the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Nov 2023
Regulating effects of mixed-cultivated grasslands in surface water conservation and soil erosion reduction along with restoration of alpine degraded hillsides
Abstract. Vegetation restoration is among the most effective measures for controlling runoff and soil erosion resulting from human activity. Nevertheless, few studies have been undertaken to analyze the effects of plant restoration on maintaining the stability of the hydrological cycle, especially, in alpine degraded hillsides where mixed-cultivated grasslands predominate in the landscape. In this research, we conducted in situ monitoring using runoff plots to investigate the impact of three strategies, each combining two grass species per plot (three species in total), on a 20-degree slope, assessing the activation and volume of surface runoff and soil loss in alpine degraded hillsides over three years (2019, 2020 and 2022). A severely degraded meadow plot was used as control. The findings indicated that mixed-cultivated grasslands can effectively manage runoff and reduce soil loss as planting ages increase. Between 2019 and 2022, the values of the runoff reduction ratio decreased for Deschampsia cespitosa and Elymus nutans (DE), Poa pratensis L.cv. Qinghai and Elymus nutans (PE), and Poa pratensis L.cv. Qinghai and Deschampsia cespitosa and (PD) from -79.3 % to -115.4 %, from -130.4 % to -156.1 %, and from -48.5 % to -87.6 %, respectively. On the contrary, the mean sediment concentration reduction ratio increased from -120.9 to 55.8 % (in DE), from 112.4 to 59.7 % (in PE), and from -94.3 to 62.1 % (in PD). This implies that protective measures should be prioritized during the initial planting stage of cultivated grasslands in alpine degraded hillsides. The key factors affecting soil loss and runoff were rainfall amount, duration and intensity (60-min intensity). We conclude that the results of this study can serve as scientific guides to design efficient policy decisions for planning the most effective vegetation restoration in the severely degraded hillside alpine meadows.
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RC1: 'Comment on hess-2023-257', Corinna Gall, 14 Nov 2023
The study by Yulei Ma et al. deals with a very interesting topic, namely the influence of different combinations of grass species on runoff formation and soil erosion to derive effective grassland restoration strategies. For this purpose, surface runoff and sediment discharge were measured under natural rainfall over a period of four years for three different mixed-cultivated grasslands and one severely degraded meadow as a control. Furthermore, precipitation, soil and vegetation characteristics were recorded in order to determine the most important factors that additionally influence runoff and soil erosion.
Overall, the manuscript is in good order and comprehensibly written. However, the abstract as well as the results and discussion section should be revised with the following comments.
I would also like to suggest changing the title of the study, as the term "surface water conservation" is not clear and also not explained in the text.
Abstract
In the present form of the abstract, the problem of the study is not clear and the presentation of the main results is also difficult for the reader to understand, as runoff reduction ratio and sediment concentration ratio are not common parameters in erosion research. Since these parameters will be explained later, I think it is acceptable to use them in the study, but in the abstract I would recommend presenting the results in a generally understandable way to increase the impact of the abstract.
Line 20: The term “maintain the stability of the hydrological cycle” is only once used in the abstract and never again in the study itself, which is confusing. Especially at the beginning of the abstract the meaning of this term is not clear.
Line 22: Please clarify by adding “restoration strategies”.
Line 26: What do you mean with “manage runoff” here?
Introduction
The introduction is well structured, so that the objective of the study can be derived from the comprehensibly presented problems of alpine grassland ecosystems.
Line 92: Remove one “the”.
Line 97: Please add “soil characteristics” for clarification.
Line 123: Please write out the abbreviations of the three mixed-cultivated grassland types in the introduction again. For example, “SDM” was never explained before in the text.
Materials and methods
The methods section is very detailed and precisely written so that no questions remain unanswered.
Line 147: Do you mean “epipedon” here? Also check the caption of Figure 1 (line 626 + 628); please also correct here “SEM”.
Line 148: Clarify the reference to Fig. 1b and Fig. 1c.
Line 150: Why is this value shown as a multiplication?
Line 161: Shouldn't the grass species reduce soil erosion and increase surface runoff? Please clarify.
Line 241: Lower the bracket after “cm3”.
Line 245: Remove “cohesion” one time.
Results
The presentation of the results in the figures is clear and comprehensible. However, the results in the text are partially generalized in comparison to the information in the figures. Here, attention should be paid to indicating in the text whether differences are significant or non-significant.
In my perspective, there is also one important result of the study that has not yet been mentioned. I guess that you selected three different grass mixtures because you originally assumed that there would be differences in runoff and soil erosion due to their different structural properties, which you also described in your study. However, there were no measurable differences between the grass mixtures, which is also an important result that should be mentioned and discussed!
Line 272: Since increased runoff and reduced soil erosion is the desired outcome, a word other than "dramatically" would be more appropriate here.
Lines 279-281: According to Fig. 3b there is no significant difference between SDM and the grass-mixtures for 2019 regarding soil erosion and also in 2022 the differences in soil erosion are not significant between treatments. However, you can state a lower soil erosion for all treatments in 2022 compared to 2020, and for 2019 for the treatments PE and PD. Please be more precise here.
Line 292-294: According to Fig. 4a this statement is true for the treatments DE and PE, but not PD. Please do not generalize the results for all treatments and be more precise.
Line 301: According to Fig 4d the mean values of RRSR are somewhere between 50 and 0. Please make it clear what is meant here.
Figure 1: Please correct the typos in the figure caption.
Figure 5: Please check that the technical terms in the figure correspond to those in the caption. Why are the median lines are missing in these boxplots? It would be better coordinated if the median values were also shown in this figure.
