Exploring water cycle dynamics by sampling multiple stable water isotope
pools in a developed landscape in Germany

Orlowski, Natalie; Kraft, Philipp; Pferdmenges, Jakob; Breuer, Lutz

doi:https://doi.org/10.5194/hess-20-3873-2016

Articles | Volume 20, issue 9

https://doi.org/10.5194/hess-20-3873-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-3873-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 9

Research article

|

20 Sep 2016

Research article |

| 20 Sep 2016

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Natalie Orlowski, Philipp Kraft, Jakob Pferdmenges, and Lutz Breuer

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Final revised paper (published on 20 Sep 2016)
Preprint (discussion started on 06 Feb 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C315: 'Review', Anonymous Referee #1, 26 Feb 2015
- AC C4993: 'Reply to referee 1', Natalie Orlowski, 24 Nov 2015
RC C454: 'Review of Orlowski et al, 2015, HESSD, Exploring water cycle dynamics through sampling multiple stable water isotope pools in a small developed landscape of Germany', Anonymous Referee #2, 06 Mar 2015
- AC C5009: 'Reply to referee 2', Natalie Orlowski, 24 Nov 2015
RC C461: 'Review on “Exploring water cycle dynamics through sampling multitude water isotope pools in a small developed landscape of Germany” by Orlowski et al. (hess-2014-477)', Anonymous Referee #3, 06 Mar 2015
- AC C5041: 'Reply to referee 3', Natalie Orlowski, 24 Nov 2015
RC C486: 'Exploring water cycle dynamics through sampling multitude stable water isotope pools in a small developed landscape of Germany', Anonymous Referee #4, 09 Mar 2015
- AC C5060: 'Reply to referee 4', Natalie Orlowski, 24 Nov 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (18 Dec 2015) by Markus Weiler

AR by Natalie Orlowski on behalf of the Authors (14 Jan 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Jan 2016) by Markus Weiler

RR by Anonymous Referee #1 (29 Jan 2016)

Suggestions for revision or reasons for rejection

While the authors have done a nice job in revision, there is still a lack of a clear central research question or gap being filled. While the presentation has improved, I still miss a clear statement at the end of the introduction motivating what the goal of the study is. P4L29-P5L29 is poorly written and does not address this concern. This is a critical need that must be addressed. This was a weakness in the first submission and it remains a fundamental shortcoming. The current study characterizes some variability and applies a model. These alone (without a strong context and motivation) are likely of limited interest to the readers of HESS where there is an expectation to see advancements of process understanding and fundamental hydrological understanding.

As a general comment, the language gets rather loose throughout the text. The terminology and presentation must be improved and tightened. Too often are blanket statements or generalizations made without clear support. The language is often not precise and rather vague. I have tried to target several examples in the minor comments section of this review, but I am sure there are more. Please improve.

Further, the study needs streamlined (this goes hand-in-hand with the comment regarding the main question). The use of a hydrologic model is a good addition to the manuscript. However, the presentation of the modeling setup (section 2.5) leaves something to be desired. Rather than lengthen an already long manuscript, I would suggest shortening the text in the manuscript and adding an extended appendix or supplementary text section. This will allow you to list equations, have schematics and cover in detail the calibration/validation aspects of the modeling. As it is currently presented, the modeling is not fully described at a level of detail needed to understand the steps to create a working model. Rather than expanding this in the manuscript, I am suggesting to expand it in an appendix. If the central question for the study is to use the chemical data to improve the modeling, then much more is needed with regards to presenting the modeling without considering the tracer data in comparison with the model results considering the tracer data (and more information would be need on exactly how the data were considered).

In connection with the two previous general comments, I suggest also moving the methods and results text pertaining to the travel time modeling into an appendix or supplementary text section. As they are currently presented, the come across as “extra” and just confuse the flow of the study. The level of detail is underdeveloped. Moving them to a separate text section would really help streamline the presentation of this study. This is something that is needed as the current presentation is overly complicated and gets confusing with all the information jumbled together. This will allow you to focus in on the central research question of the study.

Lastly, from my reading, the discussion section 4.3 appears to be the main discussion section. The other two subsections more or less are just reiterating the results. This section 4.3 (while well written) could do a better job relating to more current studies on mixing assumptions (both temporal and spatial). The authors start into that consideration (at P28L26-30) but do not go further. I suggest reducing the emphasis on sections 4.1 and 4.2 (which cover the empirical and site-specific aspects of the research) and breaking the section 4.3 up into smaller subsections that potentially relate back to central research question(s). Explore the literature on these mixing-storage topics over the past 5 year. Placing findings in that context will significantly raise the level of presentation.

Apologies for harping on the presentation and structuring. I think the study presents a nice set of data. The challenge to the authors is to leverage these data into a fundamental advancement with regards to catchment hydrology. Taking a critical view of the research question and the general manuscript structure (i.e. how the results answer the question and the discussion provides relevance) should help elucidate this aspect.

