Spatiotemporal Variation of Riverine Dissolved Organic Matter Degradation Based on EEMs-PARAFAC: A Case Study of Shili River in Jiujiang, Jiangxi Province, China, as a Typical Demonstration City of the Yangtze River protection Strategy

Round 1

Reviewer 1 Report

comments in the attached file

Comments for author File: Comments.pdf

Author Response

Comments: The paper describes spatial and temporal changes of the Fluorescent Dissolved Organic Matter (FDOM) degradation experiment in the Shili River (China), with the use of Excitation/Emission measurements (EEM) and Parallel Factor Analysis (PARAFAC). Four PARAFAC components (C1-C4) have been identified. The aromatic index (SUVA254), biological index (BIX), freshness index (:) and humification index (HIX) have been calculated and their correlations with PARAFAC components have been investigated. The authors infer that DOM present in the Shili River is mainly of autochthonous origin. DOM fluorescence intensities increased along with the direction of the river flow. The study aims to provide information for the water environmental management. The authors analyze the DOM changes caused by degradation, but they do not really draw conclusions about what those changes mean. The authors do not compare their results to the previous data from the same river (guess it had not been done) to be able to say that the “protection strategy” works out. At the same time, we do not know if this kind of study is going to be repeated.

Dear Reviewer:

We would like to thank you for spending so much time reading our manuscript entitled “Spatiotemporal variation of riverine dissolved organic matter degradation based on EEMs-PARAFAC: A case study of Shili River in Jiujiang, Jiangxi Province, China, as a typical demonstration city of the Yangtze River protection strategy” (ID: water- 2051028) and for providing valuable comments and suggestions. We would like to thank the reviewers for their thoughtful review of this manuscript. The comments and suggestions are very helpful for improving the manuscript. We have revised our manuscript accordingly, and the major revisions are marked in red. Our point-by-point responses are as follows.

DOM composition is not only an indicator of the impact of human activities on river ecosystems, but also plays an important role in the carbon cycle process affected by microbial degradation in freshwater ecosystems. Some previous studies have shown that urbanization increases the bioavailability of riverine DOM, but the sources and reasons remain unclear. At present, the study on the microbial degradation of riverine DOM has attracted extensive attention from ecologists at home and abroad. This study showed that natural degradation preferentially removed aromatic chromophore and aromatic compounds, which we added to the conclusion (line 498).

General comments:

Point 1：The EEMs are 3D, so there is no need to use ‘3D-EEMs’. ‘EEMs’ is enough.

Our response 1: Thanks very much for the valuable comments. I'm really sorry that we didn't get the concept clear. We've made changes in the manuscript in the appropriate places. Please kindly see the revised manuscript.

Point 2：The authors should use “protein-like and humic-like components” instead of “humus”, proteins”.

Our response 2: We unanimously agree with the reviewer’s comment. There are many imprecise expressions in components, so we used “protein-like and humic-like components” instead of “humus”, “proteins”(line 281, line 315, line 469, line 479). Please kindly see the revised manuscript.

Point 3：The authors should consistently use the name of the river. They are using two names: Shili and Silihe.

Our response 2: We appreciate you reading our article so carefully and we unified the river name into Shili River in the manuscript. Please kindly see the revised manuscript.

Point 4：Throughout the paper, the authors did not mention the amount of samples ,which is really important when talking about spatial and temporal changes. The number of samples matters also while implementing PARAFAC, which in theory is not made for small datasets.

Our response 3: Thank you for your constructive comments on my manuscript. We described the sampling time and number of sampling points in lines 106-113, and the total number of samples was 18. We added the sample number information to line 113, “The total number of samples is 18. ”. We added the process of processing data with parallel factors to line 156,  “Three technical parallel and distilled water standard samples were made to meet the requirements of parallel factor analysis”. Please kindly see the revised manuscript.

Point 5：The Results section should be rewritten. In my opinion, first they should describe DOM in time and space and then, after showing the baseline, they should pass to the values after degradation. That would make that section more consistent and easier to read. The data should also be shown in “a summary” table.

Our response 4: We agree with the reviewer’s assessment. Accordingly, throughout the manuscript, we have revised the Results section(lines 170-259, 318-373) and showed the data in the attached Supplemental table 2. Below is the revised section and data summary table. There are too many revisions, please kindly see the revised manuscript.

