Quantifying river water contributions to riparian trees along a losing river: Lessons from stable isotopes and iteration method

Li, Yue; Ma, Ying; Song, Xianfang; Zhang, Qian

doi:https://doi.org/10.5194/hess-2022-327

Preprints

https://doi.org/10.5194/hess-2022-327

Preprints

04 Oct 2022

| 04 Oct 2022

Status: a revised version of this preprint is currently under review for the journal HESS.

Quantifying river water contributions to riparian trees along a losing river: Lessons from stable isotopes and iteration method

Yue Li, Ying Ma, Xianfang Song, and Qian Zhang

Abstract. River water plays a critical role in riparian plant water use and riparian ecosystem restoration along losing rivers (rivers losing flow into underlying groundwater) under climate warming. How to quantify the contributions of river water to riparian plants under different water tables and the related responses of plant water use efficiency is a great challenge. In this study, experiments of stable isotopes (δ²H, δ¹⁸O and ²²²Rn) in different waters and leaf δ¹³C were conducted for riparian deep-rooted Salix babylonica (L.) during dry year (2019) and wet year (2021) along the Chaobai River in Beijing, China. The MixSIAR model in combination with an iteration method were proposed to quantify the proportional river water contribution (RWC) to riparian S. babylonica and its correlations with the depth of water table (WTD) as well as leaf δ¹³C. Results showed that riparian S. babylonica took up deep water (in 80−170 cm soil layer and groundwater) by 56.5 ± 10.8 %. River water that recharged riparian deep water was an indirect water source and contributed 20.3 % of water to riparian trees nearby the losing river. Significantly increasing river water acquisitions (by 7.0 %) but decreasing leaf δ¹³C (by −2.0 ‰) of riparian trees were observed as the WTD changed from 2.7 m in 2019 to 1.7 m in 2021 (p < 0.05). A short residence time (no more than 0.28 days) of groundwater indicated that there was rapid and frequent river recharge to riparian groundwater in 2021. It was found that the RWC to riparian S. babylonica was negatively correlated with the WTD but positively related to the leaf δ¹³C in linear functions (p = 0.000). The rising water table would stimulate riparian trees to maximize transpiration water consumptions and show a profligate water use strategy with increasing water extraction from the losing river. This study provides critical insights into understanding the mechanism of water cycle in Groundwater-Soil-Plant-Atmosphere Continuum, managing water resources and riparian afforestation along losing rivers.

Received: 15 Sep 2022 – Discussion started: 04 Oct 2022

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Yue Li et al.

Status: final response (author comments only)

RC1:
'Comment on hess-2022-327', Anonymous Referee #1, 17 Oct 2022

General comments:

This manuscript investigates the river water contribution to riparian trees. It does it by (1) determining and quantifying the sources of riparain trees water in soil and groundwater, (2) determining the sources of deep soil water and groundwater (precipitation, in-situ soil and groundwater, river water…) to finally (3) determine the proportion of river water that fed the riparian trees. This is an important work to better understand how riparian trees can affect stream flow and how we can better manage riparian zones in order to both protect rivers and riparian vegetation.

The manuscript is well-organised but I found the flow difficult to follow due to the grammar and wording mistakes throughout the manuscript (especially discussion section). The uncertainties of the MixSIAR model and iteration method are not really discussed, the MixSIAR model is also not well-enough presented in the method section. The discussion section is too light, I found that the discussion of the potential processes was too limited, as well as how do these results compare with other studies and why.

The figures are very good, there are just some grammar/wording mistakes in some captions.

Specific comments:

INTRODUCTION

Line 41: I feel that the jump to paragraph 2 (contribution of river water to riparian trees) is too quick, maybe have a small paragraph beforehand presenting the different sources of water for riparian trees (groundwater, soil water, river water?) first?

Line 41: Can you be more specific about “data comparison”? It is unclear.

M&M

Lines 112-125: I think you should develop on the storage in the field and until you put the samples in the fridge (where/in what did you stored the samples?, what method did you use to limit evaporation for the water samples?), this is important and not really described in this section. Also, use the (full) technical name of the tools you used in the field for sampling (e.g., “hydrosphore”?) or storage of samples (e.g., “brown bottle” is unclear).

