Evaluation of Eutrophication in Small Reservoirs in Northern Agricultural Areas of China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review for the paper "Evaluation of Eutrophication in Small Reservoirs in Northern Agricultural Areas of China: A Case of Assessing the Impact of Non-Point Source Pollution on Water Quality Through Zooplankton Communities" by Qianyu Jing, Yang Shao, Xiyuan Bian, Minfang Sun, Zengfei Chen, Jiamin Han, Song Zhang, Shusheng Han, Haiming Qin submitted to "Diversity".

 

 

Zooplankton communities are a key component of freshwater ecosystems, serving important ecological functions. These small, free-swimming animals have short life cycles and occupy a central position in the aquatic food web, transferring energy and materials from primary producers to secondary consumers in pelagic habitats. Zooplankton also support benthic and microbial communities in lakes and reservoirs. Because they are sensitive to changes in natural and environmental conditions, zooplankton populations are regarded as effective indicators of environmental change. Zooplankton data are used to assess water quality. This study compares the effects of eutrophication and nutrients on zooplankton inhabiting small reservoirs in an agricultural zone in China. The authors revealed significant differences in zooplankton variables before and after the reservoirs were used for farming. They also identified the most influential factors in variations in zooplankton abundance and diversity during the pre- and post-farming periods. Overall, the results are well presented, although there are some uncertainties. Additionally, some methods are not described.

 

Specific remarks.

 

Section 2.1: Include data on the depth of the sampled sites.

 

Section 2.2: Indicate the total sample size for zooplankton.

 

Section 2.2: The authors must provide a procedure for calculating zooplankton biomass. They must also specify the units of zooplankton biomass (wet, dry, or carbon mass).

 

L159. Consider replacing "were treated as one species" with "were treated as one taxon."

 

L180: Unclear sentence. Please rephrase.

 

L180-182: Consider replacing it with: "Five indicators, namely, chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), transparency (SD), and permanganate index (COD Mn), were selected as the unified indicators..."

 

Results: There is no description of the environmental conditions or nutrient levels during the study period. A section presenting these results must be added to the manuscript. Additionally, inter-period comparisons should be conducted to determine if there were differences in environmental conditions.

 

Results: Calculating the Shannon index and Pielou evenness is suggested to better visualize the diversity patterns of zooplankton in the pre- and post-farming periods.

 

Discussion: A brief interpretation of the environmental background would help readers better understand the relationships between zooplankton and the environment.

Comments on the Quality of English Language

The English requires improvements.

Author Response

Dear Editor and Reviewers:

Thank you for taking the time to review our paper and giving us the opportunity to revise it. We have made corresponding revisions to the paper in response to your valuable suggestions and comments. The revised parts are shown in the document using the revision mode. At the same time, we would like to answer your questions one by one and provide responses to the revisions (in blue font) here:

 

Comment 1: Section 2.1: Include data on the depth of the sampled sites.

Responds 1: Thank you for your advice. We have added the maximum depth data of the reservoir to Table 1 according to your requirements. (Lines 143-144)

Comment 2: Section 2.2: Indicate the total sample size for zooplankton.

Responds 2: Thank you for your advice. We have added total sample size for zooplankton on section 2.2. (Lines 147-148)

Comment 3: Section 2.2: The authors must provide a procedure for calculating zooplankton biomass. They must also specify the units of zooplankton biomass (wet, dry, or carbon mass).

Responds 3: Thank you for your advice. We have added the calculation method and units for biomass on section 2.2. (Lines 154-157)

Comment 4: L159. Consider replacing "were treated as one species" with "were treated as one taxon."

Responds 4: Thank you for your advice. We have made the replacement according to your requirements. (Line 165)

Comment 5: L180: Unclear sentence. Please rephrase.

Responds 5: Thank you for your advice. We have rephrased the unclear sentences. (Line 185)

Comment 6: L180-182: Consider replacing it with: "Five indicators, namely, chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), transparency (SD), and permanganate index (COD_Mn), were selected as the unified indicators..."

Responds 6: Thank you for your advice. We have made the replacement according to your requirements. (Lines 189-191)

Comment 7: Results: There is no description of the environmental conditions or nutrient levels during the study period. A section presenting these results must be added to the manuscript. Additionally, inter-period comparisons should be conducted to determine if there were differences in environmental conditions.