Discussion
Consider to include a discussion about the missing difference in runoff and soil erosion of the three selected grassland mixtures. If this part is missing from the discussion, the question arises as to why three different grass mixtures were chosen in the first place.
Line 372: What does the "more" refer to?
Lines 374-384: This part is more suitable for section 4.2 where you discuss the effects of grassland community characteristics on runoff and soil loss.
Citation: https://doi.org/10.5194/hess-2023-257-RC1 -
AC1: 'Reply on RC1', Gao-Lin Wu, 20 Feb 2024
Response to RC1 Corinna Gall’s comments
The study by Yulei Ma et al. deals with a very interesting topic, namely the influence of different combinations of grass species on runoff formation and soil erosion to derive effective grassland restoration strategies. For this purpose, surface runoff and sediment discharge were measured under natural rainfall over a period of four years for three different mixed-cultivated grasslands and one severely degraded meadow as a control. Furthermore, precipitation, soil and vegetation characteristics were recorded in order to determine the most important factors that additionally influence runoff and soil erosion.
Overall, the manuscript is in good order and comprehensibly written. However, the abstract as well as the results and discussion section should be revised with the following comments.
Response: We thank Corinna Gall for the positive comments about our manuscript and for constructive feedback and suggestions that will help refine our paper.
I would also like to suggest changing the title of the study, as the term "surface water conservation" is not clear and also not explained in the text.
Response: The words “surface water conservation” have been revised to “surface runoff maintenance” in the title.
Abstract
In the present form of the abstract, the problem of the study is not clear and the presentation of the main results is also difficult for the reader to understand, as runoff reduction ratio and sediment concentration ratio are not common parameters in erosion research. Since these parameters will be explained later, I think it is acceptable to use them in the study, but in the abstract I would recommend presenting the results in a generally understandable way to increase the impact of the abstract.
Response: Thank you for your valuable suggestion. To avoid confusing the reader, we have replaced the words “runoff reduction ratio” with “average runoff depth” and “sediment concentration reduction ratio” with “soil loss per unit area”, as shown in lines 29–32: “… the average runoff depth for DE, PE, PD and SDM were 0.47, 0.55, 0.45 and 0.27, …”.
Line 20: The term “maintain the stability of the hydrological cycle” is only once used in the abstract and never again in the study itself, which is confusing. Especially at the beginning of the abstract the meaning of this term is not clear.
Response: The words “the hydrological cycle” have been replaced with “the local runoff amount” in line 20.
Line 22: Please clarify by adding “restoration strategies”.
Response: We have revised the word “restoration strategies” to “mixed-cultivated grasslands” and added the explanation of mixed-cultivated grasslands, as shown in lines 22-25: “combining two grass species per plot (Deschampsia cespitosa and Elymus nutans (DE), …”.
Line 26: What do you mean with “manage runoff” here?
Response: Large-scale vegetation restoration generally reduces local water yield and influences river ecosystem health. The Qinghai-Tibetan Plateau is the headwaters for many of Asia's major rivers. Hence, it is necessary to evaluate whether vegetation restoration maintains or undercuts the gains of downstream water resources. To avoid confusing the reader, the words “manage runoff” have been replaced with “maintain runoff” in line 28.
Introduction
The introduction is well structured, so that the objective of the study can be derived from the comprehensibly presented problems of alpine grassland ecosystems.
Response: Thank you so much for your kind encouragement.
Line 92: Remove one “the”.
Response: One “the” has been erased as shown in line 112.
Line 97: Please add “soil characteristics” for clarification.
Response: The words “soil characteristics” have been added in line 117.
Line 123: Please write out the abbreviations of the three mixed-cultivated grassland types in the introduction again. For example, “SDM” was never explained before in the text.
Response: We have added the explanation of the abbreviations of the three mixed-cultivated grassland types and SDM, as shown in lines 167–169: “… Deschampsia cespitosa and Elymus nutans (DE), Poa pratensis L.cv. Qinghai and Elymus nutans (PE) …”.
Materials and methods
The methods section is very detailed and precisely written so that no questions remain unanswered.
Response: Thank you so much for your kind encouragement.
Line 147: Do you mean “epipedon” here? Also check the caption of Figure 1 (line 626 + 628); please also correct here “SEM”.
Response: This is a typo, the words “mattic epipedom” have been replaced with “mattic epipedon” in lines 195, 756 and 757, as well as the word “SEM” having been replaced with “SDM”.
Line 148: Clarify the reference to Fig. 1b and Fig. 1c.
Response: Done. We have clarified the reference to Fig. 1b and Fig. 1c, as shown in lines 195–197.
Line 150: Why is this value shown as a multiplication?
Response: This is a typo, and the value 323.58 × 106 has been corrected to 323.58 × 106 as shown in line 198.
Line 161: Shouldn't the grass species reduce soil erosion and increase surface runoff? Please clarify.
Response: We have revised the sentence as shown in line 218: “only be grazing-tolerant and good forage but also prevent soil loss and maintain surface runoff.”.
Line 241: Lower the bracket after “cm3”.
Response: We have done, as shown in line 304.
Line 245: Remove “cohesion” one time.
Response: We have done, as shown in line 308.
Results
The presentation of the results in the figures is clear and comprehensible. However, the results in the text are partially generalized in comparison to the information in the figures. Here, attention should be paid to indicating in the text whether differences are significant or non-significant.
Response: Thank you for your valuable suggestion. We have revised the expression of the result section and stated in the text whether differences are significant or non-significant, such as in lines 350–367, 376, 386–388 and 394.
