Spatiotemporal Changes in Water Quality Parameters and the Eutrophication in Lake Erhai of Southwest China
, Xiaonan Zhang 2, Fengwen Liu 2 and Hucai Zhang 2,*
Round 1
Reviewer 1 Report (New Reviewer)
The article is essentially correct in terms of its structure and the hydrochemical research methodology applied, but it does raise certain reservations about its substance. The most important ones are:
1) research goals are overly basic, indicating that the primary purpose of the work is documentation;
2) Lines 73-75 – please check the values (256,5 *106 x 10,5 = 2,7 km3);
3) the description of the location of measurement sites in Fig. 1 is imprecise;
4) the description of the study object and its catchment area is very short on substance (lack of data e.g. population and settlement, land use, water and sewage management, air pollution).
5) in the analysis of hydrochemical properties, there are only perfunctory references to the conditions prevailing in the catchment of the water body.
6) In my opinion, the section where study results are discussed requires some additions. The study results obtained have not been compared to data on other areas where water reservoirs is being exploited worldwide; moreover, no broader regional comparisons have been made. A commentary putting the numbers presented in a broader context and an analysis of cause and effect would be welcome. The study should also incorporate wider-ranging references to results of comparable international research. This will enable the issue in question to be presented in a context broader than the local or regional one.
7 ) the conclusions do not advance the state of the art in hydrological studies (the conclusion is the right place to highlight any novel study results; in its present form, none have been presented).
Author Response
We have revised the manuscript based on the suggestions and uploaded a response letter
Author Response File: 
Author Response.docx
Reviewer 2 Report (New Reviewer)
The article is well documented, for which we congratulate the authors. However, there are small corrections that need to be made, which I have marked in yellow directly on the text of the article. We also suggest to the authors a deeper analysis of the factors that generate the appearance of eutrophication and perhaps identification of future rehabilitation possibilities.
Comments for author File: 
Comments.pdf
Author Response
We have revised the manuscript based on the suggestions and uploaded a response letter
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report (New Reviewer)
My suggestion is acceptance. Congratulations to the Authors.
Regards
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
This paper describes the conclusions drawn upon long-term water quality monitoring (2016-2020) of lake Erhai in China. Authors have analyzed the data and described the results in regarding to air-temperature, different parts and depths of the lake and looked at seasonal variety. The strength of the paper lies with the large amount of data collected and analyzed.
This paper describes a large dataset but would benefit from extra embedding in international literature. Currently, 99% of the references originate from one country, only 5 references are from >2020. Most importantly: only 27 references are cited. Many statements in the discussion (but also throughout the whole manuscript) would benefit from the appropriate reference.
line 23: what are modern lakes?
line 29: CDOM write out first instance used. Not mentioned in manuscript further.
line 32: add ref
line 39: what is a shallow plateau lake?
line 40: unsystematic what?
line 42: modern basic physical? what is the meaning of modern here?
line 44: Nam Co - where is this?
line 48-52: where are these lakes situated and how are they relevant to this study?
line 59: aim describes pollution control - is not addressed further in paper
line 63: what country - China. Where in China is this area and lake? Add to figure 1.
line 64: define a shallow plateau lake
line 72: what is adequate sunshine?
line 75: figure 1: elevation in m above sea level? add where in China
line 82: add YSI multiparameter sonde. what is sampling frequency?
line 86: why focus on 2 years, and not whole sampling period? why those two depths?
line 92: what groups?
line 101: air temperature data not described in methods, where from?
line 101: why 1982-2010 and not during analyzed period 2016-2020?
line 107: rainy august-October - why not May/June - October?
line 111: where is Dali City (methods!)
line 127: figure 3 twice same information in figures. Choose one of the two (I would prefer bottom plane)
line 131: what is than 7.5 per month??
line 134: what is lower stage?
line 139: see comment line 127
line 142: remove first line
line 146: clean lake? --> oligotrophic? how do you define these (ug/l TP)
line 145: relevant studies: referred to an oxygen depletion zone in the sea - is this relevant? I have never seen this statement use for/in lakes. Phytoplankton can migrate to the surface to find oxygen needed.
