the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Jan 2022
Investigating the effects of herbaceous root types on the soil detachment process at the species level
Abstract. The changes in soil properties and root traits caused by plant growth might have great effects on the process of soil detachment by overland flow. On this basis, two typical herbaceous plants, Bothriochloa ischcemum (Linn.). Keng (BI; fibrous root system) and Artemisia vestita Wall. ex Bess (AG; tap root system), from the Loess Plateau were studied for one year under six planted densities of 5 plants m−2, 10 plants m−2, 15 plants m−2, 20 plants m−2, 25 plants m−2, and 30 plants m−2 to determine how the soil detachment rate responds to soil properties and plant root traits. In total, 24 steel tanks were planted, and two plots were used as bare soil controls. Their soil detachment rates were tested under a constant overland flow (1.5 l s−1) on a 26.2 % slope. The results showed that the soil detachment rate under the six planted densities ranged from 0.034 kg m2 s−1 to 0.112 kg m2 s−1 for BI and was ranged from 0.053 m2 s−1 to 0.132 m2 s−1 for AG, which all greatly reduced soil detachment rate and were 68.17 % to 92.33 % and 69.20 % to 87.27 % less than that of the control. In general, BI was more effective in reducing the soil detachment rate than AG, achieving a mean soil detachment rate that was 23.75 % lower. With increasing plant density, the soil detachment rate decreased as a power function (R2 = 0.23, p < 0.01). The overland flow hydraulic characteristics, soil properties and root traits influenced by plant density were positively or negatively correlated with the soil detachment rate. Specifically, the soil detachment rate decreased with velocity, bulk density, root length density, and increased with shear stress and the Darcy–Weisbach friction factor as power or exponential functions (R2 ranged from 0.16 to 0.54, p < 0.01). On this basis, the soil detachment rate (Dr) can be satisfactorily estimated by the overland flow velocity (v), soil bulk density (BD) and root length density (RLD) as a power function (Dr = 5.636v0.118 × BD−19.917 × RLD−0.170; R2 = 0.58; NSE = 0.78; p < 0.01).
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RC1: 'Comment on hess-2022-30', Anonymous Referee #1, 17 Feb 2022
This paper presents a laboratory scouring experiment to study the effects of two herbaceous on the soil detachment process. The experimental design is reasonable, but the results shown in the manuscript are not convincing in my view.
Major issue:
- The fitting results in Fig.3, Fig4. and Fig. 6 are not good (with low R2). I very much doubt the applicability of the equations shown in Fig.3, Fig4. and Fig. 6. So, as I stated above, the results shown in the manuscript are not convincing.
- According to the title of this manuscript, it aims to compare the differences between BI and AG in affecting the soil detachment process. However, in Fig.3-6, the results of BI and AG were fitted using the same equation which I think is unreasonable. To be specific, if the effects of two herbaceous on the soil detachment process are different and worthy to study, the relationships in Fig.3-6 should be different between BI and AG. It is easy to see from Fig.4, for example, the distribution characteristics of the result points between BI and AG are very different, which I think is a reason for the poor fitting results.
- In this scouring experiment, the value of overland flow is constant (1.5 L s-1). So, the scientific significance of this paper is very limited. To my knowledge, the overland flow should have significant effects on soil detachment. In the present manuscript, all the results are derived under a constant overland flow; and if the results are applicative under other overland flows or not? I doubt it! So, Eq. 10 may be correct only under the specific experimental conditions of this manuscript.
- In Fig. 7, the predicted soil detachment rate and the measured soil detachment rate are compared. What are the data of measured soil detachment rate? Are they derived from other experiments or just the results of the present experiment? If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.
Moderate issue:
- According to the manuscript, I recognize that repeated experiments are designed. However, the results of the repeated experiments are not shown in the manuscript. At least, the average values and the standard deviation of the repeated experiments should be described. Because the deviations of the repeated experiments have significant effects on the results shown in Table 1. If the deviations of the repeated experiments are very large, the comparing results between the BI and AG would be questionable; i.e. we would be not sure that the differences between BI and AG result from the species’ difference or the experimental error.
- In the Materials and methods section, there are not any figures describing the experimental conditions and treatment design. This makes readers difficult to have a clear understanding of your experiments.
- In the present manuscript, many equations have been used. The authors must add the corresponding references to the manuscript.
Citation: https://doi.org/10.5194/hess-2022-30-RC1 -
AC2: 'Reply on RC1', JianFang Wang, 21 Mar 2022
The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2022-30/hess-2022-30-AC2-supplement.pdf
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AC3: 'Reply on AC1', JianFang Wang, 22 Mar 2022
We really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you have noted. The response was given the supplement
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RC3: 'Reply on AC3', Anonymous Referee #1, 23 Mar 2022
Many thanks for your responses for my comments. Although you have carried out a one year's experiment, the data are not nearly enough to support your research objectives (Investigating the effects of herbaceous root types on the soil detachment process at the species level). Also, your current responses are reasonable but cannot improve the manuscript's scientific significance. For example, the results shown in the Fig.7 are your main research results; however, as I stated in the Major issue 4 "If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.", your response for the comment tells me that Eq. 10 is not validated.
I am very sorry for giving you some disappointing comments. However, I really suggest you to further improve the manuscript.
Citation: https://doi.org/10.5194/hess-2022-30-RC3 -
CC1: 'Reply on RC3', Bing Wang, 23 Mar 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that the model should be tested with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of the root system on the soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density, and root system affect the soil detachment process. We thought that this basic field experimental study is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties, and root types. The method stepwise was used to fit the effects of these factors on soil detachment. On one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties, and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. Eq.10 might be used in this area. For another region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with other independent data in future studies and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of the plant root systems on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attention to this. However, some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also be affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in a relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of the herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root systems on soil detachment at the species level.
All in all, studies about the effectiveness of the plant root system in reducing soil erosion at the species level were still needed, which would have great advantages for clarifying the effects of the plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking not to be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-CC1 -
CC2: 'Reply on RC3', Bing Wang, 23 Mar 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that the model should be tested with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of the root system on the soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density, and root system affect the soil detachment process. We thought that this basic field experimental study is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties, and root types. The method stepwise was used to fit the effects of these factors on soil detachment. On one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties, and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. Eq.10 might be used in this area. For another region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with other independent data in future studies and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of the plant root systems on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attention to this. However, some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also be affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in a relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of the herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root systems on soil detachment at the species level.
All in all, studies about the effectiveness of the plant root system in reducing soil erosion at the species level were still needed, which would have great advantages for clarifying the effects of the plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking not to be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-CC2 -
AC7: 'Reply on RC3', JianFang Wang, 11 Apr 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that for the model it should be test with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of root system on soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density and root system affect the soil detachment process. We thought that this basical field experimental studies is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties and root types. The method of stepwise was used to fit the effects of these factors on soil detachment. For one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. The Eq.10 might be used in this area. For other region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with another independent data in future study and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of plant root system on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attentions about this. Although some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level.
All in all, studies about the effectiveness of plant root system in reducing soil erosion at species level was still needed, which would have great advantages for clarifying the effects of plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking to not be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-AC7
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CC1: 'Reply on RC3', Bing Wang, 23 Mar 2022
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RC3: 'Reply on AC3', Anonymous Referee #1, 23 Mar 2022
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AC3: 'Reply on AC1', JianFang Wang, 22 Mar 2022
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AC6: 'Reply on RC1', JianFang Wang, 11 Apr 2022
Thank you for your valuable comments on this manuscript. We have carefully revised our paper followed by your comments.
This paper presents a laboratory scouring experiment to study the effects of two herbaceous on the soil detachment process. The experimental design is reasonable, but the results shown in the manuscript are not convincing in my view.
Major issue:
1.The fitting results in Fig.3, Fig4. and Fig. 6 are not good (with low R2). I very much doubt the applicability of the equations shown in Fig.3, Fig4. and Fig. 6. So, as I stated above, the results shown in the manuscript are not convincing.
Response:
The fitting results in Fig.3, Fig.4 and Fig. 6 showed low R2. This mainly because independent variables used in these figures would all affect the soil detachment process. When all these factors considered, the R2 was 0.58 (Eq.[10]). So, when we use one of these factors, the R2 is low.
Before we do this job, the correlation analysis was used to detect the relationship between these factors and soil detachment rate. We think that high correlation coefficient might be have a strong effect on soil detachment, and their effects on soil detachment might also be expressed as functions. After all, quantitative relationships are more intuitive than correlation coefficients. Finally, when we simultaneously considered the root traits, soil properties and hydraulic parameters, the performance seems satisfactory with a relatively high R2.
2.According to the title of this manuscript, it aims to compare the differences between BI and AG in affecting the soil detachment process. However, in Fig.3-6, the results of BI and AG were fitted using the same equation which I think is unreasonable. To be specific, if the effects of two herbaceous on the soil detachment process are different and worthy to study, the relationships in Fig.3-6 should be different between BI and AG. It is easy to see from Fig.4, for example, the distribution characteristics of the result points between BI and AG are very different, which I think is a reason for the poor fitting results.
Response:
Your suggestion is right. At first, we also want to separate these differences that caused by two different herbaceous plants, while the performance was not very good. The reason why we did not do that is the following reason. For fig.3 (now is the fig.4), plant density is the experiment treatment and it is the same for both two herbaceous plants. For the fig.4 (now is the fig.5), the variation of hydraulic parameters was mainly due to the soil surface. The aboveground part of plants was cut and the overland flow was used to detect the soil detachment rate. In this way, the impact of species in soil detachment may not be very strong. For the fig.5 (now is the fig.6), soil property such as bulk density would be varied after the vegetation growth. But the difference of bulk density between these two herbaceous plants might be slight. Overall, these two herbs only grew for one year. For the fig.6 (now is the fig.7), we put the data of the two herbs together mainly because there is a prior knowledge, that is the root length density would represent the difference between root types. Many previous studies generally use the root biomass to built the relationship between soil erosion rate and root traits. Some studies believe that the root biomass would not well reflect the effects of root type on soil erosion, and the root length density or the root surface area density are suggested and the effects of root type on soil erosion would be included. As reported by De Beats et al. (2007), Knapen et al., (2007), and Wang et al. (2021). the root length density or root surface area density would generally be used to represent root morphological differences induced by root type between herbs.
