Short-Term Meteorological Conditions Explain Cyanobacterial Blooms in a Tropical Reservoir

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The manuscript of Alvarez-Dalinger et al., titled “Short-term meteorological conditions explain cyanobacterial blooms in a tropical reservoir”, evaluates the influence of physico-chemical and meteorological variables (temperature, nutrients, average precipitation, etc.) on the composition and abundance of cyanobacteria from two bloom episodes (2018 and 2019) in Limón reservoir (Argentina).This is my second revision of the manuscript, which now contains changes that have clarified some parts of the article. However, I consider that the manuscript is jet not prepared for publication. Although the hypothesis is not novel, the authors have done a lot of work in the laboratory and the data may be useful for researchers and water managers. However, the manuscript needs more synthesis (what analyses are useful to answer the hypothesis) and improve sentences and paragraphs for better understanding.

General comments:

1.     The manuscript requires careful reading. It contains typos (some examples are in the "specific comments" section), sentences difficult to understand, and needs synthesis, especially in the results section. I can write an example, but it is something more global. For example, are biological correlations necessary for the hypothesis? If so, the manuscript needs a rationale for this, so that the reader can understand why the authors present this data. If the authors decide to continue with biological correlation analysis, this analysis need to be better explained.

2.     Figures should be improved in terms of quality and be self-explanatory. For example: Figure 2. “* The dashed black line shows the historical temperatures.” The authors still need to indicate what type of data is it, i.e., monthly average temperatures?. Figure 7. What does sub-networks mean here? And the big figure? what do you mean with red line? I do not see any red line.

3.     The authors agreed making some changes in the manuscript, but they were not thoroughly applied in the article. For example, instead of using “period”, it is better to use the year, which is a specific word (e.g., “Figure 10. Dominant cyanobacteria widths and lengths for periods I and II”.).

4.     Abstract requires more work. It contains a lot of typos and needs to be clearer. E.g., “Average temperatures favor the development of blooms as well as larger filaments” What does “average temperature” mean here? I guess author mean “average high temperatures”. E.g., “during warm seasons”, please, specify the years.

5.     I am not sure how accumulated rainfall (8 months ago) may influence the growth of cyanobacterial blooms. An explanation would be interesting.

Specific comments:

L18: the most abundant.

L23: Change “Sample dates” by “sampling dates”.

L23: A dot before cyanobacteria to start a sentence.

L25: Heterocyte.

L133: Remove the comma after Total

L135-139: This sentence needs a verb.

L141: what does historical record mean in this sentence? Probably you mean historical record of temperature and precipitation.

L149-150: I do not understand this sentence.

L64: what do you mean by n=20 here? The authors specified that they counted a minimum of 300 cells per sample.

L189-194: If there is a statistical section, perhaps this paragraph should be placed there.

L197: bloom-forming cyanobacteria species.

L219: if morphological variables refer to filament length, for example, then it is also biological.

L234: Can meteorological conditions be better?

L237: Please, rewrite for better understanding. E.g., "being 2-fold higher in December 2019 than in December 2018", or something similar.

L239-242: please, indicate that it is during the sampling period, otherwise it is not understood.

L258: physical and chemical

L263: is the dissolved oxygen concentration a mean? if the authors took data during the whole sampling date, what is this?

L279: In contrast

L289: than in

L296: Please, rewrite.

L307-308: They are not genera, but orders.

L325-328: But the authors said that (L295-296) "The mean proportion of the cyanobacteria over the total phytoplankton in the spring-summer of 2018 was 86%"

L346: Remover one “and”.

L352: Cyanobacterial morphotypes.

L380-383: Please, rewrite this sentence for clarity.

L385-387: Please, rewrite for clarity.

L414:417: Is this necessary. It creates confusion.

L418-433: very dense. What is really important for discussion and conclusion? The rest of the data may be in supplementary material.

L439: what do the sub-networks refer to? This part is still not well explained.

L448: I do not understand this sentence. Please, rewrite it for clarity.

L453: What do you mean “by group”, by phyla? Please, be specific.

L478: What do you mean by “in the first”?

