Stormwater Management and Late-Winter Chloride Runoff into an Urban Lake in Minnesota, USA

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

Comments and Suggestions for Authors

 

The manuscript focuses on Chloride runoff into Lake Winona and addresses the issue of chloride accumulation due to deicing salts used for preventing accumulation of snow or for snow removal in urban regions. The study provides data on chloride concentrations in stormwater runoff, including mean values, ranges, and comparisons to toxicity standards, and identifies kay factors influencing chloride runoff and salinization of Lake Winona based on two-year measurement (2021 and 2023) of onsite chloride concentration at various inlets of the lake. While the study provides valuable data and mitigative contributions, several methodological and conceptual limitations exist.

 

Major Limitations

 

1. The study focuses on chloride runoff during winter and early spring, but it does not provide a year-round analysis of chloride levels in Lake Winona. This limits the understanding of how chloride concentrations fluctuate across seasons and whether other environmental factors contribute to chloride loading.

 

2. The method used for on-site chloride estimation is questionable. The authors mention that it is a simple standard procedure using factory-calibrated chloride test strip titrators. These are qualitative or at best semi-quantitative method. Key problems are,

 

1. The authors don’t discuss about precision or accuracy of measurements. Were duplicate samples ever collected and checked for consistency?
2. How do they know the industry calibration was effective/valid during the time of their study? Was any sample validated by other more sophisticated analytical methods?
3. Were any measurements done on physical parameters during sample collection. E.g., pH, temperature, turbidity, etc., as these will affect chloride concentration.
4. The described method measures only Cl^-. Why measure only free chlorine. What about bound forms of chlorine?
5. If it’s a standard research method, please give appropriate references.

 

3. The authors acknowledge that groundwater chloride levels are a significant unknown for Lake Winona. However, they don’t assess the full extent of chloride infiltration and its long-term impact on the lake considering this factor. This gap limits the ability to develop comprehensive management strategies and reduces the impact of the study.

 

4. No data or predictions on inflow rates or volumes of runoff reaching the lake are presented. This is a major drawback of the manuscript and makes the interpretation of results very qualitative and gives less confidence, as lower runoff volume with high chloride concentrations cannot alter the lake chloride compositions significantly. This makes the whole study very weak.

 

5. The authors use the length of underground storm sewer lines as a surrogate to stormwater drainage areas and volume of storm water draining into the lake. They claim that no correlation was seen with concertation. Why would there even be a correlation? The amount/length of pipelines is meaningless, unless information on the temporal rates of flow (which authors don’t have) is available.

 

Specific Comments

 

1. Adding more on deicing history and management in introduction section could help in better understanding of the presented results and discussion.

 

2. Figure 2 could be removed as it does not provide much scientific information.

 

3. Lines 135-143 – Could be moved to method section or introduction section.

 

4. Figure 3 – Simple sizes could be given on the bars. The alphabets on the bars are confusing and should be better explained or use symbols.

 

5. Table 1 – How did the authors define the snowmelt periods. I was unbale to find this anywhere in the text.

 

6. Lines 165-169 – There is no chloride data of lake for the period between 1980 to 2020 is questionable, given one of the authors is from city planning department.

 

7. Figure 4 could be infused with Table 2 as it has very little information as a standalone figure.

 

8. Figure 5 – Having one panel for mean with both years data and one panel for maximum with both years data will be meaningful or the authors could show all data in one panel

 

9. Figure 6 and 7 – No need to mention “mean (+standard error)” in every figure caption.

 

10. Figure 7 and Table 1 – Giving the amount/rate of rainfall could help in the context of interpretation.

 

Other constructive suggestions to Authors

 

1. Critically assessing the effectiveness of alternatives presented in the discussion section like stormwater retention ponds, rain gardens, and other infrastructure on reducing chloride loads can add more value to the manuscript. Estimates like how much chloride reduction these measures can achieve in practice would help.

 

2. In addition, the study could benefit from adding a section on impact of climate change and changing winter weather patterns. The authors acknowledge that winter weather patterns are changing, however they do not fully explore how climate change in the form of increased frequency of freeze-thaw cycles or extreme precipitation events might affect chloride runoff and greater chloride loading in the lake.

 

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

It was an interesting work that assessed the effect of chloride in snowmelt and rainfall runoff on lake in Minnesota, USA, but the scientificity of research methods, and comparison of the research results with literature should be enforced, some comments as following:

• Introduction part, it is suggested to supplement a table to generalized the chloride concentrations from rainwater runoff and snowmelt runoff via literature reviews?  
• How to distinguish between rainfall runoff and snowmelt runoff? From the dates in Table 1, there is an intersection between the two, will it affect the research results?
• The chloride concentration in snowmelt runoff and rainwater runoff is influenced by various factors,some important influencing factors should be supplemented in themanuscript, such as types and usage amounts of snow melting agents? rainfall depth? 
• Chloride load analysis should be supplemented in the results part?
• Comparison between this workand literature should be supplemented in the discussion part, specifically in chloride concentration from rainfall runoff and snowmelt runoff?
• The monitoring data of snowmelt runoff and rainfall runoff should be separately analysis in results part?
• Discussion part can be simplified to focus on the effect of chloride on the lake water quality?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

1. There is no significant major revision in the manuscript other than removal of “storm water drainage length”.

 

2. “Adding more on deicing history and management in introduction section could help in better understanding of the presented results and discussion” – Not addressed.

 

3. Please add a detailed section on limitations of the study for everything the authors claim is beyond scope of the study.

 

4. Without data or predictions on inflow rates or volumes of runoff reaching the lake, the study is indeed weak.

 

5. Figure 1 is an exact replica of an open-source image, please change or at least modify. (https://openriver.winona.edu/cgi/viewcontent.cgi?article=1083&context=wsurrc).

 

6. Lines 69 to 77, 118-121 – Please add references

 

7. Lines 164-168 – Authors give a loose reply saying “sufficient, enough”. The questions asked to them was what is sufficient, what is enough?

 

8. Lines 180-188 – Change the reference format

 

9. Line 190 – It is not like there is “no data”. There is available data and authors can compare and discuss with peer data from which they have taken Figure 1.
10. https://alasdistrict.org/wp-content/uploads/2023/05/exec-summ-lake-winona-lake-manag.pdf
11. https://openriver.winona.edu/cgi/viewcontent.cgi?article=1083&context=wsurrc

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

1. Given the authors response “Figure 1 was produced by the City of Winona specifically for this project, at the direction of coauthor John Howard. A preliminary version of the figure was provided to another researcher so she could sample from several of the same locations (and which she used without acknowledgement). The version of the figure cited here by the reviewer has two sites on the western basin incorrectly labeled, and it also is missing one additional site that we sampled during our study. So, our Figure 1 was created for this project and is different (corrected) from the one mentioned by the reviewer” - It’s still better to slightly modify the figure to avoid misunderstanding. The authors could cite the work of the other researcher and say adapted from XYZ OR make slight modifications to the image like outer boundary or enter extra text in it. 

 

2. Lines 72-85 - Refs 42 and 43 are precisely the same. Please remove 43 and renumber the references across manuscript.

 

 

3. Lines 140-142 – Cite reference 12 only once or twice. Not required for every sentence

 

4. Typesetting Correction – Seems like there is an extra space almost after every sentence in manuscript. Needs to be corrected.

Author Response

Please see the attachment.

Author Response File: Author Response.docx