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Peer-Review Record

Concentration–Discharge Relationships in Runoff Components during Rainfall Events at the Hydrohill Experimental Catchment in Chuzhou, China

Water 2020, 12(11), 3033; https://doi.org/10.3390/w12113033
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Water 2020, 12(11), 3033; https://doi.org/10.3390/w12113033
Received: 1 September 2020 / Revised: 22 October 2020 / Accepted: 26 October 2020 / Published: 29 October 2020
(This article belongs to the Section Hydrology and Hydrogeology)

Round 1

Reviewer 1 Report

The paper about the concentration discharge relationship in different runoff components during a storm event bring new approaches about relations between precipitation-water surface-infiltration-groundwater.

Some general comments we have to made about this paper

  1. the structure of the paper must be improved...the discussion part is completely missing
  2. Hydrohill name in China is not appropriate...the authors can use local name of the area
  3. in the abstract the authors must have a synthesis of their work and results obtained not a description
  4. the authors used frequently "we" made and this is not appropriate to a scientific paper
  5. in the row 142...what means F1
  6. the results part must be improved and connected with the results obtained by others researchers
  7. row 180 and 181 the authors write this The more negative the 180slopes are, namely the more quickly the discharge changes...can the authors explain this proposition.

Author Response

Response to Reviewer 1 Comments

 

Dear reviewer,

Please find attached a revised version of our manuscript, which is now entitled “Concentration-discharge relationships in runoff components during rainfall events at the Hydrohill experimental catchment in Chuzhou, China.”Your comments were insightful and enabled us to greatly improve the quality of our manuscript. Here we provide point-by-point responses to your comments. Revisions in the text are shown using the "Track Changes" function in Microsoft Word.

Point 1: the structure of the paper must be improved...the discussion part is completely missing

Response 1:  We have restructured the entire paper, including the discussion (now starting on line 224).

Point 2: Hydrohill name in China is not appropriate...the authors can use local name of the area.

Response 2: We would like to keep the proper name of this catchment but agree that our English usage in referring to its name was awkward.  We have refined the title and text throughout the paper to note that this work took place at the internationally-renowned Hydrohill experimental catchment in Chuzhou, China.

Point 3: in the abstract, the authors must have a synthesis of their work and results obtained not a description

Response 3:  We have restructured the abstract as suggested (beginning line 13).

Point 4: the authors used frequently "we" made and this is not appropriate to a scientific paper.

Response 4: Thanks, we have changed the use of “we” throughout the paper.

Point 5: in the row 142...what means F1

Response 5: F1 had referred to a unit conversion coefficient, though we have since removed this from the paper.  We not note that  “…units for each chemical species were converted from mg/L to μeq/L, following methods by Hem… (line 155).

Point 6: the results part must be improved and connected with the results obtained by other researchers

Response 6: We have added further contextualization with other studies in the introduction and discussion (e.g., lines 227-231).

Point 7: row 180 and 181 the authors write this The more negative the slopes are, namely the more quickly the discharge changes...can the authors explain this proposition.

Response 7: We have clarified this (lines 196-198): “In the C-Q plots, the steeper (more negative) the slope, the more rapid the concentrations have changed with increasing discharge.”  We provided examples in the lines following.

Author Response File: Author Response.docx

Reviewer 2 Report

This study aims to examine the concentration-discharge relationship in four runoff components (surface runoff (SR), interflow runoff between 0 - 30cm (SSR30) and between 30 - 60cm (SSR60), and groundwater runoff between 60 - 100cm (SSR100)) in an artificial catchment, the Hydrohill catchment, in Chuzhou, China during the largest rainfall event in 2016. Principal Component Analysis (PCA) was conducted on the K+, Na+, Ca2+, Mg2+, Cl-, SO42-, and HCO3- data to limit the dimensionality of the interrelated variables driving solute chemistry, and reveal the patterns that exist in different runoff components.