Table 2  Data processing table of each sampling point parameter

More detailed comments follow:

We would like to thank you for spending so much time reading our manuscript entitled “Spatiotemporal variation of riverine dissolved organic matter degradation based on 3D-EEMs-PARAFAC: A case study of Shili River in Jiujiang, Jiangxi Province, China, as a typical demonstration city of the Yangtze River protection strategy” (ID: water- 2051028) and for providing valuable comments and suggestions. We would like to thank the reviewers for their thoughtful review of this manuscript. The comments and suggestions are very helpful for improving the manuscript. We have revised our manuscript accordingly, and the major revisions are marked in red. Our point-by-point responses are as follows.

Page 1 Abstract:

Point 1：Lines23-26: The sentence suggests that the paper is only about degraded DOM and that all spectral measurements and further analysis had been carried out for degraded samples. It also clashes with the first sentence, confusing the reader. I assume that there is a part mentioning about degradation experiment missing.

Our response 1: Thanks very much for the valuable comments. We have modified lines 22-26 of the abstract, “This study investigated the spatiotemporal distribution of dissolved organic matter (DOM) composition and its sources before and after degradation in the Shili River watershed in Jiujiang (China). Spatiotemporal variation of riverine DOM water samples before and after five days of degradation in simulated channel was characterized by spectral feature analysis using three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis”. Please kindly see the revised manuscript.

Point 2：Lines 26: Does “Across all water samples” mean ‘raw’ + degraded samples? It should be specified.

Our response 2: Thanks very much for the valuable comments. We have replaced “Across all water samples” with “Across all water samples (1#,2# and 3#) before and after degradation” in Line 27. Please kindly see the revised manuscript.

Point 3：Lines 27-30: What about the HIX index?

Our response 3: We appreciate your positive comments on our manuscript. There was no significant correlation between HIX and SUVA₂₅₄. So we added “but it has little correlation with the humification index (HIX)” after “The aromaticity index (SUVA₂₅₄) was negatively correlated with the C2 and C3 components and biological index (BIX) and freshness index (β:α)”(line 30). Please kindly see the revised manuscript.

Point 4：Lines 32-34: The sentence should be split into 2 to make more sense. What does the high temperature refer to? Water? Air?

Our response 4: Thanks very much for the specific comments. The high temperature refered to Water temperature. There were many imprecise expressions in lines 32-34, we replaced the sentence with “The fluorescence intensity of DOM increased gradually along the direction of water flow. The increase of water temperature in spring and autumn enhanced the endogenous level of DOM” in lines 34-36. Please kindly see the revised manuscript.

Point 5：Page 2 Section - Introduction:

Line 65: Shouldn’t there be a sentence end after ‘..(3D-EEMs)[6]’?

Our response 5: Thank you very much for finding this error. We have added “.”after [6] as you suggested. And capitalized the first letter of the first word of the next sentence(line 68). Please kindly see the revised manuscript.

Pages 3 and 4: Section:2.1 Study area:

Point 6：There is a lack of reference to Figure 1.

Our response 6: Thank you for giving the suggestions. We quote Figure 1 after the first sentence " Shili River is an urban river running through Jiujiang (113°56'–116°54' E, 28°41'–30°05' N) in Jiangxi Province, China (Figure 1)" in line 96. Please kindly see the revised manuscript.

Section 2.2 Sample collection and determination:

Point 7：Line 107: What do you mean by ‘... more affected by lakes’?

Our response 7: Thanks very much for the valuable comments. As the lower reaches merged into lakes, the water quality of the lower reaches was closely related to the water quality of the lakes. So we replaced ‘... more affected by lakes’ with ‘... was closely related to the water quality of the lakes’(line 111). Please kindly see the revised manuscript.

Point 8：Lines 107-108: Change ‘and again in March through June and September’ to ‘and in March, June and September”. It will make it clearer that you have sampled 4 times.

Our response 8: Thank you very much for finding this error. We changed ‘and again in March through June and September’ to ‘and in March, June and September’ in line 113 as you suggested. Please kindly see the revised manuscript.

Point 9：Lines 109-112: Please describe the experiment conditions.

Our response 9: Thanks very much for the valuable comments. The only difference between the simulated channel and the test channel was that the simulated channel was no velocity. The state of the water environment was analyzed in Section 3.1. We put “The range of pH before and after degradation was 6.54-8.23 and 6.56-8.18. The range of DO before and after degradation was 6.54-8.23 mg/L and 6.56-8.18 mg/L. The range of water temperature before and after degradation was 6.54-8.23℃ and 6.56-8.18℃.” on lines 116-119. Please kindly see the revised manuscript.