L513-515: This is not about results, but a discussion/conclusion.

L536-538: This sentence says the same as 532-535.

L566-569: Please, rewrite it for clarity.

L582: Please, revise the sentence.

L604-606: I do not understand this sentence. Please revise it.

L649: Relevant implications. Please, be more specific.

L651-657: It is difficult to me to understand the figure of subnetworks. It needs careful revision.

L721: the driest

Author Response

We want to thank the reviewers for their time and dedication. We believe that thanks to your comments, the final version has been substantially improved. Several analyzes of the study, which did not contribute to the answer to the hypothesis, have been eliminated, especially those that are purely biological, such as similarity or dominance indices, and the analysis of networks between species. We believe that the final version is synthesized and focused only on the hypothesis. Below we respond to each of your comments. The answers are highlighted in yellow and the line numbers correspond to the work with “Track changes”. As you can see in the version with “Track changes”, the English and the writing have been revised in depth by an expert.

Reviewer 1:

The manuscript of Alvarez-Dalinger et al., titled “Short-term meteorological conditions explain cyanobacterial blooms in a tropical reservoir”, evaluates the influence of physico-chemical and meteorological variables (temperature, nutrients, average precipitation, etc.) on the composition and abundance of cyanobacteria from two bloom episodes (2018 and 2019) in Limón reservoir (Argentina).This is my second revision of the manuscript, which now contains changes that have clarified some parts of the article. However, I consider that the manuscript is jet not prepared for publication. Although the hypothesis is not novel, the authors have done a lot of work in the laboratory and the data may be useful for researchers and water managers. However, the manuscript needs more synthesis (what analyses are useful to answer the hypothesis) and improve sentences and paragraphs for better understanding.

General comments:

1. The manuscript requires careful reading. It contains typos (some examples are in the "specific comments" section), sentences difficult to understand, and needs synthesis, especially in the results section. I can write an example, but it is something more global. For example, are biological correlations necessary for the hypothesis? If so, the manuscript needs a rationale for this, so that the reader can understand why the authors present this data. If the authors decide to continue with biological correlation analysis, this analysis need to be better explained.: The manuscript has been reviewed by an expert in English who has corrected the wording and coherence of the entire document. The sentences have been synthesized. In addition, several analyzes and paragraphs (from the "Results" and "Methodology" sections) that corresponded to biological analyzes and were not necessary to answer the hypotheses have been eliminated. In this way, the final version of the manuscript has been synthesized, considering only the analyzes that are relevant.
2. Figures should be improved in terms of quality and be self-explanatory. For example: Figure 2. “* The dashed black line shows the historical temperatures.” The authors still need to indicate what type of data is it, i.e., monthly average temperatures?Figure 7. What does sub-networks mean here? And the big figure? what do you mean with red line? I do not see any red line.: The figures have been corrected, particularly the heading of figure 2 ( L 294-298: “Figure 2. Historical records (HR) of rainfall and temperatures (1981-2010); and rainfall and average temperatures for the years 2018 and 2019 registered in the study area, according to data from SMN. * The dashed black line shows the historical temperatures calculated with the average monthly temperatures.”). Figure 7 corresponding to the analysis of networks, has been eliminated from the study, as well as all the analysis corresponding to it, both Methodology and Results and Discussion. We believe that the reviewers are right that although it is an interesting analysis, it is not necessary for the hypotheses raised and it generated confusion.
3. The authors agreed making some changes in the manuscript, but they were not thoroughly applied in the article. For example, instead of using “period”, it is better to use the year, which is a specific word (e.g., “Figure 10. Dominant cyanobacteria widths and lengths for periods I and II”.): We have changed the word "period" to "year" in the figures and throughout the text.
4. Abstract requires more work. It contains a lot of typos and needs to be clearer. E.g., “Average temperatures favor the development of blooms as well as larger filaments” What does “average temperature” mean here? I guess author mean “average high temperatures”. E.g., “during warm seasons”, please, specify the years.: We have corrected and synthesized the Abstract, modifying the sentences marked by the reviewer and checking that the entire paragraph is consistent. (Abstract: Cyanobacterial blooms represent a major problem in reservoirs that are used for potable water supply. El Limón Reservoir is one of the main reserves of water for consumption in the north of Argentina (22°6'12.29"S). This study analyzes the role of abiotic factors in the promotion of blooms in El Limón during warm seasons, as well as explores physical and chemical parameters on the morphological development of the most abundant cyanobacteria species.Results show that short-term meteorological variations correlate with cyanobacterial abundances in this shallow reservoir.6 and 8 months average daily temperatures before the sampling date positively correlate with cyanobacterial abundances as well as the filaments longitude, while accumulated precipitation limits the abundance of Cyanobacteria.Considering the highly probably short-term meteorological factors on cyanobacterial blooms, results alert for continuous and periodic monitoring of tropical reservoirs.)
5. 5.     I am not sure how accumulated rainfall (8 months ago) may influence the growth of cyanobacterial blooms. An explanation would be interesting.: The destabilized of the water column by rainfall would be a limiting factor in the development of cyanobacterial blooms in such a shallow reservoir. However, the response to the process of destabilization and mixing of the water column in the reservoir would not be immediate, but rather observed over a longer period of time. We have explained this in the Discussion section.