Line 115: I am not sure what is it, maybe be more specific and use the full technical name? Maybe “plexiglass hydrosphore water sample collector” ? But I am not sure about what you used.

Line 115: Why 135 precipitation samples? Before you said precipitation was sampled during the 12 campaigns, I would clarify this point. Also, what was the frequency of sampling? And the location?

Lines 120-121: So 3 trees for each plot?

Line 122: What do you mean by “several”? Was is not 3/plot? Did you take several samples in the same tree? I would use “sampled” rather than “cut”. How did you sampled the stem? What tool did you use? Also, correct to “[…], we removed the bark..”.

Line 123: Maybe specify: “stored the remaining xylem at..”? Where/in what did you store it? Glass vial?

Line 124: In what did you stored the leaves before drying them?

Lines 126-130: This is a great section with the details needed (sampling method, storage). Can you clarify: you sampled soil only at 1 location for each plot, right? I would add a reference for the oven-dry method.

Line 150: Do you have a reference to support this choice for k?

Lines 168-169: So you calculated the average isotopes values for each of the four layers? You measured soil water isotopes at 11 depths.

Line 175: I don’t understand “set as the mixture data”, please clarify. Maybe more info on the MixSIAR model would help, I find it a bit frustrating for the reader to have to look in other papers. It would also help to understand why you talk about sampling times later in the text (lines 184-188, for exemple). Maybe have a separate section just to present the model (before 2.4.1.)?

Lines 185 and 187: So when you say “soil water in 0-80 cm” and “soil water in 0-170 cm”: does the model takes the layer as a whole or does it still account for the different soil layers 0-30, 30-80, 80-170 cm? And how do you integrate the soil water isotopes measured at 11 soil depths in the model? I think more information about that is needed in the manuscript (especially for the readers - like me - who are not familiar with the model).

Line 194: Can you provide a reference for the decay coefficient?

Line 195: How was this value determined?

Lines 205-222: It is an important method here but I found this part difficult to follow. There are A LOT of symbols, maybe use a table instead of the 7 lines of text so it’s more readable? I also did not remember what was Ps and Pg, I would explain these terms here again. I would suggest to change some of the terms, or try to include the time as subscript (t-1, t) so it’s easier to follow.

RESULTS

Lines 234-235: I think the slope of the LMWL only gives an indication about how oxygen and deuterium co-evolve, it does not indicate if the value is high or low. You can have 2 measurements of lower isotopes values but still have the same slope as with 2 measurements of higher isotopes values.

Line 276: How did you get a negative residence time? Would it make more sense to use “0”?

Lines 280-291: I would also remove the first sentence here and go straight to the results. I find the first paragraph difficult to follow because you present a mix of interannual and seasonal differences, think about what you want to present. You could have a first paragraph presenting the interannual differences, a second presenting the seasonal differences (differences between months for a SAME year). From my point of view, the Figure 9 only shows the differences between plots (you only show the stats for this), not between years (despite the same scales for the y axes) and months, so I would only refer to Figure 9 in the second paragraph.

Lines 288-291: This section reads well but you say in the first sentence that there are significant differences in RWC between the 3 plots in 2021 while there is no difference (Fig 9), please correct.

Lines 299-304: I would add in the text the R2 and p values of the linear models even if they are shown in Figure 10. Why did you fit the model to the whole dataset? And not one model for each year? It should be explained in the data analysis section, maybe I missed this point.

DISCUSSION

I think that this section is not well-enough developed and that the sections should be revised in order to reflect the objectives presented in the introduction. There is also no discussion about the MixSIAR model and the iteration method presented here and on which all the results are based. I would add a section to discuss about their strengths/weaknesses and implications for the discussed results. Then, I would discuss the RWC to riparian trees and the effect of the distance from the stream. Finally, I would discuss about the link between RWC/WUE/WTD and its implications (also include management). I think the discussion about the potential processes and implications should be developed, also how do your results compare with previous work and why?

Lines 336-342: You just look to mostly report previous findings here. First, what YOUR results suggest? Then, HOW does it relates/compare to previous work?