Section 2.3 Spectral measurements and parallel factor analysis

Point 10：Lines 120-125: Why did you choose to dilute the samples with >8mg/ L DOC? Was the fluorescence signal too high? Wouldn’t it be better to change the speed of the measurements to detect a lower signal? Why did you decide to eliminate “inner filter effect’ by diluting the sample? With the PARAFAC method, you suppose to use absorption spectra to make an inner filter effect correction. Why did you decide to do it differently? Have you measured the absorption spectra? How? With what equipment? Was the PARAFAC result evaluated? How?

Our response 10: Thank you for your comment, and our reply is as follows:

(1) To prevent fluorescence quenching, we chose to dilute the samples with >8mg/ L DOC. So its fluorescence signal is not very high.

(2) All measurements were done at a scanning speed of 2000 nm/min, and the scanning speed in this study is already very low.

(3) It is almost impossible to avoid the inner filter effect when measuring the sample. The first method we generally adopt when testing the sample is to dilute the sample, but the dilution of the sample will also lead to the decrease of the signal-to-noise ratio (effective signal / interference signal), and the change of the physical and chemical properties of the sample pollution is also possible. The second is through the data method correction, so can do, but it seems that the effect is not very good.

(4) Fluorescence spectrophotometer is a kind of instrument used to scan the fluorescence spectrum emitted by fluorescent labels in liquid phase, and can measure the absorption spectra. Fluorescence spectrophotometer (RF-6000; Shimadzu) was used to conduct three-dimensional fluorescence analysis of the substance, fluorescence scanning of the substance was conducted directly, and then PARAFAC method was used to calculate the index, so as to determine the optimal number of DOM fluorescence components and the maximum fluorescence intensity of each component.

Point 11：Lines 141-151: What does ‘S_R’ stand for? How did you calculate it?

Our response 11: Thanks very much for the valuable comments. S_R provides information on DOM’s sources and molecular weights. It is the ratio of the spectral slope S_275-295 to S_350-400. We moved " S_R provides information on DOM’s sources and molecular weights." from line 236 to line 150 and added " It is the ratio of the spectral slope S_275-295 to S_350-400. "after that sentence(150). Please kindly see the revised manuscript.

Point 12：Line 148: The citation of DOMFluor toolbox is missing.

Our response 12: Thanks very much for the specific comments. We cite the following references here(line 162).

Stedmon, C.; Bro, R. Characterizing dissolved organic matter fluorescence with parallel factor analysis:a tutorial[J]. Limnology and Oceanography: Methods, 2008, 6(11): 572-579.

Kowalczuk, P.; Cooper, W. J.; Durako, M. J.; Amanda, E.K.; Michael, G.; Heather, Y. Characterization of dissolved organic matter fluorescence in the South Atlantic Bight with use of PARAFAC model: relationships between fluorescence and its components, absorption coefficients and organic carbon concentrations[J]. Marine Chemistry, 2010, 118(1/2): 22-36.

Point 13：Line 151: The information about R.U. (not R.U. units) should be mentioned in the paragraph containing the EEM measurements.

Our response 13: We unanimously agree with the reviewer’s comment. We have deleted “in R.U. units,” in Line 162 and removed the following statement in Line 133, “Maximum fluorescence intensity of DOM fluorescence component (FMAX), expressed in R.U.” Please kindly see the revised manuscript.

Pages 4-5:

Section 3.1 Spatiotemporal variation of water environmental parameters:

Point 14：Lines 159-163. The sentences about water temperature are not clear. What does it mean that”during the sampling periods…were> 25 in autumn”? All sampling periods? Or in the autumn? The best way would be to place a table with all the values of water environmental parameters with all the necessary statistics, e.g. mean, standard deviation, variation, etc., for all data and in division into seasons, before and after degradation… and describe it also in the text.

Our response 14: Thank you very much for your valuable comments. We modified the sentence in line 170, “During the sampling period, the autumn water temperature of all sampling sites before and after degradation was > 25.00°C.” We added the table in attached Table 1 (line 564). Please kindly see the revised manuscript.

Table 1 Time and space data of environment parameters

Pages 5-6:

Section 3.2 Spatiotemporal variation in DOC concentration:

Point 15：Lines 178-190. The title of the section is spatiotemporal changes while you are focusing mostly on values before and after degradation… Please add DOC values and its statistics to the table.

