Enhancing Root Water Uptake and Mitigating Salinity through Ecological Water Conveyance: A Study of Tamarix ramosissima Ledeb. Using Hydrus-1D Modeling
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSpecific comments for Plants-3148957
•What is the main question addressed by the research?
This paper investigates the influence of ecological water conveyance (EWC) on the long-term dynamics of root-zone soil water content, salt levels, and root water uptake in arid regions, with a specific focus on the riparian plant Tamarix ramosissima in the lower reaches of the Tarim River, northwestern China.
• Do you consider the topic original or relevant to the field? Does it
address a specific gap in the field? Please also explain why this is/ is not
the case.
The research is original and relevant, as it explores the use of the Hydrus-1D model to assess the impacts of EWC on water and salt dynamics in the root zone, particularly focusing on the riparian plant Tamarix ramosissima. This study fills a critical gap in understanding how EWC can be optimized to support vegetation and mitigate desertification in arid inland river ecosystems. It provides valuable insights into the complex interactions between water management practices and ecological health in these environments.
• What does it add to the subject area compared with other published
material?
This research contributes by delivering a focused, model-driven analysis with practical, species-specific recommendations for refining EWC practices in arid environments. It fills key gaps in existing literature by offering detailed insights into how these practices can be optimized for improved ecological outcomes.
The scientific questions addressed in this paper are listed in lines 106-109. The specific contribution of this study could be clarified as well.
• What specific improvements should the authors consider regarding the
methodology? What further controls should be considered?
Broader Contextualization. While the study provides detailed insights into Tamarix ramosissima, it might benefit from a broader discussion on how these findings relate to other similar species or ecosystems. This could enhance the generalizability of the conclusions.
Consideration of Long-Term Effects. The study could further explore the long-term sustainability of the recommended EWC practices. For instance, discussing the potential for salt reaccumulation over multiple growing seasons and its management could add depth to the conclusions.
Expansion of Methodology Details. While the Hydrus-1D model is well-explained, the study could benefit from a more detailed discussion on the limitations of the model and how these might affect the results. This would provide a more balanced view of the study’s findings.
• Are the conclusions consistent with the evidence and arguments presented
and do they address the main question posed? Please also explain why this
is/is not the case.
Yes, the conclusions are consistent with the evidence and arguments presented and effectively address the main research question. The study demonstrates that the Hydrus-1D model accurately simulates soil-water-salt dynamics and shows how EWC influences Tamarix ramosissima's root water uptake under varying conditions of water and salt stress. The model's calibration and validation, supported by high KGE values, reinforce the reliability of these findings. The conclusions are well-aligned with the study's focus on optimizing root water uptake and managing soil salinity through EWC practices. The emphasis on timing EWC before the growing season, based on observed sensitivity to groundwater table fluctuations, directly addresses the research question.
• Are the references appropriate?
The references are appropriate. Including additional recent or interdisciplinary studies could further strengthen the foundation of the research.
• Suggestions for Future Research
Future research could expand beyond different plant species to varying environmental conditions. Integrating the Hydrus-1D model with climate models could help predict how climate change might influence soil-water-salt dynamics and root water uptake, offering a forward-looking perspective.
• Other comments
[1] In line 17, capitalize “W” in “water” and “C” in “conveyance”. In line 26, capitalize “D” in “depth”, “W” in “water” and “T” in “table”. Apply the same capitalization corrections for lines 52-53, 62, and 108.
[2] Consider outlining the structure of the paper in the introduction.
[3] In line 110, the title of Section 2 could be revised to "Data and Method."
Author Response
We greatly appreciate the time you have taken to review our manuscript, and we consider your comments as constructive suggestions that will significantly improve our work. As the reviewer suggested, we acknowledge that the study period is limited to just one year. We will therefore explore the long-term sustainability of the recommended EWC practices in future research. Below are our detailed responses to each of your comments.
Comment 1: In line 17, capitalize “W” in “water” and “C” in “conveyance”. In line 26, capitalize “D” in “depth”, “W” in “water” and “T” in “table”. Apply the same capitalization corrections for lines 52-53, 62, and 108.
Response 1: Thank you very much for your suggestions. We have made the recommended capitalization changes as suggested in lines 17, 26, 52-53, 62, and 108.