Responds 7: Thank you for your advice. We have added the environmental conditions in the results section according to your requirements. (Lines 229-235)

Comment 8: Results: Calculating the Shannon index and Pielou evenness is suggested to better visualize the diversity patterns of zooplankton in the pre- and post-farming periods.

Responds 8: Thank you for your advice. We have calculated and added the Shannon-Wiener index and Pielou evenness index data in results to better visualize the changes in diversity. At the same time, we have also provided the calculation formulas for these two indices and added references to support them. (Lines 181-184, Lines 253-258)

Comment 9: Discussion: A brief interpretation of the environmental background would help readers better understand the relationships between zooplankton and the environment.

Responds 9: Thank you for your advice. We have included a brief description of the environmental background. (Lines 399-401)

Comment 10: Comments on the Quality of English Language. The English requires improvements.

Responds 10: Thank you for your advice. We have refined many of the sentences and will apply for an English polishing service.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Line 65: “form” change to “from”.

Figure 1: in total map (left) delete the unclear square in the right corner.

Table 1: It is desirable to add data on the average or maximum depth of the Reservoirs 1-4.

Line 156-159: Add how copepodite stages were counted and divided into species.

Add how biomass was calculated.

Line 183-186: add how W_j and TLI _(j) were calculated.

Figure 2: “Species composition” would be better changed to “Species number” or “Species richness”.

Lines 228-230 and 231-233: It is not necessary to list the species in the text; they are in Table 2.

Figure 3A: “total biomass” change to “total abundance”.

Line 266: “abundance” change to “biomass”.

Line 276: “Jiuxian Mountain Small Reservoir” change to “Jiuxian Mountain Small Reservoirs” or Jiuxian Mountain Small Reservoir group”.

Lines 311-314: specify when - before or after farming or in all cases.

Discussion

General comments. The discussion is highly speculative. The main comment is that the authors should convince readers that the changes in zooplankton that have occurred are not a consequence of seasonal dynamics, but a result of eutrophication from agricultural activities. To do this, it is necessary to consider the seasonal dynamics of zooplankton and factors from March to October in these or similar reservoirs and compare them with the existing dynamics, showing the differences from the usual seasonal dynamics in favor of anthropogenic eutrophication.

Judging by Fig. 7, the relationship of reservoirs 1-4 with specific factors (arrows) is the same before and after the farming, or remains after the farming, but the discussion emphasizes some differences that are not obvious in this figure. For example, R4 before farming is grouped around the Chl-a factor (meaning there is a maximum of Chl-a in R4), and after the farming the reservoir is located further from this arrow. Reservoir R3 before farming  was associated with total nitrogen, and also after the farming…

Perhaps it would be better to present data on the values of factors and zooplankton for each reservoir separately.

Specific comments.

Lines 348-350: the statement contradicts the Results - see lines 248-253, 264-269.

Lines 356-357: Where is it clear that the abundance of zooplankton in reservoir R4 was the highest after farming? This is not in the Results.

Lines 400-403: The statement is incorrect, it would be true in the case of mineral nitrogen and phosphorus, not total. Total nitrogen and phosphorus include both organic and mineral forms, and are generally correlated with phytoplankton and phosphorus-rich zooplankton (Daphnia)…

Lines 439-441: The statement is not supported by the data in Results that transparency decreases after farming. These data are absent.

Lines 441-442: The sentence is unclear. Has eutrophication increased or decreased?

Author Response

Dear Editor and Reviewers:

Thank you for taking the time to review our paper and giving us the opportunity to revise it. We have made corresponding revisions to the paper in response to your valuable suggestions and comments. The revised parts are shown in the document using the revision mode. At the same time, we would like to answer your questions one by one and provide responses to the revisions (in blue font) here:

 

Comment 1: Line 65: “form” change to “from”.

Responds 1: Thank you for your advice. We have corrected the error. (Line 66)

Comment 2: Figure 1: in total map (left) delete the unclear square in the right corner.

Responds 1: Thank you for your advice. We have adjusted the map according to your requirements on Figure 1. (Line 141)

Comment 3: Table 1: It is desirable to add data on the average or maximum depth of the Reservoirs 1-4.

Responds 3: Thank you for your advice. We have added the maximum depth data of the reservoir to Table 1 according to your requirements.

Comment 4: Line 156-159: Add how copepodite stages were counted and divided into species. Add how biomass was calculated.