Although some studies sample the undisturbed soil from nature grassland. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, when we use the large tank to plant herbs, the data would be limited, so we put all the data together to promote the effectivity of the data. Your suggestion is very important for our future research, and we will do our best to increase the amount of data in future study.
3.In this scouring experiment, the value of overland flow is constant (1.5 L s-1). So, the scientific significance of this paper is very limited. To my knowledge, the overland flow should have significant effects on soil detachment. In the present manuscript, all the results are derived under a constant overland flow; and if the results are applicative under other overland flows or not? I doubt it! So, Eq. 10 may be correct only under the specific experimental conditions of this manuscript.
Response:
In previous studies, their soil sample were collected under nature grassland, and they would give five or six condition of overland flow, for the soil sample was relatively easy to collect. As mentioned above, the disadvantages are also obvious. For the given overland flow condition that reported by previous study, the variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the hydraulic parameters were test in the sample area. Although only one condition of overland flow was given in this study, but there are six plant density and two herbaceous plants, which means twelve conditions of overland flow were used in this study. Besides, for the hydraulic parameters that used in the Eq.[10] was not a constant, it’s twelve.
Based on above mentioned, we emphasized in the article that we measured the hydraulic parameters of the scouring zone, and this part was revised as: “The flow velocity of scouring zone and water temperature were measured every 5 s”.(Line 218 and Line 219).
4.In Fig. 7, the predicted soil detachment rate and the measured soil detachment rate are compared. What are the data of measured soil detachment rate? Are they derived from other experiments or just the results of the present experiment? If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.
Response:
Yes, we use the measured data to build the Eq.10. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties and root types. The method of stepwise was used to fit the effects of these factors on soil detachment. For one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties and root types on soil detachment. You are right, the performance of Eq.10 showed in fig.7 was only applied to this study.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. The Eq.10 might be used in this area. For other region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with another independent data in future study and make the equation more widely applicable.
Moderate issue:
5.According to the manuscript, I recognize that repeated experiments are designed. However, the results of the repeated experiments are not shown in the manuscript. At least, the average values and the standard deviation of the repeated experiments should be described. Because the deviations of the repeated experiments have significant effects on the results shown in Table 1. If the deviations of the repeated experiments are very large, the comparing results between the BI and AG would be questionable; i.e. we would be not sure that the differences between BI and AG result from the species’ difference or the experimental error.
Response: Done as suggested.
Our experiments were indeed repeated experiment. According to your suggestion, we have increased the standard deviation of soil properties, such as bulk density, cohesion, water stable aggregates, soil organic matter and soil erodibility in table 1. We also added the standard deviation of velocity, shear stress and Darcy-weisbach friction factor in table 3.
6.In the Materials and methods section, there are not any figures describing the experimental conditions and treatment design. This makes readers difficult to have a clear understanding of your experiments.
Response: Done as suggested
We realized that the schematic diagram describing the experimental conditions and treatment design could clearly show the experimental process. This makes readers easy to have a clear understanding of our experiments. Following your suggestion, we added the schematic diagram of the experimental treatment in the materials and methods of the manuscript (Fig.1).
7.In the present manuscript, many equations have been used. The authors must add the corresponding references to the manuscript.
Response: Done as suggested.
We previously considered Eq.[1] to [9] to be the most commonly used calculation formulas, so we did not add references. As you mentioned, references for these equation were important, and the corresponding references of eq.[1] to [9] were added in manuscript. (Line 227 to Line 267).
Citation: https://doi.org/10.5194/hess-2022-30-AC6
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RC2: 'Comment on hess-2022-30', Anonymous Referee #2, 03 Mar 2022
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to built your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Moderate concern:
In mat/met section, any of the soil properties is referenced (line 239-249).
Please, define the meaning of “S” type sampling (line 239).
Number of plots should be 26, including the control-bare.
In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Many equations are used but any of them is referenced, please, equations should be referenced.
English language-grammar must be deeply revised.
Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Citation: https://doi.org/10.5194/hess-2022-30-RC2 -
AC1: 'Reply on RC2', JianFang Wang, 21 Mar 2022
We really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you have noted. The response part was listed in the supplement.
- AC4: 'Reply on AC2', JianFang Wang, 22 Mar 2022
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AC5: 'Reply on RC2', JianFang Wang, 23 Mar 2022
Thank you for your comments and detailed revision. We have revised the manuscript according to your suggestion.
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
1.As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
Response:
Yes, for some studies, the counts of plant species are four or six. The “Grain for Green” project has been implemented for 20 years. For the abandoned farmland, and the vegetation has succeeded to a stable period. In this stage, Bothriochloa ischcemum (Linn.). Keng (BI) and Artemisia vestita Wall. ex. Bess (AG) are the dominant herbaceous species. That’s the reason that we selected these two herbs.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, the runoff and sediment were collected in every 5 seconds, and repeated for 15 times in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession. These two herbaceous plants is the main community in study area.
2.I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to build your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Response:
Based on the statistical results, we compare the difference of soil properties under six plant densities. It was showed that soil organic matter decreased with plant density for both two herbs, and the soil erodibility of BI decreased with plant density. For other soil properties, the variation of them with plant density was not very clear.
Following your suggestion, we try to build treatments based on ranges of 5-10, 15-20, 25-30 plant m-2. Then we found that maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil erodibility of AG was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.
Also, we revised this part in the paper as following: “In particular, maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil organic matter content increased with increasing plant density. The soil erodibility of BI decreased with plant density. While for AG, it was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.” (Line 280 to Line 284)
Moderate concern:
3.In mat/met section, any of the soil properties is referenced (line 239-249).
Response: Done as suggested.
The soil properties of bulk density, cohesion, water stable aggregate, organic matter and soil erodibilty were measured by normal methods. The references which measured methods of soil properties were added in the materials and methods (Line 239 to Line 249).
4.Please, define the meaning of “S” type sampling (line 239).
Response: Done as suggested.
“S’’ type sampling refers to taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S, and the soil sample would well represent the soil properties of this slope. This part was revised as: “the soil properties were measured by taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S” (Line 240 and Line 241).
5.Number of plots should be 26, including the control-bare.
Response:
You are right. The total number of plots were 26 including the control-bare. Among these, twenty-four plots were used for planting under six plant density and two herbaceous plants. This part was revised as “In total, twenty-six steel tanks were used, and including two control-bare” (Line 178 and Line 179).
6.In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
Response: Done as suggested.
Before analyzing and quantifying relationships between the soil detachment rate and hydraulic parameters, soil properties, and root traits, the normal distribution of these indexes was test by using the method the one-sample nonparametric tests. The statistical analyses part was also revised (Line 271 and Line 272)
7.From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Response:
Yes, soil moisture has great effects on soil erosion process, which would be correlated to the initial runoff time and soil erosion rate. For the effects of driving force on soil erosion process, rainfall and overland flow is commonly used. Many studies consider the overland flow as a sub-process of the rainfall, and the soil moisture close to the saturated water content when the rill erosion occurs. Hence, they allow the soil sample to fully absorb water (capillary water) and to simulate the effects of overland flow on soil detachment during the rill erosion process. As a result, the effects of soil moisture on soil detachment is eliminated (Zhang et al., 2003; Wang et al., 2018). In our study, we also to sprinkle water several times for each soil tank until the soil moisture saturated before scouring test. So, in our study, soil moisture would be not affected the soil detachment process.
8.Many equations are used but any of them is referenced, please, equations should be referenced.
Response: Done as suggested.
After much consideration, we think that references should be added. Therefore, the corresponding references of eq.[1] to [9] were added in manuscript (Line 227 to Line 267).
9.English language-grammar must be deeply revised.
Response: Done as suggested.
Before we submit the paper, the full text was revised by a American native speaker provided by the website of Elsevier. This time, the paper was checked by a researcher who worked in the US for almost thirty years.
10.Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Response: Done as suggested.
All units were checked and revised. The sentences “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG” was revised as “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 kg m2 s-1 to 0.132 kg m2 s-1 for AG” (Line 25).
Citation: https://doi.org/10.5194/hess-2022-30-AC5 -
AC8: 'Reply on RC2', JianFang Wang, 11 Apr 2022
Thank you for your comments and detailed revision. We have revised the manuscript according to your suggestion.
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
1.As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
Response:
Yes, for some studies, the counts of plant species are four or six. The “Grain for Green” project has been implemented for 20 years. For the abandoned farmland, and the vegetation has succeeded to a stable period. In this stage, Bothriochloa ischcemum (Linn.). Keng (BI) and Artemisia vestita Wall. ex. Bess (AG) are the dominant herbaceous species. That’s the reason that we selected these two herbs.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, the runoff and sediment were collected in every 5 seconds, and repeated for 15 times in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession. These two herbaceous plants is the main community in study area.
2.I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to build your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Response:
Based on the statistical results, we compare the difference of soil properties under six plant densities. It was showed that soil organic matter decreased with plant density for both two herbs, and the soil erodibility of BI decreased with plant density. For other soil properties, the variation of them with plant density was not very clear.
Following your suggestion, we try to build treatments based on ranges of 5-10, 15-20, 25-30 plant m-2. Then we found that maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil erodibility of AG was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.