In my perspective, there is also one important result of the study that has not yet been mentioned. I guess that you selected three different grass mixtures because you originally assumed that there would be differences in runoff and soil erosion due to their different structural properties, which you also described in your study. However, there were no measurable differences between the grass mixtures, which is also an important result that should be mentioned and discussed!
Response: Thank you for your valuable suggestion. We have added a description of differences between the grass mixtures in the 3.1 and 3.2 sections, as shown in lines 364–365: “No significant differences (P > 0.05) were detected in runoff depth and soil …”, in lines 386–388: “The SRB values of DE, PE and PD in 2022 were significantly (P < 0.05) higher than those of 2019, …”, and in lines 308–310: “No significant differences (P > 0.05) observed in RRB, SRB, CRB ...”. Also, we have added a discussion about the difference in runoff and soil erosion of the three mixed-cultivated grasslands in the 4.2 section, as shown in lines 466–479: “The matching of morphological characteristics of plants can effectively reduce soil loss (Liu et al., 2022). In this study, …”.
Line 272: Since increased runoff and reduced soil erosion is the desired outcome, a word other than "dramatically" would be more appropriate here.
Response: The word “dramatically” has been erased in line 348.
Lines 279-281: According to Fig. 3b there is no significant difference between SDM and the grass-mixtures for 2019 regarding soil erosion and also in 2022 the differences in soil erosion are not significant between treatments. However, you can state a lower soil erosion for all treatments in 2022 compared to 2020, and for 2019 for the treatments PE and PD. Please be more precise here.
Response: We have revised the expression, as shown in lines 358–364 “As depicted in Fig. 3b, soil loss in DE, PE and PD (except for DE in 2019) was significantly (P < 0.05) …”.
Line 292-294: According to Fig. 4a this statement is true for the treatments DE and PE, but not PD. Please do not generalize the results for all treatments and be more precise.
Response: I am sorry maybe a misunderstanding exists. As shown in Fig. 4a, the mean RRB values of the cultivated-grassland communities DE, PE, and PD were -79.3%, -130.4% and -48.5% in 2019, -36.9%, -53.5% and -21.5% in 2020, and -115.4%, -156.1% and -87.6% in 2022, respectively. Hence, the increase rate of runoff in 2022 was significantly (P < 0.05) higher than that in 2019 and 2020.
Line 301: According to Fig 4d the mean values of RRSR are somewhere between 50 and 0. Please make it clear what is meant here.
Response: I am sorry maybe a misunderstanding exists. The unit of the y-axis of Fig. 4d is in percentage (%). As shown in Fig. 4d, the mean RRSR values of the cultivated-grassland communities DE, PE, and PD were 30.3%, 29.5% and 22.8% in 2019, 20.0% 61.6%, and 62.0% in 2020, -26.0% -105.7%, and -132.2%, respectively.
Figure 1: Please correct the typos in the figure caption.
Response: We have corrected the typos in the caption of Figure 1. The words “mattic epipedom” have been replaced with “mattic epipedon” in lines 755 and 756, as well as the word “SEM” has been replaced with “SDM”.
Figure 5: Please check that the technical terms in the figure correspond to those in the caption. Why are the median lines are missing in these boxplots? It would be better coordinated if the median values were also shown in this figure.
Response: We have revised the technical terms to match those in the figure and the caption, and added median lines in Fig. 5.
Discussion
Consider to include a discussion about the missing difference in runoff and soil erosion of the three selected grassland mixtures. If this part is missing from the discussion, the question arises as to why three different grass mixtures were chosen in the first place.
Response: We have added a discussion about the difference in runoff and soil erosion of the three mixed-cultivated grasslands in the 4.2 section, as shown in lines 466–479: “The matching of morphological characteristics of plants can effectively reduce soil loss (Liu et al., 2022). In this study, …”.
Line 372: What does the "more" refer to?
Response: To avoid confusing the reader, we have removed the word “more” in line 483.
Lines 374-384: This part is more suitable for section 4.2 where you discuss the effects of grassland community characteristics on runoff and soil loss.
Response: We have moved this part to the 4.2 section, as shown in lines 466–479.
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AC1: 'Reply on RC1', Gao-Lin Wu, 20 Feb 2024
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RC2: 'Comment on hess-2023-257', Veerle Vanacker, 31 Jan 2024
This manuscript describes the results of empirical research on the effectiveness of three different restoration measures in a grassland ecosystem. Given that native grasslands are increasingly subject to degradation, such empirical work can be very relevant for restoration efforts. The strength of this work lies in the collection of empirical data on surface runoff and soil loss rates from 4 runoff plots that were monitored over three years. As there are no replicates, the evaluation of the effectiveness of the treatments is based on a time series of events. The experimental site has been the subject of previous publications (Niu et al., 2022; Liu et al, 2019; 2022) that focused on soil mitigation by vegetation restoration.
The following points caught my attention, and they might guide the revisions. Besides these points, I have some detailed comments that are listed below.
1-The abstract is informative but contains very specific terms that are not commonly used in hydrology or soil sciences. As such, it is hard to understand the main findings based on the abstract alone. This could be addressed by using standard hydrology or soil science terms in the abstract, or by defining clearly new terms like 'mixed-cultivated grasslands', 'runoff reduction ratio' and 'mean sediment concentration reduction ratio'.