Comment 2: Consider outlining the structure of the paper in the introduction.
Response 2: Included this structured outline in the introduction. The added and modified content is as follows:
This study aims to investigate the impact of EWC on the long-term dynamics of root-zone soil water content, salt levels, and root water uptake of T. ramosissima in the lower reaches of the Tarim River, northwestern China. To address these objectives, we employed the Hydrus-1D model. The scientific questions addressed include: What is the effect of water and salt stress on root water uptake? How does the DWT affect root water uptake? Can EWC sustainably enhance root water uptake and support riparian vegetation in arid regions?
The paper is structured as follows: Section 2 describes our research methodology in detail, including data collection and analysis methods. The results of our research are presented in Section 3, followed by a discussion of the implications of these findings in Section 4. Finally, in Section 5, we conclude the paper by summarizing the key points and suggesting areas for future research.
Comment 3: In line 110, the title of Section 2 could be revised to "Data and Method."
Response 3: Changed the title of Section 2 to "Data and Methods".
Reviewer 2 Report
Comments and Suggestions for Authorsattached
Comments for author File: 
Comments.pdf
attached
Author Response
We sincerely value the time you have dedicated to reviewing our manuscript, and we view your feedback as valuable suggestions for enhancing our work. Below, you will find our comprehensive responses to each of your comments.
Comment 1: Describe and show in the Fig 1, how many locations the measurements for water content, salinity dynamics and root and plant growth were measured. If the measurements were done at one location, then probably Fig. 1 is not required.
Response 1: Thank you for your valuable suggestion. As the measurements were indeed carried out at a single location, we have followed your recommendation and removed Figure 1 from the manuscript.
Comment 2: It is not clear how authors have estimated hydraulic parameters such as η, α, elaborate. How authors measured EC in the soil cores (Fig. 2) and how the conversion equation for EC1:5 and ECe at L 210 and Eq 13 for osmotic pressure head derived?
Response 2: We have optimized and adjusted the empirical parameter α, n. (Lines: 326-327). To measure soil salinity, we used the soil diluted extract method with a soil/water ratio of 1/5 (EC1:5). (Lines: 132-133). We have reorganized the language to describe the relationship between EC1:5 and ECe, following the approach outlined by Slavich, P. G. and Petterson, G. H. (1993). (Lines: 208-213). The conversion of ECsw to osmolality pressure head is based on the relationship presented by the US Salinity Laboratory Staff (1954) for estimating the osmotic pressure of soil solutions using EC measurements. (Lines: 221-223).
Comment 3: How authors estimated ECsw of groundwater < 10 dS/m by capacitive water level probe? Did authors calibrate the probe as groundwater EC seems quite high? If groundwater EC is so high (81- 119 dS/m), then clarify why the salinity of the soil in the immediate vicinity of groundwater (Fig 2 and Fig. 4) is very low?
Response 3: We have carefully reviewed and made the necessary corrections to the measuring range of the CTD-Diver, which should now be stated as 0-120 ms/cm. (Lines: 150). Based on the information provided in Figure 1, the TDS value of the groundwater ranges from 22.23 to 27.66 dS·m−1. We have already taken corrective measures prior to conducting the test. Furthermore, Figure 2 illustrates that the EC value near the groundwater level reaches 20 ms/cm. On the other hand, Figure 4 indicates that the EC value of the lower soil is relatively low. This could be attributed to the fact that the depth of the soil is only 130cm, and there is still a certain distance from the groundwater level.
Comment 4: How authors estimated the values for different pressure head thresholds (h1 h4) applied in their model for Tamarix spp. and how he50 for salinity threshold was estimated, specify.
Response 4: The parameters of the Feddes model were obtained from Moayyad with Grinevskii and are as follows: h1 = -0.1 cm, h2 = -2 cm, h3-1 = -80 cm, h3-2 = -250 cm, and h4 = -15,000 cm. Additionally, the parameters of the S-shaped function developed by van Genuchten were fitted as follows, without taking water stress into consideration: hφ50 = 324.6cm and p = 3. (Lines: 262-264).
Comment 5: Describe the boundary conditions for water and salinity which were imposed at the bottom boundary of the modelling domain, also provide the domain depth. How much was the contribution of shallow groundwater in the root water uptake?