Also, we revised this part in the paper as following: “In particular, maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil organic matter content increased with increasing plant density. The soil erodibility of BI decreased with plant density. While for AG, it was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.” (Line 280 to Line 284)
Moderate concern:
3.In mat/met section, any of the soil properties is referenced (line 239-249).
Response: Done as suggested.
The soil properties of bulk density, cohesion, water stable aggregate, organic matter and soil erodibilty were measured by normal methods. The references which measured methods of soil properties were added in the materials and methods (Line 239 to Line 249).
4.Please, define the meaning of “S” type sampling (line 239).
Response: Done as suggested.
“S’’ type sampling refers to taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S, and the soil sample would well represent the soil properties of this slope. This part was revised as: “the soil properties were measured by taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S” (Line 240 and Line 241).
5.Number of plots should be 26, including the control-bare.
Response:
You are right. The total number of plots were 26 including the control-bare. Among these, twenty-four plots were used for planting under six plant density and two herbaceous plants. This part was revised as “In total, twenty-six steel tanks were used, and including two control-bare” (Line 178 and Line 179).
6.In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
Response: Done as suggested.
Before analyzing and quantifying relationships between the soil detachment rate and hydraulic parameters, soil properties, and root traits, the normal distribution of these indexes was test by using the method the one-sample nonparametric tests. The statistical analyses part was also revised (Line 271 and Line 272)
7.From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Response:
Yes, soil moisture has great effects on soil erosion process, which would be correlated to the initial runoff time and soil erosion rate. For the effects of driving force on soil erosion process, rainfall and overland flow is commonly used. Many studies consider the overland flow as a sub-process of the rainfall, and the soil moisture close to the saturated water content when the rill erosion occurs. Hence, they allow the soil sample to fully absorb water (capillary water) and to simulate the effects of overland flow on soil detachment during the rill erosion process. As a result, the effects of soil moisture on soil detachment is eliminated (Zhang et al., 2003; Wang et al., 2018). In our study, we also to sprinkle water several times for each soil tank until the soil moisture saturated before scouring test. So, in our study, soil moisture would be not affected the soil detachment process.
8.Many equations are used but any of them is referenced, please, equations should be referenced.
Response: Done as suggested.
After much consideration, we think that references should be added. Therefore, the corresponding references of eq.[1] to [9] were added in manuscript (Line 227 to Line 267).
9.English language-grammar must be deeply revised.
Response: Done as suggested.
Before we submit the paper, the full text was revised by a American native speaker provided by the website of Elsevier. This time, the paper was checked by a researcher who worked in the US for almost thirty years.
10.Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Response: Done as suggested.
All units were checked and revised. The sentences “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG” was revised as “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 kg m2 s-1 to 0.132 kg m2 s-1 for AG” (Line 25).
Citation: https://doi.org/10.5194/hess-2022-30-AC8
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AC1: 'Reply on RC2', JianFang Wang, 21 Mar 2022
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EC1: 'Comment on hess-2022-30', Carla Ferreira, 24 Mar 2022
Dear Prof. Yan-Fen Yang,
Thanks for submitting your manuscript to this SI. Understanding the impact of different herbaceous plants and plant densities on soil erosion by overland flow is relevant for the scientific community and stakeholders. However, major revisions should be performed before considering the possible publication of your manuscript. Please, consider the comments from both reviewers to improve your manuscript. Additionally, consider the following comments:
Specific comments:
The Introduction section is quite long and should be shortened.
In the Methodology section:
L200: why are you presenting accumulated temperature? (what is its meaning for the herbaceous species?).
L204: why the selection of this slope? Is it representative of the Loess Plateau?
L205: for how long were the tanks scoured?
L239: please, describe the sampling procedure
L221: not clear how the soil sampling did not disturb the overland flow and sediment measurements
L223: please, better explain the pretest performed
L224: so, only one experiment of 75 s was performed for each tank?
Section 2.3: it is not clear how long the overland flow and sediment measurements took
Section 2.5: why only analyzing the correlations between all variables? What about differences between experiments with the two plants? What about differences with the different plant densities?
Section 3: the results of the correlation between variables should be indicated, and not only the level of significance. From the conclusions we can see that the correlations are rather low (mostly <0.5), although statistically significant. Thus, considering the very limited number of replications the correlations may be questionable.
Section 4: the limitations of the study must be clearly indicated and discussed
Section 4.3: it would be interesting to compare your results with results from similar studies with other herbaceous plants
Section 5: the findings are not new. A better link with the two types of plants can be more useful. Please, clearly identify the main findings/novelty of this study and the practical/real implications of this study.
Fig. 1: please, improve the legend to better describe the data shown, including the lines and dots
Fig. 2: please, improve the legend to better describe the meaning of the letters
Figs. 3 to 6: it may be interesting to draw different power functions for both plant types
Table 1 and 3: you may include the results of statistical differences between both plant type experiments in this table
Citation: https://doi.org/10.5194/hess-2022-30-EC1 -
AC9: 'Reply on EC1', JianFang Wang, 18 Apr 2022
Dear editor
Thank you for inviting us to submit a revised draft of our manuscript entitled “Investigating the effects of herbaceous root types on the soil detachment process at the species level” to Hydrology and Earth System Sciences. We really appreciate the time and effort you and each of the reviewers have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you and the reviewers have noted. The revised part was marked in blue font in the manuscript. The following is a point-by-point response to the questions and comments.
Specific comments:
The Introduction section is quite long and should be shortened.
Response
Done as suggested. After careful consideration, we shortened the introduction and simplified the sentences that were too tedious. The total number of words were decreased from 1,643 to 1,402. This part was revised in the manuscript.
In the Methodology section:
L200: why are you presenting accumulated temperature? (what is its meaning for the herbaceous species?).
Response
The plant growth and development have a lower limit temperature, and it was called the biological starting point temperature. When the temperature is above the lower limit, plants would grow and develop, generally considered to be 10℃. Therefore, cumulative temperature greater than 10℃ was used to represent the effect of temperature on vegetation growth and development in the study area, which is more biologically significant than the traditional average temperature.
L204: why the selection of this slope? Is it representative of the Loess Plateau?
Response
Yes, the slope is representative of the Loess Plateau. Two decades years ago, most of the sloping farmland on the Loess Plateau was 15°, which resulted in serious soil erosion. To control soil erosion, the “Grain for Green” project was implemented and vegetation began to succeed naturally. The sloping farmland is converted into grassland, which becomes the dominant ecosystem in this region. Therefore, the slope of 15° was selected in this study.
L205: for how long were the tanks scoured?
Response:
The scouring time for this study was 75 s. Here are some following reasons:
Soil erosion generally including sheet erosion, rill erosion, and gully erosion based on the soil erosion type. For sheet erosion, there is a small amount of erosion and mainly caused by the rainfall. For gully erosion, the amount of erosion is usually large and gravity erosion often occurs, which beyond the traditional erosion process. Among these two erosion types, rill erosion generally is a transitional state in which sheet erosion develops to gully erosion. If corresponding preventive measures are taken at this stage, the type of soil erosion can be prevented from developing to serious gully erosion, so that soil erosion can be effectively controlled.
During the rill erosion process, the soil detachment mainly attributes to the overland flow. For this study, the rill net was well developed and the rill outline was obvious when the tank was scoured for almost 75 s. Meanwhile, the scouring depth was greater than 2 cm after the tank was scoured by overland flow for 75 s, which belongs to rill erosion based on the definition of the rill erosion. Based on the designed flow discharge in this study, long scouring time might result in gully erosion, which complicates the soil erosion process.
Besides, in most of the previous studies, their scouring depth was controlled at 2 cm and the corresponding scouring time was ranged from 3 to 180 s. Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. Therefore, the scouring time of 75 s was used for all the soil detachment rate tests.
L239: please, describe the sampling procedure
Response:
Done as suggested. The sampling procedure was revised as following:
“Each tank was left for five days to dry out and it would more suitable for sampling. Then the soil sample were collected in different location of the tank (upper, middle, and lower parts of the slope) to test the soil bulk density, cohesion, aggregation, and soil organic matter content. Specifically, the bulk density was measured using a steel ring 5 cm in height and 5 cm in diameter. Soil cohesion was determined using an Eijkelkamp pocket vane tester (14.10, Eijkelkamp Agrisearch Equipment, Giesbeek). Soil aggregation was measured via a series of sieves with bore diameters of 0.25 mm, 0.5 mm, 1 mm, 2 mm, and 5 mm, and the soil organic matter content was measured using potassium dichromate (Wang et al., 2018a). Except for the soil cohesion was replicated for nine times, all other soil properties were replicated for three times, respectively, and their mean values were represented the soil properties of this slope. The soil erodibility was calculated based on the soil organic matter content as (Sharpley and Williams., 1990):”(Line 254 to Line 266).
L221: not clear how the soil sampling did not disturb the overland flow and sediment measurements
Response
The sentence “To reduce the potential effects of soil sampling on experimental results, testing was generally stopped at a certain scouring depth of 2 cm” is mixed, we revised this part as following:
“When the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Considering the scouring time would affect the results of soil detachment calculating, the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. The scouring time of 75 s was then timed for all scouring tests.”(Line 233 to Line 237)
L223: please, better explain the pretest performed
Response
Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. In most of the previous studies, although their scouring depth was controlled at 2 cm, the corresponding scouring time was varied greatly and ranged from 3 to 180 s. In order to eliminate or reduce this effect as much as possible, the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. When the scouring time was 75s, the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Then its scouring time of 75 s was then timed for all scouring tests. We also added this information in the paper (Line 233 to 237).
L224: so, only one experiment of 75 s was performed for each tank?
Response
Yes, the test time for all the steel tank was finally set at 75 s.
Based on the designed flow discharge in this study, long scouring time might result in gully erosion, which the gravity erosion might be occurred and thus made the soil erosion process more complicate. During the rill erosion process, the soil detachment mainly attributes to the overland flow.
