Review Reports - Using Chemical Monitoring Data to Distinguish Natural Background Concentrations and Anthropogenic Impacts in Lake Sevan Tributaries, Armenia

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors/scientists,

It's a nice research work with very nice conceptual design. From my site at present no suggestion for improvement of the quality of work. Keep it up for new reasearch work.

Author Response

Comment: It's a nice research work with very nice conceptual design. From my site at present no suggestion for improvement of the quality of work. Keep it up for new reasearch work.

Response: We sincerely thank you for the positive assessment of our manuscript and for the encouraging comments. We greatly appreciate your support and kind words.

Reviewer 2 Report

Comments and Suggestions for Authors

The study utilized 16 sampling sites with data from 2010-2024 to explore long-term trends in chemical water quality with respect to certain minerals and metals, and how these results can possibly be understood by geology and/or anthropogenic impacts in the Lake Sevan, Armenia region/catchment. The authors report observations using cluster and correlation analyses to support their findings, and identify a few limitations.

Areas for Potential Improvement:

1. The analysis appears thorough and the discussion seems well-aligned with the results observed. There are aspects of the manuscript that would potentially benefit from articulating some of the limitations or some of the additional factors to be considered if making a conclusion that the 'monitoring network is sufficient to characterize natural background water quality' and 'detect human impacts in the tributaries'. Therefore, a limitations section could be added to the discussion. The end of 4.2. does include some limitation from lines 663-667.

2. The manuscript has an apparent focus on minerals and metals; however, additional parameters may also be of interest for monitoring for anthropogenic impacts, which could include physical (temperature, pH, ~maybe conductivity/TDS), and biological approaches to water quality (macroinvertebrate biotic integrity or fish biotic integrity and microbiological [fecal indicator bacteria levels, like E. coli]. For example, is Lake Sevan raising in temperature which could also go along with the increased frequency in cyanobacteria blooms? As a reviewer, I am not suggesting temperature is responsible for the blooms or for that to be included unless the science or observations back it up, it is just an example that general physical parameters may also have a lot of utility, are often simple to measure, and in some regions, land use changes can cause changes in tributary temperature and turbidity, especially when combined with other factors like the amount of flow or depth of the tributaries. Please consider emphasizing in the title and conclusions the focus on background minerals and metals, and somewhere in the discussion consider any additional contributions from biological and physical parameters beyond benthic photosynthetic organisms impacting DO if those are valuable parts of the monitoring program just not discussed in this manuscript.

3. Additionally, it is not apparent from the sampling or the supplementary tables as to whether or not the sample collection dates/times are approximate to one another. Specifically, precipitation and flow rates likely impact concentrations of the parameters assessed. This may be a non-differential problem that evens out over the large sample size. Was hydrologic changes, impacts of extreme weather (e.g. flooding?) or precipitation considered? It may be a stable region; however, differential impacts from changes due to increased frequency in extreme hydrologic events in some larger systems can complicate water quality and land use.

4. Regarding the nutrients section (4.1.3) is there any information on the type of agriculture? Row crop, livestock? What is the source of the P and N? Fertilizer or manure? (or both)?

Minor Suggestions:

A. Consider spelling of wastewater - waste water or wastewater? Usually, it is wastewater, there are a few places where it is spelled waste water.

B. Include the sampled years (2010-2024) in the abstract section, number of sites (16), and maybe consider to include the number of samples used or average number of samples per site, to inform the analysis.

C. Consider adding units of the measurements (e.g. mg/L or ppb, ppm, etc.) and improve table formatting to the supplemental tables (centered headings, horizontal lines at least across the top).

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached file

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Taking the Sevan Tributaries, Armenia as a case study, this paper reports the feasibility and limitations of using long-term hydrological and biogeochemical monitoring data from upstream and downstream river reaches to separate natural background levels from anthropogenic impacts. On this basis, approaches to improve such evaluation methods are proposed. The findings provide useful insights for the ecological and environmental management of rivers and watersheds. Nevertheless, considerable uncertainties and limitations remain in this work, and the suggestions below can be referred to during revision.

Comments:

Since this study fails to quantitatively distinguish anthropogenic sources from natural background values using long-term monitoring data, it is suggested that the title be revised into an interrogative sentence or highlight the limitations of the method. In addition, could the adjective “long-term” be added before “monitoring data” to better align with the descriptions in the abstract and emphasize the importance of long-term monitoring datasets?
The abstract lacks clear conclusions and is not entirely aligned with the Conclusions section.
In the third paragraph of the abstract: The study fails to achieve its original research objectives. Concluding with only general descriptions would be of limited practical value. In other words, a qualitative assessment could be roughly drawn merely based on geographical knowledge and the scale of socio-economic activities within the watershed without conducting this research. Therefore, quantitative discrimination between natural background conditions and anthropogenic impacts should be the top priority.
The final sentence of the abstract is incomplete. Is data compilation and analysis sufficient to support sustainable management of vulnerable watersheds? The authors need to clarify what specific research should be carried out.
The statistical analyses used (cluster analysis and correlation analysis) are routine. It is suggested to incorporate techniques including isotopes and indicator factors to improve the research depth.
Section 3.4: Reliance solely on correlation coefficient magnitudes for evaluation is questionable.
Lines 459–461 and Line 518 contain multiple unexplained issues, bringing greater uncertainties to the present work.
Were interannual variations of the long-term data considered in the analysis?
Accurate quantification of background values is the major challenge of this study, relevant solutions need to be supplemented in the Discussion.
Please specify the units of data in the supplementary tables.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached file.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This work provides a systematic evaluation of monitoring data from Lake Sevan, Armenia, with the aim of distinguishing natural hydrochemical background conditions. The study benefits from a long-term, multi-parameter dataset covering the full basin, and applies hierarchical clustering to characterize spatial water quality patterns. The topic is of clear regional relevance for Lake Sevan protection and watershed management, and the core conclusions are broadly supported by the presented data. Nevertheless, several issues need to be addressed before publication.