Response 5: The current simulation has not yet reached the depth of the shallow groundwater. In our future work, we plan to incorporate the influence of shallow groundwater into the model.
Comment 6: What does ‘eight tube-calibrated 5TE sensors mean (L141), describe how authors calibrated moisture sensors for water and salinity dynamics in the soil profile.
Response 6: Modified ‘eight tube-calibrated 5TE sensors’ to ‘eight 5TE sensors’ (Lines: 144).
Comment 7: Calibration and validation usually performed over complete growing seasons, provide details for the calibration and validation procedure adopted (Fig 4).
Response 7: Added and modified content in “2.3.5. Model calibration and validation” (Lines: 249-269). The added and modified content is as follows:
The HYDRUS-1D model was calibrated based on the site-specific boundary condi-tions, volumetric soil water content (θ) and electrical conductivity of soil solution (ECsw), measured from the soil profiles in the observation plots. The calibration period spanned from May 1 to August 1, 2021, while the verification period extended from August 1 to November 1, 2021, covering the entire plant growing season. Saturated water content (θs) and hydraulic conductivity (Ks) were calculated from these soil cores,. The remaining van Genuchten-Mualem parameters were derived using Rosetta pedotransfer functions ap-plied to particle size distribution and bulk density datasets [29]. The dispersivity (λ) was adjusted to an average value of 8.7 based on the properties of 76 silt loam soils, as noted by Vanderborght and Vereecken [30]. For the aquifer, dispersivity was set at 125 cm, consid-ering its material characteristics, thickness, and hydraulic conductivity. The Feddes model parameters, taken from Moayyad and Grinevskii [31;32], were set as follows: h1 = -0.1 cm, h2 = -2 cm, h3-1 = -80 cm, h3-2 = -250 cm, and h4 = -15,000 cm. The S-shaped function param-eters by van Genuchten were fitted without considering water stress, resulting in hφ50 = 324.6cm and p = 3. Root distribution was specified according to measured root dry weight distribution along the soil profile.
The inverse parameter estimation in Hydrus-1D utilized a gradient-based, local op-timization strategy based on the Marquardt–Levenberg method [33]. The model’s valida-tion employed data from the 2021 growing season. Consistency between the predicted and observed data was assessed using the Kling–Gupta Efficiency index (KGE)
Comment 8: L226-228, describe how you adjusted the generic crop coefficients (FAO-56) for site specific conditions.
Response 8: The crop coefficient was determined based on the fraction of ground cover and the height of T. ramosissima. According to the FAO56 recommendations, the crop coefficient for the middle season is 1.05. It increases linearly from 0.55 to 1.05 during the first 10 days of development and decreases linearly from 1.05 to 0.55 during the last seven days of defoliation (Lines: 232-237).
Comment 9: L294, what does germination mean here, did you plant new Tamarix shrub?
Response 9: The previous statement was inaccurate, it should be the process of Tamarix plants greening up in spring (Lines: 333).
Comment 10: I am not sure whether Tamarix is an irrigated annual species or perennial shrub? Authors should justify what is the economic implications for applying 500- 600 mm water as irrigation (L 354-355) to Tamarix in a water starved arid region?
Response 10: Tamarix is a perennial shrub. The simulated optimal water amount for survival is 500-600 mm, but it does not mean that this amount of water is fixed for the plant. Ecological water conveyance is aimed at alleviating the ecological problems caused by the interruption of river flow.
Comment 11: Define ecological water conveyance, how it will help afforestation with Tamarix within the riparian zone possessing shallow water table conditions.
Response 11: Ecological water conveyance refers to the process of transferring water to specific areas in a way that mimics natural water flow, in order to support the ecological balance and sustainability of the environment. In the context of the Tarim River in Xinjiang, China, ecological water conveyance aims to address the ecological issues caused by the reduction of natural water flow in the river.
In the riparian zone with shallow water table conditions, ecological water conveyance can help afforestation with Tamarix by providing the necessary water for the plants to thrive. Ecological water conveyance can ensure that the Tamarix plants receive the appropriate amount of water to support their growth and survival in the riparian zone. This process can help restore and maintain the ecological balance of the area, promoting the growth of Tamarix and other vegetation within the riparian zone.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsMy comments and suggestions have been appropriately addressed by the authors and necessary changes have been made in the revised manuscript.