Responds 4: Thank you for your advice. We have added the situation of the copepod nauplii and the method for calculating biomass. Meanwhile, we have increased and improved the methods for collecting and processing zooplankton samples. (Lines 147-165)

Comment 5: Line 183-186: add how Wj and TLI (j) were calculated.

Responds 5: Thank you for your advice. We have added the calculation methods for Wj and TLI (j) on “2.4. Date Statistical Analysis”. (Lines 193-198)

Comment 6: Figure 2: “Species composition” would be better changed to “Species number” or “Species richness”.

Responds 6: Thank you for your advice. We made the modifications in Figure 2 according to your suggestion (We replaced “Species composition” with “Species richness”). (Line 250)

Comment 7: Lines 228-230 and 231-233: It is not necessary to list the species in the text; they are in Table 2.

Responds 7: Thank you for your advice. We made the deletion according to your suggestion.

Comment 8: Figure 3A: “total biomass” change to “total abundance”.

Responds 8: Thank you for your advice. We made the modifications in Figure 4A according to your suggestion. (Line 271)

Comment 9: Line 266: “abundance” change to “biomass”.

Responds 9: Thank you for your advice. We have corrected the error. (Line 306)

Comment 10: Line 276: “Jiuxian Mountain Small Reservoir” change to “Jiuxian Mountain Small Reservoirs” or Jiuxian Mountain Small Reservoir group”.

Responds 10: Thank you for your advice. We have corrected the error. (Lines 314-315)

Comment 11: Lines 311-314: specify when - before or after farming or in all cases.

Responds 11: Thank you for your advice. We have rewritten the sentence according to your suggestion to make it better clear. (Lines 350-359)

Discussion

Comment 1: General comments. The discussion is highly speculative. The main comment is that the authors should convince readers that the changes in zooplankton that have occurred are not a consequence of seasonal dynamics, but a result of eutrophication from agricultural activities. To do this, it is necessary to consider the seasonal dynamics of zooplankton and factors from March to October in these or similar reservoirs and compare them with the existing dynamics, showing the differences from the usual seasonal dynamics in favor of anthropogenic eutrophication.

Responds 1: Thank you for your advice. We have rephrased the discussion section and included some references to support our conclusions.

Comment 2: Judging by Fig. 7, the relationship of reservoirs 1-4 with specific factors (arrows) is the same before and after the farming, or remains after the farming, but the discussion emphasizes some differences that are not obvious in this figure. For example, R4 before farming is grouped around the Chl-a factor (meaning there is a maximum of Chl-a in R4), and after the farming the reservoir is located further from this arrow. Reservoir R3 before farming was associated with total nitrogen, and also after the farming…

Responds 2: Thank you for your advice. Based on your suggestion, we checked the data on environmental factors and found that the data used was incorrect. We corrected the data and re-made redundancy analysis (RDA) of zooplankton abundance and environmental factors. The new results are as follows: Transparency (Trans), pH, permanganate index (COD_Mn), electrical conductivity (Cond) and chlorophyll a (Chl-a) had significant effects on the community structure of zooplankton before farming. Total nitrogen (TN), total phosphorus (TP) and electrical conductivity (Cond) had significant effects on the community structure of zooplankton after farming. (Figure 8)

Comment 3: Perhaps it would be better to present data on the values of factors and zooplankton for each reservoir separately.

Responds 3: Thank you for your advice. We have included the physical and chemical data of each reservoir to better reflect the relationship between environmental factors and the reservoirs.

 

Specific comments.

Comment 1: Lines 348-350: the statement contradicts the Results - see Lines 248-253, 264-269.

Responds 1: Thank you for your advice. We have revised the discussion section based on the results, ensuring that the discussion is in line with the findings. (Lines 391-404)

Comment 2: Lines 356-357: Where is it clear that the abundance of zooplankton in reservoir R4 was the highest after farming? This is not in the Results.

Responds 2: Thank you for your advice. We have supplemented the data on the abundance and biomass of each reservoir in the results section to support our conclusion. (Lines 281-284, Lines 300-303)

Comment 3: Lines 400-403: The statement is incorrect, it would be true in the case of mineral nitrogen and phosphorus, not total. Total nitrogen and phosphorus include both organic and mineral forms, and are generally correlated with phytoplankton and phosphorus-rich zooplankton (Daphnia)…

Responds 3: Thank you for your advice. We verified the relevant content by reviewing the literature and provided a correct exposition. (Lines 452-464)

Comment 4: Lines 439-441: The statement is not supported by the data in Results that transparency decreases after farming. These data are absent.