When the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. When the scouring time was 75 s, the outline of the rill net was obvious. Then the 75 s was applied all scouring tests.
Section 2.3: it is not clear how long the overland flow and sediment measurements took
Response
As mentioned above, based on the rill outline and rill net development, the designed flow discharge, and also the effects of scouring time on soil detachment rate calculation, the scouring time for all the steel tank was finally set at 75 s.
During the scouring time of 75 s, runoff and sediment samples were collected every 5 s. Meanwhile, the corresponding flow velocity and water temperature were also measured. Totally, 15 group data of runoff, sediment, flow velocity, and water temperature were tested for each steel tank.
Section 2.5: why only analyzing the correlations between all variables? What about differences between experiments with the two plants? What about differences with the different plant densities?
Response
Done as suggested. The differences with the herbaceous plant type and plant densities were analyzed. The following results and discussion section in this paper were also revised. Now this part was revised as following:
“The differences in soil detachment rate, hydraulic parameters, soil properties, and root traits among plant densities and two herbaceous plants were evaluated using the analysis of post hoc multiple comparisons (The Student–Newman–Keuls, significance level = 0.05). Two-way ANOVA was used to analysis the main effects of plant densities and herbaceous plant type, and their interaction effects on soil properties, root traits, hydraulic parameters, and soil detachment rates. Pearson's correlation analyses (p<0.05) were used to analyze relationships among hydraulic parameters, soil properties, root traits, and soil detachment. The qualified relationships between soil detachment rate and hydraulic parameters, soil properties, or root traits were fitted by using nonlinear regression. Stepwise regression was used to estimate soil detachment rate by hydraulic parameters, soil properties, and root traits. The coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) were used to evaluate model performance. All analyses were conducted using SPSS 22.0 and Origin 2018 software.”(Line 286 to Line 298)
Section 3: the results of the correlation between variables should be indicated, and not only the level of significance. From the conclusions we can see that the correlations are rather low (mostly <0.5), although statistically significant. Thus, considering the very limited number of replications the correlations may be questionable.
Response
Done as suggested. Based on the previous data analysis, the method of Two-way ANOVA was used to detect the influence of plant density, herbaceous plant type, and their interaction effects on soil properties, root traits, hydraulic parameters, and soil detachment rate. The corresponding parts of 3.1, 3.2, and 3.3 section were revised and marked.
Also, following the comments of reviewer, the effects of two herbaceous on the soil detachment process are different and worthy to study. We separated fitted these differences that caused by two different herbaceous plants. Besides, each plant density had two repetition tanks, each tank had 15 group data of runoff, sediment, flow velocity, and water temperature. While on the previous analysis, these data were averaged to one value. For this time, the averaged 15 group data were used and the fig.4, fig.5, fig.6, and fig.7 were revised.
In previous studies, their soil sample were collected under nature grassland, and they would give five or six condition of overland flow, for the soil sample was relatively easy to collect. However, the variation of overland flow is ignored when the flow through the scouring area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length in previous studies. In fact, the hydraulic parameters in the scouring area are closely related to soil erosion. In this study, the hydraulic parameters were test in the scouring area. Although only one condition of overland flow was given in this study, but there are six plant density and two herbaceous plants, which means twelve conditions of overland flow were used in this study.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, its variation during the scouring process was considered and 15 group data were collected in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession this time, for these two herbaceous plants is the main community in study area.
Section 4: the limitations of the study must be clearly indicated and discussed
Response
Done as suggested. Based on data analysis and discussion, the limitation of the study were clearly indicated and discussed in section 4. The corresponding parts of 4.1, 4.2, and 4.3 section were revised and marked.（Line 404 to Line 415, Line 421 to Line 427, Line 455 to Line 459, Line 531 to Line 544）
Section 4.3: it would be interesting to compare your results with results from similar studies with other herbaceous plants
Response
Done as suggested. We compare our results with results from similar studies with other herbaceous plants, and this part was revised as following:
“Previous studies showed that root traits of tree, shrubs, and herb would be used to quantify the effect of plant root system on soil erosion (Parhizkar et al., 2021). The soil detachment rate is insensitive to many of those root traits. When focusing the effects of root system on soil erosion at herbaceous species level, only root length density significantly decreased the soil detachment rate in this study. The quantified relationship between soil detachment rate and root length density were also compared with previous studies (Fig.8). For both planted herbaceous plants all with fibrous root system, BI in this study and ryegrass that reported by Mamo and Bubenzer (2001), the soil detachment rate of BI was almost one magnitude greater than that of ryegrass. The main reason is that the highly planted ryegrass density, which ranged from 4 to 7 plant per cylinders (diameter is 10 cm). Besides, the soil detachment rate was still much higher than that of natural grassland reported by Liu et al. (2019), due to the soil erosion resistance was enhanced by herbaceous plants after thirty-six years of growth. In general, the soil detachment rate of AG in this study was still much high than that of reported by Mamo and Bubenzer (2001) and Liu et al. (2019), showing a low efficiency of herbaceous plant with tap root system in reducing soil detachment. Although only the typical herbaceous plants were selected in this study, some useful results were drawn. Plant root generally scanned using specific software and the root diameter is a mean value for a certain length of root. As a result, the variation in root diameter narrowed. The huge difference in average root diameter among arboreal forest, shrubs, and grassland might cover up this issue. While at herbaceous species level, the difference in average root diameter among herbaceous plants is relatively small, and this problem is highlighted, resulting the effect of root diameter on soil erosion does not seem to be as good as literatures mentioned. Correspondingly, the effects of root surface area density and root volume ratio on soil detachment are also affected, which calculated by root diameter and root length. Determination of root length is not affected by scanning process, and detachment rate decreased with root length density as power functions. So, it may be more effective to study the effect of root diameter differences on soil erosion based on the root order or diameter class, and the root length density would take a priority when detecting the effects of plant root system on soil erosion at herbaceous species level.”(Line 514 to Line 544)
Section 5: the findings are not new. A better link with the two types of plants can be more useful. Please, clearly identify the main findings/novelty of this study and the practical/real implications of this study.
Response
Done as suggested. Our conclusion were rewrote from the perspective of the species level (BI and AG). We also added the main finding and the practical/real implications of this study. This part was revised as following:
“The herbaceous plant root system would significantly reduce the soil erosion and its effects also exhibited different behaviors according to herbaceous type. The soil detachment rate significantly decreased with increasing plant density for two herbaceous plants, becoming 85.80% and 81.19% lower than that of the control for the BI and AG grasslands, respectively. BI, which has a fibrous root system, effectively reduced the soil detachment rate, achieving a mean soil detachment rate that was 23.75% less than that of AG, which has a tap root system. The hydraulic characteristics of overland flow, soil properties, and root traits induced by plant density and herbaceous type closely related to the soil detachment, which could be estimated effectively using the overland flow velocity, soil bulk density, and root surface length density. The performance of the model developed in this study was satisfactory. Moreover, the response of soil detachment rate to root diameter does not seem to be as sensitive as mentioned in literatures. Meanwhile, the root order or diameter class was suggested, and the root length density was recommended to detect the effects of plant root system on soil erosion at herbaceous species level.”(Line 546 to Line 560)
Fig. 1: please, improve the legend to better describe the data shown, including the lines and dots
Response
Done as suggested. The legend was added, and the lines and dots was revised in Fig.1 (Now it is Fig.2).
Fig. 2: please, improve the legend to better describe the meaning of the letters
Response
Done as suggested. The meaning of the letters was presented in notes of Fig. 2 (Now it is Fig.3).
Figs. 3 to 6: it may be interesting to draw different power functions for both plant types
Response
Done as suggested. Different power functions for two plant types were drawn separately in Fig. 3 to Fig. 6 (Now it is Fig 4 to Fig.6).
Table 1 and 3: you may include the results of statistical differences between both plant type experiments in this table
Response
Done as suggested. Differences analysis was added in the Table 1 and Table 3.
Citation: https://doi.org/10.5194/hess-2022-30-AC9
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AC9: 'Reply on EC1', JianFang Wang, 18 Apr 2022
Status: closed
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RC1: 'Comment on hess-2022-30', Anonymous Referee #1, 17 Feb 2022
This paper presents a laboratory scouring experiment to study the effects of two herbaceous on the soil detachment process. The experimental design is reasonable, but the results shown in the manuscript are not convincing in my view.
Major issue:
- The fitting results in Fig.3, Fig4. and Fig. 6 are not good (with low R2). I very much doubt the applicability of the equations shown in Fig.3, Fig4. and Fig. 6. So, as I stated above, the results shown in the manuscript are not convincing.
- According to the title of this manuscript, it aims to compare the differences between BI and AG in affecting the soil detachment process. However, in Fig.3-6, the results of BI and AG were fitted using the same equation which I think is unreasonable. To be specific, if the effects of two herbaceous on the soil detachment process are different and worthy to study, the relationships in Fig.3-6 should be different between BI and AG. It is easy to see from Fig.4, for example, the distribution characteristics of the result points between BI and AG are very different, which I think is a reason for the poor fitting results.
- In this scouring experiment, the value of overland flow is constant (1.5 L s-1). So, the scientific significance of this paper is very limited. To my knowledge, the overland flow should have significant effects on soil detachment. In the present manuscript, all the results are derived under a constant overland flow; and if the results are applicative under other overland flows or not? I doubt it! So, Eq. 10 may be correct only under the specific experimental conditions of this manuscript.
- In Fig. 7, the predicted soil detachment rate and the measured soil detachment rate are compared. What are the data of measured soil detachment rate? Are they derived from other experiments or just the results of the present experiment? If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.
Moderate issue:
- According to the manuscript, I recognize that repeated experiments are designed. However, the results of the repeated experiments are not shown in the manuscript. At least, the average values and the standard deviation of the repeated experiments should be described. Because the deviations of the repeated experiments have significant effects on the results shown in Table 1. If the deviations of the repeated experiments are very large, the comparing results between the BI and AG would be questionable; i.e. we would be not sure that the differences between BI and AG result from the species’ difference or the experimental error.