2-The study emphasizes the need to measure the effectiveness of vegetation restoration on runoff and erosion in (degraded) grasslands, and the authors make the point that the degradation of grasslands is poorly studied. The introduction contains general statements of the importance of grasslands, and the issue of environmental degradation of these ecosystems. As they are written, the statements are rather general (such as 'water and soil are crucial for human survival'), and merit to be further specified. How much of the grasslands are degraded worldwide? Which degradation is most common (physical, chemical, biological)? How severe is the degradation, what are the declines in soil fertility or soil structure, soil erosion or soil quality reported for grasslands globally, and specific regions? What are the erosion rates commonly reported for specific regions?
3-Degradation of grassland ecosystems is worthwhile to document and study, and the authors make this point. They also emphasize the need to study alpine meadows as they are fragile ecosystems (L106). This point could be further developed by including quantitative data on grassland degradation in the paragraph on L104-117. What is the decline in vegetation cover over the region, and what are the main degradation processes? In how far this affects river hydrology downstream? The authors mention that the degradation of the meadows reduced runoff and river streamflow, but what are the processes involved? How was runoff reduced by grassland degradation? Can the authors provide data from the literature to show the effects on streamflow? As this study is part of a larger programme on soil erosion in the area, reference to previous studies (and their results) is necessary to show the added value of this particular contribution.
4-Throughout the manuscript, the authors refer to the 'maintenance of runoff' as one of the fundamental objectives of restoration efforts (L88-89). This merits to be further explained and contextualised, as this might be very specific for arid and semi-arid regions such as the region under study. In most regions, restoration efforts aim to reduce runoff generation through e.g. buffer strips or revegetation (see e.g. Vanacker et al., 2022) as runoff enhances entrainment and transport of sediment. Therefore, the combination of soil loss reduction and runoff maintenance is somewhat unexpected and could benefit from some additional explanation and framing.
5-The effect of the measures is quantified through "reduction ratios" of runoff, soil erosion and sediment concentration. The authors compared the reduction ratios between the three treatments to assess their effectiveness. In the discussion, reference is also made to 'significant increased surface runoff' compared to the SDM-reference site. It is not entirely clear how this was assessed as this would imply demonstrating that the reduction ratios are significantly different from '0' while fig4 shows the results of the ANOVA - with significance of difference in reduction ratios between the three treatments. An analysis like the one presented in Fig5 (using absolute values of soil loss, runoff and sediment concentration) would be an alternative solution.
6-The soil erosion measurements on the experimental site with its 4 runoff plots have been described in earlier work by e.g. Niu et al. (2021) and previous publications by Liu et al. (2019, 2022). Previous studies mostly focused on plant characteristics and how they affect runoff rates and soil losses, and it would be worthwhile to indicate how this particular study is related to previous work. This can be done in the description of the experimental site, or at the end of the introduction.
Detailed comments
L20: What do the authors mean by the "stability of the hydrological cycle", "runoff reduction ratio", "sediment concentration reduction ratio"? Can they refer to commonly used terminology in the discipline?
L22: Can the authors rephrase the sentence? What do they mean by "strategy"?
L42: Are the grasslands always 'natural habitats', or just 'habitats'? What do they mean by 'natural'?
L45-46: Some quantitative data on degradation are necessary here to back up these statements. What do the authors understand with 'severe degradation'? Can they include some data on soil erosion rates? compaction? productivity decline?
L48: Please rephrase 'treatening drivers'
L79: Can the authors refer to a standard definition of surface runoff here, for example from handbook on soil erosion?
L81: Rainfall intensity (instead of 'rate')?
L83: Can the authors rephrase runoff is 'carrier of sediment transport'?
L84: Please check sentence 'such as vegetation restoration'
L86: The reference to a specific study region is a bit of the context here.
L88-89: Here, the authors mention that 'the fundamental objective of restoration efforts is to maintain runoff while reducing its level of sediment concentration'. This statement needs to be better framed/explained, as many restoration activities focus on runoff reduction through e.g. enhanced infiltration. Therefore, this statement cannot be written as such, and needs to be contextualised and explained. Please refer here to specific contexts including sufficient scientific references.
L95: Please rephrase 'reciprocal cementation'
L111: this statement is counter-intuitive, please provide some data (from literature) to show the effects.
L115: The term "artificial grasslands" needs to be explained/defined here
L123-125: Please check that you define the abbreviations 'DE, PE and PD and SDM' before using them.
L136-137: It is common practise to refer to the meteorological station(s) (and the period of measurements) when mentioning meteorological data. Can the authors provide the name and location of the station (and mention the reference period)?
L137: 'not showing distinct seasons, just cold and warm ones' -> this is not clear, please check.
L147: 'mattic epipedom' -> this is not clear, please check.
L149: It is very good to have these numbers, it would be interesting to contextualise them (compare them with rates in other regions)
L152: Can the authors define 'mixed-cultivated grasslands'? why 'mixed'? why 'cultivated?
L156: The abbreviations could be defined here.
L161: Please clarify: Is the objective to prevent soil loss, and water loss? So, one is searching for vegetation with low evaporative demand?
L163: habits?
L173: please check the wording here. the authors probably refer to animal grazing, not entirely clear what is considered to be 'artificial grassland construction'
L205: can the authors specify where there was no snowfall during the monitoring period, or whether the gauge did not sample snow? In a conventional rain gauge, snow would also fall in the pluviometer.
L207: is the average rainfall intensity corresponding to rainfall amount divided by duration of event? please specify.
L214: one could refer here to the pore size of the filter paper.
L227: Did the authors include the dead and/or living vegetation in the assessment of the vegetation cover?