Specific comments:

L18: the most abundant.: We have corrected this observation.

L23: Change “Sample dates” by “sampling dates”:We have corrected this observation

L23: A dot before cyanobacteria to start a sentence : We have corrected this observation

L25: Heterocyte:  We have corrected this observation

L133: Remove the comma after Total : We have corrected this observation

L135-139: This sentence needs a verb. : L203-212 “Total solids, dissolved solids and suspended solids (mg/L), true and apparent color; soluble reactive phosphorus (mg SRP/L); nitrates, nitrites and ammonium (mg N/L); alkalinity, carbonates and bicarbonates (mg CaCO3/L); hardness, calcium and magnesium (mg CaCO3/L); chemical oxygen demand (COD) (mg O2 /L) were determined in the laboratory, according to APHA (2005) standardized techniques. Chlorophyll a (CL-a) was determined with the modified Scor-Unesco technique (Cabrera Silva, 1984).”

L141: what does historical record mean in this sentence? Probably you mean historical record of temperature and precipitation.  L213-220 “The daily temperatures and precipitations and their historical records were provided by the National Meteorological Service of Argentina (SMN), the historical records considered were between 1981 and 2010. The average daily temperatures and accumulated rainfall was calculated considering 14, 30 days and 6 and 8 months prior to sampling to assess short-term weather effects.  “

L149-150: I do not understand this sentence. L223-228: “The possible limitation of nutrients in the reservoir was evaluated by means of the N/P ratio  (Kosten et al., 2009).”

L64: what do you mean by n=20 here? The authors specified that they counted a minimum of 300 cells per sample.: We have deleted this sentence.

L189-194: If there is a statistical section, perhaps this paragraph should be placed there.: We have removed the network analysis, so this paragraph on statistical analysis was removed as well.

L197: bloom-forming cyanobacteria species. We have corrected this observation

L219: if morphological variables refer to filament length, for example, then it is also biological.: We have corrected this observation

L234: Can meteorological conditions be better? We have corrected this observation L 322: “3.1. Meteorological Climatic conditions”

L237: Please, rewrite for better understanding. E.g., "being 2-fold higher in December 2019 than in December 2018", or something similar.: We have corrected this observation

L239-242: please, indicate that it is during the sampling period, otherwise it is not understood.: L 499-503: Abundances differed between years for Aphanocapsa delicatissima (U=10, p=0.028) and Raphidiopsis mediterranea (U=10, p=0.028), while Cylindrospermopsis raciborskii and Aphanizomenon gracile did not show significant differences between years.

L258: physical and chemical:  We have corrected this observation

L263: is the dissolved oxygen concentration a mean? if the authors took data during the whole sampling date, what is this?: L 311-314:  The mean concentration of dissolved oxygen in 2018 was 9.7 (±2.06) mg/L, while in 2019 it was 8.64 (±1.23). In both years, supersaturation was observed in 75% of the samples (samples were taken between 10 to 12 a.m.).

