Microbial Enzyme Activities Outperform Conventional Indicators in Revealing Systematic Patterns of Dissolved Organic Matter-Driven Microbial Changes Across a Human-Impacted Lake Network
, Quanhong Li 2,†, Shuli Liu 1, Dan Lu 3, Dongdong Cui 2, Xincheng Jin 4, He Qin 2, Zhuo Huang 1,* and Sergio Zubelzu 5
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript investigates the relationship between DOM and microbial indicators in a lake system. However, significant modifications are required. The novelty needs to be clearly articulated. Methodology and the interpretation of results must be considerably improved. English correction is also recommended. Specific comments are provided below:
- The experiments are based on E. coli and BC based on the coliminder system. The comparison with conventional microbial analyses is not provided. The authors must discuss the limitations of coliminder tests to quantify the microbial enzyme activity. QA/QC details must be provided for coliminder analyses.
- The study is based on a single sampling. Robust conclusions about the sources, DOM composition, and microbial activity cannot be arrived at based on a single sampling event.
- Sampling locations are not provided.
- Validation of models based on 38 samples will not be sufficient. The model parameters (confidence levels and error) must be reported. Sensitivity analyses must be performed.
- Without PARAFAC modeling, EEM data interpretation will not be complete. This must be acknowledged as a limitation.
- Source apportionment purely based on fluorescence peaks is not reliable.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript “Microbial enzyme activities…lake network” describes work in which the authors utilized modern methodologies to assess anthropogenic impacts on water quality in several freshwater lake areas. The work is very interesting and the paper is well-written; however, I cannot recommend that this paper is ready for publication.
The reason that I make the statement above is that the results of this paper are based on a temporally single water collection performed in summer. No replicate sampling was done and yet the authors are strident in their assertion that water quality readings are due to farming, or recreation, or… In my opinion, arrival at this conclusion is only possible after repeated sampling over multiple seasons. In addition, no measurements were conducted to confirm author assertions. For example, differences in pH are due to lime applications to agricultural fields and yet, no data is provided on pH measurements of soils that the authors claim are washing into the lake and elevating the pH. In Line 292, the authors claim that organic pollutants are causing elevated COD and TOC. Yet, no measurement of organic pollutant concentrations were presented. Thus, though the study is interesting, as are the methods used, publication of these results is premature.
What I would support, rather than outright rejection, is that the authors would revise broad statements to reflect that there is no proof of the connection between anthropogenic activities and water quality. For example, in Line 302: “…these findings suggest that water quality may be affected by predominant land use…” In other words, remove the assertions and point to trends and potential explanatory factors. This paper could be shifted into a methods paper. The methods utilized were unique and with some rewriting and removal of definitive statements, it could be a good methods paper.
I have additional comments below to be incorporated into this paper:
- The abstract uses multiple acronyms that are not defined. What is TH (Line 30)? What ae MH and GZ (Line 35)? These have not been defined.
- Line 54 – the sentence ending in “eutrophic” requires a reference.
- Line 65 – the statement that E. coli “poses direct risks” is untrue. E. coli, though a marker of anthropogenic input (as stated in the paper), poses a “potential risk.” Not all E. coli are pathogenic.
- Line 67 – is a word missing here? Perhaps the authors mean to say “microbial presence”?
- Line 72 – the sentence beginning in “Numerous” should start a new paragraph. The existing paragraph is extremely long.
- Line 149-150 – if this paper moves forward for edits (is not rejected), this point MUST be stressed throughout. NO firm conclusions can be drawn on a single sampling.
- Line 494 – remove the word “comprehensively.” This study has holes that must be filled before it is comprehensive.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript titled “Microbial enzyme activities outperform conventional indicators in revealing systematic patterns of dissolved organic matter driven microbial changes across a human-impacted lake network” explored impact of human activities on three lake sectors in China. The authors integrated EEM spectroscopy, SOM and statistical analyses to achieve three aims in for the study, namely: (i) characterize spectral properties, source origins and spatial heterogeneity of DOM 105across the three lake sectors; (ii) quantify the correlation between DOM characteristics (e.g., humification degree, bioavailability, source type) and the activity of BC and E. coli; and (iii) identify DOM-related and environmental factors regulating microbial indicator dynamics.
The introduction was well written, just that much attention was not given to DOM and how it relates with microbial change (e.g., E. coli), which was the main subject matter in the study.
I also noticed that the three lake sectors you claimed to have studied were not well described. What informed the selection of the three lakes, I know you mentioned human activities including: tourism, intensive agriculture and urbanization sub-lakes but you did not tell us which of the three lakes belong to each of the anthropogenic activities. Then, you just mentioned that I quote “lake network, three rep-124resentative areas were selected for analysis, a tourism and sightseeing area (GZ), an intensive agricultural area (TH) and a populated urban area (MH). The GZ area is dominated by tourism, and various human activities in its surroundings impact the local water quality. As GZ is a scenic area, strict environmental protection measures have been imposed to maintain good water quality and provide ecological protection. TH is an intensive agricultural area, with agricultural activities occurring widely 130in the surrounding region and a relatively high intensity of agricultural surface source inputs affecting water quality. Besides, as MH is situated in a densely populated urban area, its water quality is heavily influenced by domestic activities.”, first, you did not tell us the full meaning of GZ, TH and MH? Second, does it mean some area are impacted by one than one anthropogenic activities? If yes, how do you delineate the sites based in these different impacts? How do you know which impact is affecting the patterns microbial changes based on DOM concentration? Lines 144-148 appears to be a repetition of what you have mentioned much earlier. Then, the first sentence of the paragraph (lines 149-155) is hard to read, please check other statements as some of them are hard to read.
The results section was well written, but there appear to be issues with your combining the results with the discussion, as you made so many claims that we not substantiated with any literature. In my opinion, you only interpreted your results without discussing them. I would suggest you separate the results from the discussion and give us a more detailed implication of your results in the next stage of your submission.
Please, seek the help of an English editor to help with your grammatical constructions.
See the attached document for other comments.
All the best.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThis study presents an integrated method combining rapid microbial detection, EEM and DOM-microbe correlation to analyse human disturbances across segmented connected lakes in Hubei. It maintains scientific support for targeted trophic status management of human-influenced freshwater.
The novelty of the study is high. The objectives of the study were supported by the results. The manuscript is well written and organised. But it still needs some improvement. After a revision it can be accepted. Please see the attached PDF file for more details.
Line 38 Abstract It offers Our study provides a scientific support for targeted water quality management of human-influenced freshwater.
Line 47 Introduction The ecological/trophic status of lake
Line 56: delete state index use trophic status
Line 67 use a critical link/a key intersection instead of pivotal nexus
Line 78 not sytems ecosystems
Line 121 not zone use area
Lİne 122 picturesque Heterogeneous/Interconnected/Extensive
Lİne 137 W/m2
Lİne 141 on site in situ
Line 146,147,148 These differing pressures result in varied physicochemical conditions; hence, this study aims to elucidate how these differences shape DOM composition.
Lİne 159 in situ
Lİne 199 remove in this study
Lines 208 and 209 E.coli must be italic
The quality of figures 8 and 9 are low. If possible, please improve the quality and readability.
Comments for author File: Comments.pdf
Throughout the manuscript, certain phrasings appear overly poetic and tend to hinder the overall flow of the text. In scientific writing, clarity and precision must always take precedence over literary or stylistic expressions. The authors should revise the text to adopt a more direct and rigorous academic tone. Please see the attached PDF file for more details.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for your careful consideration of each of my reviewer comments. The resulting manuscript is greatly improved, and I support publication at this time.