L229: each year? or each month? as the authors refer to 'monthly measurements' on L227
L239: 'NCP' is not defined, please check
L272: 'dramatically' not needed here
L273: p < 0.05
L278: influenced by planting age
The description of the experimental design and the monitoring is very detailed and includes valuable information on the rationale behind the plant selection.
L309: runoff amount?
L314: Why is R the most relevant one? Is this because it has the highest influence?
L326: Can the authors specify the added value of this study compared to Liu et al (2019, 2022). Are these studies conducted on similar plots, and yield similar results?
L356: Can the authors specify if Niu et al. (2021) concerns similar plots or experiments? If so, this needs to be mentioned upfront in the description of the experimental site.
Figure 1 - nice figure
Figure 3 - the title of the Y-axis in Fig3b refers to 'soil erosion module' -> is this the same thing as the 'soil erosion' stated above?
Data availability: It is common practice to provide the raw data as spreadsheets in the supporting information. A database with the observations and measurements per plot and event would facilitate further research on the topic, and review studies.Citation: https://doi.org/10.5194/hess-2023-257-RC2 -
AC2: 'Reply on RC2', Gao-Lin Wu, 20 Feb 2024
This manuscript describes the results of empirical research on the effectiveness of three different restoration measures in a grassland ecosystem. Given that native grasslands are increasingly subject to degradation, such empirical work can be very relevant for restoration efforts. The strength of this work lies in the collection of empirical data on surface runoff and soil loss rates from 4 runoff plots that were monitored over three years. As there are no replicates, the evaluation of the effectiveness of the treatments is based on a time series of events. The experimental site has been the subject of previous publications (Niu et al., 2022; Liu et al, 2019; 2022) that focused on soil mitigation by vegetation restoration.
The following points caught my attention, and they might guide the revisions. Besides these points, I have some detailed comments that are listed below.
Response: We thank Professor Veerle for her positive comments and critical and constructive suggestions. We believe that the reviewers addressed important points and that these comments allowed us to further clarify and strengthen the manuscript.
1-The abstract is informative but contains very specific terms that are not commonly used in hydrology or soil sciences. As such, it is hard to understand the main findings based on the abstract alone. This could be addressed by using standard hydrology or soil science terms in the abstract, or by defining clearly new terms like 'mixed-cultivated grasslands', 'runoff reduction ratio' and 'mean sediment concentration reduction ratio'.
Response: Thank you for your valuable suggestion. To avoid confusing the reader, we have explained the term “mixed-cultivated grasslands” in the abstract section, as shown in lines 23–25: “each sowing two grass species per plot (Deschampsia cespitosa and Elymus nutans (DE), …”. In addition, we have replaced the words “runoff reduction ratio” with “average runoff depth” and “sediment concentration reduction ratio” with “soil loss per unit area”, as shown in lines 29–31: “the values of the average runoff depth for DE, PE, PD and SDM were 0.47, 0.55, 0.45 and 0.27, …”.
2-The study emphasizes the need to measure the effectiveness of vegetation restoration on runoff and erosion in (degraded) grasslands, and the authors make the point that the degradation of grasslands is poorly studied. The introduction contains general statements of the importance of grasslands, and the issue of environmental degradation of these ecosystems. As they are written, the statements are rather general (such as 'water and soil are crucial for human survival'), and merit to be further specified. How much of the grasslands are degraded worldwide? Which degradation is most common (physical, chemical, biological)? How severe is the degradation, what are the declines in soil fertility or soil structure, soil erosion or soil quality reported for grasslands globally, and specific regions? What are the erosion rates commonly reported for specific regions?
Response: The extent of degraded grassland worldwide has been described in lines 45–47: “Despite the importance of grasslands, about half of them are degraded globally, …”. Also, the effects of grassland degradation on soil structure and soil erosion have been added in lines 48–55: “Grassland degradation causes the loss of up to 90% of the soil structure that facilitates …”.
3-Degradation of grassland ecosystems is worthwhile to document and study, and the authors make this point. They also emphasize the need to study alpine meadows as they are fragile ecosystems (L106). This point could be further developed by including quantitative data on grassland degradation in the paragraph on L104-117. What is the decline in vegetation cover over the region, and what are the main degradation processes? In how far this affects river hydrology downstream? The authors mention that the degradation of the meadows reduced runoff and river streamflow, but what are the processes involved? How was runoff reduced by grassland degradation? Can the authors provide data from the literature to show the effects on streamflow? As this study is part of a larger programme on soil erosion in the area, reference to previous studies (and their results) is necessary to show the added value of this particular contribution.
Response: Thank you for your valuable suggestion. We have added the main degradation processes of alpine meadows, as well as the processes involving meadows degradation and the reduction of river streamflow, as shown in lines 117–142: “Over 50% of the alpine meadows have been subject to an increasing degree of degradation (Bardgett et al., 2021), with the extent of degradation depending”.
4-Throughout the manuscript, the authors refer to the 'maintenance of runoff' as one of the fundamental objectives of restoration efforts (L88-89). This merits to be further explained and contextualised, as this might be very specific for arid and semi-arid regions such as the region under study. In most regions, restoration efforts aim to reduce runoff generation through e.g. buffer strips or revegetation (see e.g. Vanacker et al., 2022) as runoff enhances entrainment and transport of sediment. Therefore, the combination of soil loss reduction and runoff maintenance is somewhat unexpected and could benefit from some additional explanation and framing.
Response: Thank you for your valuable suggestion. We have added the explanation of the maintenance of runoff in arid and semi-arid regions, as shown in lines 56–61: “Precipitation is the main water source of soil moisture supply in semi-arid areas and the conversion of precipitation to runoff is one of the major contributors to river streamflow …”.