L279: In contrast We have corrected this observation

L289: than in We have corrected this observation

L296: Please, rewrite.  L 385-388: The average relative abundance of Cyanobacteria in spring-summer of 2018 was 86%, while in the spring-summer 2019 it was 96%, with samples reaching 99% (November-19).

L307-308: They are not genera, but orders. L 398-400: In both years, the orders genera Synechococcales and Nostocales dominated with 21 and 7 species in the 2018, respectively, and 8 and 6 in the 2019.

L325-328: But the authors said that (L295-296) "The mean proportion of the cyanobacteria over the total phytoplankton in the spring-summer of 2018 was 86%" : We have removed Olmstead Tukey's dominance analysis that generated this confusion and that was not necessary for the hypotheses.

L346: Remover one “and”. We have corrected this observation

L352: Cyanobacterial morphotypes. We have corrected this observation

L380-383: Please, rewrite this sentence for clarity. We have corrected this observation : L 446- 455: During the 2018 sampling period 2018 blooms were observed in 3 of the 4 samplingses, while in the 2019 blooms were observed in allsall. In all cases, the blooms were dominated by the species Aphanocapsa delicatissima, Raphidiopsis mediterranea, and Aphanizomenon gracile. In the sampling carried out in January 2020, the most important bloom in terms of density was observed, with 9 species of Ccyanobacteria exceeded that exceeded 10,000 cells/mL and , all the species registered were being potentially toxic.

L385-387: Please, rewrite for clarity.: We have corrected this observation: L 451-455: In the sampling carried out in January 2020, the most important bloom in terms of density was observed, with 9 species of Ccyanobacteria exceeded that exceeded 10,000 cells/mL and , all the species registered were being potentially toxic.

L414:417: Is this necessary. It creates confusion.; We have deleted this paragraph.

L418-433: very dense. What is really important for discussion and conclusion? The rest of the data may be in supplementary material.: We have deleted this paragraph

L439: what do the sub-networks refer to? This part is still not well explained.: We have deleted this part.

L448: I do not understand this sentence. Please, rewrite it for clarity. We have deleted this part.

L453: What do you mean “by group”, by phyla? Please, be specific.: . We have deleted this part

L478: What do you mean by “in the first”?  L 555; “In 2018”

L513-515: This is not about results, but a discussion/conclusion. We have removed this paragraph

L536-538: This sentence says the same as 532-535.: We have corrected this observation

L566-569: Please, rewrite it for clarity. : We have corrected this observation : L 704: 2018 was rainier than 2019,  so the stability of the water column would have been interrupted, with greater turbidity due to external contributions by runoff. The synergic effect of these factors probably acts as a limiting factor for the development of Cyanobacteria this year.

L582: Please, revise the sentence: We have corrected this observation: L 719-722: Cyanobacterial blooms observed in El Limón in 2019-2020 would also have limited the abundances of the other species, probably in an event of interspecific competition, being the richness being much lower of 2019 much lower than the richness registered in 2018 compared to the previous year.

L604-606: I do not understand this sentence. Please revise it.: We have deleted this part.

L649: Relevant implications. Please, be more specific. : We have corrected this observation : L810-814: Although in this study we focus on meteorological variables and physical and chemical parameters, the biological interactions between the species of the community should have relevant implications and should be further analyzed (Lozano, 2022). 

L651-657: It is difficult to me to understand the figure of subnetworks. It needs careful revision.: We have deleted this figure.

L721: the driest: We have corrected this observation

Reviewer 2:

This manuscript describes the effects of short-term meteorological conditions that may explain cyano-bacterial blooms in a shallow freshwater tropical lake.  The research spent considerable effort analyzing a water sample from a single location and a net sample collected during each of seven months (Sept-Dec) in 2018 and 2019.  A limited number of environmental measurements were also collected at the same time but were only shown as averages for the year in tables or figures.  Some critical measured parameters, e.g. ammonium, were not reported at all : We have added in the table 1 the data referring to ammonium values (N-NH3 and NH4).