- In the Materials and methods section, there are not any figures describing the experimental conditions and treatment design. This makes readers difficult to have a clear understanding of your experiments.
- In the present manuscript, many equations have been used. The authors must add the corresponding references to the manuscript.
Citation: https://doi.org/10.5194/hess-2022-30-RC1 -
AC2: 'Reply on RC1', JianFang Wang, 21 Mar 2022
The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2022-30/hess-2022-30-AC2-supplement.pdf
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AC3: 'Reply on AC1', JianFang Wang, 22 Mar 2022
We really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you have noted. The response was given the supplement
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RC3: 'Reply on AC3', Anonymous Referee #1, 23 Mar 2022
Many thanks for your responses for my comments. Although you have carried out a one year's experiment, the data are not nearly enough to support your research objectives (Investigating the effects of herbaceous root types on the soil detachment process at the species level). Also, your current responses are reasonable but cannot improve the manuscript's scientific significance. For example, the results shown in the Fig.7 are your main research results; however, as I stated in the Major issue 4 "If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.", your response for the comment tells me that Eq. 10 is not validated.
I am very sorry for giving you some disappointing comments. However, I really suggest you to further improve the manuscript.
Citation: https://doi.org/10.5194/hess-2022-30-RC3 -
CC1: 'Reply on RC3', Bing Wang, 23 Mar 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that the model should be tested with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of the root system on the soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density, and root system affect the soil detachment process. We thought that this basic field experimental study is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties, and root types. The method stepwise was used to fit the effects of these factors on soil detachment. On one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties, and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. Eq.10 might be used in this area. For another region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with other independent data in future studies and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of the plant root systems on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attention to this. However, some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also be affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in a relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of the herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root systems on soil detachment at the species level.
All in all, studies about the effectiveness of the plant root system in reducing soil erosion at the species level were still needed, which would have great advantages for clarifying the effects of the plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking not to be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-CC1 -
CC2: 'Reply on RC3', Bing Wang, 23 Mar 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that the model should be tested with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of the root system on the soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density, and root system affect the soil detachment process. We thought that this basic field experimental study is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties, and root types. The method stepwise was used to fit the effects of these factors on soil detachment. On one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties, and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. Eq.10 might be used in this area. For another region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with other independent data in future studies and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of the plant root systems on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attention to this. However, some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also be affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in a relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of the herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root systems on soil detachment at the species level.
All in all, studies about the effectiveness of the plant root system in reducing soil erosion at the species level were still needed, which would have great advantages for clarifying the effects of the plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking not to be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-CC2 -
AC7: 'Reply on RC3', JianFang Wang, 11 Apr 2022
Firstly, we really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper.
We know that for the model it should be test with another group of independent data. Such as some hydrological models and soil erosion models. As we explained, the aim of this paper was to investigate the effects of herbaceous root types on the soil detachment process at the species level. That is, we pay much attention to the effects of root system on soil detachment process. In this paper, we explore mechanistically how the overland flow, soil properties, plant density and root system affect the soil detachment process. We thought that this basical field experimental studies is the basis for hydrological model or soil erosion model building, not that we are going to build a model.
It is for this reason, we want the relevant model would use our results. In other words, we hope that our paper can provide some useful results for the model building. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties and root types. The method of stepwise was used to fit the effects of these factors on soil detachment. For one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties and root types on soil detachment.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. The Eq.10 might be used in this area. For other region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with another independent data in future study and make the equation more widely applicable. This is a basic experimental study, we are unlikely to treat it like regular model building, after all our data is measured and limited, not massively collected.
There is some interesting about this paper. Such as, studying the effects of plant root system on soil erosion at the species level, which is necessary to determine the mechanism of regional vegetation measures on controlling soil erosion. However, relevant studies about soil erosion pay no attentions about this. Although some hydrological process model has been noticing that. Other problems for the relevant studies are also obvious. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level.
All in all, studies about the effectiveness of plant root system in reducing soil erosion at species level was still needed, which would have great advantages for clarifying the effects of plant root system on controlling soil erosion and improving the accuracy of soil erosion model.
Finally, we respect your decision. We hope our interpretation is acceptable. Every discussion is an opportunity for us to learn and improve. It also allows our thinking to not be limited by inherent knowledge. Thank you very much again.
Citation: https://doi.org/10.5194/hess-2022-30-AC7
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CC1: 'Reply on RC3', Bing Wang, 23 Mar 2022
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RC3: 'Reply on AC3', Anonymous Referee #1, 23 Mar 2022
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AC3: 'Reply on AC1', JianFang Wang, 22 Mar 2022
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AC6: 'Reply on RC1', JianFang Wang, 11 Apr 2022
Thank you for your valuable comments on this manuscript. We have carefully revised our paper followed by your comments.
This paper presents a laboratory scouring experiment to study the effects of two herbaceous on the soil detachment process. The experimental design is reasonable, but the results shown in the manuscript are not convincing in my view.
Major issue:
1.The fitting results in Fig.3, Fig4. and Fig. 6 are not good (with low R2). I very much doubt the applicability of the equations shown in Fig.3, Fig4. and Fig. 6. So, as I stated above, the results shown in the manuscript are not convincing.
Response:
The fitting results in Fig.3, Fig.4 and Fig. 6 showed low R2. This mainly because independent variables used in these figures would all affect the soil detachment process. When all these factors considered, the R2 was 0.58 (Eq.[10]). So, when we use one of these factors, the R2 is low.
Before we do this job, the correlation analysis was used to detect the relationship between these factors and soil detachment rate. We think that high correlation coefficient might be have a strong effect on soil detachment, and their effects on soil detachment might also be expressed as functions. After all, quantitative relationships are more intuitive than correlation coefficients. Finally, when we simultaneously considered the root traits, soil properties and hydraulic parameters, the performance seems satisfactory with a relatively high R2.
2.According to the title of this manuscript, it aims to compare the differences between BI and AG in affecting the soil detachment process. However, in Fig.3-6, the results of BI and AG were fitted using the same equation which I think is unreasonable. To be specific, if the effects of two herbaceous on the soil detachment process are different and worthy to study, the relationships in Fig.3-6 should be different between BI and AG. It is easy to see from Fig.4, for example, the distribution characteristics of the result points between BI and AG are very different, which I think is a reason for the poor fitting results.
Response:
Your suggestion is right. At first, we also want to separate these differences that caused by two different herbaceous plants, while the performance was not very good. The reason why we did not do that is the following reason. For fig.3 (now is the fig.4), plant density is the experiment treatment and it is the same for both two herbaceous plants. For the fig.4 (now is the fig.5), the variation of hydraulic parameters was mainly due to the soil surface. The aboveground part of plants was cut and the overland flow was used to detect the soil detachment rate. In this way, the impact of species in soil detachment may not be very strong. For the fig.5 (now is the fig.6), soil property such as bulk density would be varied after the vegetation growth. But the difference of bulk density between these two herbaceous plants might be slight. Overall, these two herbs only grew for one year. For the fig.6 (now is the fig.7), we put the data of the two herbs together mainly because there is a prior knowledge, that is the root length density would represent the difference between root types. Many previous studies generally use the root biomass to built the relationship between soil erosion rate and root traits. Some studies believe that the root biomass would not well reflect the effects of root type on soil erosion, and the root length density or the root surface area density are suggested and the effects of root type on soil erosion would be included. As reported by De Beats et al. (2007), Knapen et al., (2007), and Wang et al. (2021). the root length density or root surface area density would generally be used to represent root morphological differences induced by root type between herbs.
Although some studies sample the undisturbed soil from nature grassland. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relatively large tank (200 cm in length and 50 cm in width) to avoid these possible impacts. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, when we use the large tank to plant herbs, the data would be limited, so we put all the data together to promote the effectivity of the data. Your suggestion is very important for our future research, and we will do our best to increase the amount of data in future study.
3.In this scouring experiment, the value of overland flow is constant (1.5 L s-1). So, the scientific significance of this paper is very limited. To my knowledge, the overland flow should have significant effects on soil detachment. In the present manuscript, all the results are derived under a constant overland flow; and if the results are applicative under other overland flows or not? I doubt it! So, Eq. 10 may be correct only under the specific experimental conditions of this manuscript.
Response:
In previous studies, their soil sample were collected under nature grassland, and they would give five or six condition of overland flow, for the soil sample was relatively easy to collect. As mentioned above, the disadvantages are also obvious. For the given overland flow condition that reported by previous study, the variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the hydraulic parameters were test in the sample area. Although only one condition of overland flow was given in this study, but there are six plant density and two herbaceous plants, which means twelve conditions of overland flow were used in this study. Besides, for the hydraulic parameters that used in the Eq.[10] was not a constant, it’s twelve.
Based on above mentioned, we emphasized in the article that we measured the hydraulic parameters of the scouring zone, and this part was revised as: “The flow velocity of scouring zone and water temperature were measured every 5 s”.(Line 218 and Line 219).
4.In Fig. 7, the predicted soil detachment rate and the measured soil detachment rate are compared. What are the data of measured soil detachment rate? Are they derived from other experiments or just the results of the present experiment? If the datasets used to build Eq. 10 are in turn used to validate Eq. 10, the result is nonsense.
Response:
Yes, we use the measured data to build the Eq.10. For this study, the soil detachment capacity was affected by the hydraulic parameters of overland flow, the soil properties and root types. The method of stepwise was used to fit the effects of these factors on soil detachment. For one hand, factors that had no effects or little effects would be eliminated. For another hand, the selected parameters in Eq.10 would well reflect the effects of overland flow, soil properties and root types on soil detachment. You are right, the performance of Eq.10 showed in fig.7 was only applied to this study.