Responds 4: Thank you for your advice. We have included the transparency data in the newly added Table 2. (Lines 236-237)

Comment 5: Lines 441-442: The sentence is unclear. Has eutrophication increased or decreased?

Responds 5: Thank you for your advice. We have rewritten the sentence according to your suggestion to make it better clear. (Lines 478-482)

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Review to Diversity-n2

1. Line 148: “a depth of 50 by…” change to “a depth of 50 cm by…”.
2. Copepods, in particular, Сyclopoida, in addition to naupliar stages have 6 copepodite stages, and only the 6th are sexually mature individuals and by them the species is identified. Younger copepodites of stages 1-4 are almost impossible to identify to species. Therefore, a group of "Cyclopoida copepodites" is usually distinguished or they are combined together with nauplii and called "Juvenile Cyclopoida". Therefore, it should be explained in the text how copepodites were taken into account.
3. Line 197: change SD to Trans, since Transparency is marked as Trans, not SD.
4. Line 453: it would be better “(TP) are the nutrients…” change to “(TP) include the nutrients…”.
5. Line 467: It would be better change “favorable environment for the growth of phytoplankton” to “favorable environment for the growth of bacterioplankton and phytoplankton” since organic matter is substrate for diverse bacteria.
6. Line 479-480: “Based on the observed water body characteristics at the field experiment site and the measured transparency values of the reservoirs,” - This part of the sentence seems redundant and can be removed.
7. Line 481: “water body” change to “water bodies”.
8. Line 482-483: It would be better change “reservoir water body has” to “reservoirs have” or “reservoirs 1-4 have”

Comments for author File: Comments.docx

Author Response

Dear Editor and Reviewers:

Thank you for taking the time to review our paper and giving us the opportunity to revise it. We have made corresponding revisions to the paper in response to your valuable suggestions and comments. The revised parts are shown in the document using the revision mode. At the same time, we would like to answer your questions one by one and provide responses to the revisions (in blue font) here:

Comment 1: Line 148: “a depth of 50 by…” change to “a depth of 50 cm by…”.

Responds 1: Thank you for your advice. We have corrected the error. (Line 148)

Comment 2: Copepods, in particular, Сyclopoida, in addition to naupliar stages have 6 copepodite stages, and only the 6th are sexually mature individuals and by them the species is identified. Younger copepodites of stages 1-4 are almost impossible to identify to species. Therefore, a group of "Cyclopoida copepodites" is usually distinguished or they are combined together with nauplii and called "Juvenile Cyclopoida". Therefore, it should be explained in the text how copepodites were taken into account.

Responds 2: Thank you for your advice. We have explained in the part of 2.2 Sample Collection and Identification how copepodites were taken into account. (Line 161-164)

Comment 3: Line 197: change SD to Trans, since Transparency is marked as Trans, not SD.

Responds 3: Thank you for your advice. We have corrected the error. (Line 198)

Comment 4: Line 453:  it would be better “(TP) are the nutrients…” change to “(TP) include the nutrients…”.

Responds 4: Thank you for your advice. We have changed “(TP) are the nutrients…” to “(TP) include the nutrients…” (Line 453)

Comment 5: Line 467: It would be better change “favorable environment for the growth of phytoplankton” to “favorable environment for the growth of bacterioplankton and phytoplankton” since organic matter is substrate for diverse bacteria.

Responds 5: Thank you for your advice. We have changed “favorable environment for the growth of phytoplankton” to “favorable environment for the growth of bacterioplankton and phytoplankton” (Line 467-468)

Comment 6: Line 479-480: “Based on the observed water body characteristics at the field experiment site and the measured transparency values of the reservoirs,” - This part of the sentence seems redundant and can be removed.

Responds 6: Thank you for your advice. We have removed the sentence “Based on the observed water body characteristics at the field experiment site and the measured transparency values of the reservoirs,” (Line 479-480)

Comment 7: Line 481: “water body” change to “water bodies”.

Responds 7: Thank you for your advice. We have changed “water body” to “water bodies” (Line 480)

Comment 8: Line 482-483: It would be better change “reservoir water body has” to “reservoirs have” or “reservoirs 1-4 have”

Responds 7: Thank you for your advice. We have changed “reservoir water body has” to “reservoirs have” (Line 481)

Author Response File: Author Response.docx