Our study seeks to evaluate the effect of rainfall and average temperatures in a shallow reservoir located in a tropical environment, which is why we only consider rainfall and temperatures as predictor environmental variables. However, we have presented and analyzed the data considering the average rainfall and temperatures of: 1) the day of sampling; 2) the 14 days prior to the sampling day; 3) the 30 days prior to the sampling day; 4) the 6 months prior to the sampling day and, 5) the 8 months prior to the sampling day. In addition, the analysis is carried out considering the historical records of rainfall and temperature of the last 30 years in the study area. This is why we believe that although we have used only 2 environmental variables, they have been analyzed in extreme depth, with an important meteorological database.

While the analysis of phytoplankton content of the lake required considerable effort, the environmental measurements were minimal and were analyzed by correlation which by themselves cannot demonstrate cause/effect.  In addition N/P ratios in water samples only show ambient nutrient concentrations and nothing related to their utilization by the organisms.  The authors may be correct that lake temperatures may be the primary driver of cyano-bacterial populations in the lake but the dynamics are only speculation and not supported by the data presented.: While it is true that the way in which organisms use or fix nutrients is interesting, we believe that it is beyond the objectives of our study. The study seeks to evaluate the impact of short-term rainfall and temperatures on cyanobacterial blooms. However, when analyzing the frequency of appearance of heterocysts, the N/P ratio and the trophic state of the reservoir, we believe that there is an approximate idea of ​​the use of nutrients by cyanobacteria.   

We have added a few sentences indicating that our results could indicate that temperature is the primary driver of blooms in this reservoir, although this is not definitive, for example in Conclusion:  L 864-868: Short-term meteorological variability had a determiningseems to have an important influence on the establishment of cyanobacterial blooms in El Limón as a shallow tropical reservoir. The temperatures correlate with influenced variables such as the length and width of the filaments and the abundance of both heterocytous and non-heterocytous species.

In some other sentences we implicit the idea that the interactions between organisms are also relevant, for example: L 810: Although in this study we focus on meteorological variables and physical and chemical parameters, the biological interactions between the species of the community should have relevant implications and should be further analyzed (Lozano, 2022). 

Once again thank you very much for your effort and time.

Sincerely yours,

Eng. Florencia Alvarez Dalinger

Author Response File: Author Response.docx

Reviewer 2 Report (New Reviewer)

This manuscript describes the effects of short-term meteorological conditions that may explain cyano-bacterial blooms in a shallow freshwater tropical lake.  The research spent considerable effort analyzing a water sample from a single location and a net sample collected during each of seven months (Sept-Dec) in 2018 and 2019.  A limited number of environmental measurements were also collected at the same time but were only shown as averages for the year in tables or figures.  Some critical measured parameters, e.g. ammonium, were not reported at all.  

While the analysis of phytoplankton content of the lake required considerable effort, the environmental measurements were minimal and were analyzed by correlation which by themselves cannot demonstrate cause/effect.  In addition N/P ratios in water samples only show ambient nutrient concentrations and nothing related to their utilization by the organisms.  The authors may be correct that lake temperatures may be the primary driver of cyano-bacterial populations in the lake but the dynamics are only speculation and not supported by the data presented.    

Author Response

We want to thank the reviewers for their time and dedication. We believe that thanks to your comments, the final version has been substantially improved. Several analyzes of the study, which did not contribute to the answer to the hypothesis, have been eliminated, especially those that are purely biological, such as similarity or dominance indices, and the analysis of networks between species. We believe that the final version is synthesized and focused only on the hypothesis. Below we respond to each of your comments. The answers are highlighted in yellow and the line numbers correspond to the work with “Track changes”. As you can see in the version with “Track changes”, the English and the writing have been revised in depth by an expert.

Reviewer 2:

This manuscript describes the effects of short-term meteorological conditions that may explain cyano-bacterial blooms in a shallow freshwater tropical lake.  The research spent considerable effort analyzing a water sample from a single location and a net sample collected during each of seven months (Sept-Dec) in 2018 and 2019.  A limited number of environmental measurements were also collected at the same time but were only shown as averages for the year in tables or figures.  Some critical measured parameters, e.g. ammonium, were not reported at all : We have added in the table 1 the data referring to ammonium values (N-NH3 and NH4).

