the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Soil-vegetation-water interactions controlling solute flow and transport in volcanic ash soils of the high Andes
- 1Departamento de Ingeniería Civil y Ambiental, Facultad de Ingeniería Civil y Ambiental, Escuela Politécnica Nacional, Quito, 170525, Ecuador
- 2Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, UCLouvain, Louvain-la-Neuve, 1348, Belgium
- 3Programa para el Manejo de Agua y Suelo (PROMAS), Facultad de Ingeniería Civil, Universidad de Cuenca, Cuenca, 010203, Ecuador
- 4Environmental Sciences, Earth and Life Institute, UCLouvain, Louvain-la-Neuve, 1348, Belgium
- 5Fondo para la Protección del Agua (FONAG), 170509, Quito, Ecuador
- 6Empresa Pública Metropolitana de Agua Potable y Saneamiento (EPMAPS), Quito, 170519, Ecuador
- 1Departamento de Ingeniería Civil y Ambiental, Facultad de Ingeniería Civil y Ambiental, Escuela Politécnica Nacional, Quito, 170525, Ecuador
- 2Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, UCLouvain, Louvain-la-Neuve, 1348, Belgium
- 3Programa para el Manejo de Agua y Suelo (PROMAS), Facultad de Ingeniería Civil, Universidad de Cuenca, Cuenca, 010203, Ecuador
- 4Environmental Sciences, Earth and Life Institute, UCLouvain, Louvain-la-Neuve, 1348, Belgium
- 5Fondo para la Protección del Agua (FONAG), 170509, Quito, Ecuador
- 6Empresa Pública Metropolitana de Agua Potable y Saneamiento (EPMAPS), Quito, 170519, Ecuador
Abstract. Vegetation plays a key role in the hydrological and biogeochemical cycles. It can influence soil water fluxes and transport which are critical for chemical weathering and soil development. In this study, we investigated soil water balance and solute fluxes in two soil profiles with different vegetation types (cushion-forming plants vs. tussock grasses) by measuring soil water content, flux, and solute concentrations and by modeling soil hydrology. We also analyzed the role of soil water balance in soil chemical weathering. The influence of vegetation on soil water balance and solute fluxes is restricted to the A horizon. Evapotranspiration is 1.7 times higher and deep drainage is 3 times lower under cushion-forming plants than under tussock grass. Likewise, cushions transmit almost threefold less water from the A to lower horizons. This is attributed to the vertical distribution of soil properties associated with the root systems. Under cushion-forming plants, DOC and metals (Al, Fe) are mobilized in the A horizon. Solute fluxes that can be related to plant nutrient uptake (Mg, Ca, K) decline with depth as expected from bio-cycling of plant nutrients. Dissolved silica and bicarbonate are minimally influenced by vegetation and represent the largest contributions of solute fluxes. Soil chemical weathering is higher and constant with depth below tussock grasses; while lower and declining with depth under cushion-forming plants. This difference in soil weathering is attributed mainly to the water fluxes. Our findings reveal that vegetation can modify soil properties in the uppermost horizon altering the water balance, solute fluxes, and chemical weathering throughout the soil profile.
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Sebastián Páez-Bimos et al.
Status: final response (author comments only)
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RC1: 'Comment on hess-2022-294', Anonymous Referee #1, 22 Oct 2022
In general, I found the paper to be well written and the study well-designed and carried out.
I found – however – some points to be limited that needs to be addressed. First, the research gap was not clarified and the presented hypothesis was already addressed in other studies (see comments below). Some additional explanation on why the approach observation/modeling was used, would help the readers to capture the study design and idea early on in the work. I also found that the modeling was no explained with the necessary detail and should be accompanied by an uncertainty assessment.
Line 50 “the water balance”
L60: what about porosity and soil particle surface area?
The break from L62 to L64 is quite harsh.
L89 and 90: We already know that the hypothesis is true. It has been shown in numerous studies before. The paper would greatly benefit to make the research gap more clear and have the hypothesis and questions clearly linked to that. While the intro gives a good overview of what has been done, the research gap is only vaguely noted “Soil vegetation-water interactions are not fully understood”. After that, the authors summarize things that are known, and not what is wrong in our current status quo. Points that are made e.g. in L116, should be in the introduction. This applies in general for section 2. Points that are made related to the research gap need to move into the intro.
An explanation on the methodological choices would be helpful, which type of measurement supports which question and for what is the modelling needed?
L123-125: not needed/relevant
L215: what are the sensitive parameters? Do you enforce that the relation between ksat from one depth to the other is retained? What parameter ranges were used for the inverse simulation? Why? In general, 3.4. lacks the necessary details to reproduce or understand the simulation setup.
Fig. 3. I guess the horizontal grey bars indicate the boundaries of a horizon. Yet, this needs to be explained in the captions and not left for guessing. CU-UR and TU-UP should also be explained in the caption or written out to make the figure stand-alone from the text.
L309ff. Do the authors have any idea on the general variation of these soil properties beyond the two profiles? I am wondering if the difference is random or if this is really an effect/linked to the vegetation. I understand that the sampling is laborious, but I guess we all know sites where ksat does change by several orders of magnitude on very small spatial differences. Even though I agree that the A horizons of the sites seem to be quite different.
L327: What are the calibrated values and how do they differ between the profiles and to the measured values? What are the “sensitive paramters” (L.215).
