Establishing Total Phosphorus Boundaries to Support Good Ecological Status of Greek Lakes and Reservoirs in Accordance with the Water Framework Directive

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper aims to  determine nutrient boundaries for lakes in Greece, it is well written, concise and provide important insights.

1) “Specific boundaries for good ecological status could be used to maintain healthy biological communities. For this, biological quality elements (BQE; e.g. phytoplankton, macrophytes, phytobenthos, benthic invertebrate fauna and fish) provide significant insights – this is true, however, different elements and different methods are indicative of different pressures.” It is important to use nutrient-sensitive element and methods (Poikane et al., 2020; Nikolaidis et al., 2025)

2) “Establishing nutrient thresholds plays a key role in achieving this objective [4,11,12]” References are not correct, probably the confusion with numbers ?

3) “management strategies should be implemented to reduce environmental stressors, support ecosystem restoration, and promote the long-term health and sustainability of aquatic ecosystems [13,14].” References are not correct, probably the confusion with numbers ?

4)  L 396 “Poikane et al. [1] in their study about setting nutrient thresholds in lakes from several European countries, used among others, phytoplankton data from reservoirs found in the Mediterranean region, characterized as deep, large calcareous (type LM8), to  which our lake type of GR-DR could be compared”. This should be reconsidered as the study Poikane et al., 2020  investigates Mediterranean reservoirs – water bodies built on rivers using the dams; these water bodies differ substantially from natural lakes the subject of this study.  

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Phytoplankton comprises various taxonomic groups: cyanobacteria (Cyanophyta, Cyanobacteria), green algae (Chlorophyta), diatoms (Bacillariophyceae), dinoflagellates (Dinoflagellates), and euglena. The groups present in each lake type are not specified. The lack of detailed characteristics of the phytoplankton prevents broader comparisons between studies. There is no comparative analysis of EQR and TP between individual lake types. Analysis of Figure 2 indicates that DNL lakes are the least polluted, while VSNL lakes are the most polluted. No information is available on the reasons for this. The full names of the lake types are not provided.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The article addresses the important issue of eutrophication of aquatic ecosystems, with the authors analysing these issues in the legal context of the Water Framework Directive. The article is well organised and the methodology used is appropriate for the objective set. I recommend the article for publication, subject to the following comments.

1) Please specify the sampling location. Was it at the deepest point of the lake or at another location? How does this affect the composition of the sample and, consequently, the results obtained?

2) The measurement data does not include basic (easy to measure) parameters such as water temperature and DO. This is crucial in the context of the research conducted and the further interpretation of the results.

3)         In addition to the division into lake depth classes, please provide the characteristics of the catchment area and take this into account in the interpretation. With the same morphometric parameters of lakes and different types of catchment areas, the results may differ in the context of the research being conducted.

4) …Additionally, as climate change increasingly affects hydrological regimes, thermal conditions, and biological responses, future boundary definitions may need to become more stringent to safeguard ecological integrity…  At this point, this is a general statement. The reader knows nothing about the current climatic conditions in Greece and the further prospects for their change (please use relevant literature in this regard).

5)         Please expand on the issue of internal lake supply. Many studies have identified this as a key factor influencing eutrophication, rather than supply from the catchment area.

6) In the Conclusions section, please address the weaknesses/limitations of the proposed methodology.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The article highlights the successful establishment of nutrient concentration boundary values using pressure–response relationships between nutrients and biological communities. However following minor correction are required.

Add a paragraph on practical implication of this method.

Authors need to clarify How was the comparison done as there is no observed data.

What are the expected outcome if data base is expanded. Will the present approach suffice for a large scale data set or what are the challenges/ modification need to be done for application on very large scale.

How uncertainties in the dataset were handled. Also carify how seasonal and temporal variations adressed. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Response to Reviewer 2 Comments accepted