5-The effect of the measures is quantified through "reduction ratios" of runoff, soil erosion and sediment concentration. The authors compared the reduction ratios between the three treatments to assess their effectiveness. In the discussion, reference is also made to 'significant increased surface runoff' compared to the SDM-reference site. It is not entirely clear how this was assessed as this would imply demonstrating that the reduction ratios are significantly different from '0' while fig4 shows the results of the ANOVA - with significance of difference in reduction ratios between the three treatments. An analysis like the one presented in Fig5 (using absolute values of soil loss, runoff and sediment concentration) would be an alternative solution.
Response: I am sorry maybe a misunderstanding exists. "The surface runoff volume of the three mixed grasslands was significantly increased compared to that of SDM" this result is derived from Fig. 3a. Whereas, Fig. 4a displayed the effectiveness of the three mixed grasslands in maintaining runoff. As shown in Fig. 3a, the average runoff depths of SDM in 2019, 2020, and 2022 were 0.23, 0.34 and 0.25 mm, respectively, all significantly less than (except for 2020) the average runoff of mixed-cultivated grassland DE PE and PD, which measured 0.44, 0.59 and 0.50 mm in 2019, 0.55, 0.51 and 0.38 mm in 2020, 0.43, 0.54 and 0.40 mm in 2022. To avoid confusing the reader, we have revised the expression of the findings in Figure 3, as shown in lines 352–317: “The average runoff depths of SDM in 2019, 2020, and 2022 were 0.23, 0.34 and 0.25 mm, …”.
6-The soil erosion measurements on the experimental site with its 4 runoff plots have been described in earlier work by e.g. Niu et al. (2021) and previous publications by Liu et al. (2019, 2022). Previous studies mostly focused on plant characteristics and how they affect runoff rates and soil losses, and it would be worthwhile to indicate how this particular study is related to previous work. This can be done in the description of the experimental site, or at the end of the introduction.
Response: The earlier work Niu et al. (2021) focused on the effect of different degrees of alpine meadow degradation, i.e., different meadow patch coverage, on runoff and soil loss; Liu et al. (2019) investigated the effects of gramineae and legume grasses on runoff and sediment reduction runoff and sediment reduction under rainfall simulation scenarios in the Loess Plateau. Yes, the soil erosion measurements on the experimental site with its 4 runoff plots in the manuscript have been described in our previous publication (Liu et al., 2022), but the work focused on the effects of plant morphological characteristics on runoff and soil loss. Hence, we have added a description of the previous work as shown in lines 138–140: “Recent studies by Niu et al. (2021) and Ma et al. (2023b) …”, and in lines 163–165: “Only Liu et al. (2022) the effects of plant morphological characteristics on runoff …”.
Detailed comments
L20: What do the authors mean by the "stability of the hydrological cycle", "runoff reduction ratio", "sediment concentration reduction ratio"? Can they refer to commonly used terminology in the discipline?Response: The words “stability of the hydrological cycle” have been replaced with “stability of the local runoff amount” as shown in line 20. Meanwhile, the terms “sediment concentration reduction ratio (CRE)”, “sediment reduction ratio (SRE)” and “runoff reduction ratio (RRE)” have been replaced with sediment concentration reduction benefit (CRB)”, “sediment reduction benefit (SRB)” and “runoff reduction benefit (RRB)”, respectively, based on the previous studies Zhao et al. (2014) and Liu et al. (2019), such as in lines 311–314, 317–318, and 371–373.
L22: Can the authors rephrase the sentence? What do they mean by "strategy"?
Response: The word “strategy” means three mixed-cultivated grasslands. To avoid confusing the reader, we have rephrased the sentence, as shown in lines 21–26: “In this research, we conducted in situ monitoring using runoff plots to investigate the impact of three mixed-cultivated grasslands, each sowing two grass species per plot (Deschampsia cespitosa and Elymus nutans (DE), Poa pratensis L.cv. Qinghai and Elymus nutans (PE) and Poa pratensis L.cv. Qinghai and Deschampsia cespitosa (PD)), on a 20-degree slope, assessing the activation and volume of surface runoff and soil loss in alpine degraded hillsides over three years (2019, 2020 and 2022).”.
L42: Are the grasslands always 'natural habitats', or just 'habitats'? What do they mean by 'natural'?
Response: We have erased the word “natural” as shown in line 42.
L45-46: Some quantitative data on degradation are necessary here to back up these statements. What do the authors understand with 'severe degradation'? Can they include some data on soil erosion rates? compaction? productivity decline?
Response: Thank you for your valuable suggestion. The assessment method of grassland degradation by Gang et al. (2014) cited in this study was based on net primary productivity. Global grassland net primary productivity (NPP) has declined by 58.84 Tg C per year. The aforementioned information has been incorporated into lines 46–48: “… (based on net primary productivity), which has become a major issue for humanity to overcome (Gang et al., 2014; Török et al., 2021). Global grassland net primary productivity (NPP) has declined by 58.84 Tg C per year.”.
L48: Please rephrase 'threatening drivers'
Response: We have erased the sentence in the resubmitted manuscript in line 48.
L79: Can the authors refer to a standard definition of surface runoff here, for example from handbook on soil erosion?
Response: We have revised the sentence as shown in line 98: “Surface runoff – also known as stormwater runoff or overland flow …”.
L81: Rainfall intensity (instead of 'rate')?
Response: The words “rainfall rate” have been replaced with “rainfall intensity” as shown in line 101.