Our response 15: We agree with the reviewer’s assessment. Accordingly, throughout the manuscript, we have revised the Results section(lines 170-259, 318-373) and showed the data in the attached table 2. Below is the revised section and data summary table. There are too many revisions, please kindly see the revised manuscript.

Section 3.3 Visible absorption spectral characteristics.

Point 16：Please change the title of this section. The specific UV absorbance is not in the visible range of light.

Our response 16: Thanks very much for the valuable comments. We changed the title of this section to” Uv-vis absorption spectra of DOM”(line 216). Please kindly see the revised manuscript.

Point 17：Line 214: What does it mean that the difference was ‘weak’?

Our response 17: Thanks very much for the specific comments. I'm sorry we didn't have an accurate expression. “Weak “ meant that the difference between spatial and temporal in SUVA₂₅₄ is not significant. We modified it as “The spatial and temporal difference of S_R before and after degradation was significant, but but not SUVA₂₅₄.” in line 246. Please kindly see the revised manuscript.

Point 18：Section 3.4 There is an unnecessary point in the title...Do you mean 3-D fluorescent component of DOM?

Our response 18:  Thanks very much for the valuable comments. We unanimously agree with the reviewer’s comment. We modified the title as “3-D fluorescence analysis of DOM” in line 260. Please kindly see the revised manuscript.

Point 19：Lines 220-233: You should cite articles/people while talking about peaks A,C,M …

Our response 19: Thanks very much for the specific comments. We have cited references in Lines 265-274 as you suggested, “Figure 5 shows the 3D fluorescence spectra of four effective fluorescent components (C1 to C4) in DOM, as identified by PARAFAC, and the distribution of their maximum ex-citation/emission wavelengths in water samples before versus after degradation. The strong fluorescence peak of component C1 at Ex = 255 nm and Em = 420 nm appeared at a position similar to the terrestrial humic-like fluorescence peak A[22], which mainly corre-sponds to short-wavelength fulvic-like substances. It is a comprehensive product of terri-genous input, microbial activity and photochemical oxidation process [23,24]. The maxi-mum excitation and emission wavelengths of component C2 were Ex = 230 nm and Em = 342 nm, respectively, whose maximum peak lay close to that of the protein-like fluores-cence peak T2[22]. This fluorescent component was similar to the tryptophan-like spectral peak, representing short-wavelength tryptophan-like substances in water and fluorescent substances arising mainly from autochthonous inputs. Component C3 had its maximum excitation wavelength at Ex = 295 nm, with maximum emission wavelengths at Em = 338 and 342 nm, close to the position of the protein-like fluorescence peak T1[25], which mainly denotes tryptophan-like substances.”

References

22. Xi, Y.; Wang, T.; Ni, J. R.; Han, P.; Yi, M. L.; Jiang, Y.; Ma, R. Q.; Cui, F. Characterization of dissolved organic matter fractions in the Ning-Meng Section of the Yellow River and relationship with metal ions. Environmental Science. 2018, 39(9): 4114-4121.
23. Fellman, J. B.; D’Amore, D. V.; Hood, E.; Boone, R. D. Fluorescence characteristics and biodegradability of dissolved organic matter in forest and wetland soils from coastal temperate watersheds in southeast Alaska. J. 2008, 88(2): 169-184.
24. Ning, C.W.; Bao Y.; Huang, T.; Wang, J. Sources and Spatial Variation of Dissolved Organic Matter in Summer Water of Inflow Rivers Along Chaohu Lake Watershed. J. Environmental Science. 2021, 42(08): 3743-3752.
25. He, W.; Hur, J. Conservative behavior of fluorescence EEMPARAFAC components in resin fractionation processes and its applicability for characterizing dissolved organic matter. J. Water Research. 2015, 83: 217-226.

Point 20：Lines 249-254: What is this? Looks like a part of a figure caption…

Our response 20: Thanks very much for the specific comments. It's actually part of figure caption, and we moved it to the Figure 5 caption(lines 289-293). Please kindly see the revised manuscript.

Point 21：Line 256: Should there be: The total fluorescence intensity or The mean total fluorescence intensity?

Our response 21: Thanks very much for the specific comments. We replaced "The fluorescence intensity" with "The total fluorescence intensity" in line 295. Please kindly see the revised manuscript.

