Reconstruction and Trends of Total Phosphorus in Shallow Lakes in Eastern China in The Past Century

Round 1

Reviewer 1 Report

The manuscript is an important contribution to the understanding of the causes of lake eutrophication. The manuscript analyses the changes in phosphorus levels in several lakes over 100 years. The manuscript lacks a detailed analysis of the catchment management of the lakes studied. Such information would allow a more accurate interpretation of the data obtained. Please also describe in more detail how the manuscript will contribute to future lake restoration. The paper also suggests directions and methods for future lake restoration.

Author Response

Response 1: We appreciate the comment. Actually, it is impossible to collect detailed changes in driving factors and lake characteristic over past century. In order to preliminarily interpretate different trends, we collected catchment background data in eastern China. First, we inferred that human-induced factor is the most important reasons for fast TP increase, as the huge magnitude of change due to fast development exceed climate changes in influencing in short time (one century). Second, we found that lakes not experienced fast increase in TP mainly locate in the Middle Yangtze River basin. One possible reason can be that the nutrient enrichment speed is lower in the lower reaches of Yangtze River. Lake structure differences can be another possible cause. Water regulations stabilized hydrological condition and reduced water depth, so that the expansion of macrophytes can consume TP in lake water.

To have a more accurate interpretation of the data obtained, we have added a new figure (Figure 5) and rewritten “4.1. Possible reasons of different TP trajectories” in “Discussion”. 

Response 2: Our findings indicated the prevalence of regime shift in lake TP. According to the suddenness and irreparability of regime shift, it will be hard to recover these lakes by merely external loading control. Other methods such as biomanipulation and water regulation should be used at the same time. Meanwhile, we also found different trends in lake TP. This not only calls for more studies on diversity of ecosystem responses, but also provides important information for policy makers. Policy makers should pay more attention to lakes with decrease and fluctuate TP trends in the past, as they showed rising change in recent decade and can deteriorate under current uneven resource allocation in restoration and future climate warming.

Two paragraphs have been accordingly added in 4.3 of “Discussion” to more clearly state how the manuscript will contribute to future lake restoration.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors

I regret to inform you that the manuscript is not fit for the publication in its present form. I have given some comments which may improve the standard of the article.

The general comments are as follows:

The manuscript is not having any novelty or scientific significance. It lacks scientific standard.

The eutrophication has been labelled as a sudden process!

It is just a review of literature, on the basis of which, the results have been framed and discussion portrayed as a fairy tale. 

I doubt, if the permission has been taken from the primary contributors.

The methodology adopted is insignificant and confusing.

The results and discussion looks fabricated.

Conclusion is baseless. The manuscript is not having any novelty or scientific significance. It lacks scientific standard.

The eutrophication has been labelled as a sudden process!

It is just a review of literature, on the basis of which, the results have been framed and discussion portrayed as a fairy tale. 

I doubt, if the permission has been taken from the primary contributors.

The methodology adopted is insignificant and confusing.

The results and discussion looks fabricated.

Conclusion is baseless. 

Comments for author File: Comments.pdf

Author Response

Response to general comments: This is the first statistical study on difference in historical TP changes in eastern China lakes using data generated from paleolimnological methods. A big part of the data we collected was from published papers. Other data including unpublished data and original data (before analysis) of published papers, we got permission from original authors. We also had the permission from the primary contributors. Based on a review of literature, we re-analyzed the data and statistically discussed the variability of TP changes over past century in eastern China. We clarified the eutrophication type and enriched the methodology and discussion according to reviewers’ comments.

Author Response File: Author Response.docx

Reviewer 3 Report

These comments must be addressed before this manuscript is accepted.

The authors must explain the causes of the tendencies of decrease, increase and fluctuations in the levels of TP-

The TP levels recorded in your history should argue how it influences the imbalance of natural ecosystems. How should this be addressed to meet the sustainable development goals? What are the political implications and environmental legislation that should be implemented?

Author Response

Response 1: We appreciate the comment. Another reviewer also put up this point in the original paper. Specifically, in order to preliminarily interpretate different trends, we collected catchment background data in eastern China. First, we inferred that human-induced factor is the most important reasons for fast TP increase, as the huge magnitude of change due to fast development exceed climate changes in influencing in short time (one century). Second, we found that lakes experienced fast increase in TP mainly locate in the lower Yangtze River basin whereas those lakes whose TP decreased or fluctuated mainly in the middle Yangtze River basin. One possible reason can be that the nutrient enrichment speed is lower in the lower reaches of Yangtze River. Lake structure differences can be another possible cause. Water regulations stabilized hydrological condition and reduced water depth, so that the expansion of macrophytes can consume TP in lake water.

To have a more accurate interpretation of the data obtained, we have added a new figure (Figure 5) and rewritten “4.1. Possible reasons of different TP trajectories” in “Discussion”.  

Response 2: Previous studies of chironomid composition in 32 lakes and macrophyte change in 14 lakes in eastern China discussed the existence of lake ecosystem response diversity (Luo 2017, Huang et al. 2021). Another sediment total organic carbon (TOC) research also found spatial variability of lake ecosystem responses in China (Yifan et al. 2021). The varied trends of lake water TP in eastern China since 1900 in this study can complement other results, leading to a more comprehensive understanding of the potential mechanism of ecosystem resilience.

Our findings indicated the prevalence of regime shift in lake TP. According to the suddenness and irreparability of regime shift, it will be hard to recover these lakes by merely external loading control. Other methods such as biomanipulation and water regulation should be used at the same time. Meanwhile, we also found different trends in lake TP. This not only calls for more studies on diversity of ecosystem responses, but also provides important information for policy makers. Policy makers should pay more attention to lakes with decrease and fluctuate TP trends in the past, as they showed rising change in recent decade and can deteriorate under current uneven resource allocation in restoration and future climate warming.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have tried to incorporate all the comments. The revised version of the manuscript is much better than the first one. All the sections of the manuscript have been thoroughly modified.

I suggest to check some minor grammatical errors in the manuscript.