzau, S.; Wiedner, C.; Rücker, J.; Köhler, J.; Köhler, A.; Dolman, A.M. Seasonal Patterns of Nitrogen and Phosphorus Limitation in Four German Lakes and the Predictability of Limitation Status from Ambient Nutrient Concentrations. PLOS ONE 2014, 9, e96065, doi:10.1371/journal.pone.0096065).
We changed the text and explicitly stated the links to the hypothesis throughout discussion. Also the PEG models function as the basic description in plankton succession and it is easy to understand the differences and similarities comparing it with plankton succession in described water bodies. We tried to clarify it through multiple small changes (eg. L 390 - 413), but we feel that there is no way how to test the significance in difference between the described plankton behavior and PEG model.
My conclusion is that the authors need to go back to square one and decide what this manuscript is all about. What hypotheses are they really going to test and/or what questions are they going to ask. They should clearly pose those hypotheses and/or ask those questions in the Introduction. The presentation of the results should be consistent with the hypotheses/questions, and the discussion of the results should address whether the hypotheses should be accepted or rejected and/or what the answers were to the questions.
The results include more data as background for the more important statements in discussion. If we limit the results to cyanobacteria and nutrients only, the criticism will probably come soon as well as that we did not include other algae as e.g. diatoms. We follow the general trend in scientific literature to show all relevant background and leave reader to decide whatever he or she wants to use for following studies and cite in their papers.
We linked the hypotheses to discussion and explicitly stated their validity or weaknesses (e.g. L 483)
The manuscript suffers from some inconsistencies. I would assume, for example, that the average depth of a lake equals the volume divided by the area. However, the volume/area ratio of DH is 2.1 m, not 2.4 m, and the volume/area ratio of SV is 1.6 m, not 2.0 m. It is unclear to me why the average depth of BZ is listed as NA. The volume/area ratio for that lake is 1.5 m.
We provided official data used by fisheries. It is based on historical cadastral zoning and some geodetic measurements in past. They are some peculiarities as these areas use to be slightly larger due to the assumption of the maximum water level in ponds (that is not often recently used). There are no better data available, and we accepted them as they were.
However, we accepted the comment from the reviewer and recalculated the mean depth of ponds according to the volume: area assumption.
In line 150, consicted should be consisted.
We corrected the typos through the MS, including L 150.
In line 211, bellow should be below.
We corrected the typos through the MS, including L 211.
Round 2
Reviewer 2 Report
I have reviewed the revised version of manuscript water-1727070 by Ivanova et al. The manuscript is improved, but there are still some issues. First, let’s look at Table 1. Let’s use Hejtman-Hamersky pond as an example. The area is listed as 68 ha, which is 68 ´104 m2. The volume is listed as 1.6 ´103 m−3. That does not make any sense. The units of volume must be cubic meters, i.e, m3, not m−3. I will assume that the volume is 1.6 ´103 m3. The average depth is therefore 1.6 ´103 m3 ÷ 68 ´104 m2 = 0.00235 m. I would guess that the average depth is supposed to be 2.35 meters, and if the volume is really 1.6 ´103 m3, the surface area is 672 m2. I think the average depths in Table 1 are probably correct, but something is wrong with either the volumes or surface areas. The volume of 6,63 for Bezdrev should presumably be 6.63.
I think the biggest problem with this manuscript is that it is far too long. Much of the information in the manuscript could go in Supplementary Information. The following is the statement of hypotheses to be tested (lines 71–78):
We hypothesized that the concentrations of main nutrients, both P and N, are positively correlated in the biomass of phytoplankton (Hypothesis 1a), which will be further reflected in zooplankton biomass (Hypothesis 1b). We also try to explain the seasonal development of phytoplankton and particularly the cyanobacterial dominance in eutrophic and hypertrophic fishponds. We hypothesized that high population density of zooplankton will preferentially consume algae, thus providing a free niche for the development and dominance of cyanobacteria (Hypothesis 2).
So there are three hypotheses, 1a, 1b, and 2. Now let’s look at the Results. There are four sections:
3.1. Physicochemical water parameters
3.2. Phytoplankton communities
3.3. Zooplankton communities
3.4. Fish and feed supplement
What happened to the hypotheses? They seem to have been forgotten. Instead, the authors wander all over the place reporting everything they can imagine. That sounds like someone’s dissertation, not a scientific paper. If the goal of this manuscript is to test three hypotheses, then the Results section should focus on the results of testing those hypotheses. Did the authors accept or reject the hypotheses? The Results do not tell us. All the details catalogued in the Results section can go in Supplementary Information. The Results section should focus on the results of the hypothesis testing.
Author Response
I have reviewed the revised version of manuscript water-1727070 by Ivanova et al. The manuscript is improved, but there are still some issues.