Lines 344-345: This point is super interesting, can you try to make the story about this clearer?

Lines 381-382: I don’t think you can really compare your “optimal” WTD with values from other studies because it is not the same site. I would rather discuss the potential reasons of these differences. Clarify the “knee point”, I see what you mean but I would reword, a “break point” instead?

Line 390: You talk about accurate separation and quantification of RWC to riparian trees but we don’t know the limitations and uncertainty of the model and iteration method.

CONCLUSION

Lines 401-408: I think this is too much results, the conclusion should not be like an abstract. I would focus more on the implications of your findings for riparian zones management and future research.

Technical corrections:

INTRODUCTION

Line 34: English is not my mother tongue but should it be “replenishment” instead of “replenishing”?

Lines 38-40: This is a very interesting question but some parts of the sentence need to be edited to have a clearer sentence. By “where” I guess you mean the sources? At the first read I thought you were talking about where along the river, I would use “source” to be clearer. I would change “responses to the variations in the water table” to “response to water table variations”. Also, be more precise about what you are talking about: is it the river water or groundwater level? When you say “revegetated riparian species” it means that the species are revegetated, which is false, I would change to “tree water requirement of revegetated riparian zones/areas” for exemple (it is the riparian zone/area that have been revegetated). Finally, I am not sure that the word “balance” is the best one to use here, I would improve the wording of the sentence.

Line 47: Can you be more specific about the “different waters”? Different “water sources”?

Line 51: Do you mean “change in river water level”?

Lines 62-66: I would improve the wording of the sentences. From my point of view, it does not read that well while it is important to state clearly the knowledge gap/issue here. Also, “estimations” of what?

Lines 67-81: Maybe I’m too picky but be more specific when you use WUE: is it WUE of plant (lines 69, 70)? Trees (lines 73, 79)? Similarly for RWC, I would specify “RWC to riparian trees” (line 67).

Line 75: Water table depth: of groundwater?

Lines 82-88: Great, very clear objectives here.

Line 86: I would specify “tree WUE”.

M&M

Line 94: I think “dried up from X to X” would be more correct. Or “during X up to X”?

Lines 95-96: The end of the sentence is a bit unclear due to the wording. I would change to “more than 33 km2 of riparian zone has been revegetated until 2020” or “from 2007 to 2020”. Have the trees been planted?

Line 100: I would change to “from April to November 2019 and 2021”.

Line 101: “were collected”, not “was”.

Line 104: I think it is “water level gauge”.

Line 105: “from April to November”.

Line 106: “with a total precipitation of”.

Line 107: I would correct and say “which was 1.8 times higher than for the drier year 2019 (445.6 mm)”.

Line 108: I would also correct here: “fluctuated between X and X m” and “mean WTD across the three plots”.

Line 109: Use “higher” not “larger” to compare values. Also, change to “higher than in X”.

Lines 109-110: Is it not the opposite? The WTD is lower (shallower GW) closer to the stream (see Figures 1 and 3).

Lines 112-113: Please write the months in full.

Line 132: I would say “extract water from xylem and soil samples” instead.

Line 133: “above 99%”.

Line 137: I would use “xylem” rather than “stem” in this section.

Line 138: Correct to “for both the IRIS and IRMS systems”.

Lines 141-151: It is a clear section, but I am not familiar with ²²²Rn and don’t really understand the sentence on lines 145-146 “to ensure… less than 80 Bq/m3”. Can you clarify?

Lines 153-156: I feel that these sentences do not belong here but in the introduction, for me the section starts on line 156 at “in this study…”.

Line 157: I would correct with “isotopes were integrated/used within/in the MixSIAR model and an iteration method was proposed to identify..”. What do you mean by the “original”?

Lines 158-159: I am not sure “merge” is the correct word, please correct the wording and grammar of the sentence.

Lines 159-163: I would check the wording of these sentences, I found it difficult to understand (maybe follow the section titles you used for 2.4.1., 2.4.2. and 2.4.3.? – they are clear). For exemple, what do you mean by “root water uptake patterns”? The sources? “Without considering river water as a direct water source”? Also, using “figured out” connotes a lack of accuracy, so I would use “determined” instead, for exemple.

