Deep desiccation of soils observed by long-term high-resolution measurements on a large inclined lysimeter

Merk, Markus; Goeppert, Nadine; Goldscheider, Nico

doi:https://doi.org/10.5194/hess-25-3519-2021

Articles | Volume 25, issue 6

https://doi.org/10.5194/hess-25-3519-2021

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

https://doi.org/10.5194/hess-25-3519-2021

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

Articles | Volume 25, issue 6

Research article

|

22 Jun 2021

Research article |

| 22 Jun 2021

Deep desiccation of soils observed by long-term high-resolution measurements on a large inclined lysimeter

Markus Merk, Nadine Goeppert, and Nico Goldscheider

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Final revised paper (published on 22 Jun 2021)
Preprint (discussion started on 02 Jul 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Deep desiccation of soils observed by long-term high-resolution measurements on a large inclined lysimeter', Katrin Schneider, 03 Aug 2020
- AC1: 'Reply to RC1', Markus Merk, 16 Sep 2020
RC2: 'Merk et al.', Jannis Groh, 11 Aug 2020
- AC2: 'Reply to RC2', Markus Merk, 16 Sep 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (16 Sep 2020) by Natalie Orlowski

AR by Markus Merk on behalf of the Authors (16 Sep 2020) Author's response Manuscript

ED: Publish subject to revisions (further review by editor and referees) (25 Sep 2020) by Natalie Orlowski

ED: Referee Nomination & Report Request started (03 Nov 2020) by Natalie Orlowski

RR by Jannis Groh (30 Nov 2020)

Suggestions for revision or reasons for rejection

Dear Markus Merk and co-authors,

the manuscript has partially improved, but as already mentioned in the first revision of the draft, there is nearly no discussion, broader interpretation and comparison to other studies of the results in the section 4. In addition, drainage data that is now shown are poorly evaluate in the context of the main message of the manuscript. I think thes data can nicely show/help to quantify the impact of SWC depletion on recharge from this study. Many other study can not do this, because the don’t have the data from lysimeter. So I want to encourage the authors to add this analysis in a sub-section of Results and Discussion section, which would be an important information for the water sector, especially in the context of climate change.
I recommend again that the manuscript section 4 needs a broader discussion, interpretation and comparison of the results before publication in HESS.

General

1) It was difficult to follow up the response in text on the review, as authors did not adapt lines in the response from the revised version of the manuscript.

2) I recommend adding a section where the authors link the soil moisture depletion with the drainage data. Many other studies lack on the this information and the authors should use the available data from the lysimeter to link impacts of changing soil moisture on drainage/ recharge which is of high importance for the water sector

Specific comments:

L99: Missing units in the following sentences: “For the year 2002, the porosity of the RL is 0.4, usable field capacity 0.25 and the wilting point at 0.14. The 100 permeability was estimated as kf = 1:0 10􀀀6. Values were observed to be variable over time.”

L100: Please explain the statement that values were observed to be variable over time.

L128: Again, please provide units for the given wilting point and field capacity

First response Review round 1 L102-107: Totally unclear why the authors want to use the model uFC? This should be explained in the section.

As noted by the reviewer in a previous comment, any soil moisture time series could be used. We used external data by the DWD to compare with measured soil moisture and validate our findings. Added this explanation to the manuscript.

Response: Validating measurements with external simulation data?
L171: Change Zhao et al. 2019b to Zhao et al. 2019a, and change vice versa in line 176 Zhao et al. 2019a to Zhao et al. 2019b

L240: Figure caption of Fig. 6. “real evapotranspiration”. Please use in this context actual evapotranspiration, because there is “no unreal” evapotranspiration. It is also not clear to me where this data is coming from and if it is an outcome of the simulation from the AMBAV model (than please refer to simulated actual evapotranspiration) or if it is indeed measured actual evapotranspiration EC-tower, lysimeter? Please clarify this please

L199: reformulate this sentence, as low precipitation does not lead to a drying out. It is the large atmospheric demand for ET paired with low P [….].

L201: not clear from which figure I can actual see this?

L180-227: I could not find any discussion of their results in this section, also newly added discharge in the Figure is not presented in the text nor its effect from depleting soil water storage/ decline in soil moisture profile on DL is given. In addition, the potential and actual evapotranspiration is not present in the text and discussed.

L242: thanks to add the other SWC time series in the corresponding subplot (gray lines), but the authors should mention this in the legend of the figure and also in the text figure caption.

First response Review round 1: L271: I could not fi nd any data in the manuscript that actual shows that hysteresis plays are role at this site. So please clarify the following sentence: “There are clearly hysteresis eff ects during drying and re-wetting of the soil”.

Section 4.1 is dedicated to the asymmetry of drying and re-wetting. This asymmetry could also be called a hysteresis, as drying and re-wetting do not follow the same temporal paths. Additionally, we added a citation to Augenstein et al. (2015). They investigated and found evidence for the hysteresis between soil moisture and discharge.

Response: there is no hint on hysteresis in this section. Observed changes in SWC might be related to hysteresis, change in soil surface cover (large ET, which reduce SWC), or actually to a change of soil properties itself. Dear authors there is no discussion of the presented results.

L274: the authors should have a closer look at this data, and should show recharge data from both lysimeter in a better way to connect depleted soil moisture to changes in the recharge behavior of the soils over time.

L276: this statement is not clear to me? Did the authors mean characteristic length of evaporation i.e. this means the depth until which a wet soil dries out during stage 1 evaporation? But it’s an vegetated soil so E and T occurs (see next commentary). I suggest rather that it is an impact of many different factors, e.g. high ET that reduce soil moisture and also seasonal low P, but also to other factors like changes in the vegetation cover. As this is a main outcome the results should be discussed in a much broader context and should be compared with other studies.

L276: Also here it is rather related to ET and not only to E.

L336-354: this is actually the first and only part of the Results and Discussion section, where the authors discuss their results in the light of previous studies. This need to be done in a proper way in each of the previous section, if not the autos should change in L180 Results and Discussion to Results and add after this an separate Discussion section.

L367-368: so this indicates that changes in the vegetation cover might be the large driver of the observed depletion of SWC

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RR by Katrin Schneider (03 Dec 2020)

ED: Publish subject to revisions (further review by editor and referees) (07 Dec 2020) by Natalie Orlowski

AR by Markus Merk on behalf of the Authors (13 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (further review by editor) (16 Mar 2021) by Natalie Orlowski

AR by Markus Merk on behalf of the Authors (31 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (12 Apr 2021) by Natalie Orlowski

AR by Markus Merk on behalf of the Authors (19 Apr 2021)

Short summary

Soil moisture levels have decreased significantly over the past 2 decades. This decrease is not uniformly distributed over the observation period. The largest changes occur at tipping points during years of extreme drought, after which soil moisture levels reach significantly different alternate stable states. Not only the overall trend in soil moisture is affected, but also the seasonal dynamics.