Our study seeks to evaluate the effect of rainfall and average temperatures in a shallow reservoir located in a tropical environment, which is why we only consider rainfall and temperatures as predictor environmental variables. However, we have presented and analyzed the data considering the average rainfall and temperatures of: 1) the day of sampling; 2) the 14 days prior to the sampling day; 3) the 30 days prior to the sampling day; 4) the 6 months prior to the sampling day and, 5) the 8 months prior to the sampling day. In addition, the analysis is carried out considering the historical records of rainfall and temperature of the last 30 years in the study area. This is why we believe that although we have used only 2 environmental variables, they have been analyzed in extreme depth, with an important meteorological database.

While the analysis of phytoplankton content of the lake required considerable effort, the environmental measurements were minimal and were analyzed by correlation which by themselves cannot demonstrate cause/effect.  In addition N/P ratios in water samples only show ambient nutrient concentrations and nothing related to their utilization by the organisms.  The authors may be correct that lake temperatures may be the primary driver of cyano-bacterial populations in the lake but the dynamics are only speculation and not supported by the data presented.: While it is true that the way in which organisms use or fix nutrients is interesting, we believe that it is beyond the objectives of our study. The study seeks to evaluate the impact of short-term rainfall and temperatures on cyanobacterial blooms. However, when analyzing the frequency of appearance of heterocysts, the N/P ratio and the trophic state of the reservoir, we believe that there is an approximate idea of ​​the use of nutrients by cyanobacteria.   

We have added a few sentences indicating that our results could indicate that temperature is the primary driver of blooms in this reservoir, although this is not definitive, for example in Conclusion:  L 864-868: Short-term meteorological variability had a determiningseems to have an important influence on the establishment of cyanobacterial blooms in El Limón as a shallow tropical reservoir. The temperatures correlate with influenced variables such as the length and width of the filaments and the abundance of both heterocytous and non-heterocytous species.

In some other sentences we implicit the idea that the interactions between organisms are also relevant, for example: L 810: Although in this study we focus on meteorological variables and physical and chemical parameters, the biological interactions between the species of the community should have relevant implications and should be further analyzed (Lozano, 2022). 

Once again thank you very much for your effort and time.

Sincerely yours,

Eng. Florencia Alvarez Dalinger

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report (New Reviewer)

The text of the manuscript is much improved and it is obvious that quite a lot of improvement was made in the overall writing.The English was originally good but the revised version is even better.  The figures and tables are good although some analytes (NH3) were not discussed in the results or discussion which is a pity since other nitrogen species had an effect on the cyanobacterial abundances as well as the filaments longitude.  Also, it would have been useful to have the nitrogen species identified that were used in the N/P ratios since it is unusual that NH3 is not a preferred form of N since it is energetically preferred because it is already reduced for utilization in protein production versus the oxidized forms of nitrate or nitrite.  The use of correlations to deduce dynamics remains a bit of an issue since they do not necessarily show a cause/effect relationship.  There is agreement that temperature probably does provide the greatest effect in the cyanobacterial dynamics in the lake.

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

Cyanobacterial blooms are a water-quality concern worldwide, and understanding the potential for increased occurrence under various climate change scenarios is important for water-resource planning. The manuscript entitled "Climate change risks for water reservoirs in tropical areas: cyanobacterial blooms in Limón Argentina" is timely, and of broad interest. However, I have two major concerns about the analyses presented in this manuscript: 1) Phytoplankton communities were described based on a minimum cell count of 100 individuals of the most frequent species, rather than a total of 400 individuals and 2) the analysis and conclusions are based on a total of 9 samples collected across two summer seasons. The minimum count of 100 individuals of the most frequent species may have precluded full characterization of the phytoplankton community; the literature generally considers a minimum count of 300-400 individuals the most robust approach. The small sample size used in statistical analyses is a more substantive concern. While descriptive analyses are presented in the manuscript are appropriate, the small sample size precludes rigorous statistical analyses of environmental conditions influencing cyanobacterial abundance, community composition, and morphology and differences between years. The general patterns observed match those reported in the literature, but data are insufficient to statistically support the conclusions about the influence of climate change on small waterbodies. Therefore, I cannot recommend this manuscript for publication in Water.    