Lines 165-168: I found these sentences difficult to understand, I would check the wording. What do you mean by “which was mixed proportionally”, “relatively stable”,”in terms of seasonal variations in SWC, water isotopes and WTD”? I am also not sure these sentences are needed here.

Line 170: I don’t understand why you refer to Figures 2, 3 and S1 here, I don’t see the link with why you separated the soil in 4 layers. Correct “in the 170-230 cm layer”.

Line 172: I would change “determined” to “used as direct water sources”.

Lines 173-174: I would change “stem” to “xylem” since you measured isotopes of xylem water.

Lines 177-179: I don’t think these sentences are needed here since you develop this point in section 2.4.2.

Line 181: I would specify “deep soil water (80-170 cm) and groundwater”, also check grammar of the sentence.

Lines 181-184: There are some wording and gramatical mistakes I think. Change “could be” by “can be”? “were applied” by “were used”? “in the 80-170 cm layer”.

Lines 183-190: I like this part, it’s clear, and the Figure S2 is great! I just wonder if it would be better to have the figure in the main text rather than in the Supplement.

Lines 191-192: I am not sure about the wording here: “recharged from the river to the underlying aquifer and/or riverbank”… or maybe I misunderstood.

Line 199: I would not use “figured out” in a manuscript, I would use “determined” instead. Please correct the “figured out” throughout the manuscript.

Line 200: I am not sure about the use of “merge” here.

Line 202: What do you mean by “be consistent”? Can you change “proportions” to “contribution”?

Line 222: I am not sure “recharge” is the best word, maybe say “we estimated the proportions of old and current river water in the riparian deep water”, but should it be “in the riparian trees” instead (the aim of the section 2.4.3.)?

Lines 224-229: This section is a bit difficult to read, the first sentence it too long, I would try to separate it. Also, check the grammar and wording. The “regression analysis method” is unclear.

RESULTS

This section is well-organised and the results are presented concisely and quite clearly. There are some grammar and wording mistakes, especially when you present the isotopes results. You can’t say “d2H in precipitation was more depleted”, but say “precipitation was more depleted in d2H” or “d2H in precipitation was higher/lower than…”. Check throughout the section 3.1 (lines 232, 239, 240, 242-243, 244-245…). Also, you use a lot of “than these/that” (line 233) or “with that in” (line 236) to compare results between years, I would correct and use “than in” or “compared to” instead. Check also the use of “the”.

Line 232: I would not use “it was evident”, just present the results clearly and briefly.

Line 234: Use “higher” rather than “larger” to compare values.

Line 236: I would rather say “SWC of each soil layer” than say “of all four layer”, at the first read I thought you combined all the soil layers together but you analysed the difference between the plots for each soil layer separately from what I understood.

Lines 246-253: This part reads better, it’s clear and concise.

Line 250: I would correct to “decreased with increasing distance from the riverbank”.

Line 253: What do you mean by “evidently”? Is it significant? and “plummeted”?

Lines 255-278: This section reads well and is well organised, check the mistakes I refered to previsouly. I would remove the first sentence and would go straight to the results.

Line 257: I am not sure about the use of the word “in-situ” to refer to the water that is already in the deep soil or groundwater compartment… But I don’t really what word you could use instead so I’m not very helpful on this point.

Line 261: “15.7%”.

Line 262: “deep soil water”, “the lowest”, “and in June”.

Line 265: I would correct: “significant interannual and seasonal differences in the water sources…”.

Lines 268-269: Please correct the wording of this sentence.

Lines 271, 272: You should refer to Figure 3 here to help the reader understand since you present some of the WTD results.

Lines 275-276: As I mentioned before, I still don’t understand this sentence, maybe a wording mistake or me… Check the grammar as well.

Line 282: Please put the unit “%” after each result, “mean of X% ± X%”, check and correct throughout the manuscript.

Lines 282, 284, 285, 286: Correct the grammar: “higher” not “more” or “larger”, “lowest” not “least”, “highest” not “most” to compare values. You can say “X was higher/lower than X” or “X was the highest/lowest in…”.