Point 22：Line 258: should be ‘lower’ instead of “less”.

Our response 22: Thanks very much for the specific comments. We replaced " less " with" lower "in line 298. Please kindly see the revised manuscript.

Point 23：Line 266: Instead of writing that stream segment prone to “pollution”, you should rather say that it was under larger inflow of terrestrial matter. Can you say why?

Our response 23: We are extremely grateful to reviewer for pointing out this problem. We revised this sentence on lines 303-306, “Before degradation, the content of humic-like components was always greatest at point 2# in summer and winter, indicating that the exogenous level of DOM was higher in the middle reaches of summer and winter.”.

Point 24：Line 281: Have you tested if the differences in FI values were statistically different?

Our response 24: We thank the reviewer for pointing out this issue. As can be seen from the box-plot in Figure 7 showed P>0.05 in the significance test. So we said that the FI values had minor or negligible differences across the three sampling points. And we revised this sentence to “Spatial variation analysis revealed that P>0.05 in the significance test. The FI values had minor or negligible differences across the three sampling points.” in lines 332-333. Please kindly see the revised manuscript.

Pages 10-11:

Section 4.1 Temporal variation of DOM sources before and after degradation:

Point 25：You should rewrite this subtitle. The source of DOM before and after degradation was the same: you had the same water in the samples. What changed over time was the composition of DOM and its optical characteristics.

Our response 25: Thank you for your valuable comments. The water samples before and after degradation are indeed the same, so we modify the title as” Temporal variation of DOM sources”(line 391). Please kindly see the revised manuscript.

Point 26：Line 328: Shouldn’t it be >1 and <10 mgL-1? Please check the units.

Our response 26: Thanks very much for the specific comments. We unified the DOC units into " mg/L"(lines 394-396). Please kindly see the revised manuscript.

Point 27：Line 330: Is the river called Shili or Shilihe?

Our response 27: We appreciate you reading our article so carefully and We unified the name of river in the manuscript as “Shili River”. Please kindly see the revised manuscript.

Point 28：Lines 351-354: You repeat the same sentence as in lines 346-349.

Our response 28: We appreciate you reading our article so carefully and we deleted the repeated sentences in lines 429-431. Please kindly see the revised manuscript.

Section 4.2 Spatial distribution of DOM spectral features:

Point 29：Line 366: ‘the upstream was the smallest” – please rewrite this sentence.

Our response 29: Thank you very much for finding this expression error. We rewrote the sentence on line 443, ” The values of DOM fluorescence parameters FI, BIX and β:α in Shili River were the lowest in the upstream”. Please kindly see the revised manuscript.

Point 30：Lines 379-382: FI,BIX, b:a, are the indexes that tell us about theoretical sources of DOM, not the values of DOM. You cannot infer from them that “DOM…after degradation was higher” and that “the HIX values was lower…”Please rewrite those sentences.

Our response 30: Thank you very much for finding this expression error. We rewrote the sentence in lines 455-460, “After degradation, the light absorption parameters (S_R) and partial fluorescence parameters (FI, BIX, β:α) were higher than those before degradation, indicating that the DOM endogenous level of Shili water was higher than that before degradation, while the HIX value after degradation was lower than that before degradation, that is, the DOM humus degree of Shili water was lower than that before degradation.”. Please kindly see the revised manuscript.

Page 12:

Section 5 Conclusions:

Point 31：Line 401: Please name the components humic-like and protein-like.

Our response 31: We have changed the component name to “humic-like and protein-like” according to your suggestion(line 479). Please kindly see the revised manuscript.

Point 32：Line 406: What do you mean by: higher pollution degree??

Our response 32: Some studies had pointed out that tryptophan-like components were also contained in human sewage tailwater (References are below). The areas with high urbanization degree in the middle reaches have higher protein-like components. So the area is highly affected by human activity. We revised this sentence to ”The areas with high urbanization degree in the middle reaches have higher protein-like components and highly affected by human activity” in line 484. Please kindly see the revised manuscript.

Li, M. Y.; Song Y. Y.; Zhang X. L.; Huang H. O. Removal Behavior of Protein-like Dissolved Organic Matter During Different Water Treatment Processes in Full-Scale Drinking Water Treatment Plants. J. Environmental Science. 2021, 42(7): 3348-3357.

Point 33: Lines 420-423: Such a conclusion is, in my opinion, exaggerated!!