Thank you for second round of revision, we significantly shortened the MS, striping it by >3000 characters. We also partially reworded Abstract and Discussion to address the other comments. However, we propose that MS will be less cited by others. These data, particularly specific phytoplankton groups are rarely published for last 30 years. The reason is that to gain these data needs a lot of time and workforce. And author of every ecology paper dealing with e.g. Dinophycae looks for comparison to cite a fresh MS. As a compromise, we transferred the phytoplankton and zooplankton data to tables, giving colleagues working on their particular groups at least a glimpse what we found.
First, let’s look at Table 1. Let’s use Hejtman-Hamersky pond as an example. The area is listed as 68 ha, which is 68 ´104 m2. The volume is listed as 1.6 ´103 m−3. That does not make any sense. The units of volume must be cubic meters, i.e, m3, not m−3. I will assume that the volume is 1.6 ´103 m3. The average depth is therefore 1.6 ´103 m3 ÷ 68 ´104 m2 = 0.00235 m. I would guess that the average depth is supposed to be 2.35 meters, and if the volume is really 1.6 ´103 m3, the surface area is 672 m2. I think the average depths in Table 1 are probably correct, but something is wrong with either the volumes or surface areas. The volume of 6,63 for Bezdrev should presumably be 6.63.
We have to apologize for this issue. There was a typo, as you correctly revealed. The m-3 were corrected to m6. It fits now.
I think the biggest problem with this manuscript is that it is far too long. Much of the information in the manuscript could go in Supplementary Information. The following is the statement of hypotheses to be tested (lines 71–78):
We hypothesized that the concentrations of main nutrients, both P and N, are positively correlated in the biomass of phytoplankton (Hypothesis 1a), which will be further reflected in zooplankton biomass (Hypothesis 1b). We also try to explain the seasonal development of phytoplankton and particularly the cyanobacterial dominance in eutrophic and hypertrophic fishponds. We hypothesized that high population density of zooplankton will preferentially consume algae, thus providing a free niche for the development and dominance of cyanobacteria (Hypothesis 2).
So there are three hypotheses, 1a, 1b, and 2. Now let’s look at the Results. There are four sections:
3.1. Physicochemical water parameters
3.2. Phytoplankton communities
3.3. Zooplankton communities
3.4. Fish and feed supplement
We changed headings to:
Chemical analyses
Phytoplankton
Zooplankton
Fish and feed supplement
It is a cosmetic change; however it might to make things clearer.
What happened to the hypotheses? They seem to have been forgotten. Instead, the authors wander all over the place reporting everything they can imagine. That sounds like someone’s dissertation, not a scientific paper. If the goal of this manuscript is to test three hypotheses, then the Results section should focus on the results of testing those hypotheses. Did the authors accept or reject the hypotheses? The Results do not tell us. All the details catalogued in the Results section can go in Supplementary Information. The Results section should focus on the results of the hypothesis testing.
There are no significant statistical results to show as proof that our hypotheses were or were not correct. This is a result of widely variable biological system, and if you go to the holy grail of plankton succession paper, the latest PEG model paper (~400 citations from 2012) there is no single statistical analysis. We fully comply with the publication routine in field.
If we go one by one to hypotheses,
Hypothesis 1:
We hypothesized that the concentrations of main nutrients = 3.1. Physicochemical water parameters (there is TP, TOC, NO3-N, NH4-N, TN, SRP, and Chl-a - all nutrients but chl a), are positively correlated in the biomass of phytoplankton = 3.2. Phytoplankton communities and chl a from previous section.
…. which will be further reflected in zooplankton biomass (Hypothesis 1b) = Zooplankton communities. The important links between them are further described in discussion.
(Hypothesis 2): We hypothesized that high population density of zooplankton will preferentially consume algae, thus providing a free niche for the development and dominance of cyanobacteria
We show that high fish density together with the high nutrient input from feed = 3.4. Fish and feed supplement, a) suppress zooplankton (that is described in Discussion) b) providing phosphorus to ponds (that is described in Discussion) and the zooplankton is not the factor limiting growth of algae (described in Discussion ), as normally explained, but the absence of nitrogen that is supplied to ponds by cyanobacteria giving them the competitive edge over the alagae.
The data included in this paper are quite big, ….. compared to other papers, …
Yes we admit that the data are big, but it was not a weakness it was the strength of this paper, although the interpretation of many of them is not possible at the moment. The paper is descriptive, we all know it, however we intensively work on elucidating the questions that it brought. And as the research of hypertrophic and eutrophic water bodies has recently intensified elsewhere, it will have its audience.
Round 3
Reviewer 2 Report
Comments for author File: 
Comments.pdf
Author Response
I have reviewed Water-1727070 version 3 by Ivanova et al. This manuscript still has issues. For example, the authors repeatedly misspell hypothesis throughout the manuscript. The words “nutrients concentrations” in the second line of the abstract should be “nutrient concentrations”. In line 74, “correlated in” should be “correlated with”. The word “bellow” should be “below” in line 192. In line 103 they say that the euphotic layer is the upper one meter of the water column but offer no explanation to justify that assumption. The authors report values of “transparency” (lines 184–197) that vary between 0.1 and 3.5 m, but they never say how “transparency” was measured. I would guess that they measured Secchi depths, but if so, the word Secchi appears nowhere in the manuscript. If “transparency” varied from 0.1 to 3.5 meters, it is hard to believe that the depth of the euphotic zone did not vary dramatically between ponds and with time. If the transparency, however defined, was as shallow as 0.1 m, I doubt that the euphotic zone extended to a depth of 1 meter, and if the transparency was 3.5 meters, I would guess that the depth of the euphotic zone exceeded 1 meter.