Lines 288-291: Use “between” not “among” to make comparisons. The first part of sencond sentence is perfect but the end is unclear “whereas….. in 2021” (“corresponding value”?, “along the distances”?), please correct the wording and grammar, or you could just say that there was no significant differences in 2021.

Line 292: I would slightly change the title to: “relationships between leaf d13C, RWC to riparians trees and WTD”.

Lines 293-298: Check the wording and grammar mistakes (“the” missing, “higher” not “larger”, “significant” not “significantly”…) as commented above, write the months in full, use “significant” instead of “remarkably” (line 294).

Lines 299-304: This section reads better. Correct “RWC to riparian trees”. I would move the last sentence to the discussion section.

DISCUSSION

The flow of your thoughts is difficult to follow, I would try to be clearer in my explanations. There are wording and grammar mistakes that need to be corrected, also check the tense you use.

Line 307-326: The section is well-organised but you don’t need to repeat the results in this section (lines 307-310, 316-317, 324-325).

Line 311: I find it difficult to understand what do you mean by “contradictons”, please develop your thoughts and the processes inolved.

Line 311: I would be more precise and not use “interactions”, we don’t know if it is river-GW flow or GW-river flow, in your study you only looked at river-GW flow, say it.

Line 321: Same comment for “exchange”, it is not clear enough.

Line 323: I don’t think that “weakened” is the right word to use here.

Line 326: “distance” from what?

Lines 329-335: The section here is also well-organised but I still find it difficult to follow your story.

Line 329: You can say “smaller than..” or say “small”, please correct.

Lines 331-335: I like this part, just check the grammar and wording (“or that stored”).

Line 346: Here and throughout the manuscript, don’t forget: “RWC to riparian trees”.

Line 347-349: These 2 sentences should be switched, I would first briefly remind the result and then say what it suggests, you did the opposite here.

Line 349: I would reword “along the gradient of distance”.

Line 351: The technical word “dimorphic” should be explained at first use to help the non-expert reader to understand what you mean.

Lines 351-355: Interesting difference between tree species, try to reword to clarify this point. The sentence on lines 354-355 is repeating the one on lines 351-353.

Line 357: I don’t think “balance and coordination” are the right words here.

Lines 361-369: I like the ideas here but I would improve the wording and check the grammar to improve the flow.

Line 362: “profligate” is not the right word here, it can’t be used to derscribe water-use strategy.

Line 366: Say “river water” not “river flow”.

Lines 371-374: This is results, not discussion.

Lines 375-380: I like the ideas here, grammar and wording need to be improved.

Line 375: Correct the grammar: “previous studies that showed an…”.

Line 376: No need to add the equation.

Line 377: I think “coordinate” is not the right word here, maybe “optimise”?

Line 379: I would reword “balancing the relationship” and “flow reservation”.

Line 383: I would say “groundwater table” rather than “water table”, it is clearer, please check throughout the manuscript

Lines 386-397: I find the flow of this section hard to follow, thoroughly check the wording and grammar, don’t hesitate to ask an english native speaker.

CONCLUSION

Lines 399-412: Check and correct the wording and grammar.

Lines 399-401: I like this part, reminding the objective f the study.

Figures:

Figure 1: Great figure!! It is very clear, easy to read and show all the info needed. As I see dams along the river, I wonder if water was released during the study periods and how it could have affected river flow and the results?

Figure 2: Check the reference to Figure 2 in the text, lines 106-107 should only refer to Figure 2a. I would change the caption to “Monthly average precipitation amount from 1961 to 2021 and monthly total precipitation amount for the observation years 2019 and 2021 (a), Daily total precipitation amount and precipitation isotopes during 2019 (b) and 2021 (c).

Figure 3: The figure is clear but I would show groundwater level (on same scale as river water level) instead of water table depth so we can actually compare with river water level, but maybe I’m being too picky if the aim of the figure is only to show the seasonal variations.

Figure 4: Nice flowchart, the reference is missing in the text.

Figure 5: This is again a very nice figure. I would check and correct the wording of the caption (3 first sentences). Maybe try to increase the front size? I would use xylem instead of stem, as suggested before.