 

General Comments:

The authors had set up an interesting experiment in analyzing the concentration-discharge relationship by separating the total runoff into four sub-components and this study provided a good contribution in filling the knowledge gap in the research community. However, the discussion provided (L230-231) and the take-home messages (L281-283; L293-295) were a bit general in the sense that even without decomposing the runoff into four sub-components, similar/same conclusion can be drawn. It would be better if the authors could discuss the hydro-chemical processes in specific to each runoff component and explain why similar/different phenomenon happen in different runoff components. For instance, how do multiple processes in the soil layers constitute a positive relationship between concentrations of Cl- and K+ and discharge in SSR60 and groundwater runoff only?  

The authors mentioned that the "soil could be the main source of the hydro-chemical ions" (L296) and "main controlling factors resulting in such relationship" (282-283). However, as there are not much information regarding the spatial distribution of the soil property, lithology, and vegetation characteristics, I would assume the soil is quite homogeneous (silt-loam) across the catchment. In this regard, I wonder how such homogeneity produced different responses in some concentration-discharge relationship (e.g. Cl- and K+  in SSR60 and SSR100)? Are there any evidences or observations that support the claim?

The authors should provide a more vigorous statistical analysis to support the results instead of just qualitative description in Section 4.2. The authors had fitted linear regression, however, they did not show any results of the statistical test (e.g. p-value, significance level, coefficient of the slope). It would be much better if these information are provided.

 

Specific Comments:

L1-3: It would be better to include the geographical information in the title (e.g. in China, in Chuzhou, in southeast China).

L46-47: The authors stated that "many researchers", however, only one reference was provided. The authors should add more references here to support their claims. Also, it would be better if the authors could expand the discussion here to review more recent studies.

L83-84: Please provide more information about the climatology of the catchment, e.g. rainfall pattern, wet/dry season, temperature range.

L110: Please show the locations of the four rain gauges on the map (Figure 1).

L114: How were these 125 samples collected? At what time interval?

L121-122: How did the authors determine those points in real time?

L147: How did the authors define a rainfall event? It seems to me the rainfall event described in this study could be counted as three individual rainfall events as there were two periods of ~10 hours with zero precipitation.

L149-151: It would be better to quantify the amount/percentage instead of just qualitative description.

L180-181: This statement is very general. Please provide the fitted regression results and its respective statistical tests. It seems to me that the regression lines in some cases are poorly fitted as there are lots of variability in low flow (small discharge).

L182-184: Same issue as the above, please provide some statistical summaries.

L191-192: This statement is quite confusing. What messages did the authors want to deliver?

L202-203: This statement is unclear, reads like a broken sentence. Please revise.

L204: While this statement could be true, however, the results shown in Figure 4 reveal the SR and SSR30 have similar slope of fitted regression lines, which could mean that they are driven by similar processes.

L246: Had the authors actually analyzed "different discharge during the flood event"? Did the storm event produce any flooding across the catchment? Did the flood bypass the gauging room at the catchment outlet?

L293-295: What are the boarder implications of the findings in the context of hydrochemistry? It would be better to be more specific and provide more discussion here.

Figure 4: Please explain why the x-axis is not in log-scale? 

Remarks:

L18 & L114 & L147-148: inconsistent information, please check

L35: add "C-Q" after "Concentration-discharge relationships" before using the abbreviation in the remaining text

L150: what does TDS stand for?

L150: typo "SSR10"

L203-208: This sentence is long and clumsy, please revise.

L255-256, L262 & Table 1: inconsistent information, please check.

L258: better use "higher" instead of "bigger"

Figure 5: please indicate which panel (a, b, c, ...) refers to which runoff components in the caption.

Author Response

Response to Reviewer 2 Comments

Dear reviewer,

Please find attached a revised version of our manuscript, which is now entitled  “Concentration-discharge relationships in runoff components during rainfall events at the Hydrohill experimental catchment in Chuzhou, China.”We appreciate your insightful comments, which enabled us to greatly improve the quality of the manuscript. Here we provide point-by-point responses to your comments.  Revisions in the text are shown using the "Track Changes" function in Microsoft Word.