L83: Can the authors rephrase runoff is 'carrier of sediment transport'?
Response: The words “carrier of sediment transport” have been replaced with “serves as the main agent for sediment transport” as shown in lines 103–104.
L84: Please check sentence 'such as vegetation restoration'
Response: The sentence “such as vegetation restoration” has been revised to “such as through vegetation restoration” as shown in line 105.
L86: The reference to a specific study region is a bit of the context here.
Response: We have revised the sentence as shown in lines 106–108: “However, for the arid and semi-arid regions, surface runoff is the major water supply source to the river streamflow, thereby it is vital for ensuring the sustainability of ecosystems (Liu et al., 2020; Robinson et al., 2003).”.
L88-89: Here, the authors mention that 'the fundamental objective of restoration efforts is to maintain runoff while reducing its level of sediment concentration'. This statement needs to be better framed/explained, as many restoration activities focus on runoff reduction through e.g. enhanced infiltration. Therefore, this statement cannot be written as such, and needs to be contextualised and explained. Please refer here to specific contexts including sufficient scientific references.
Response: Thank you for your valuable suggestion. The scientific references have been added in lines 56–61: “Precipitation is the main water source of soil moisture supply in semi-arid areas and the conversion of precipitation to runoff is one of the major contributors to river streamflow ...”.
L95: Please rephrase 'reciprocal cementation'
Response: We have erased the words “reciprocal cementation and” in line 115.
L111: this statement is counter-intuitive, please provide some data (from literature) to show the effects.
Response: We have added references on alpine meadow degradation disrupting the soil water balance and reducing surface runoff, as shown in line 144.
L115: The term "artificial grasslands" needs to be explained/defined here
Response: We have defined the term “artificial grassland” in lines 147–149: “Artificial grassland – also known as tamed grassland, sowed grassland and cultivated grassland – refers to fields that have been broken up and replanted with exotic grasses and forbs and utilized for hay crop production or cattle grazing (Fisher et al., 2018).”
L123-125: Please check that you define the abbreviations 'DE, PE and PD and SDM' before using them.
Response: We have added the explanation of the abbreviations of the three mixed-cultivated grassland types and SDM, as shown in lines 167–169: “… Deschampsia cespitosa and Elymus nutans (DE), Poa pratensis L.cv. Qinghai and Elymus nutans (PE) …”.
L136-137: It is common practise to refer to the meteorological station(s) (and the period of measurements) when mentioning meteorological data. Can the authors provide the name and location of the station (and mention the reference period)?
Response: we have added the period of measurements and date resource in lines 183–187: “In the study region, the average annual temperature is -3.1°C, with monthly variations from -14.7°C in January to 7.5°C in July between 1981 and 2018, according to data sourced from the European Centre for Medium-Range Weather Forecasts. …”.
L137: 'not showing distinct seasons, just cold and warm ones' -> this is not clear, please check.
Response: We have revised the sentence, as shown in lines 182–183: “… not showing the typical four-season pattern (spring, summer, autumn, winter), but rather just two main seasons: cold and warm.”
L147: 'mattic epipedom' -> this is not clear, please check.
Response: This is a typo, we have carefully checked the whole paper and replaced the words “mattic epipedom” with the words “mattic epipedon”, such as in lines 195, 756 and 757.
L149: It is very good to have these numbers, it would be interesting to contextualise them (compare them with rates in other regions)
Response: Thank you for your valuable suggestion. The erosion rates in other regions have been added in lines 52–55: “For example, in the Swiss alpine uplands, water erosion ranges from 0.14 to 1.25 t ha-1month-1 according to the phenological …”.
L152: Can the authors define 'mixed-cultivated grasslands'? why 'mixed'? why 'cultivated?
Response: We have added the explanation of the terms “cultivated grasslands” in lines 147–149: “Artificial grassland – also known as tamed grassland, sowed grassland and cultivated grassland – refers to fields that have been broken up and replanted with exotic grasses and forbs and utilized for hay crop production or cattle grazing (Fisher et al., 2018).”. Also, we have added the explanation of “mixed” in line 23 “… each sowing two grass species per plot …”, and in lines 200–201: “mixed-cultivated grasslands – fields were ploughed and replanted with two grass species …”
L156: The abbreviations could be defined here.
Response: To enhance reader comprehension of the paper, we have provided definitions of abbreviations in lines 23–25, 167-169, and 240–242.
L161: Please clarify: Is the objective to prevent soil loss, and water loss? So, one is searching for vegetation with low evaporative demand?
Response: To avoid confusing the reader, the word “prevent soil and water loss” have been revised to “prevent soil loss and maintain surface runoff” in line 218.
L163: habits?
Response: The word “habits” has been revised to “living habits”, as shown in line 220.
L173: please check the wording here. the authors probably refer to animal grazing, not entirely clear what is considered to be 'artificial grassland construction'
Response: I am sorry maybe a misunderstanding exists. Artificial grassland – also known as tamed grassland, sowed grassland and cultivated grassland – refers to fields that have been broken up and replanted with exotic grasses and forbs and utilized for hay crop production or cattle grazing (Fisher et al., 2018). In this study, owing to overgrazing and rodent activity, the mattic epipedon of the alpine meadow has been completely removed, exposing the subsoil and forming a severely degraded meadow. Establishing artificial grassland is widely used to restore severely degraded meadows in the study area (Li et al., 2023; Shang et al., 2008; Wu et al., 2010).
L205: can the authors specify where there was no snowfall during the monitoring period, or whether the gauge did not sample snow? In a conventional rain gauge, snow would also fall in the pluviometer.
