Review Reports

Line number

Comment

1.      Keywords

Consider adding tree-pit as a keyword, since this is typical name for these systems.

2.      Ln 54

“Whereas vegetation uptakes nutrients and heavy metals from the surface water”. This sentence seems out of place here, since it’s not linked with previous sentence. Also I am not sure what you mean by “surface water” since plants mostly consume nutrients through root uptake which is happening below ground level.  

3.      Ln 57-59

Fix English

4.      Ln 65-66

Fix English

5.      Ln 66

“Design of modular BRS hence requires minimal surface area and shorter construction time.” I am not sure I understand this. Why does module BRS require less surface area? Surface area of the BRS system in general is dependent on the impervious catchment area that is servicing (~2-5% of impervious catchment area), so modular systems will still have to follow this. I don’t see how they can be “more efficient”.

But I do agree that they are more practical for construction as they can be built more quickly and not in-situ but somewhere else, and then just brought to the location. Is this what you were trying to say?

6.      Ln 68-69

I agree that there were less tree studies, but you haven’t listed any here. Quick Scopus search shows a few papers here (e.g. Tirpak et al (2019) - Investigating the hydrologic and water quality performance of trees in bioretention mesocosms) so you should conduct more literature review in this area. There are a number of commercially available systems, generally called tree-pits (commercial names are different) that are doing exactly the same thing as you are. You need to show how your work (other than it’s apparent rigorous measurement methods) is different from all these other solutions.

7.      Ln 77-78

This is not true. There are a lot of tree pit designs for stormwater treatment, plenty of commercial ones too, but what is lacking is in-depth measurements of their performance across different conditions. Some studies have been done in US (see William Hunt) and Australia (see Ana Deletic), but I agree that there is a space for more. So I do think your work has scientific relevance, but I don’t think you explained it well.

8.      Ln 87

What is “real surface water” if not stormwater? What is the difference?

9.      Ln 93

You figure 1 says that extended detention depth is 0.2m. Which one is it?

10.   Ln 132

Your MBT system size is 40% of the catchment area. That is huge compared to standard BRS design (~2%). It’s hard to compare the results since you will obviously get much better removal. Also, since your stormwater is only coming from a “clean” roof (generally much cleaner compared to road runoff), your concentrations of TN and TP are lower than typical stormwater. It would be good to mention that.

11.   Ln 160

It would be useful to provide a small table with input range of pollutant concentrations for Phase 1 and 2.

12.   Ln 163

Similar to above, add just a dosing volume and period of dosing (leave the calculations in the appendix)

13.   Ln 203

Maybe don’t call these systems “tanks” since they have plants and media (it’s a bit misleading). I suggested calling them either tree-pits or biofilters, or something else, but tanks are usually just empty storages for liquid.

14.   Results - Figures

I am not very clear on what goes into “wet” and what into “Dry” period. How many sampling runs? What period? It needs to be clearly explained in the methods. Does dry mean that dosing patterns were different? Unclear and needs more details.

15.   LN 218

Plant uptake can be significant in field systems too. Check more literature.

16.   Ln 215 – 223

What was the change in performance over time? It is typical that TN and TP performance changes due to plant uptake in different periods.

17.   Figure 2

Add larger text for every graph showing what pollutant they represent. You only included that in a very small text at the bottom of the graphs, and it’s not very clear

18.   Results

It would be good to add graph, or explain the changes in performance over time.

19.   Figure 3

Same as Figure 2 comments

20.   Figure 4

I am not very clear on the method for this figure. Please add this to Methods section. I assume you just did subjective observations through glass side of the tank. I don’t find this Figure useful because it is really hard to understand what is what, and considering all of this data was estimated rather than measured, I believe that text description alone should be sufficient. I would remove this Figure or simplify it.

21.   Figure 5a

Your text box is covering data. Move it to the side.