Minor comments
P1: J. Pferdmenges does not have an affiliation.
P2L1: “smoothed out” is not precise. Adjusted terminology.
P2L27: Provide here a clear definition of what you mean with “low angle”. Also, make it clear that “low angle” is different from “lowland” since that is the focus of the next few sentences.
P2L27: Remove “very early,”
P3L22: Again, see work by van der Velde ([Van der Velde Y, Torfs PJJF, van der Zee SEATM, Uijlenhoet R. 2012. Quantifying catchment-scale mixing and its effects on time-varying travel time distributions. Water Resources Research 48: W06536]).
P4L10: “Following the way”? This is vague and confusing.
P4L29-P5L29: This section is poorly written and disconnected from the rest of the introduction. Parts seem like methods. It should be removed since it adds no value to presenting the study. Rather, end the introduction here with a simple statement of the gap in research being targeted and the research question(s) answered. Be concise and clear to motivate the research.
P8L5: Change “was fallen” to “fall”
P8L19: Change “was” to “were”
P8L28: “as connecting compartment”? Vague and confusing.
P10L10: I think it should be “connection” rather than “connectivity”. Connectivity has taken on special meaning in the literature that is not consistent with how it is necessarily being used here.
P11L9: Check the significant figures in your numbers.
P15L28: Perhaps you mean “proposed”?
P16L4: “higher than further below”” is confusing. Re-write.
P18L13-L23: This should be its own results subsection and not presented with the section on stream water variability. Further, perhaps consider taking this and the methods text describing this approach into their own stand-alone appendix or supplementary text section. This would really help streamline the presentation.
P19L12-13: Confusing sentence. Re-write.
P20L28: Change “:” to “.”

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RR by Anonymous Referee #2 (04 Mar 2016)

Suggestions for revision or reasons for rejection

Review of Revision:
Exploring water cycle dynamics by sampling multiple stable water isotope pools in a small developed landscape of Germany
By Orlowski et al. in HESS
The authors improved several aspects of the paper with this revision and accounted for three of my main concerns:
- They use a rigorous statistical methodology for analysing their stable isotope data
- The present the results from transfer function analysis of stable isotope data to determine catchment transit times (no good fit achieved- which is also a result)
- And restructured the paper, eventually increasing readability
The paper is well written. Yet, I don’t think the paper is ready to be published, and still requires some work. Besides the changes and the rework the introduction does not sufficiently frame the research question. The authors outline four objectives: 1. Linkages between water cycle components, 2. investigate transformation of precipitation to soil and groundwater, 3. Analysis of landscape characteristics …. On soil water isotopic composition and 4. estimate groundwater ages and flow directions… via … model.
While these are definitely interesting questions to ask, the “why” remains unclear. Several times the other use the term “poorly understood” in the introduction, while it is never clear to me, what exactly is poorly understood. For example, the authors claim that groundwater-surface water interactions and mechanism that explain the release of old water to streams fall in this category. I think there exist a plurality of work for both problems; so why not pinpointing on what exactly is not understood? For me, this needs some more attention. The big question: What brings this work beyond the local case study?
Moreover, the use of the CMF model seems a little bit weak. As there is no calculation of streamflow age, nor any validation of the modelled ages, it seems somewhat useless to me.
What would generally be interesting, seeing the claimed decoupeling of precipitation with groundwater and streamflow, is the calculation of the isotopic signal in groundwater recharge. Can the soil profiles, and meterological data combined with a simple approach be used to show that the soils modify the precipitation isotope signal in a way that it is consistent with the values in stream and groundwater. This would show that the system is not decoupled, but the soils behave in a translator flow way, or at least as a filter for incoming precipitation. This could also underpin the claim in the conclusion that it was shown “that groundwater was predominantly recharged during winter”. I think this interpretation is right, but the proof is not convincingly presented. An alternative could be that a larger groundwater system controls the streamflow.
Some minor comments:
Title: “small” is rather subjective here with catchments of >3km2 and ~10km2
Abstract, L19 “decoupled” is a strange word for me in this perspective. As precipitation contributes to groundwater, but with the soils acting as filter.
P2L16: origion of? Formation of?
P3L23-28: this is not done yet?
P4L14: I think this sentence is grammatically wrong
P4L18: Replace “This” with “The enrichment…”
P5L21: What is your hypothesis? What is the question that differentiates this work from a local case study?
P10L28ff. How is the model validated? How useful is it to leave out soil processes if they are the only component where stable isotopes change? I am not convinced about the added value of the GW model (and I don`t think it is needed for the work)
P15L13ff. Now you mention the stream water in the precipitation results, this is a little bit strange, since the stream results are not presented yet
P15L26: Insert “they” before “exhibited”
P15L27-30. These lines seem unnecessary, since repetitive.
P18L20/21: This conclusion only related to Transfer function based methods.
P21L3: Any change for streamflow age infromation?
P21L5ff.: Since there was no objective in the introduction that relates to precipitation, this discussion is somewhat oversized (but good)
P23-25: Can you calculate the stable isotope composition of recharge from your data?That would be very helpful. So you have a Hewlett and Hibbert like translator flow for GW recharge? Or is only winter rainfall contributing?
P14: How do you define baseflow? I would rather say, that the stream is always groundwater dominated, but you also observe higher flows, which are not really baseflow situations. But again, here the stream is groundwater fed.
P27-30: They work; they just show 100% groundwater contributions for the observed samples.
P28L4: I am not fully happy with the term “disconnected”, as GW levels react instantaneously.
P29L14ff. - So what is new? What is the beyond study area relevance?
- Show clearer that it is winter precipitation recharging
P29L21-22: Delte “old water paradox” as this is repetitive and vague. There is a wide range of processes that are behind this paradox. It would be better to clarify this functioning

