Water Quality of Lake Erhai in Southwest China and Its Projected Status in the near Future
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript presents an analysis of the water quality trends and spatial variations in Lake Erhai based on monitoring data from 2009-2019. The authors built a 2D hydrodynamic and water quality model to predict the future water quality in 2025 under different flow scenarios. Overall, the study is relevant and the methods are generally sound, but there are some issues that should be addressed:
Strengths:
· Comprehensive analysis of long-term water quality data to characterize trends and spatial patterns
· Use of a validated hydrodynamic-water quality model to make projections for 2025
· Relating water quality to potential drivers like rainfall, agriculture, pollution control measures
· Clear presentation of results through figures and tables
· Practical recommendations provided for lake management
Weaknesses/Comments:
1. The modeling approach could be explained in more detail - what are the key assumptions, limitations, input data sources etc? The model calibration and validation should be elaborated.
2. The discussion of results is fairly descriptive. More insights connecting the observations to underlying processes/mechanisms would strengthen the interpretation.
3. The impacts of climate change, which may significantly alter rainfall patterns and water balance, are not really considered in the 2025 projections.
4. In Figures, the text is very small please enlarg.
Overall, this manuscript makes a useful contribution by analyzing long-term water quality data for an important lake and providing projections for the near future. With some revisions to address the above points, especially improving the details around the modeling aspects, it could become a valuable resource for understanding and managing the water quality issues in Lake Erhai. I would recommend publication after major revisions to improve clarity and interpretability.
Comments on the Quality of English LanguageSome grammatical issues and awkward phrasing throughout - the manuscript would benefit from language editing. For example:
· "With the socioeconomic development of the Lake Erhai basin, the water quality of Lake Erhai has deteriorated in recent decades." Better: "The water quality of Lake Erhai has deteriorated in recent decades due to socioeconomic development in the lake basin."
· "However, water quality monitoring data show that the pollutant concentrations in Lake Erhai still exceed the acceptable value, and the pollutant concentrations risk exceeding the water quality standard limits in the future." Better: "However, water quality monitoring data shows that pollutant concentrations in Lake Erhai still exceed acceptable values, and there is a risk of further exceeding water quality standard limits in the future."
· "The analysis of the monthly average rainfall from 2009 to 2019 at Dali Meteorological Station revealed that the average monthly rainfall gradually increased from May to October and gradually decreased from November to April." Better: "Analysis of the monthly average rainfall data from 2009 to 2019 at the Dali Meteorological Station revealed that average monthly rainfall gradually increased from May to October and gradually decreased from November to April."
· "The CODMn index was Class II–III, the TP index was Class II–III, and the TN index was Class III." This could be rephrased more clearly.
· "Consequently, non-point source pollution still needs to receive greater attention after the measures for comprehensive water pollution control in the Erhai basin have been implemented." The phrasing here is quite convoluted. This could be split into two sentences.
· "According to this water quality prediction, without additional pollution control measures, the pollutant concentrations of Lake Erhai will exceed the Class II water quality standard by 2025." Better: "According to the water quality predictions, without additional pollution control measures, pollutant concentrations in Lake Erhai will exceed the Class II water quality standard by 2025."
· There are several instances of lack of articlese.g. "...the trend of water quality deterioration has been curbed..." should be "...the trend of water quality deterioration has been curbed..."
Author Response
1.Comment: The modeling approach could be explained in more detail - what are the key assumptions, limitations, input data sources etc? The model calibration and validation should be elaborated.
Response: In sections 2.2, we added the assumptions and limitations of model. In sections 3.4, we added input data sources. In sections 2.3, we supplemented the model calibration and validation. For better clarification, we added tables 2.
2. Comment: The discussion of results is fairly descriptive. More insights connecting the observations to underlying processes/mechanisms would strengthen the interpretation.
Response: In sections 3.2 and 3.3, the discussion and analysis were supplemented. For better clarification, we added tables 3 and 4.
3. Comment: The impacts of climate change, which may significantly alter rainfall patterns and water balance, are not really considered in the 2025 projections.
Response: We explained in sections 3.4. In order to reflect the impact of rainfall change on water balance, based on the long-term series of runoff results from 1952 to 2014 in Lake Erhai, the empirical frequency method was used to determine the water inflows into lake in three typical hydrological years (high-, normal-, and low-flow years). The water inflows and pollutants into lake in three typical hydrological years were used as boundary conditions for the prediction.
4.Comment: In Figures, the text is very small please enlarg.
Response: We Modified Figure 1, Figure 9,Figure 10 and Figure 11.