In this study, the selected two herbaceous and soil properties are typical of the hilly and gully area of the Loess Plateau. The Eq.10 might be used in this area. For other region, as you mentioned, this equation should be calibrated. Following your suggestion, we would verify this equation with another independent data in future study and make the equation more widely applicable.
Moderate issue:
5.According to the manuscript, I recognize that repeated experiments are designed. However, the results of the repeated experiments are not shown in the manuscript. At least, the average values and the standard deviation of the repeated experiments should be described. Because the deviations of the repeated experiments have significant effects on the results shown in Table 1. If the deviations of the repeated experiments are very large, the comparing results between the BI and AG would be questionable; i.e. we would be not sure that the differences between BI and AG result from the species’ difference or the experimental error.
Response: Done as suggested.
Our experiments were indeed repeated experiment. According to your suggestion, we have increased the standard deviation of soil properties, such as bulk density, cohesion, water stable aggregates, soil organic matter and soil erodibility in table 1. We also added the standard deviation of velocity, shear stress and Darcy-weisbach friction factor in table 3.
6.In the Materials and methods section, there are not any figures describing the experimental conditions and treatment design. This makes readers difficult to have a clear understanding of your experiments.
Response: Done as suggested
We realized that the schematic diagram describing the experimental conditions and treatment design could clearly show the experimental process. This makes readers easy to have a clear understanding of our experiments. Following your suggestion, we added the schematic diagram of the experimental treatment in the materials and methods of the manuscript (Fig.1).
7.In the present manuscript, many equations have been used. The authors must add the corresponding references to the manuscript.
Response: Done as suggested.
We previously considered Eq.[1] to [9] to be the most commonly used calculation formulas, so we did not add references. As you mentioned, references for these equation were important, and the corresponding references of eq.[1] to [9] were added in manuscript. (Line 227 to Line 267).
Citation: https://doi.org/10.5194/hess-2022-30-AC6
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RC2: 'Comment on hess-2022-30', Anonymous Referee #2, 03 Mar 2022
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to built your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Moderate concern:
In mat/met section, any of the soil properties is referenced (line 239-249).
Please, define the meaning of “S” type sampling (line 239).
Number of plots should be 26, including the control-bare.
In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Many equations are used but any of them is referenced, please, equations should be referenced.
English language-grammar must be deeply revised.
Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Citation: https://doi.org/10.5194/hess-2022-30-RC2 -
AC1: 'Reply on RC2', JianFang Wang, 21 Mar 2022
We really appreciate the time and effort you have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you have noted. The response part was listed in the supplement.
- AC4: 'Reply on AC2', JianFang Wang, 22 Mar 2022
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AC5: 'Reply on RC2', JianFang Wang, 23 Mar 2022
Thank you for your comments and detailed revision. We have revised the manuscript according to your suggestion.
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
1.As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
Response:
Yes, for some studies, the counts of plant species are four or six. The “Grain for Green” project has been implemented for 20 years. For the abandoned farmland, and the vegetation has succeeded to a stable period. In this stage, Bothriochloa ischcemum (Linn.). Keng (BI) and Artemisia vestita Wall. ex. Bess (AG) are the dominant herbaceous species. That’s the reason that we selected these two herbs.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, the runoff and sediment were collected in every 5 seconds, and repeated for 15 times in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession. These two herbaceous plants is the main community in study area.
2.I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to build your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Response:
Based on the statistical results, we compare the difference of soil properties under six plant densities. It was showed that soil organic matter decreased with plant density for both two herbs, and the soil erodibility of BI decreased with plant density. For other soil properties, the variation of them with plant density was not very clear.
Following your suggestion, we try to build treatments based on ranges of 5-10, 15-20, 25-30 plant m-2. Then we found that maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil erodibility of AG was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.
Also, we revised this part in the paper as following: “In particular, maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil organic matter content increased with increasing plant density. The soil erodibility of BI decreased with plant density. While for AG, it was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.” (Line 280 to Line 284)
Moderate concern:
3.In mat/met section, any of the soil properties is referenced (line 239-249).
Response: Done as suggested.
The soil properties of bulk density, cohesion, water stable aggregate, organic matter and soil erodibilty were measured by normal methods. The references which measured methods of soil properties were added in the materials and methods (Line 239 to Line 249).
4.Please, define the meaning of “S” type sampling (line 239).
Response: Done as suggested.
“S’’ type sampling refers to taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S, and the soil sample would well represent the soil properties of this slope. This part was revised as: “the soil properties were measured by taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S” (Line 240 and Line 241).
5.Number of plots should be 26, including the control-bare.
Response:
You are right. The total number of plots were 26 including the control-bare. Among these, twenty-four plots were used for planting under six plant density and two herbaceous plants. This part was revised as “In total, twenty-six steel tanks were used, and including two control-bare” (Line 178 and Line 179).
6.In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
Response: Done as suggested.
Before analyzing and quantifying relationships between the soil detachment rate and hydraulic parameters, soil properties, and root traits, the normal distribution of these indexes was test by using the method the one-sample nonparametric tests. The statistical analyses part was also revised (Line 271 and Line 272)
7.From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Response:
Yes, soil moisture has great effects on soil erosion process, which would be correlated to the initial runoff time and soil erosion rate. For the effects of driving force on soil erosion process, rainfall and overland flow is commonly used. Many studies consider the overland flow as a sub-process of the rainfall, and the soil moisture close to the saturated water content when the rill erosion occurs. Hence, they allow the soil sample to fully absorb water (capillary water) and to simulate the effects of overland flow on soil detachment during the rill erosion process. As a result, the effects of soil moisture on soil detachment is eliminated (Zhang et al., 2003; Wang et al., 2018). In our study, we also to sprinkle water several times for each soil tank until the soil moisture saturated before scouring test. So, in our study, soil moisture would be not affected the soil detachment process.
8.Many equations are used but any of them is referenced, please, equations should be referenced.
Response: Done as suggested.
After much consideration, we think that references should be added. Therefore, the corresponding references of eq.[1] to [9] were added in manuscript (Line 227 to Line 267).
9.English language-grammar must be deeply revised.
Response: Done as suggested.
Before we submit the paper, the full text was revised by a American native speaker provided by the website of Elsevier. This time, the paper was checked by a researcher who worked in the US for almost thirty years.
10.Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Response: Done as suggested.
All units were checked and revised. The sentences “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG” was revised as “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 kg m2 s-1 to 0.132 kg m2 s-1 for AG” (Line 25).
Citation: https://doi.org/10.5194/hess-2022-30-AC5 -
AC8: 'Reply on RC2', JianFang Wang, 11 Apr 2022
Thank you for your comments and detailed revision. We have revised the manuscript according to your suggestion.
This manuscript deals with overland flow lab experiment to study the effects of two different herbaceous type with different root system architecture on the soil detachment process. They explore the influence of 7 plant densities (including the control-bare with no plants). The paper explores the associated interaction between the promoted changes in soil properties as bulk density, soil cohesion, soil aggregation and soil organic content due to the influence of the root architecture and density.
Major concern:
1.As a general, there is a huge effort on the dataset collection and soil laboratorial analyses otherwise, the experimental set-up is poor in terms of statistical confidence. The experimental design is not appropriate for a scientific journal since it counts only with two replicates per treatment (line 178), so the reliability of results and thus conclusions are not convincing me.
Response:
Yes, for some studies, the counts of plant species are four or six. The “Grain for Green” project has been implemented for 20 years. For the abandoned farmland, and the vegetation has succeeded to a stable period. In this stage, Bothriochloa ischcemum (Linn.). Keng (BI) and Artemisia vestita Wall. ex. Bess (AG) are the dominant herbaceous species. That’s the reason that we selected these two herbs.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, the runoff and sediment were collected in every 5 seconds, and repeated for 15 times in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession. These two herbaceous plants is the main community in study area.
2.I would recommend to explore in the dataset if densities 5 and 10, 15 and 20, and 25 and 30 plant/m2 could be aggregated, in other words, are differences between 5 vs 10, 15 vs 20, 25 vs 30 plant/m2? If statistically there are no differences, then you could try to build your treatments based on ranges of 5-10, 15-20, 25-30 plant/m2, in order to get more statistical confidence, and then properly discuss your results.
Response:
Based on the statistical results, we compare the difference of soil properties under six plant densities. It was showed that soil organic matter decreased with plant density for both two herbs, and the soil erodibility of BI decreased with plant density. For other soil properties, the variation of them with plant density was not very clear.
Following your suggestion, we try to build treatments based on ranges of 5-10, 15-20, 25-30 plant m-2. Then we found that maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil erodibility of AG was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.
Also, we revised this part in the paper as following: “In particular, maximum bulk density, cohesion and water stable aggregate values occurred when the plant density ranged between 15 plants m-2 and 20 plants m-2. The soil organic matter content increased with increasing plant density. The soil erodibility of BI decreased with plant density. While for AG, it was high when the plant density ranged between 5 plants m-2 and 10 plants m-2.” (Line 280 to Line 284)
Moderate concern:
3.In mat/met section, any of the soil properties is referenced (line 239-249).
Response: Done as suggested.
The soil properties of bulk density, cohesion, water stable aggregate, organic matter and soil erodibilty were measured by normal methods. The references which measured methods of soil properties were added in the materials and methods (Line 239 to Line 249).
4.Please, define the meaning of “S” type sampling (line 239).
Response: Done as suggested.
“S’’ type sampling refers to taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S, and the soil sample would well represent the soil properties of this slope. This part was revised as: “the soil properties were measured by taking mixed soil sample on the slope (soil tank in this study) in the shape of letter S” (Line 240 and Line 241).
5.Number of plots should be 26, including the control-bare.