We have to apologize for this issue. We corrected identified misspellings. We also added in the section 2.2. Chemical parameters the Secchi depth. As the primary production nor light intensity was not measured in this study, we also changed the sentence concerning the euphotic layer just to the upper layer.
The authors propose to test several hypotheses (lines 72–80):
- The concentrations of main nutrients, both P and N, are positively correlated in the biomass of phytoplankton
- This correlation will be “further reflected in zooplankton biomass”
- The high population density of zooplankton will preferentially consume algae, thus providing a free niche for the development and dominance of cyanobacteria
The first hypothesis seems testable if the null hypothesis is that there is no correlation.
The statistical analysis employing the relationships between phytoplankton and main nutrients were added to MS and reflected in the results.
The second hypothesis does not seem testable because the authors do not define what they mean by “further reflected”.
We deleted the second hypothesis because there is no way how to statistically test it due to various reasons, namely the unknown time lag between phyto and zooplankton production, which has to be reflected in two/four day sampling periods which makes it practically impossible to cover seasonal trends.
The first part of the third hypothesis seems testable if the null hypothesis is that the zooplankton show no preference for algae versus cyanobacteria. The second part of the third hypothesis should perhaps be an additional hypothesis because it implicitly assumes that grazing by zooplankton was sufficient to control the population of algae. The results of the study seem to show that nitrogen-fixing cyanobacteria are able to dominate (a) if nitrogen is the limiting nutrient and/or (b) if preferential grazing by zooplankton is sufficient to hold the algal population in check. It seems odd to me that the possibility of nitrogen limitation (because of denitrification) is not mentioned in the hypotheses.
We simplified H3, but we didn’t find the means how to test it, just to compare general trends in the figures provided in the results. Hypothesis 3, is then about the general explanation of cyanobacterial dominance in eutrophic shallow waters. Although many other hypotheses on cyanobacterial dominance were set as better light usage, lower energy requirements, better CO2 uptake compared to algae, etc., the common explanation nowadays is as follows:
“the most notorious decoupled energy transfer is found in eutrophic/hypertrophic systems dominated by cyanobacteria. Early-onset of cyanobacterial growth can even prevent the occurrence of the clear water phase (Deneke & Nixdorf 1999) because of the strong food limitation of large-bodied generalist filter-feeding zooplankton, like Daphnia, due to mechanical interference with the filtering apparatus, through grazing deterrents and growth inhibition or even death of the grazer caused by endotoxins retained in the cyanobacterial cells (Rohrlack et al. 1999).”
Sommer, U., Adrian, R., De Senerpont Domis, L., Elser, J. J., Gaedke, U., Ibelings, B., Jeppesen, E., Lürling, M., Molinero, J. C., Mooij, W. M., van Donk, E. & Winder, M. 2012. Beyond the Plankton Ecology Group (PEG) Model: Mechanisms Driving Plankton Succession. Annual Review of Ecology, Evolution, and Systematics 43:429-48.
The denitrification was not measured, and there is no hard proof that this mechanism is in play, we just discuss this matter in the discussion section. The nitrogen limitation is an idea that was not considered before, it is contra intuitive, and we consider is like the biggest contribution to the scientific understanding of phytoplankton limitation in eutrophicated water bodies. However, it has to be proved either by others or by us in further studies.
Several questions that are addressed in the Results and Discussion are never mentioned in the hypotheses. For example, there is mention of the PEG model. The authors point out in lines 347–349 that there was no spring peak of phytoplankton and no clear-water phase. One of the hypotheses could certainly have been that the unmodified PEG model would be sufficient to describe the plankton dynamics in these fish ponds.
This idea was already implicated in the study design as this study as a basal thing; however, it is similarly difficult to test it. However, if you suggested to add it to the hypotheses, why not. This hypothesis was added to MS:
If the purpose of this manuscript was to test hypotheses (and after all, that is the scientific method), it seems very odd to me that the hypotheses are never mentioned in the Results section of the manuscript. The important results are whether the hypotheses should be accepted or rejected. Instead, the Results is a rambling enumeration of everything. This is the old problem of the forest versus the trees. The idea in scientific writing is to get to the point and to see patterns. The enumeration of every single result can go in Supplementary Information. The Results section should be a systematic examination of the results of the hypothesis testing. The Discussion should then be a discussion of why the observed results were obtained.
We describe the results as pure results. The discussion then covers their implications. This is absolutely correct. The expert on phytoplankton or ecologist dealing with eutrophic lakes can compare their trends with us and use the data according to specific particular areas of their interest.