5. Comment: Some grammatical issues and awkward phrasing throughout - the manuscript would benefit from language editing.
Response: We corrected the grammatical and spelling errors.
Reviewer 2 Report
Comments and Suggestions for Authorsplease see the attached file.
Comments for author File: 
Comments.pdf
minor spell check required.
Author Response
1.Comment: How can measures improve the quality of the lake water? In my opinion, only actions set after such measures can have an effect on the water quality. If these actions have an impact, the authors have to collect the empirical data in the future for conformation of the model.
Response: In section 4, we made recommendation. To further analyze the effect of these measures to protect Lake Erhai, the collection of the empirical data in the future will help improve our model.
2. Comment: If there are meteorological factors, which affect the quality of the water, how can this problem be circumvented?
Response: We explained in sections 3.4. In order to reflect the impact of rainfall change on water balance, based on the long-term series of runoff results from 1952 to 2014 in Lake Erhai, the empirical frequency method was used to determine the water inflows into lake in three typical hydrological years (high-, normal-, and low-flow years). The water inflows and pollutants into lake in three typical hydrological years were used as boundary conditions for the prediction.
3. Comment: Line 40: please change km2 to km2. Response: We changed km2 to km2. 4. Comment: Line 66: please use the abbreviation after the first appearance in the text (e.g. total nitrogen(TN)).
Response: We used the abbreviation after the first appearance in the text.
5. Comment: please improve the quality of figure 1.
Response: We Modified Figure 1.
6. Comment: what is the reason for low TP values in the years 2014 and 2015?
Response: We explained in sections 3.4. For better clarification, we added Figure 5.
Reviewer 3 Report
Comments and Suggestions for AuthorsMinor remarks:
Pertaining to the coupled equations (1) and (2), there should be a relationship between the discharge quantities M, N used in the solute transport equation (2) and the velocity components u, v used in the hydrodynamic model (1); please specify.
Is the "water depth" h defined relative to the variable water level z, or relative to a fixed level? Or was h supposed to denote a hydraulic potential, rather than "water depth"? Please check.
Please specify the biochemical response term F(C).
(Without this term, the equation system is incomplete.)
Please specify initial and boundary conditions for h, z, u, v (M, N) and C.
Please use capitalization consistently (either z or Z, either c or C).
Line 151: "3,969 computational meshes" -> maybe you meant mesh elements or cells? please check.
Line 151: "control equations" -> you meant the governing equations (or model equations)
Line 152: "discredited" -> "discretized"
Table 1 (showing the results of parameter calibration)
The finding of E_x = E_y looks somewhat strange; normally, one would expect values for E_x significantly larger than for E_y. Please explain or comment your finding.
Author Response
1.Comment: Pertaining to the coupled equations (1) and (2), there should be a relationship between the discharge quantities M, N used in the solute transport equation (2) and the velocity components u, v used in the hydrodynamic model (1); please specify.
Response: In section 2.2, we added description. M is the discharge per unit width in the x direction, M= u×h; N is the discharge per unit width in the y direction, N= v×h.
2. Comment: Is the "water depth" h defined relative to the variable water level z, or relative to a fixed level? Or was h supposed to denote a hydraulic potential, rather than "water depth"? Please check.
Response: In section 2.2, we added description. Water depth is the water level minus the elevation of the lake bottom.
3. Comment: Please specify the biochemical response term F(C). (Without this term, the equation system is incomplete.)
Response: In section 2.2, we added description. For better clarification, we added Equation 3 and 4.
4. Comment: Please specify initial and boundary conditions for h, z, u, v (M, N) and C.
Response: In section 3.4, we added description. The prediction was based on the hydrodynamic conditions and water quality of Lake Erhai at the end of 2018.
5. Comment: Please use capitalization consistently (either z or Z, either c or C).
Response: I corrected the errors.
6. Comment: Line 151: "3,969 computational meshes" -> maybe you meant mesh elements or cells? please check.
Response: I changed “meshes” to “mesh elements”.
7. Comment: Line 151: "control equations" -> you meant the governing equations (or model equations).
Response: I changed “control equations” to “model equations”.
8. Comment: Line 152: "discredited" -> "discretized"
Response: I changed “discredited” to “discretized”.
9. Comment: Table 1 (showing the results of parameter calibration) .The finding of Ex = Ey looks somewhat strange; normally, one would expect values for Ex significantly larger than for Ey. Please explain or comment your finding.
Response: In section 3.4, we added description.Because the difference between the velocity components in the x and y direction is small in the lake, the same values were used for transverse and longitudinal diffusion coefficient.