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ED: Reconsider after major revisions (07 Apr 2016) by Markus Weiler

AR by Natalie Orlowski on behalf of the Authors (02 Jun 2016) Author's response Manuscript

ED: Reconsider after major revisions (28 Jun 2016) by Markus Weiler

ED: Referee Nomination & Report Request started (29 Jun 2016) by Markus Weiler

RR by Anonymous Referee #2 (07 Jul 2016)

Suggestions for revision or reasons for rejection

Review of Revisions: Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape of Germany
I think the paper clearly improved from the last version, I think it can be published if the following aspects are commented (for my first concern) and changed (for #2 and #3).
I think there are some points in the modelling that could lead to several rounds of arguing, but I leave this here. I would just appreciate if the authors could comment on the following concerns regarding the model setup.
1) The model still does not convince me, as I see it as a pure model exercise. The authors stated that the model can simulate isotope transport, so why not showing the resulting stable isotope in the stream? I am aware that the length of the time series is with the current travel times not long enough, but you could repeat the same input time series and see if this somewhat fits the observation. Currently, I am a little but concerned that a change in model parameters will have huge impacts on the calculated travel times. Furthermore, I was wondering if it is possible to also model the streamflow age, and not only the groundwater age? The last point, not unimportant, how is the model treating celerities versus velocities as it was mentioned several times in the manuscript?
2) A point that needs to be improved: You state several times that mixing calculation did not work, bc you yielded 100% groundwater contribution (L598/599). For me this statement is wrong, as already mentioned in my previous review. Why is it not working? It is, 100% is a clear result. It just shows that there is no precipitation water /new water in streamflow. I cannot see how the claim “not working” can be justified. Either change or elaborate more.
3) Other comments that can be improved with minor revisions:
P2L46: delete “further”
P2L52: “low angle”. As commented by me in a earlier review, and again by the other fellow reviewer this time. What is low angle, you define it later as low mountain range and give elevation changes page 5 L126. But if you call it angle, that it should be related to the slope (i.e. mean, median slope of the catchment). But low mountain and low angle are completely different things. If you have mountains, than you cannot have low angle, which mean to me that the catchments is more or less flat.
P3L90: add “partly” between “is” and “intercepted”
P7L194: You are using elevation/altitude/height inconsistent. Furthermore, it must be elevation at this instance. See: McVicar, T. R., & Körner, C. (2013). On the use of elevation, altitude, and height in the ecological and climatological literature. Oecologia, 171(2), 335-337.
P8L222. The Newman et al. reference is not in the literature list. Please add, please also recheck the consistency between text and reference list
L233: I think the current terminology also refers to piezometer samples as travel time, not as residence times…
L281-283. Please rewrite the sentence
L291: replace “could be” by “was”
L292: What is unclear to me is if there was not any snow in 2011-2012 or if it was not sampled
L294: change “Further” to “Furthermore”
L300 “sampl ed” to “sampled”
L301: “lower…events”. I don’t understand what this sentence should mean.
L358-360: Rewrite
L375: Contrary to the earlier findings of 100% Groundwater, you can see here the rainfall influence on streamflow. How big is the contribution of new water to streamflow, can you explain the inconsistency with the findings that groundwater contributes 100%, and how would this effect your general interpretation.
L379: I see it somewhat useless to report the results of a bad fit. I recommend deleting 379-381, and just report that no good fit was achieved. A numeric result might mislead.
L383: delete “Even a”
L389: I would not write that it was assumed that the signal directly transfers. Just write what you see.
L398: Again, I would not report the ages
L420: can you also extend this to streamflow
L565: But you got insights to the source of streamflow. The source is groundwater.
L576: “allowed” to “able”
L598: For me this is not obvious at all, if it would be obvious, you would not achieve any result
L1058: Does this statement hold, under the recent developments following the work of Botter (2010, 2011).
L1059: You don’t have a flat line….

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ED: Publish subject to minor revisions (Editor review) (07 Jul 2016) by Markus Weiler

AR by Natalie Orlowski on behalf of the Authors (17 Jul 2016) Author's response Manuscript

ED: Publish subject to minor revisions (Editor review) (20 Jul 2016) by Markus Weiler

AR by Natalie Orlowski on behalf of the Authors (27 Jul 2016) Author's response Manuscript

ED: Publish as is (16 Aug 2016) by Markus Weiler

Short summary

The 2-year measurements of δ²H and δ¹⁸O in rainfall, stream, soil, and groundwater revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions in the Schwingbach catchment. We established a hydrological model to estimate spatially distributed groundwater ages and flow directions. Our model revealed complex age dynamics and showed that runoff must have been stored in the catchment for much longer than event water.