Figure 6: Very nice figure, I would however correct the caption with “Seasonal variations in the (proportional) contributions of soil water and groundwater to riparian trees in the three plots..”. Try to increase the front size.

Figure 7: Nice figure, correct the “in-situ” in the legend at the top of the figure and the y axis “contributions of water sources to riparian soil water in the 80-170 cm layer in the three plots”, check the grammar in the caption. I would increase the front size as well.

Figure 8: Nice figure as well, just correct the “in-situ” in the legend, check the caption and try to increase the front size.

Figure 9: Nice and clear figure, correct the y axis “contributions of river water to riparian trees”, I would try to better highlight the yearly average, maybe using bold? I did not notice it at first look. Check and correct the caption: “different letters show a significant difference in the RWC to riparian trees between two plots”, maybe say “RWC to riparian trees in the three plots for each sampling campaign” rather than “seasonal variation” since you only show the statistical results of the differences between plots for a same campaign. The stats results for September 2021 look weird, D45 looks different than D05 and D20 not different from D05 and D45, can you check that?

Figure 10: Very nice figure as well, maybe just try to increase the front size. Check the grammar in the caption.

Supplement:

Figure S1: From the text, I don’t see why this figure is useful. It is also pretty heavy, there is a lot of information.

Figure S2: Amazing figure!

Tables:

Table 1: Nice table, is it the average or median values? Also, I would add the SD or SE for each date (I think you took 3 samples for each plot and date, right?).

Table 2: Why do you show the results only for 2021? Maybe I missed something… What do you mean by “null”? It can means zero, so please clarify.

Citation: https://doi.org/10.5194/hess-2022-327-RC1
- AC1: 'Reply on RC1', Ying Ma, 08 Jan 2023
  
  The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2022-327/hess-2022-327-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/hess-2022-327-AC1
RC2:
'Comment on hess-2022-327', Remy Schoppach, 16 Nov 2022

This manuscript from Li et al. aims at quantifying the contribution of river water to the transpiration flux of trees growing in the riparian area. This is an important topic, of interest for the community. Globally, the paper quality suffers from a clear lack of structure, elusive objectives and a poor discussion. Figures are of relatively good quality. Clearly the authors are not native speakers, but the paper remains easily readable from a language perspective, except for the discussion. The effort put in the language is appreciated but the structure and the reasoning need to be substantially improved.

Introduction lack of reasoning on the scientific gap. In some parts, it really reads like a discussion where the authors compare contrasting results from the literature without highlighting the questions it raises. Some concepts are not even introduced (e.g. the use of radon as an indicator or the need of an iteration method). The introduction requires a straight flow of ideas leading to a scientific gap that this paper aims to fill. The lack of structure is also visible as some parts of the introduction are displayed in the M&M.

The results section is somehow hard to read. Most sub-sections are similar to the previous ones and the reader gets easily lost between the contribution to riparian deep soil water, the contribution to superficial water, the contribution to 30-80 cm water, the contribution to 80-170cm water, and this for three sites and two years.

In my opinion, the main weakness of this manuscript is the absence of meteorological data and transpiration measurements/ photosynthetic rates. For exmple, there is no data on evaporative demand. Also, the reader has no idea of the difference in radiation and transpiration rate between the two years of sampling. For example, there is no data on tree transpiration or potential evapotranspiration. Therefore, even if the proportion of river water seems to be lower in 2019 than in 2021, the total amount of water taken up from the river might actually be higher in 2019 than in 2021 if the transpiration rate was twice higher.

In this manuscript the authors showed that the higher the proportion of river water to transpiration flux is, the higher the WTB is. In my opinion, this simply indicates that there is more "free" water for both tree uptake and groundwater refiling. More importantly, the authors have no idea on the transpiration flux, they only rely on proportional sources of the total water found in the tree. Therefore, the entire discussion is misleading. The argument is also valid for the WUE. As the authors compare two different years, without any data on the radiation amounts received by the trees, they simply can’t infer the role of WTD or RWC on the WUE. It is simply not possible to evaluate the drivers of the WUE of trees growing in different environments without “quantifying” these environments. For example, if trees recieved twice less radiation amounts in 2021 than in 2019, the photosynthetic rate have likely been highly reduced, which as a direct impact on WUE, independently from WTD or WRC. This criticism is developed in the specific comments below.

