Spatial and Temporal Characterization of Escherichia coli, Suspended Particulate Matter and Land Use Practice Relationships in a Mixed-Land Use Contemporary Watershed
Round 1
Reviewer 1 Report
This is a important work looking into using SPM as a potential proxy for E. coli contamination with with different land use practices. While the study showed that SPM would not be a great proxy in every scenario, the holistic approach show the importance of environmental drivers, land use, and how both can affect fecal contamination.
My overall comments/suggestions are in terms of the statistics used and how to present some of these results (see below), and for the conclusion section to be more of a discussion and not repeat results (see comments below).
Specific comments/suggestions
Line 219: Sampling period is marked as weekly from Jan 2018-Jan 2019; however, it is not clear if it was 52 sampling events or the sample size for those. Sample size for each station is mentioned (n = 22), but it isn't clear how many samples were taken per station. I suggest this to be added.
Lines 255-256: In addition to the SPM vs E coli correlations and PCA, were there any statistics (other than descriptive) done to compared sites temporally and spatially? If so, it might be worth it mention it in addition to the descriptive stats presented (Table 2 & 3)
Figure 3: Is the Y axis log-scale? If so, I recommend specifying this. I also suggest to explain what the box colors represent; if these do not represent something, colors might not be needed.
Table 3: are all the E. coli averages arithmetic or geometric means?
Figure 4: Same comment about the color of the boxes, and due to variability of bacteria, I suggest presenting concentrations as log-scale.
Figure 6: X axis is a bit confusing in terms of identifying specific sites -the sites identified by squares/triangles between the vertical lines identified with numbers (e.g., between 3 and 6) are not clear which number they are.
Lines 451: Presenting p-values as zeros (0.00) tends to be confusing as these would tend to be really small. I suggest presenting p-values as p < 0.01, which suggest a very small number (same goes for tables; e.g., Table 4). Also, throughout the manuscripts sometime they authors use an actual p-value number (e.g., line 509), and other the less than ("<") symbol. I suggest just using one for consistency.
Lines 496-498: PCAs are only a visual representation of the data; therefore I suggest re-wording this statement as Spearman correlation would be the one supporting PCA results.
Lines 527-529: Are these correlations then mostly due to seasonality or is there a way to tease these apart? (e.g., environmental forces, land use)
Lines 568-569: was the same data used in PCA used for Spearman correlation or did one analysis results influenced data used in the other?
Line 619: the word nested scale is used in four different ways: scale nested, scale-nested, nested scale, and nested-scale. I recommend selecting one throughout the manuscript for consistency.
Conclusion: I suggest to reword some of the sentences (e.g., lines 625-626, 634-637) to reflect only conclusions based on the study and not repeating numbers/p-values/results from the previous sections.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript is focusing on how land use impact on the correspondence between E. coli and SPM in a mixed-land use watershed. Based on their weekly data in one year, they concluded that (1) agriculture practices is the most impacting factor and (2) SEM may not be a good proxy E. coli indicator. The manuscript is well written and the results are clearly represented and explained by the results. The major concerns/suggestions are (1) MPN numbers that from Colilert are not CFUs and need to explain the conversion; (2) weekly water samples were under what kind of conditions, regarding 2018 is such a wet year? baseflows or stormflows etc.? are the authors able to categorize these samples and tease apart the storm impacts on different samples and their relationship with SEM? (3) Not to be picky. I am curious how the authors categorize the landuse type, for instance site #11 and #12, agriculture and forested are comparable enough. (4) Figure 1: Need to use different color to highlight West Run to different it from catchment delineations etc. Also, I would recommend use other symbols to show the sites instead of squares.(5) Table 2 and Fig. 3 are kind of redundant: suggest only show one of them; and same for Table 3 and Fig. 4. (6) Figure 5 is repeating the data from Fig. 3 and 4; (7) Need statistical support when two different categories are compared: e.g. line 349-350, line 489-490, line 496-498; (8) Line 474-486: This is really a nice explanation on how to interpret PCA but I am not sure if it necessary here.
Author Response
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Reviewer 3 Report
Certainly, the topic is of great interest. a possible relationship between E.coli concentration, SPM and land use practices could be an interesting approach to understand water pollution problems.
Experimental analysis applied to 22 scale-nested watersheds and results obtained they are quite interesting, including suggested seasonal.
In my opinion the paper can be accepted even if with minor revisions.
Minor revisions:
- It is not usual to introduce acronyms in the abstract, in my opinion but not only, acronyms must be included in the manuscript.
- Formatting must be reviewed, the space between paragraphs is not correct and different from the paper style format and it is included only after tables and figures.
Author Response
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Author Response File: Author Response.docx