Our response 33: Thanks very much for the valuable comments. The manuscript has been revised according to your suggestion(line 500-505), ” Urban water environment has been paid more and more attention. It is imperative to strengthen urban water pollution prevention and control. We should strengthen the prevention and management of urban water pollution, strictly implement the national laws and regulations on water pollution prevention and control, make rational use of new water pollution prevention and control technologies, and reduce the discharge of waste water ” Please kindly see the revised manuscript.

Figures:

Point 1: Figure 2, left panel: Why do only a few bars have error bars? Does it mean that the rest were just single measurements?, right panel: Please describe the graph with more precision in the caption. What can be seen in this graph? Mean? median? standard deviation? quartiles? It is not clear. In the caption you have “…Ten Mile River”. Shouldn’t it be the Shili River?

Point 2: Figure 3, left panel: Why do only a few bars have error bars? Does it mean that the rest were just single measurements?, right panel: Please describe the graph with more precision in the caption. What can be seen in this graph? Mean? median? standard deviation? quartiles? What does the brace mean. It is not clear.

Point 3: Figure 4, left panel: Why do only a few bars have error bars? Does it mean that the rest were just single measurements?, right panel: Please describe the graph with more precision in the caption. What can be seen in this graph? Mean? median? standard deviation? quartiles? It is not clear.

Our response 1-3: Thank you for your question. We have briefly summarized the answers to your questions.

(1) Water samples were collected from December 2020, March to June and September 2021, and once a month, a total of 18 water samples were collected from the three sampling sites. We divide March, April and May into spring, June into summer, September into autumn, and December into winter. Bar charts were made for water sample parameters of each sampling point in each season. The bar charts in spring had error bars while those in other seasons did not, because spring included three sampling times in three months, while those in other seasons were one sampling time.

(2) We added a more accurate description of the figure in the corresponding figure title(line 212, line 250, line 256), ”The Box-plot consists of five numerical points: minimum observation (bottom edge), 25% quantile (Q1), median, 75% quantile (Q3), and maximum observation (top edge). In the box-plot significance analysis, a * means it is significant at the 0.05 alpha level, ** means it is significant at the 0.01 alpha level, and *** means it is significant at the 0.001 alpha level”

Point 4: Figure 5: The caption stands that there should be 4 parts of the graph, but only 3 are visible…Bigger fond should be used. The “Loadings” part should have a better resolution.

Point 5: Figure 6: The fond/resolution is too small. Is there a writing on the bars? I cannot see that. What is on the left graph?

Our response 4-5: Thank you very much for your careful review of my manuscript. Your comments are very valuable. We made the modification according to your suggestion. We used (A), (B) and (C) at the bottom of figure 5 to represent the three columns respectively, and deleted the fourth part of the name,” and (D) fluorescence intensity comparison of each component before and after degradation.”. We replaced the clear picture in place and adjusted the font to make it bigger.

Point 6: Figure 7, left panel: Why do only a few bars have error bars? Does it mean that the rest were just single measurements?, right panel: Please describe the graph with more precision in the caption. What can be seen in this graph? Mean? median? standard deviation? quartiles? It is not clear. What do the brace and the dots mean? Please change: “b:a in the Shilihe River” to “β:α in the Shili River”. Change to “β:α“ on the axes.

Our response 6: Thank you for your question. We have briefly summarized the answers to your questions.

(1) Water samples were collected from December 2020, March to June and September 2021, and once a month, a total of 18 water samples were collected from the three sampling sites. We divide March, April and May into spring, June into summer, September into autumn, and December into winter. Bar charts were made for water sample parameters of each sampling point in each season. The bar charts in spring had error bars while those in other seasons did not, because spring included three sampling times in three months, while those in other seasons were one sampling time.

(2) We added a more accurate description of the figure in the corresponding figure title(line 373), ”The Box-plot consists of five numerical points: minimum observation (bottom edge), 25% quantile (Q1), median, 75% quantile (Q3), and maximum observation (top edge). In the box-plot significance analysis, a * means it is significant at the 0.05 alpha level, ** means it is significant at the 0.01 alpha level, and *** means it is significant at the 0.001 alpha level”

(3) We changed: “b:a in the Shilihe River” to “β:α in the Shili River”. Change to “β:α“ on the axes. The revised figure was shown below:

In addition:

We rechecked the manuscript again. We modified "SUVA254" and "SR" in the manuscript to "SUVA₂₅₄" "S_R".

