Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model

Sternagel, Alexander; Loritz, Ralf; Wilcke, Wolfgang; Zehe, Erwin

doi:https://doi.org/10.5194/hess-23-4249-2019

Articles | Volume 23, issue 10

https://doi.org/10.5194/hess-23-4249-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-23-4249-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 10

Research article

|

22 Oct 2019

Research article |

| 22 Oct 2019

Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model

Alexander Sternagel, Ralf Loritz, Wolfgang Wilcke, and Erwin Zehe

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Final revised paper (published on 22 Oct 2019)
Preprint (discussion started on 01 Apr 2019)

Interactive discussion

Status: closed

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

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RC1: 'Review - more examples of application are required', Anonymous Referee #1, 06 May 2019
- AC1: 'Response to review #1', Alexander Sternagel, 20 May 2019
RC2: 'Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model', Anonymous Referee #2, 07 May 2019
- AC2: 'Response to review #2', Alexander Sternagel, 22 May 2019
RC3: 'Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model', Anonymous Referee #3, 08 May 2019
- AC3: 'Response to review #3', Alexander Sternagel, 22 May 2019
SC1: 'well written, add context', Michael W. I. Schmidt, 15 May 2019
- AC4: 'Response to short comment', Alexander Sternagel, 27 May 2019

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (29 May 2019) by Alberto Guadagnini

AR by Alexander Sternagel on behalf of the Authors (09 Jul 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Jul 2019) by Alberto Guadagnini

RR by Anonymous Referee #3 (17 Jul 2019)

RR by Anonymous Referee #2 (09 Aug 2019)

Suggestions for revision or reasons for rejection

In my opinion, the authors replied quite satisfactorily to my first review. They added an additional infiltration test to illustrate the feasibility of the LAST-Model, they compared the results of the model with the ones of a numerical one (HYDRUS-1D) and they (partially) improved the explanation of LAST-model parametrisation.
However, there are some typos and I still have some doubts about the feasibility of designing a physically based structure of the preferential flow domain suitable for the model proposed.

Specifically, in Section 3.2 devoted to the parametrization of the model, is written: “Horizontal layers in different depths of the vertical soil profiles were excavated and in each layer the amount of present macropores counted as well as the diameters and depths measured”. Is this the procedure one should use in order to apply your model? In order to use LAST-model, should one excavate at different depths, until an (unknown) “predefined length” (=LM), count the number of macropores (=nmac), measure their diameters (=dmac) and use these numbers as input parameters for your model? Especially because the model looks extremely sensitive to these parameters. In the 5.2 Result and Discussion Section is written that a possible explanation for the discrepancy between the model and the data observed at Site 33 is that “examination of the macropore network were performed on different dates” … Does it mean that even if I carefully parametrize the pfd zone (with LM, nmac, dmac) I have to consider a temporal evolution of this parameters, depending e.g. to saturation conditions?
It looks like a long and expensive preliminary work, for a relatively simple 1D double domain water flow and tracer transport model or am I missing something? I write “relatively simple” in the sense that there are many hypothesis underlying your model (e.g. no lateral exchange, diffusive exchange between solutes in the matrix, reverse diffusion from the matrix into the macropores…).
As a curiosity, do you have any idea about why HYDRUS model is able to reproduce site 23 and not site 31?

MINOR COMMENTS:

Please revise carefully the notation, there are still some typos that I had already pointed out in my first revision, e.g:
- In Eq. 2, 3, 4: please use consistent notation for the times sign with the rest of the manuscript
- Eq. 3: is dz = 𝑑𝑧𝑝𝑓𝑑 ?
- Eq. 5: is 𝑑𝑚𝑎𝑐 = 𝐷𝑀 ?
- In the text the number of macropore is indicated both with nmac and 𝑛𝑚𝑎𝑐
- Table 1, 2, text: please write consistently f big or fbig
- Eq. 6: It would not be preferable to write d𝑞𝑚𝑖𝑥 consistently with 𝑑𝑧𝑝𝑓𝑑 instead of 𝑞𝑚𝑖𝑥?
- Eq. 7: is rM = 2 𝐷𝑀 ?
- Fig. 4: Please use consistent notation in the axes i.e. use the dot and not the comma to separate decimal digits
- In my first review, I asked you to highlight the differences/similarities of your model with previous double-continuum models, your replied that “ This similarity arises from the fact that both the LAST-Model and double-domain models work with two different domains. But apart from that, the two domains of our model and these of the double-domain models have not much in common because we really established a separate, physically and geometrically described macropore domain with the particle-based Lagrangian approach to simulate water flow and solute transport. The other double-domain models rely on separated overlapping continua…” I would specify that there are already double domain models that do not rely on overlapping continua, but take into account physically and geometrically separate domains (e.g. Russian, et al. ( 2013) Water Resour. Res., 49, 8552– 8564, doi:10.1002/2013WR014255).

Considering the large number of parameters that characterise your model I would not introduce new parameters without pointing out which the independent ones are.

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ED: Publish subject to revisions (further review by editor and referees) (09 Aug 2019) by Alberto Guadagnini

AR by Alexander Sternagel on behalf of the Authors (04 Sep 2019) Author's response Manuscript

ED: Publish as is (22 Sep 2019) by Alberto Guadagnini

AR by Alexander Sternagel on behalf of the Authors (24 Sep 2019) Manuscript

Short summary

We present our hydrological LAST-Model to simulate preferential soil water flow and tracer transport in macroporous soils. It relies on a Lagrangian perspective of the movement of discrete water particles carrying tracer masses through the subsoil and is hence an alternative approach to common models. Sensitivity analyses reveal the physical validity of the model concept and evaluation tests show that LAST can depict well observed tracer mass profiles with fingerprints of preferential flow.