L333: I would partly disagree. When you have a KGE of 0.08, you barely explain anything of the observed behavior. So what is the problem? What could be the problem? Preferential flow? Also, a full uncertainty analysis of the simulation should be added rather than 3 simulations in Figure 4. Furthermore, I am having a hard time to distinguish the different lines on the plot.
L521: Replace “The soil hydrology’ simulations” by “The simulation of the soil water balance”
L558: Can you estimate the residence time? Or the general difference between your sites?
L585ff. In this section, mostly literature is cited, however it would be more straightforward to argue from your observation rather than relying on a reference. Of course, other work can then be references.
- AC1: 'Reply on RC1', Sebastián Páez-Bimos, 19 Dec 2022
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CC1: 'Comment on hess-2022-294', Esther Geertsma, 07 Nov 2022
This review was prepared as part of graduate program course work at Wageningen University, and has been produced under supervision of Prof Jos van Dam. The review has been posted because of its good quality, and likely usefulness to the authors and editor. This review was not solicited by the journal.
The review is included in the supplement.
- AC3: 'Reply on CC1', Sebastián Páez-Bimos, 19 Dec 2022
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RC2: 'Comment on hess-2022-294', Anonymous Referee #2, 15 Nov 2022
This manuscript evaluates soil water and solute fluxes in two soil profiles under two different vegetation, i.e., the cushion-forming plants (CU- UR) and tussock grasses (TU-UP). This evaluation was based on measurements of soil water content, water flux density, and solute concentrations and the outputs from the well-known HYDRUS-1D model. These measurements and modeling allowed for evaluating the role of soil water balance on soil chemical weathering, which was one of the paper's main objectives.
Overall, the paper is well-written and suits the scope of HESS. Nevertheless, essential points must be included or further analyzed, especially in the methodology and discussion sections. These major points are described below, and a few minor considerations are described afterward.
In the introduction, the statement "we hypothesize that vegetation type has an impact on water and solute fluxes (...)'' does not suit well as a hypothesis since it has been well demonstrated, especially in the context of root water uptake modeling. Therefore, the hypothesis should be stated just as a particular case for these two vegetation types, not as an overall case.
There needs to be more information about how ETa and ETp were determined. Only lines 229-230 say that "ETa was derived from potential evapotranspiration (ETp) according to the surface pressure head and soil moisture'' and in the supplementary material 3 it is stated that "... ETp [was] based on the Penman-Monteith equation''. Notice that ETp from the Penman-Monteith method requires values of parameters such as crop canopy resistance and albedo. What were the values for each vegetation type? Furthermore, ETp is usually partitioned into potential transpiration and soil evaporation in hydrological modeling. Therefore, the authors should also shortly describe this and present the values of the parameters for each vegetation.
The methodology lacks information about root measurements, yet Figure 3 shows the vertical distribution of root diameter and abundance. Only the maximum rooting depth for each vegetation is given (lines 133--134). The authors also need to show how they determined the relative distribution of root length density over depth. How was it considered in the HYDRUS model? What about the transpiration reduction function? As far as I know, Hydrus-1D has two options for transpiration reduction functions: the Feddes and Jarvis model. I would like to know about values used for the empirical threshold parameters and if they can impact the simulation results.
At the beginning of section 5.1, the authors compare ETa from CU-UR and TU-UP and cite values from other studies(in the second paragraph) but do not explain why ETa from CU-UR is higher than ETa from TU-UP. This difference is enhanced in dry periods but is also not explained. This discussion is brought back only in the fourth paragraph. First, in my opinion, this discussion should be placed right after the first paragraph. Second, the authors show some evidence for the higher (lower) ETa from CU-UR (TU-UP) but need to address why this happens. For instance, the authors should explain why in 2A horizon under tussocks, which has about 50% of the roots (roughly looking at Figure 3f ), the highest soil moisture is observed, but annual ETa is well below ETp. Overall, the discussions are mainly based on soil water content, but when it comes to actual transpiration, one should look at the soil pressure head. Thus, the differences in soil hydraulic functions between soil layers and the two soil profiles need to be considered in the discussions. Papers related to root water uptake modeling might be useful to enhance these discussions.
The discussion about soil water flux needs further analysis (section 5.1, 494--506). The authors attribute the differences in vertical water fluxes and deep drainage to the vertical distribution of soil water storage. However, notice that soil water content distribution is also affected by water flux. Also, stating that "soil water storage capacity is limited by lower θT AW and KSAT'' is misleading since a high hydraulic conductivity promotes the reduction of soil water content in the soil layer. I think this discussion should be based on the soil hydraulic functions from each soil profile, considering the hydraulic conductivity and soil retention curve rather than on soil water content or soil water storage.
Minor comments:
1) l187. There is no Figure 2e.2) l218. The Kling-Gupta efficiency (KGE) may not be well known as the other measures for goodness-of-fit and may need some description and citation.
3) l228. What do you mean by surface pressure head?
4) l334--336. These relations are not clear to me. Can we see them in any table?
5) l410. Measured or simulated values in Table 3?
7) Fig 7. The line colors for each soil horizon are hard to recognize in the figure.
6) l494. ``There is approximately 3-fold less water flux transmitted from the A to the underlying horizons under cushion plants (Table 3, Fig. 7b)''. It does not match to what is shown in Table 3.
7) The Equation 1 from the supplementary material 3 must have the sink term for root water uptake.
- AC2: 'Reply on RC2', Sebastián Páez-Bimos, 19 Dec 2022
Sebastián Páez-Bimos et al.
Sebastián Páez-Bimos et al.
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