Reviewer 2 Report

It is hard to get the conclusion via 4 months data that climate change is more decisive to cyanobacterial blooms. Temperatures ranged between 23.2 and 25.6°C in 2018, and between 21.7 and 28.9 °C in 2019. The authors should be very careful to analyze the environmental factors.

Reviewer 3 Report

The manuscript of Alvarez-Dalinger et al., titled “Climate change risk for water reservoirs in tropical areas: cyanobacterial blooms in Limón, Argentina”, evaluates the influence of physico-chemical and meteorological variables (temperature, nutrients, average precipitation, etc.) on the composition and abundance of cyanobacteria from two bloom episodes (2018 and 2019) in Limón reservoir (Argentina). The manuscript is interesting for water managers and researchers, but I have several concerns related to the lack of a clear hypothesis, the lack of synthesis in the results section, the lack of data to follow some parts of the manuscript, and the need for clarity throughout the text and figures.

Hope the following comments can help the authors:

General comments:

1.     The article lacks a clear hypothesis.

2.     The objectives could be better described: i) instead of “determine the conditions”, change it to “assess the environmental conditions…”, ii) what do you mean by “phytoplanktonic context”? Please, be more specific. For example, “characterize phytoplankton composition and abundance”.

3.     The Materials and methods are missing some analyses that are in the Results and Discussion sections. For example, the correlation network between phytoplankton species. This analysis should be explained in the M&M section.

4.     The Results section has a lot of data that would require further synthesis. I would suggest synthesizing this section. Presenting the data in tables may help to alleviate the text.

5.     Some results that are presented as mean±s.d. in the text would be necessary to have them separated by sampling dates in a table in supplementary information. Therefore, some sentences would be easily followed. For example, L272-273 indicate that the mean nitrate values in 2018 double those of 2019, but I cannot access these values. In addition, the same occurs for the biological information. For example, L316-324 describes differences in the number of Nostocales and Synechococcales species between 2018 and 2019, but Suppl. Material 1 does not distinguish between sampling dates or years. Therefore, the text cannot be followed properly.

6.     It would be necessary to explain why authors have chosen to group phytoplankton species into the categories of “colonial”, “filamentous” and “N-fixing filamentous” rather than presenting the data by genus/family or other ecologically relevant category. The category of forming colonies is compatible with being either N-fixing or non-N-fixing cyanobacteria, so I do not understand which category has been prioritized if both are present.

7.     The morphological analysis (width and length of filaments or colonies) is shown for the species R. mediterranea, C. raciborskii and A. gracile in the results section (e.g., Fig. 8, 9, and 10), whereas in the Materials and Methods it is stated that this analysis has also been performed for A. delicatissima, as “these four were the most frequent/abundant in 2018 and 2019”. Why is there no graph for A. delicatissima? Please, this should be explained. Also, the fact that these four species were the most frequent/abundant in 2018 and 2019 is contradicted by sentence L390-392, which states that “the blooms were dominated by the species A. delicatissima, R. mediterranea and Merismopedia punctata.”. Please, clarify it.

8.     Some figures/tables are difficult to understand and must be clearly described. Some suggestions are:

a.      Fig. 2: indicate the meaning of the dash line.

b.    Fig. 3: indicate A and B in the figures, as well as the index used for the trophic status. In plot A, could it be possible that the purple area corresponds to a low P concentration resulting into a high N/P ratio?

c.      Fig 5: Please, indicate the units on the Y-axis.

d. Table 1: what does “Sampling date” mean for the variables “Temperature” and “Rainfall”? If “Sampling date” means the 14-30 days prior to samplings (L141), I would suggest changing the label. Does “temperature” of “water” mean water temperature at the time of sampling? Moreover, if rainfall of 6 months means the average rainfall of the 6 months prior to a sampling date, the average rainfall of Sept, Oct, Nov and Dec. would be very similar, since it takes into account similar data. Does this give reliability to the result?

e.   Fig 7: Please, explain the meaning of all the figures properly. For example, there are larger and smaller figures, what does each figure mean? Also, the description of the figure states “Circle sizes are related to mean abundance of the four months in each year”, but, what does “mean abundance” mean here? Of what?

f.  Figures 8 and 9: Where is the information from Aphanocapsa delicatissima? Moreover, authors can combine both figures into one by differentiating width and length with labels A and B.

g.     Figure 10: Please, indicate years (2018 and 2019) instead of “periods I and II”).

