Diel patterns in stream nitrate concentration produced by in-stream processes

Greiwe, Jan; Weiler, Markus; Lange, Jens

doi:https://doi.org/10.5194/bg-18-4705-2021

Articles | Volume 18, issue 16

https://doi.org/10.5194/bg-18-4705-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-18-4705-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 16

Research article

|

18 Aug 2021

Research article |

| 18 Aug 2021

Diel patterns in stream nitrate concentration produced by in-stream processes

Jan Greiwe, Markus Weiler, and Jens Lange

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Final revised paper (published on 18 Aug 2021)
Supplement to the final revised paper
Preprint (discussion started on 26 Nov 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review bg-2020-429', Anonymous Referee #1, 29 Dec 2020
- AC1: 'Reply on RC1', Jan Greiwe, 25 Jan 2021
RC2: 'review 2020-429', Anonymous Referee #2, 04 Jan 2021
- AC2: 'Reply on RC2', Jan Greiwe, 25 Jan 2021
RC3: 'bg-2020-429', Anonymous Referee #3, 05 Jan 2021
- AC3: 'Reply on RC3', Jan Greiwe, 25 Jan 2021
RC4: 'Reviewer Comment', Anonymous Referee #4, 03 Feb 2021
- AC4: 'Reply on RC4', Jan Greiwe, 15 Feb 2021

Peer-review completion

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

ED: Reconsider after major revisions (26 Mar 2021) by Tom J. Battin

AR by Jan Greiwe on behalf of the Authors (29 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 May 2021) by Tom J. Battin

RR by Anonymous Referee #2 (28 May 2021)

Suggestions for revision or reasons for rejection

This is my second review of this paper. The authors have properly addressed most of my original concerns.
My only major comment is to better organize the section on interpreting the clusters, preferably with a visualization. I think this would help with the interpretability of the hypothesized controls of the clusters and would make a powerful contribution.
Other minor comments are below.

Line 28: End the abstract with a broad conclusion statement.
Line 145: How did the water authority measure discharge? At least list the method.
Line 287: It still isn’t clear to me where the 95% CI come from. A model (time-series, regression, etc.) must have been used to get these values, and I don’t see anything about a model in the methods.
Line 325/ Figure 4: This is still challenging to interpret. If the points were close to the shaded area does that mean that transport dictated the difference in NO3 between sites. In other words, when the values are less than the shaded area, differences in NO3 between sites are caused by in-stream processes. Please add a line in the caption that describes the main conclusion to take away from this graph.
Also, the authors have not addressed my comment about how its possible to have a negative travel time.
Line 563: Yes, if GW N inputs are constant, they shouldn't affect the signal (shape of the diel curve). Although, GW N inputs would mess with your interpretation of transport vs. in-stream processes. I would talk about that here.
Line 564: What does longitudinally stable mean? It implies stability over space, say between sensors, but that doesn’t fit with the context of this sentence. Do you mean stabile in time, e.g., a similar pattern over multiple days? Please describe.
Line 585-589: I would remove this reference. If there is no riparian vegetation in your stream this is irrelevant.
Line 603: How would diel temperature variation affect denitrification and not nitrification? This correlation should be described more fully.
Also, what about the possibility of diel changes in heterotrophic respiration (see: Hotchkiss and Hall 2014, https://doi.org/10.4319/lo.2014.59.3.0798). How might that describe some of the clusters?
Line 608-609: But above you seem definitive that diel changes in lateral inputs are negligible. Which one is it?
Lines 585-615: Thank you for toning down the language about the causes of the diel patterns. However, this section seems to have lost its teeth. You are definitely on the right track in using nitrification and denitrification to explain the clusters that aren’t closely related with autotrophic based assimilation, but the current explanation is disjointed and could use some organization.
I suggest creating a conceptual diagram/figure with hypotheses about the controls on each cluster, and using this figure to write about each cluster in this section. Frame it as hypotheses that readers can use in their research to pursue controls on diel trends that they see. I think this would be very powerful and useful for folks that use diel data. You are on the right track, I just think a little organization and a visualization would make what you are describing more obvious and insightful.

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RR by Anonymous Referee #1 (18 Jun 2021)

Suggestions for revision or reasons for rejection

I very much enjoyed reading this revised manuscript. The authors did an excellent job of responding to reviewer questions and concerns, and I find the paper much improved.