The current version lacks sufficient scientific discussion. The authors should further develop the discussion by drawing more on the results of this study.
Why do negative minimum values exist in Table S2? These values should be compared against ultrapure water blanks and properly processed, rather than being simply presented in the table. Did the authors perform comparison with ultrapure water?
How was total phosphorus (TP) determined? This is not clearly specified in Section 2.2.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached file

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has made some considerable improvement; however, it still seems to present chemical water quality assessment alone is adequate for documenting anthropogenic impacts to to Lake Sevan and its tributaries. For that reason, a few more revisions are encouraged with more specific follow-up on the previous suggestions.

Item #1: The title may need a slight edit at the end of the title: "Using Chemical Monitoring Data to Distinguish Natural Background Concentrations and Anthropogenic Impacts-Lake Sevan Tributaries, Armenia" -- maybe to "Using Chemical Monitoring Data to Distinguish Natural Background Concentrations and Anthropogenic Impacts *in* Lake Sevan Tributaries, Armenia"

Item #2: Line 155 should re-iterate 'chemical' water quality rather than 'water quality' to make clear that biological, including microbiological, and physical parameters were not part of the assessment.

Item #3: The previous revision request encouraged as follows: "Please consider emphasizing additional contributions from biological and physical parameters beyond benthic photosynthetic organisms impacting DO if those are valuable parts of the monitoring program just not discussed in this manuscript." An area of the manuscript for which this comment was targeted is more clearly described here: "Both BOD5 and COD had higher concentrations at the downstream SSs (Figure S1, 561 Table S3). Since both municipal wastewater and agriculture are well known as sources of BOD5 and COD [56], the higher downstream concentrations were interpreted as the result of human impacts. The slightly higher concentrations of DO at the downstream SSs were attributed to photosynthesis based on the higher nutrient concentrations there compared 565 to the upstream SS".

THEREFORE for Item #3: Are there publicly available data on BOD5 from the effluent? Are fecal indicator bacteria available from agricultural impacted sites or failing human wastewater systems? Were chlorophyll a concentrations obtained to document more photosynthesis. Since the answer is likely no, the authors should mention the value added by those types of results or more clearly indicate in their limitations or as part of the discussion on those topics, should consider emphasizing that definitive testing would more likely clarify the veracity of the speculations. *Alternatively, the authors could cite papers or research from this watershed that did take these measurements that support the claims.

Item #4: The limitations section now includes, "Using biological monitoring for the characterization of river water quality is a common approach [85, 86]" which is a helpful addition. It would be more useful for the readers to know a little more about examples of biological monitoring in greater detail, which could state, biological monitoring such as... " [insert examples]" or be described in a follow-up sentence.

Author Response

Response 1: Many thanks for this comment and the proposed change in the title. We took over the change and the title is now:

Using Chemical Monitoring Data to Distinguish Natural Background Concentrations and Anthropogenic Impacts in Lake Sevan Tributaries, Armenia

Response 2: Many thanks for this comment. We indeed did not carefully enough mention the limitation to chemical water quality in our study in the text of the manuscript. Thanks to the comment, we have checked the entire manuscript again and added “chemical” at ca. 40 locations in the manuscript. Due to this high number widely spread in the manuscript, we do not list all these changes in detail here. However, in some cases, “chemical” was not added because of the more general context or because of relation to biological monitoring.

Response 3: As expected by the reviewer, the proposed kinds of data are not available, unfortunately. Therefore, we made it better visible by re-wording that our interpretation is quite likely but without a clear proof. We also added a short explanation why we see considerable evidence that we are likely not wrong due to our observation that there are abundant macrophytes in the downstream sections, supported by photos of one of the authors. The revised text reads now:

The slightly higher concentrations of DO at the downstream SSs were interpreted as being most likely the result of photosynthetic activity of phytobenthos, mainly macrophytes, based on the higher nutrient concentrations there compared to the upstream SSs. This is supported by the abundant occurrence of macrophytes in the downstream parts of the rivers (Figure S5).

Response 4: Many thanks for this comment. According to the recommendations of the reviewer, we added a very short explanation of typical approaches of biological monitoring and its particular valuey, following the sentence "Using biological monitoring for the characterization of river water quality is a common approach [85, 86]".

It has a long tradition of more than 100 years and is still mainly based on regular investigations of the composition and abundance of benthic invertebrates, phytobenthos and fish in case of rivers [85]. Monitoring pathogens also belongs to biological monitoring [85]. The particular value of biological monitoring is the integration over time since the organisms are exposed to the river water and all its chemical constituents over the entire time of their live in the river. Considerable changes in the chemical water quality are often indicated by changes in the composition and abundance of the organisms present in the rivers, even when monthly chemical sampling does not indicate such changes as e.g. in case of occasional inflow of toxic waste water.