Author Response File: Author Response.docx

Reviewer 2 Report

In this study, the authors investigated the spatiotemporal distribution of DOM composition and its sources in the Shili River watershed in Jiujiang (China) by the aromaticity index (SUVA254), biological index (BIX) and freshness index (β:α). The manuscript was clearly organized and the summary was complete, the conclusions were reliable. However, some revisions were needed prior to a possible publication in this journal.

1. In Short title, it should include 3D-EEMs-PARAFAC.

2. In 3.1 part, it is recommended to add a table or figure for representing the data in this section.

3. About 3.3 part, the content of the figure 4 is very rich, but the description in 3.3 part is very little. So, it is recommended to describe the phenomenon in detail.

4. Line 219, is “3.4.3” right?

5. In Fig 5, the picture is too small to read clearly. Besides, there is an A/B/C/D in the figure note, but not in the figure.

6. In Fig 8, the picture is too small to read clearly.

7. In 4 part, the discussion is not enough.

8. Line 328, is the unit “mg/L-1” right?

Author Response

Comments: In this study, the authors investigated the spatiotemporal distribution of DOM composition and its sources in the Shili River watershed in Jiujiang (China) by the aromaticity index (SUVA254), biological index (BIX) and freshness index (β:α). The manuscript was clearly organized and the summary was complete, the conclusions were reliable. However, some revisions were needed prior to a possible publication in this journal.

Dear Reviewer:

We would like to thank you for spending so much time reading our manuscript entitled “A systematic bibliometric review of low impact development research articles” (ID: water-1846275) and for providing valuable comments and suggestions. We would like to thank the reviewers for their thoughtful review of this manuscript. The comments and suggestions are very helpful for improving the manuscript. We have revised our manuscript accordingly, and the major revisions are marked in red. Our point-by-point responses are as follows.

Point 1：In Short title, it should include 3D-EEMs-PARAFAC.

Our response 1: Thank you very much for your constructive comments. We have changed the Short title to “Spatiotemporal variation of riverine dissolved organic matter degradation based on EEMs-PARAFAC” in line 7. Please kindly see the revised manuscript.

Point 2：In 3.1 part, it is recommended to add a table or figure for representing the data in this section.

Our response 2: Thank you very much for your valuable comments. We added the table in attached Supplemental Table 1 (line 564). Please kindly see the revised manuscript.

Table 1 Time and space data of environment parameters

Point 3：About 3.3 part, the content of the figure 4 is very rich, but the description in 3.3 part is very little. So, it is recommended to describe the phenomenon in detail.

Our response 3: Thank you for pointing this out. Accordingly, throughout the manuscript, we have revised the Results section(lines 216-247) and showed the data in the attached Supplemental table 2. There are too many revisions, Please kindly see the revised manuscript.

Point 4：Line 219, is “3.4.3” right?

Our response 4: We appreciate you reading our article so carefully and we deleted the repeated sentences in line 260. Please kindly see the revised manuscript.

Point 5：In Fig 5, the picture is too small to read clearly. Besides, there is an A/B/C/D in the figure note, but not in the figure.

Our response 5: Thank you very much for your careful review of my manuscript. Your comments are very valuable. We made the modification according to your suggestion. We used (A), (B) and (C) at the bottom of figure 5 to represent the three columns respectively, and deleted the fourth part of the name,” and (D) fluorescence intensity comparison of each component before and after degradation.”. We replaced the clear picture in place and adjusted the font to make it bigger. Please kindly see the revised manuscript.

Point 6： In Fig 8, the picture is too small to read clearly.

Our response 6: Thank you for your constructive comments on my manuscript. We replaced the clear picture in place and adjusted the font to make it bigger(lines 388). Please kindly see the revised manuscript.

Point 7： In 4 part, the discussion is not enough.