I still have some (very) minor comments and technical notes that I am sure the authors can easily solve.

Minor comments

1. I suggest a small reordering in the methods and results. In section 2.3.1., I would begin with seasonal patterns of stream nitrate concentrations and then move to diel patterns. (i.e. move lines 109-113 earlier in this section). Same in the results (i.e. move lines 167-176 at the beginning of section 3.1).

2. Looking at Fig. 5, I wonder if it is possible to add some test (i.e. ANOVA) that support your results. This shouldn’t be difficult to do, and it might support your rational.

3. Finally, I still have some minor concerns about the discussion.

First, the section “lateral inputs” is not needed. The first paragraph of this section can easily go to “General patterns”, as the authors talk about how lateral inputs affect longitudinal patterns of stream nitrate concentrations at seasonal scale. Similarly, the second paragraph links nicely to line 308, where the authors say that cluster D might be caused by intense evapotranspiration.

Similarly, I think the section “in-stream vs transport” can easily fit in “interpretation of diel patterns”.

The rational on how evapotranspiration influences diel patterns is confusing. The authors said that intense evapotranspiration can cause cluster D. However, the authors also said that there were no diel patterns of water level, which goes against the previous hypothesis. Please, clarify it.

I did not follow why the relation between Cdiel and water temperature suggest that nitrification denitrification may be the underlying processes. Please, can you develop a little bit more this rational?

Technical notes
Title: “stream nitrate concentration”?
Ln 9. This sentence is quite long. I suggest to start a new one on “We performed a k-means cluster analyses to ....”.
Ln 15. Perhaps add “Results from cluster analyses show that at least 70% …”
Ln 16: “or physical (lateral inputs) processes”
Ln 2. This sentence seems quite off here. I suggest to either move it at the beginning of the introduction or to delete it and simply say “Among the different nutrients, nitrate is of special interest …”
Ln 42. Add here also the hypothesis that diel signals might also be due to diel variations in groundwater NO3- inputs due to evapotranspiration.
Ln 50. Move the ref at the end of the sentence.
Ln 61. “Al our site, “
Ln 66. “gravel bed,”
Ln 88. “in the latter dilution measurement,”
Ln 92. Perhaps is better to indicate which patterns of NO3- concentrations you are referring to. I suggest to change the heading to “Identification of diel patterns in stream NO3- concentration”
Ln 99. Remove “e.g.”
Ln 100. You did a great job here; this reads much clearer now! However, I would perhaps clarify that “diel portion of the solute concentration signal” means “Residuals concentrations”, i.e. add residuals concentrations in parenthesis after “concentration signal”.
Ln 124. Clarify that you did this exercise for both reaches and all clusters. Also, can you add the number of days for each reach separately? If you do so, data would match perfectly with Fig 4.
Lnn138, “Particularly, we assessed daily means of nitrate concentration, water level and water temperature”
Ln 155. Add a comma after “(n=119)”
Lm 166. “stream nitrate concentration”
Ln 172. This rho is negative. So either the symbol is wrong, or the relation between water temperature and daily average nitrate concentration is negative.
Ln 183. “differed between stream reaches and among clusters”
Ln 194. “In both reaches, the time lags roughly ranged between zero and travel time estimates”
Fig 4. Nitpicking, but perhaps it is better to show first the upper reach.
Ln 232: “In our data, we found patterns in stream nitrate concentration”
Ln 238. “On diel scale, “
Fig 6. Nitpicking, but can you highlight the zero line to make it easier for the reader?
Ln 270-274. This rational does not make sense in the current version of the discussion. I suggest deletion.
Ln 281. “, when cluster B prevailed”
Ln 319. “Germany,”

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ED: Publish subject to minor revisions (review by editor) (22 Jun 2021) by Tom J. Battin

AR by Jan Greiwe on behalf of the Authors (06 Jul 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (17 Jul 2021) by Tom J. Battin

AR by Jan Greiwe on behalf of the Authors (23 Jul 2021)

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Short summary

We analyzed variability in diel nitrate patterns at three locations in a lowland stream. Comparison of time lags between monitoring sites with water travel time indicated that diel patterns were created by in-stream processes rather than transported downstream from an upstream point of origin. Most of the patterns (70 %) could be explained by assimilatory nitrate uptake. The remaining patterns suggest seasonally varying dominance and synchronicity of different biochemical processes.