Response:
You are right. The total number of plots were 26 including the control-bare. Among these, twenty-four plots were used for planting under six plant density and two herbaceous plants. This part was revised as “In total, twenty-six steel tanks were used, and including two control-bare” (Line 178 and Line 179).
6.In 2.5. Statistical analyses should explain if data is normal or non-normal, so the use of parametric or non-parametric test. This item should be properly developed.
Response: Done as suggested.
Before analyzing and quantifying relationships between the soil detachment rate and hydraulic parameters, soil properties, and root traits, the normal distribution of these indexes was test by using the method the one-sample nonparametric tests. The statistical analyses part was also revised (Line 271 and Line 272)
7.From my understanding, soil moisture also influences soil detachment, so repeated overland flow experiments would modify the initial soil moisture content, which must to be considered as a co-factor or factor on soil detachment processes, mainly on repeated overland flow experiences. Proper statistical tools should be properly applied for the repeated measurement statistical analyses.
Response:
Yes, soil moisture has great effects on soil erosion process, which would be correlated to the initial runoff time and soil erosion rate. For the effects of driving force on soil erosion process, rainfall and overland flow is commonly used. Many studies consider the overland flow as a sub-process of the rainfall, and the soil moisture close to the saturated water content when the rill erosion occurs. Hence, they allow the soil sample to fully absorb water (capillary water) and to simulate the effects of overland flow on soil detachment during the rill erosion process. As a result, the effects of soil moisture on soil detachment is eliminated (Zhang et al., 2003; Wang et al., 2018). In our study, we also to sprinkle water several times for each soil tank until the soil moisture saturated before scouring test. So, in our study, soil moisture would be not affected the soil detachment process.
8.Many equations are used but any of them is referenced, please, equations should be referenced.
Response: Done as suggested.
After much consideration, we think that references should be added. Therefore, the corresponding references of eq.[1] to [9] were added in manuscript (Line 227 to Line 267).
9.English language-grammar must be deeply revised.
Response: Done as suggested.
Before we submit the paper, the full text was revised by a American native speaker provided by the website of Elsevier. This time, the paper was checked by a researcher who worked in the US for almost thirty years.
10.Units should be carefully revised. See line 25 for the soil detachment rate (i.e.: six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG,)
Response: Done as suggested.
All units were checked and revised. The sentences “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 m2 s-1 to 0.132 m2 s-1 for AG” was revised as “six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 kg m2 s-1 to 0.132 kg m2 s-1 for AG” (Line 25).
Citation: https://doi.org/10.5194/hess-2022-30-AC8
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AC1: 'Reply on RC2', JianFang Wang, 21 Mar 2022
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EC1: 'Comment on hess-2022-30', Carla Ferreira, 24 Mar 2022
Dear Prof. Yan-Fen Yang,
Thanks for submitting your manuscript to this SI. Understanding the impact of different herbaceous plants and plant densities on soil erosion by overland flow is relevant for the scientific community and stakeholders. However, major revisions should be performed before considering the possible publication of your manuscript. Please, consider the comments from both reviewers to improve your manuscript. Additionally, consider the following comments:
Specific comments:
The Introduction section is quite long and should be shortened.
In the Methodology section:
L200: why are you presenting accumulated temperature? (what is its meaning for the herbaceous species?).
L204: why the selection of this slope? Is it representative of the Loess Plateau?
L205: for how long were the tanks scoured?
L239: please, describe the sampling procedure
L221: not clear how the soil sampling did not disturb the overland flow and sediment measurements
L223: please, better explain the pretest performed
L224: so, only one experiment of 75 s was performed for each tank?
Section 2.3: it is not clear how long the overland flow and sediment measurements took
Section 2.5: why only analyzing the correlations between all variables? What about differences between experiments with the two plants? What about differences with the different plant densities?
Section 3: the results of the correlation between variables should be indicated, and not only the level of significance. From the conclusions we can see that the correlations are rather low (mostly <0.5), although statistically significant. Thus, considering the very limited number of replications the correlations may be questionable.
Section 4: the limitations of the study must be clearly indicated and discussed
Section 4.3: it would be interesting to compare your results with results from similar studies with other herbaceous plants
Section 5: the findings are not new. A better link with the two types of plants can be more useful. Please, clearly identify the main findings/novelty of this study and the practical/real implications of this study.
Fig. 1: please, improve the legend to better describe the data shown, including the lines and dots
Fig. 2: please, improve the legend to better describe the meaning of the letters
Figs. 3 to 6: it may be interesting to draw different power functions for both plant types
Table 1 and 3: you may include the results of statistical differences between both plant type experiments in this table
Citation: https://doi.org/10.5194/hess-2022-30-EC1 -
AC9: 'Reply on EC1', JianFang Wang, 18 Apr 2022
Dear editor
Thank you for inviting us to submit a revised draft of our manuscript entitled “Investigating the effects of herbaceous root types on the soil detachment process at the species level” to Hydrology and Earth System Sciences. We really appreciate the time and effort you and each of the reviewers have dedicated to providing insightful feedback on ways to strengthen our paper. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you and the reviewers have noted. The revised part was marked in blue font in the manuscript. The following is a point-by-point response to the questions and comments.
Specific comments:
The Introduction section is quite long and should be shortened.
Response
Done as suggested. After careful consideration, we shortened the introduction and simplified the sentences that were too tedious. The total number of words were decreased from 1,643 to 1,402. This part was revised in the manuscript.
In the Methodology section:
L200: why are you presenting accumulated temperature? (what is its meaning for the herbaceous species?).
Response
The plant growth and development have a lower limit temperature, and it was called the biological starting point temperature. When the temperature is above the lower limit, plants would grow and develop, generally considered to be 10℃. Therefore, cumulative temperature greater than 10℃ was used to represent the effect of temperature on vegetation growth and development in the study area, which is more biologically significant than the traditional average temperature.
L204: why the selection of this slope? Is it representative of the Loess Plateau?
Response
Yes, the slope is representative of the Loess Plateau. Two decades years ago, most of the sloping farmland on the Loess Plateau was 15°, which resulted in serious soil erosion. To control soil erosion, the “Grain for Green” project was implemented and vegetation began to succeed naturally. The sloping farmland is converted into grassland, which becomes the dominant ecosystem in this region. Therefore, the slope of 15° was selected in this study.
L205: for how long were the tanks scoured?
Response:
The scouring time for this study was 75 s. Here are some following reasons:
Soil erosion generally including sheet erosion, rill erosion, and gully erosion based on the soil erosion type. For sheet erosion, there is a small amount of erosion and mainly caused by the rainfall. For gully erosion, the amount of erosion is usually large and gravity erosion often occurs, which beyond the traditional erosion process. Among these two erosion types, rill erosion generally is a transitional state in which sheet erosion develops to gully erosion. If corresponding preventive measures are taken at this stage, the type of soil erosion can be prevented from developing to serious gully erosion, so that soil erosion can be effectively controlled.
During the rill erosion process, the soil detachment mainly attributes to the overland flow. For this study, the rill net was well developed and the rill outline was obvious when the tank was scoured for almost 75 s. Meanwhile, the scouring depth was greater than 2 cm after the tank was scoured by overland flow for 75 s, which belongs to rill erosion based on the definition of the rill erosion. Based on the designed flow discharge in this study, long scouring time might result in gully erosion, which complicates the soil erosion process.
Besides, in most of the previous studies, their scouring depth was controlled at 2 cm and the corresponding scouring time was ranged from 3 to 180 s. Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. Therefore, the scouring time of 75 s was used for all the soil detachment rate tests.
L239: please, describe the sampling procedure
Response:
Done as suggested. The sampling procedure was revised as following:
“Each tank was left for five days to dry out and it would more suitable for sampling. Then the soil sample were collected in different location of the tank (upper, middle, and lower parts of the slope) to test the soil bulk density, cohesion, aggregation, and soil organic matter content. Specifically, the bulk density was measured using a steel ring 5 cm in height and 5 cm in diameter. Soil cohesion was determined using an Eijkelkamp pocket vane tester (14.10, Eijkelkamp Agrisearch Equipment, Giesbeek). Soil aggregation was measured via a series of sieves with bore diameters of 0.25 mm, 0.5 mm, 1 mm, 2 mm, and 5 mm, and the soil organic matter content was measured using potassium dichromate (Wang et al., 2018a). Except for the soil cohesion was replicated for nine times, all other soil properties were replicated for three times, respectively, and their mean values were represented the soil properties of this slope. The soil erodibility was calculated based on the soil organic matter content as (Sharpley and Williams., 1990):”(Line 254 to Line 266).
L221: not clear how the soil sampling did not disturb the overland flow and sediment measurements
Response
The sentence “To reduce the potential effects of soil sampling on experimental results, testing was generally stopped at a certain scouring depth of 2 cm” is mixed, we revised this part as following:
“When the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Considering the scouring time would affect the results of soil detachment calculating, the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. The scouring time of 75 s was then timed for all scouring tests.”(Line 233 to Line 237)
L223: please, better explain the pretest performed
Response
Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. In most of the previous studies, although their scouring depth was controlled at 2 cm, the corresponding scouring time was varied greatly and ranged from 3 to 180 s. In order to eliminate or reduce this effect as much as possible, the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. When the scouring time was 75s, the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Then its scouring time of 75 s was then timed for all scouring tests. We also added this information in the paper (Line 233 to 237).
L224: so, only one experiment of 75 s was performed for each tank?
Response
Yes, the test time for all the steel tank was finally set at 75 s.
Based on the designed flow discharge in this study, long scouring time might result in gully erosion, which the gravity erosion might be occurred and thus made the soil erosion process more complicate. During the rill erosion process, the soil detachment mainly attributes to the overland flow.