9.     There are some analyses, such those classifying the species into dominant, constant, occasional, and rare that have not been discussed further in the Discussion section. If this information does not contribute much to the objective and it is not discussed, you may want to consider not including it in this manuscript or dedicate some sentences in the discussion section.

10.  The authors perform correlations tests (Spearman) to assess whether there is a significant correlation between environmental variables and biological data (i.e., Total cyanobacteria, Non-N-fixing cyanobacteria, N-fixing cyanobacteria and colonial cyanobacteria) (Table 1). Moreover, they also performed correlation tests to evaluate whether there is a significant correlation between environmental variables with the abundance of specific cyanobacteria (Table 2). However, the rationale for the second analysis is lacking.

Specific comments:

L12: replace “enhance” by “triggered”.

L16-17: “Phenotypic development” is not clear. Please, rewrite the sentence.

L24-29: The authors do not compare deep/shallow reservoirs in this study.

L71: Please, be more specific by indicating the new areas.

L101: Do you mean “average annual temperature”?

L103: is the reservoir monomictic?

L114: Please, indicate in this paragraph the location of the sampling (shore? pelagic? One point or more?)

L115: Please rewrite. For example: During two consecutive warm periods in 2018 and 2019, sampling was conducted monthly from September to December.

L121: depth

L124: For how long the samples were refrigerated until analysis? Please, indicate.  

L137: This sentence is repeated with the following one.

L144: Why do not authors also use the results from SRP, DIN and chl-a to calculate the trophic state?

L184: what do you mean by “period”? If you mean “year”, please, better use “year”.

L200-203: A reference would be needed here.

L207: relative abundance/frequency of what? Please, rewrite for a better understanding.

L229: Please, indicate the figure.

L229-239: The description of the data does not correspond to Figure 2. For example, the maximum precipitation of both years (2018 and 2019) was not recorded in December, but in January and February in 2018, and in March in 2019. Therefore, the whole paragraph seems confusing to me.

L247: better to indicate “years” instead of “period”.

L247-248: The authors previously indicated in L236 that there were no temperature differences between years, so this sentence seems a bit redundant. Also, the values are a bit different. Please, clarify it.

L285: Please, replace “CL a” by “CL-a” for clarification.

L306: Please, include “over the total phytoplankton” after cyanobacteria, or something similar, to be more specific.

L330: what do you mean by “composition” here?

L380: I do not quite understand the concept of “accumulated temperature”. Do you mean the average temperature over the previous 6 or 8 months?

L392: what do authors mean with “the most important bloom” here? Please, rewrite.

L404: I do not find the criteria in the results sections (i.e., titles) to be indicative of the results/analysis. For example, the section “Bloom-forming species” has also data from correlation analyses, which theoretically should go into the section called “Correlation analysis” (L364).

L405: Please, change to: “The abundance and morphological variation of 4 species of bloom-forming cyanobacteria present in both years were analyzed”.

L408-410: It would be easier to understand if the authors write the full name of the cyanobacteria species here.

L420: increase by 566% respect to…?

L427-429: It is the first time in the manuscript that authors indicate “true and apparent color”. Did authors do this correlation with total cyanobacteria?

L601: Please, indicate the authors.

L647-649: Please, rewrite this sentence for clarity.

L649-655: I found this sentence difficult to follow because there is no information about A. delicatissima in the network figure (I assume authors are referring to Fig. 7).

L714: I would say that “short-term climatic variability” is not correct here, as two-years of data is too few to say “climatic”. Could “meteorological” be more correct here?