Specific comments:

Abstract:

Line 16: write active. We propose instead of “were proposed”

Line 19: contributed by

Line 20: why using “but” instead of “and”. Is the increase in river water acquisition in contradiction with the decrease in leaf δ¹³C ? If yes, you need to explain why.

There is no explanation of the decrease in leaf δ¹³C the abstract?

Line 24. How the rising water table would “stimulate” trees to maximize transpiration? I think this is simply the results of a higher water availability leading to a less negative water potential in the root-zone and subsequent lower stomata regulation. There is no clue for any “stimulation” of the plant?

Moreover, the reasoning is a bit ambiguous as you say that a rising water table increases the transpiration and the water extraction from the river (but not from the groundwater?). This is puzzling to me.

Line 27: why using capital letters for Groundwater-Soil-Atmosphere Continuum?

Introduction:

Line 30: I’m not aware of a consequence of groundwater overexploitation on the alteration of precipitation regime. Maybe consider re-writing.

Line 35: contributed “by”

Line 38: delete “deeply”

Line 39: their responses to the variation in the water table (response of what, transpiration? Variation in what, level?) Please be specific.

Also, I don’t understand how a “deep understanding” could help “balancing the river flow and the revegetated riparian species”? It could help implementing management strategies maybe? But the understanding will not balance anything.

Is “revegetated species” an already used term? I’m not native speaker but I don’t think a species can be revegetated. A riparian area could be, but not a species, right?

Line 41 to 43: contribution to what? Transpiration flux I guess, but please write it. Please also insert the references within the sentence after each corresponding argument.

Line 45: “a separate water source”. Separate from what, other sources? If yes, maybe list them.

Line 53: There was a debate or there is?

Line 63: inaccurate estimation of what? Please consider re-writing the entire sentence

Line 65: You can’t just state that “how to separate and quantify the contribution of … is a great challenge” without reasoning it. Why is it a great challenge? If you don’t explain it, the reader gets confused and can only believe you. You need first to introduce the reasons making this a challenge.

Line 70 to 80 reads like a discussion more than an introduction.

Line 83: the first objective is the propose an iteration method. This comes from nowhere as no part of the introduction introduce the issue related to iteration methods? Also, what is an iteration method together with water stable isotopes?

M&M

Line 94: has been seriously degraded instead of degraded seriously.

Line 95: What is ecological water? How is that “ecological water” supplied? This part of context is worth being developed a bit more. Is it via a systematic water release by dams?

Line 103: via a pressure stage gauge

Line 108: Fluctuated between

Line 109: The mean WTD in the three plots was significantly (p<0.5) deeper in 2019 (value) than in 2021 (value).

Line 105 to 110: Should this section displayed in the Results instead of M&M?

Line 118: There is not mention of the ²²²Rn in the introduction. Therefore, the reader has no idea what ²²²Rn is and why you determine the its concentration?

Line 120: Is it Three trees in each of the three plots or one three per plot? Please re-write to avaoid confusion.

Line 133: Did you measure the efficiency of the extraction and how? By weighting your fresh and dry samples? Please explain it.

Line 141: Is there something missing in this sentence. What is exactly C_Air?

Line 153 to 156: This is introduction, not M&M.

Line 160: Based on what did you decided to not consider river water as a direct source for tree water uptake? You have to justify this choice one way or another. Or at least explain it.

Line 173: What is the correction proposed by Li et al. (2021). Please explain briefly how this works.

Line 183: Try to avoid saying “As shown in figS2a”. Just write your sentence and refer to the figure at the end.

Line 194: Please add a reference for Eq. 2 and for the coefficient values.

Line 195: this is the first time you indicate that ²²²Rn is Radon. Should come earlier in my opinion.

Results

Line 262: was the lowest

Line 276: that is recharged

Line 282: were significantly higher

Line 285-286-287: Please consider re-writing

Line 293: reference the corresponding figure

Line 294: -27.7 is not remarkably larger than -29.7

Line 295: a significant increase

Line 297: before when (chose one)

Line 303: This statement is dropped without any explanation. I suggest to move it to the discussion and to actually discuss it.