 Point 1: the discussion provided (L230-231) and the take-home messages (L281-283; L293-295) were a bit general in the sense that even without decomposing the runoff into four sub-components, similar/same conclusion can be drawn. It would be better if the authors could discuss the hydro-chemical processes in specific to each runoff component and explain why similar/different phenomenon happen in different runoff components. For instance, how do multiple processes in the soil layers constitute a positive relationship between concentrations of Cl- and K+ and discharge in SSR60 and groundwater runoff only?

Response 1: Thanks for your valuable comment. We have reworked the discussion. The hydro-chemical processes specific to each runoff component were discussed and similar/different phenomenon that happened in different runoff components was also explained (e.g. paragraph starting line 235). We assume the positive relationship between concentrations of Cl- and K+ and discharge in SSR60 and groundwater runoff was due to the small values, and this will be further studied in future experiments and research.

Point 2: The authors mentioned that the "soil could be the main source of the hydro-chemical ions" (L296) and "main controlling factors resulting in such relationship" (282-283). However, as there are not much information regarding the spatial distribution of the soil property, lithology, and vegetation characteristics, I would assume the soil is quite homogeneous (silt-loam) across the catchment. In this regard, I wonder how such homogeneity produced different responses in some concentration-discharge relationship (e.g. Cl- and Kin SSR60 and SSR100)? Are there any evidences or observations that support the claim?

Response 2: Thanks for this comment. In our reworking of the paper, we added further information on the soil properties of the soils and implications for hydrochemistry (e.g., paragraph starting line 277).

Point 3: The authors should provide a more vigorous statistical analysis to support the results instead of just qualitative description in Section 4.2. The authors had fitted linear regression, however, they did not show any results of the statistical test (e.g. p-value, significance level, coefficient of the slope). It would be much better if these information are provided.

Response 3: We have added statistical information about the slope coefficients to the discussion (lines 196-202) and added them to Figure 5.

For your specific comments:

 Point 4: L1-3: It would be better to include the geographical information in the title (e.g. in China, in Chuzhou, in southeast China).

Response 4: We have changed the title of the paper per your suggestion.

Point 5: L46-47: The authors stated that "many researchers", however, only one reference was provided. The authors should add more references here to support their claims. Also, it would be better if the authors could expand the discussion here to review more recent studies.

Response 5: We have provided additional references (lines 51-52) and also further discussion later in the paper (lines 226-231).

Point 6: L83-84: Please provide more information about the climatology of the catchment, e.g. rainfall pattern, wet/dry season, temperature range.

Response 6: We have added information about the climatology of this catchment was provided (lines 87-90).

Point 7: L110: Please show the locations of the four rain gauges on the map (Figure 1).

Response 7: We apologize that we provided old information – the four rain gauges were removed prior to this study, and the rainfall distribution is evenly distributed in this catchment, so the rainfall data can be obtained by any one of the gauges which are now shown in Figure 1. We clarified this in the paper (lines 121-122).

Point 8: L114: How were these 125 samples collected? At what time interval?

Response 8: Thanks, we have added information about the sample collection on lines 129-135.  Rainfall samples were collected at one-hour intervals. Surface runoff and subsurface runoff water samples can be collected by using the section negative pressure sampling system located in a gauging room. The sampling system was shown in Fig. 2 (see lines 116-120 on page 4). The hydrograph can be monitored in real-time and be shown on the screen on the wall. To keep consistent with the hydrograph, when there are typical points like peak points, valley points, and inflection points on the hydrograph, the water samples will be collected at that time. Thus, there is no fixed time interval for the subsurface runoff samples collecting.

 

Point 9: L121-122: How did the authors determine those points in real-time?

Response 9: We made up a little program by using Matlab. This program is about hydrograph showing in real-time. We combine this program and hydrograph software. Thus, when the hydrograph begins to change (this can be seen on the screen), we will collect water samples according to those points.