line 149: not really reoxygenation as it follows the ChlA concentration thus is produced by phytoplankton (thus affecting pH, previous section).
line 153: how do you define anaerobic (mg/l)
line 156: how do you define hypoxic, anaerobic? (mg/l)
line 157/ 158: leading to a large number of - would remove and say probably due to microorganisms...
line 160: can decomposition ever be complete?
line 162: I don't follow this statement. Why is this the case, what reoxygenation? Seems to me a product of your algae peak in autumn.
line 169-170: references needed
line 176: when is spring festival? think about international audience (also with describing location etc.)
line 178: sentence doubled
line 177: reference!
line 167-186: describe values found: range ChlA from 1.0-13.0 ug/l is really low compared to lakes with urban input worldwide etc. Compare and evaluate values found compared the other comparable lakes (within region etc.) in discussion. Abstract says mesotrophic lake, is not described or stated in article itself! add to TN/TP section/ChlA section + define.
line 208: why would you expect a negative correlation ChlA - TN
line 215: water body species?
line 216: endogenous release: sediment P release under anoxic conditions. References!
line 219: like most lake P limited - add references. Describe in discussion
line 221: water quality parameters are low? Do you mean; differences in concentrations are low?
line 224: natural physical factors, do you mean pH? pH is not really a physical factor in my opinion.
line 231: lower temperature, higher chlorophyl-a concentration???
line 237: R2 are very low...
line 234: add international references
line 244: average air temperature
line 247: dominant wind direction important info, add methods
line 153: flew - flowed
line 260: low oxygen content --> death of algae --> ChlA release. I think should be reversed: death of algae caused low oxygen due to microbial activity which leads to nutrient release.
line 266-302: add references
line 296: dissolved oxygen increases- there were more aquatic plants --> more aquatic plants (or algae)= more oxygen.
line 303: improved --> higher
line 306-310: reads as algae concentration determines water temperature. Adjust sentence
line 311: dissolved oxygen
line 318: middle trophic stage: elaborate. How do you define, determine trophic stage etc.
line 319: high chlorophyl-A concentration - is relative! very low compared to European lakes. Address this in section chlorophyl-a
line 330: not completely sound reasoning. Where there blooms in the analyzed period? not mentioned in the manuscript so far!
- A brief summary (one short paragraph) outlining the aim of the paper, its main contributions and strengths.
- General concept comments
Article: highlighting areas of weakness, the testability of the hypothesis, methodological inaccuracies, missing controls, etc.
Review: commenting on the completeness of the review topic covered, the relevance of the review topic, the gap in knowledge identified, the appropriateness of references, etc.
These comments are focused on the scientific content of the manuscript and should be specific enough for the authors to be able to respond. - Specific comments referring to line numbers, tables or figures that point out inaccuracies within the text or sentences that are unclear. These comments should also focus on the scientific content and not on spelling, formatting or English language problems, as these can be addressed at a later stage by our internal staff.
Reviewer 2 Report
The purpose of a scientific publication should not be to learn how a given lakes works. It is a well-known phenomenon that the authors here are writing about. You could say it is a textbook example, no more that has been known for decades, cited from the abstract:
„In summer around August, the water had decreased and low DO content, highest T and increased Chl-a content with the dropping pH value at the bottom of the lake, leading to an increased risk of algal blooms. Pearson’s correlation coefficient and principal component analysis showed a significant positive correlation in Chl-a to T and TP in the mesotrophic Lake Erhai (p<0.01), indicating that total phos-phorus content was one of the triggering factors for the algal bloom outbreak.”
For science, there are no new findings in the manuscript. It is not even included in the objectives, and therefore not in the conclusion chapter also (cited from abstarct): Abstract: To understand the eutrophication reasons at Lake Erhai………
The evaluation of the graphs is not sufficiently detailed, see Fig.8.
It has not taken the effort to compare its results with other water bodies see line 233 „This result is consistent with that on chlorophyll-a in many lakes ……