When the rill occurred, rill net was developed, and the rill depth was greater than 2 cm, testing was generally stopped. Considering that the soil detachment rate was calculated based on the scouring time, the varied scouring time may affect the test results. the maximum planting density of 30 plant m-2 with relatively low erodibility in this study was firstly tested. When the scouring time was 75 s, the outline of the rill net was obvious. Then the 75 s was applied all scouring tests.
Section 2.3: it is not clear how long the overland flow and sediment measurements took
Response
As mentioned above, based on the rill outline and rill net development, the designed flow discharge, and also the effects of scouring time on soil detachment rate calculation, the scouring time for all the steel tank was finally set at 75 s.
During the scouring time of 75 s, runoff and sediment samples were collected every 5 s. Meanwhile, the corresponding flow velocity and water temperature were also measured. Totally, 15 group data of runoff, sediment, flow velocity, and water temperature were tested for each steel tank.
Section 2.5: why only analyzing the correlations between all variables? What about differences between experiments with the two plants? What about differences with the different plant densities?
Response
Done as suggested. The differences with the herbaceous plant type and plant densities were analyzed. The following results and discussion section in this paper were also revised. Now this part was revised as following:
“The differences in soil detachment rate, hydraulic parameters, soil properties, and root traits among plant densities and two herbaceous plants were evaluated using the analysis of post hoc multiple comparisons (The Student–Newman–Keuls, significance level = 0.05). Two-way ANOVA was used to analysis the main effects of plant densities and herbaceous plant type, and their interaction effects on soil properties, root traits, hydraulic parameters, and soil detachment rates. Pearson's correlation analyses (p<0.05) were used to analyze relationships among hydraulic parameters, soil properties, root traits, and soil detachment. The qualified relationships between soil detachment rate and hydraulic parameters, soil properties, or root traits were fitted by using nonlinear regression. Stepwise regression was used to estimate soil detachment rate by hydraulic parameters, soil properties, and root traits. The coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) were used to evaluate model performance. All analyses were conducted using SPSS 22.0 and Origin 2018 software.”(Line 286 to Line 298)
Section 3: the results of the correlation between variables should be indicated, and not only the level of significance. From the conclusions we can see that the correlations are rather low (mostly <0.5), although statistically significant. Thus, considering the very limited number of replications the correlations may be questionable.
Response
Done as suggested. Based on the previous data analysis, the method of Two-way ANOVA was used to detect the influence of plant density, herbaceous plant type, and their interaction effects on soil properties, root traits, hydraulic parameters, and soil detachment rate. The corresponding parts of 3.1, 3.2, and 3.3 section were revised and marked.
Also, following the comments of reviewer, the effects of two herbaceous on the soil detachment process are different and worthy to study. We separated fitted these differences that caused by two different herbaceous plants. Besides, each plant density had two repetition tanks, each tank had 15 group data of runoff, sediment, flow velocity, and water temperature. While on the previous analysis, these data were averaged to one value. For this time, the averaged 15 group data were used and the fig.4, fig.5, fig.6, and fig.7 were revised.
In previous studies, their soil sample were collected under nature grassland, and they would give five or six condition of overland flow, for the soil sample was relatively easy to collect. However, the variation of overland flow is ignored when the flow through the scouring area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length in previous studies. In fact, the hydraulic parameters in the scouring area are closely related to soil erosion. In this study, the hydraulic parameters were test in the scouring area. Although only one condition of overland flow was given in this study, but there are six plant density and two herbaceous plants, which means twelve conditions of overland flow were used in this study.
In previous studies, they choose more plant species than we do. But some problems they would not be solved very well. For example, in the sampling process, the root would not completely collect due to the limitation of the sample (generally used the rectangular ring with 20 cm in length and 10 cm in width, or circular ring with 10 cm in diameter). The scouring process by overland flow may also affected by the edge wall of the steel ring. The roots of other herbs are also mixed in the sample ring. These factors would all affect the results. It is because of this, we planted the herbs in relative large tank (200 cm in length and 50 cm in width) to avoid these possible impact. With these large soil samples that used in this study, our results would well reflect the effects of herbaceous plant root system on soil detachment, for the root system integrity can be maintained and the initial soil properties of all sites keep consistent, and the influence of edge effect on test results can be ignored. Besides, there are no other herbs root in the sample soil, it is helpful for us to study the effects of herbaceous plants root system on soil detachment at species level. However, the tradeoff for this is that we can't set up too many experimental treatments.
In previous studies, the given overland flow condition is considered as unchanged. The variation of overland flow are ignored when the overland flow through the sample area. This is mainly because the hydraulic parameters cannot be measured, for the sample size is small, especially for short length. In fact, the hydraulic parameters in the sample area are closely related to soil erosion. In this study, the varied hydraulic parameters were test in the sample area, which means that our treatment was added under the six plant density and two herbaceous plants.
Although there is a shortage in treatment, the repetition was added in this study to ensure the data accuracy. For example, two repetitions were designed for each plant density, the measurement of soil properties and vegetation characteristics were tested for six times, For soil detachment rate test, its variation during the scouring process was considered and 15 group data were collected in each soil tank. We will also increase the treatment accounts in future research. For this study, we mainly focused on the effect of herbs on soil detachment at the stable stage of succession this time, for these two herbaceous plants is the main community in study area.
Section 4: the limitations of the study must be clearly indicated and discussed
Response
Done as suggested. Based on data analysis and discussion, the limitation of the study were clearly indicated and discussed in section 4. The corresponding parts of 4.1, 4.2, and 4.3 section were revised and marked.（Line 404 to Line 415, Line 421 to Line 427, Line 455 to Line 459, Line 531 to Line 544）
Section 4.3: it would be interesting to compare your results with results from similar studies with other herbaceous plants
Response
Done as suggested. We compare our results with results from similar studies with other herbaceous plants, and this part was revised as following:
“Previous studies showed that root traits of tree, shrubs, and herb would be used to quantify the effect of plant root system on soil erosion (Parhizkar et al., 2021). The soil detachment rate is insensitive to many of those root traits. When focusing the effects of root system on soil erosion at herbaceous species level, only root length density significantly decreased the soil detachment rate in this study. The quantified relationship between soil detachment rate and root length density were also compared with previous studies (Fig.8). For both planted herbaceous plants all with fibrous root system, BI in this study and ryegrass that reported by Mamo and Bubenzer (2001), the soil detachment rate of BI was almost one magnitude greater than that of ryegrass. The main reason is that the highly planted ryegrass density, which ranged from 4 to 7 plant per cylinders (diameter is 10 cm). Besides, the soil detachment rate was still much higher than that of natural grassland reported by Liu et al. (2019), due to the soil erosion resistance was enhanced by herbaceous plants after thirty-six years of growth. In general, the soil detachment rate of AG in this study was still much high than that of reported by Mamo and Bubenzer (2001) and Liu et al. (2019), showing a low efficiency of herbaceous plant with tap root system in reducing soil detachment. Although only the typical herbaceous plants were selected in this study, some useful results were drawn. Plant root generally scanned using specific software and the root diameter is a mean value for a certain length of root. As a result, the variation in root diameter narrowed. The huge difference in average root diameter among arboreal forest, shrubs, and grassland might cover up this issue. While at herbaceous species level, the difference in average root diameter among herbaceous plants is relatively small, and this problem is highlighted, resulting the effect of root diameter on soil erosion does not seem to be as good as literatures mentioned. Correspondingly, the effects of root surface area density and root volume ratio on soil detachment are also affected, which calculated by root diameter and root length. Determination of root length is not affected by scanning process, and detachment rate decreased with root length density as power functions. So, it may be more effective to study the effect of root diameter differences on soil erosion based on the root order or diameter class, and the root length density would take a priority when detecting the effects of plant root system on soil erosion at herbaceous species level.”(Line 514 to Line 544)
Section 5: the findings are not new. A better link with the two types of plants can be more useful. Please, clearly identify the main findings/novelty of this study and the practical/real implications of this study.
Response
Done as suggested. Our conclusion were rewrote from the perspective of the species level (BI and AG). We also added the main finding and the practical/real implications of this study. This part was revised as following:
“The herbaceous plant root system would significantly reduce the soil erosion and its effects also exhibited different behaviors according to herbaceous type. The soil detachment rate significantly decreased with increasing plant density for two herbaceous plants, becoming 85.80% and 81.19% lower than that of the control for the BI and AG grasslands, respectively. BI, which has a fibrous root system, effectively reduced the soil detachment rate, achieving a mean soil detachment rate that was 23.75% less than that of AG, which has a tap root system. The hydraulic characteristics of overland flow, soil properties, and root traits induced by plant density and herbaceous type closely related to the soil detachment, which could be estimated effectively using the overland flow velocity, soil bulk density, and root surface length density. The performance of the model developed in this study was satisfactory. Moreover, the response of soil detachment rate to root diameter does not seem to be as sensitive as mentioned in literatures. Meanwhile, the root order or diameter class was suggested, and the root length density was recommended to detect the effects of plant root system on soil erosion at herbaceous species level.”(Line 546 to Line 560)
Fig. 1: please, improve the legend to better describe the data shown, including the lines and dots
Response
Done as suggested. The legend was added, and the lines and dots was revised in Fig.1 (Now it is Fig.2).
Fig. 2: please, improve the legend to better describe the meaning of the letters
Response
Done as suggested. The meaning of the letters was presented in notes of Fig. 2 (Now it is Fig.3).
Figs. 3 to 6: it may be interesting to draw different power functions for both plant types
Response
Done as suggested. Different power functions for two plant types were drawn separately in Fig. 3 to Fig. 6 (Now it is Fig 4 to Fig.6).
Table 1 and 3: you may include the results of statistical differences between both plant type experiments in this table
Response
Done as suggested. Differences analysis was added in the Table 1 and Table 3.
Citation: https://doi.org/10.5194/hess-2022-30-AC9
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AC9: 'Reply on EC1', JianFang Wang, 18 Apr 2022
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