Point 10: L147: How did the authors define a rainfall event? It seems to me the rainfall event described in this study could be counted as three individual rainfall events as there were two periods of ~10 hours with zero precipitation.

Response 10: Thanks, we have clarified this in the title and the paper.  There were three sequential rainfall events.

Point 11: L149-151: It would be better to quantify the amount/percentage instead of just qualitative description.

Response 11: We presented details of the concentration ranges, as well as the rankings, on lines 169-180.

Point 12: L180-181: This statement is very general. Please provide the fitted regression results and its respective statistical tests. It seems to me that the regression lines in some cases are poorly fitted as there are lots of variability in low flow (small discharge).

Response 12: Many thanks for the comment. The relationship equations are now shown in Figure 5. We agree that the poorly fitted regression lines show the slow changes of concentration with discharge.  We did not include regression correlation coefficients, as the lines are just an indicator of the rate of change.   

Point 13: L182-184: Same issue as the above, please provide some statistical summaries.

Response 13: We added statistical information about the slope coefficients in the text (lines 197-205).

Point 14: L191-192: This statement is quite confusing. What messages did the authors want to deliver?

Response 14:  We have reworked the discussion. For this particular spot, we are aiming to show some similarity of our results to prior studies (line 227-235).

Point 15: L202-203: This statement is unclear, reads like a broken sentence. Please revise.

Response 15: We have clarified this, now on lines 237-244.

 Point 16: L204: While this statement could be true, however, the results shown in Figure 4 reveal the SR and SSR30 have a similar slope of fitted regression lines, which could mean that they are driven by similar processes.

Response 16: Thanks for this valuable comment. We agree with this comment, and this statement in the paper may not be expressed exactly. the concentration of ions in SR may also be affected by the surface soil. This statement was changed according to your comment and added some more discussion in lines 237-244.

Point 17: L246: Had the authors actually analyzed "different discharge during the flood event"? Did the storm event produce any flooding across the catchment? Did the flood bypass the gauging room at the catchment outlet?

Response 17: We have clarified the wording here to refer to the rainfall event.  For more details, please find it in lines 236-245.  The end of the runoff troughs is installed in the gauging room and the runoff flows directly through the troughs into the gauging room. Thus, any pulse of rainfall will not bypass the gauging room.

Point 18: L293-295: What are the boarder implications of the findings in the context of hydrochemistry? It would be better to be more specific and provide more discussion here.

Response 18:  We have improved this discussion as suggested (lines 245-267).

Point 19: Figure 4: Please explain why the x-axis is not in log-scale? 

Response 19: Even though these three rainfall events were big this year, the discharge in this catchment is less than 1 L/m3. Thus, if the x-axis is on the log-scale, the data will be negative on the x-axis.

For your remarks:

Point 20: L18 & L114 & L147-148: inconsistent information, please check

Response 20: Thanks, we have clarified and corrected this.

Point 21: L35: add "C-Q" after "Concentration-discharge relationships" before using the abbreviation in the remaining text

Response 21: Thanks, we have introduced this acronym (line 39).

Point 22: L150: what does TDS stand for?

Response 22: We realized that there is no need to show the results for TDS (total dissolved solids), and the TDS data was deleted from the figure.

Point 23: L150: typo "SSR10"

Response 23: This mistake was corrected.

Point 24: L203-208: This sentence is long and clumsy, please revise.

Response 24: Agreed; we have revised this sentence (and much of the other writing).

Point 25: L255-256, L262 & Table 1: inconsistent information, please check.

Response 25: We have checked the text and table for consistency and fixed the errors.

Point 26: L258: better use "higher" instead of "bigger"

Response 26: We have made this change as suggested.

Point 27: Figure 5: please indicate which panel (a, b, c, ...) refers to which runoff components in the caption.

Response 27: We have added this information (now Figure 6).

Thanks again for all the helpful comments.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be published in this form

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