Our response 7: Thank you very much for your suggestion, we followed your suggestion to add some analysis in lines 409-409, “Biogeochemical processes such as microbial degradation, photodegradation and ad-sorption and desorption of particulate matter are typical processes that affect the compo-sition and biogeochemical activity of DOM in river systems [34]. Generally speaking, the content and quality of DOC are largely controlled by the microbial and photodegradation of DOM [35]. DOM has different characteristics at different degradation stages. A longer degradation cycle can decompose the hard-to-degrade substances in DOM, while a shorter degradation cycle can change the relative abundance of different substances in DOM. But the chemical composition in DOM will not be affected by the short-term degradation process [36]. In summer, SUVA254 values changed significantly before and after degradation, indicating that natural degradation preferentially removed aromatic chromophore and aromatic compounds.” And References are below:

34. Yang, L. Y.; Hong, H. S. Dynamic changes of dissolved organic matter in river-estuarine system and its influencing factors. D. Xiamen University. 2012.
35. Catalán, N.; Ortega, S. H.; Gröntoft, H. Effects of beaver impoundments on dissolved organic matter quality and biodegradability in boreal riverine systems. J. Hydrobiologia. 2017, 793(1): 135-148.
36. Song, N.; Bai, L.; Xu, H.; He, L. J. The composition difference of macrophyte litter-derived dissolved organic matter by photodegradation and biodegradation: Role of reactive oxygen species on refractory component. J. Chemosphere, 2020, 242: 125155.

Point 8： Line 328, is the unit “mg/L-1” right?

Our response 8: Thanks very much for the specific comments. We unified the DOC units into " mg/L"(lines 394-396). Please kindly see the revised manuscript.

In addition:

We rechecked the manuscript again. We modified "SUVA254" and "SR" in the manuscript to "SUVA₂₅₄" "S_R".

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Line 459: please change DOM humus degree into DOM humification degree

Table 1 and 2: I cannot find the references to those tables in the text.

Table 2: Please add the total N values (no of samples) and N values from which the statistics were calculated. So many decimal places are unnecessary

Figure 5(B): peaks describsions are impossible to see even with the zoom. please remove them

Figure 8: The values on the graph are hard to see even with zoom. Maybe it would be better with black font or maybe you should just remove them.

Author Response

Dear Reviewer:

Comments :We would like to thank you for spending so much time reading our manuscript entitled “Spatiotemporal variation of riverine dissolved organic matter degradation based on EEMs-PARAFAC: A case study of Shili River in Jiujiang, Jiangxi Province, China, as a typical demonstration city of the Yangtze River protection strategy” (ID: water-2051028) and for providing valuable comments and suggestions. We would like to thank the reviewers for their thoughtful review of this manuscript. The comments and suggestions are very helpful for improving the manuscript. We have revised our manuscript accordingly, and the major revisions are marked in red. Our point-by-point responses are as follows.

Point 1：Line 459: please change DOM humus degree into DOM humification degree.

Our response 1: Thanks for your careful checks. We are sorry for our carelessness. Based on your comments, we changed “DOM humus degree” into “DOM humification degree” in line 465.

Point 2：Table 1 and 2: I cannot find the references to those tables in the text.

Our response 2: We sincerely appreciate the valuable comments. We have checked the manuscript carefully and added the reference of Table 1 in Section 3.1 of the manuscript(line187), “Detailed water environment parameters data were provided in Table 1 of the supplementary materials.”. And we added the reference of Table 2 in Section 3.2, 3.3 and 3.5 of the manuscript(lines 210, 233, 250, 339, 353, 365 and 379), “Detailed data were provided in Table 2 of the supplementary materials.”.

Point 3：Table 2: Please add the total N values (no of samples) and N values from which the statistics were calculated. So many decimal places are unnecessary.

Our response 3: We agree with the reviewer’s assessment. Accordingly, we added the total N values and N values from which the statistics were calculated (line 640). And we have revised Table 2 in the supplementary materials (line 641).

Table 2  Data processing table of each sampling point parameter

(Note: The total N value is 18 and the N values from which the statistics were calculated is 15.)

Point 4：Figure 5(B): peaks descriptions are impossible to see even with the zoom. please remove them.

Our response 4: We feel great thanks for your professional review work on our article. We have removed the description of the peaks(line289).

Point 5：Figure 8: The values on the graph are hard to see even with zoom. Maybe it would be better with black font or maybe you should just remove them.

Our response 5: We think this is an excellent suggestion. We removed the values in Figure 8(line 394).

Author Response File: Author Response.docx

Reviewer 2 Report

All the comments and suggestions have been addressed carefully by authors, I have no other comments about this paper.

Author Response

Dear Reviewer:

We would like to thank you for spending so much time reading our manuscript entitled “Spatiotemporal variation of riverine dissolved organic matter degradation based on EEMs-PARAFAC: A case study of Shili River in Jiujiang, Jiangxi Province, China, as a typical demonstration city of the Yangtze River protection strategy” (ID: water-2051028).

Author Response File: Author Response.docx