Scenario-Based Assessment of Water Quality and Ecological Impacts of Pump Station Overflows in a Peri-Urban Estuary

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

A really valuable contribution to the literature. The research is timely and significant and should be published. The manuscript is really well written. The methods employed are appropriate and robust. The focus on pump stations, really adds to a limited area of understanding. One minor comment, in Figure 2, the text in one of the components seems to be cut off? Perhaps something that can be corrected before final proof?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The paper analyzes the impact of tidal properties on wastewater at pump stations for pumping and distribution purposes. Research is fluent throughout the entire manuscript, and methodology is well-defined. Authors are considering the full possibilities and duration of the tidal impact (24 hours), as well as the minimum possible duration of 2 hours. 

Authors are also presenting a practical purpose of the research, not only the scientific impact, which is strongly welcomed. Methodology is also conservative, providing insight into extreme situations, such as the flooding of the pump station. PCA analysis gives the final insight into the obtained results. 

Although the research is well provided, there are only some gaps, which should be elaborated.

-From the paper, I can not read the impact of the precipitation on the river volume; please comment on this. 

-Maybe not for this paper, but for future papers/research, I am proposing the use of the Multicriteria methods to rank particular locations regarding contamination and potential risk. 

-Are total suspended solids related to the impact of the sea or river? Please explain this. I'm just asking about the values in Table 2.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This is an interesting and comprehensive assessment of pumping station overflow pollution risks to the ecosystem of a tidal estuary in New Zealand. Before publication of the study the following points should be addressed:

Introduction: The combination of physicochemical water quality measurements with ecotoxicity testing is a strength of the study, but justify why some other pollutant of concern weren't included, especially faecal indicator bacteria, microbial pathogens, pharmaceuticals, and microplastics.

Methods: Provide a little bit more info about how the ecotoxicity tests were done so readers understand the overall approach without having to read the cited standard method.

Results:

Dilution calculation: Discuss if complete mixing of discharge with river/tidal water is realistic also based on evidence from your sampling of events

Wastewater quality: Would be good to include some literature values for comparison, discuss differences between baseflow and overflow conditions (why some pollutants are more dilute than others under overflow conditions) add units in Table 2.

Seawater quality: Discuss what variation in salinity etc says about mixing conditions in the estuary. Consider alternative ways of presenting the data in Table 3 as it is difficult to compare the numbers across sites and conditions and a figure might be easier to interpret. If you keep Table 3 add units for all parameters. You mention mg/L for turbidity in the footnote. Should that be NTU? For the PCA in Figure 2 did you transform parameters (for example z-score) to make parameters with different units comparable?

Effluent toxicity: You mention algae were stimulated rather than inhibited in their growth. Is excessive algal growth a potential ecosystem risk? Add units for LC10 and LC50. Is this all % of sample added to water that leads to the respective outcomes? A few literature references to previously reported ecotox metrics for wastewater would be useful.

Discussion: This would benefit from more comparison of the case study findings with other reports in the literature. Are your findings in line/contrary to other reports or entirely novel?

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

No

Comments on the Quality of English Language

No

Author Response

Dear reviewer, 

We appreciate the time and effort that you have dedicated to providing feedback on our paper. 

Kind regards