Discussion

Line 311: what are the interactions? Do you mean exchange of water?

Line 311: “These contradictions”. What contradictions?

Line 312: might be due to that the. Please re-write

Line 314: previous studies “showing”. There is a word missing here

Line 314: You mention previous studies, but cite only one.

Line 319: The rising water table stimulated exchanges. Stimulated isn’t an appropriate word here. Maybe triggered?

In don’t understand this part of the discussion. It sounds obvious to me that if the water table reach 1.7 m below the surface it will exchange water with the soil layer standing at that same depth and in a larger proportion compared to a situation where the groundwater level is 1m deeper.

Line 326: Again, you mentioned previous studies and cite only one.

Line 329: a smaller proportion than what?

Line 331: “is simila”r and “Nearby perennial streams”

Line 334: what is “that” in the sentence?

Line 340: The authors actually did not measure the isotopic signature of the bound water in fine pore and neither the exchange between this water and the river water, so yon can’t state that it rarely exchanges. What you can do is to speculate and use this argument as an explanation.

Line 348: significantly more river water. Actually no, you don’t know. A higher proportion maybe, but I would bet that it is the opposite for the amounts.

Line 356: The was a balance and coordination…. because obvious differences were found. What you did not find these differences? This entire sentence isn’t clear and I don’t see the point of it.

Line 359: If you say the tree grew more reliance on… you need to compare it with something. Otherwise you should not use “more”. More than what? More than who, another species?

Line 360 to 370: I don’t understand how the authors can actually infer a profligate water-use strategy whereas they have no ideas on the water fluxes. They have no transpiration measurements, no evaporative demand measurements. What about the radiation amount? This is a key variable driving water-use efficiency. If the radiation over 2021 growing season was twice less than the radiation in 2019, it is easily imaginable that the photosynthetic rate was substantially impacted and subsequently the WUE.

Line 378: In my opinion the argument developed here is misleading. The water table is low, likely because of the high evapotranspiration, which indicates a high transpiration rate, and very likely an even higher photosynthetic rate, leading to a high WUE. Under the same radiation conditions but with a much higher WTD, the WUE would be as high and probably even higher, and not the opposite as suggested by the authors.

Line 411: That is wrong, the authors did not measure the transpiration so they don’t know if a WTD of 4m minimize the plant transpiration.

Fig 1.

I like the figure, it describes the sampling site very well. Please indicate what dotted line represents in right panel (I guess water table level). Also indicate if it represents a measured level or just a schematic representation.

Fig3.

The figure indicates an average river water level of 29m. What does it mean exactly? What is the reference, the zero level? Could it be the distance from the river bed? Is it such a deep river?

I think most large European rivers displayed a depth of 2 to 5 m. I’ve never been to this place but 29m deep sounds more like a lake than a river. BTW, how a 29m deep river can lose flow?

Fig.4

The Flowchart and its symbols must be explained in the legend.

Table2: units of residence time

Citation: https://doi.org/10.5194/hess-2022-327-RC2
- AC2: 'Reply on RC2', Ying Ma, 08 Jan 2023
  
  We have carefully addressed all the comments made by Dr. Remy Schoppach and one anonymous reviewer on our manuscript (hess-2022-327) . The comments have helped us greatly improve the overall quality of the manuscript. The point-point response to all the comments by both reviewers has been listed in the attached file "Response letter".
  
  Citation: https://doi.org/10.5194/hess-2022-327-AC2

Yue Li et al.

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https://doi.org/10.5194/hess-2022-327-supplement

Yue Li et al.

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Short summary

An iteration method together with multiple stable isotopes and MixSIAR model was proposed to quantify the river water contribution (RWC) to riparian deep-rooted S. babylonica nearby a losing river. River water could indirectly contribute 20.3 % of water to riparian trees. River recharged riparian groundwater rapidly with a short groundwater residence time (no more than 0.28 days). The leaf δ¹³C negatively correlated with RWC but positively related to the depth of water table in linear functions.


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