Response: I am sorry maybe a misunderstanding exists. We only monitored surface runoff and soil erosion during the growing season of four runoff plots, and analyzed the corresponding rainfall conditions during that period. We intend to clarify that within the study area's growing season (spanning from June 15 to August 25), there was no occurrence of snowfall, solely rainfall. To avoid confusing the reader, the sentence has been revised to “Snow was not collected, and only rainfall was recorded during the growing season (from June 15 to August 25).” in lines 262–263.
L207: is the average rainfall intensity corresponding to rainfall amount divided by duration of event? please specify.
Response: Yes. We have added the explanation in lines 264–265: Average rainfall intensity (ARI) was calculated by dividing the total rainfall amount by the duration of the rainfall event.
L214: one could refer here to the pore size of the filter paper.
Response: We have added the pore size of the filter paper in line 272.
L227: Did the authors include the dead and/or living vegetation in the assessment of the vegetation cover?
Response: Yes. Dead (standing litter) and surviving vegetation were included in the assessment of vegetation cover. We have added the information in line 289: “Vegetation cover (VC), including dead (standing litter) and living vegetation, …”.
L229: each year? or each month? as the authors refer to 'monthly measurements' on
Response: We measured vegetation cover in the middle of June, July, and August.
L239: 'NCP' is not defined, please check
Response: We have added the definition of NCP in line 301.
L272: 'dramatically' not needed here
Response: We have erased the word “dramatically” in line 348.
L273: p < 0.05
Response: we have carefully checked the whole paper and replaced “P < 0.05” with “p < 0.05”, such as in lines 349, 353 and 359.
L278: influenced by planting age
Response: We have erased the words “the age of the” in line 358.
The description of the experimental design and the monitoring is very detailed and includes valuable information on the rationale behind the plant selection.
Response: Thank you so much for your kind encouragement.
L309: runoff amount?
Response: The words “runoff yield” have been replaced with “runoff amount” in line 402.
L314: Why is R the most relevant one? Is this because it has the highest influence?
Response: We have revised the sentence in line 407: “Soil loss was significantly influenced by R, RI60, ARI and LB.”.
L326: Can the authors specify the added value of this study compared to Liu et al (2019, 2022). Are these studies conducted on similar plots, and yield similar results?
Response: The earlier work Liu et al. (2019) investigated the effects of gramineae and legume grasses on runoff and sediment reduction runoff and sediment reduction under rainfall simulation scenarios in the Loess Plateau. Yes, the soil erosion measurements on the experimental site with its 4 runoff plots in the manuscript have been described our previous publication (Liu et al., 2022), but the work focused on the effects of plant morphological characteristics on runoff and soil loss. Hence, we have added a description of the previous work as shown in lines 163–165: “Only Liu et al. (2022) the effects of plant morphological characteristics on runoff …”.
L356: Can the authors specify if Niu et al. (2021) concerns similar plots or experiments? If so, this needs to be mentioned upfront in the description of the experimental site.
Response: The earlier work Niu et al. (2021) focused on the effect of different degrees of alpine meadow degradation, i.e., different meadow patch coverage, on runoff and soil loss. Hence, we have added a description of the previous work as shown in lines 130–132: “Recent studies by Niu et al. (2021) and …”, and in lines 142–144: “The long-term and widespread degradation of hillside alpine meadows has disrupted …”.
Figure 1 - nice figure
Response: Thank you so much for your kind encouragement.
Figure 3 - the title of the Y-axis in Fig3b refers to 'soil erosion module' -> is this the same thing as the 'soil erosion' stated above?
Response: We have revised the title of the Y-axis “soil erosion module” to “soil loss per unit area” in Fig. 3b.
Data availability: It is common practice to provide the raw data as spreadsheets in the supporting information. A database with the observations and measurements per plot and event would facilitate further research on the topic, and review studies.
Response: Thank you for your comment and feedback. Data availability has been revised to “The data that support the findings of this study are available on request from the corresponding author.”.
References
Bardgett, R.D., Bullock, J.M., Lavorel, S., Manning, P., Schaffner, U., Ostle, N., Chomel, M., Durigan, G., Fry, E.L., Johnson, D., Lavallee, J.M., Le Provost, G., Luo, S., Png, K., Sankaran, M., Hou, X.Y., Zhou, H.K., Ma, L., Ren, W.B., Li, X.L., Ding, Y., Li, Y.H., and Shi, H.X.: Combatting global grassland degradation, Nat. Rev. Earth Env., 2(10), 720–735, https://doi.org/10.1038/s43017-021-00207-2, 2021.
Fisher, R.J., Sawa, B., and Prieto, B.: A novel technique using LiDAR to identify native-dominated and tame-dominated grasslands in Canada, Remote Sens. Environ., 218, 201-206, https://doi.org/10.1016/j.rse.2018.10.003, 2018.
Li, J., Jiang, X., Zhou, X.H., Yin X., Niu, K.: Grasses mixture-planting rather than fertilization depresses soil microbial diversity in an alpine artificial grassland, Plant Soil, https://doi.org/10.1007/s11104-023-06395-8, 2023.
Liu, Y.F., Dunkerley, D., López-Vicente, M., Shi, Z.H., and Wu, G.L.: Trade-off between surface runoff and soil erosion during the implementation of ecological restoration programs in semiarid regions: A meta-analysis, Sci. Total Environ., 712, 136477, https://doi.org/10.1016/j. scitotenv.2019.136477, 2020.
Ma, Y.L., Liu, Y.F., López-Vicente, M., and Wu, G.L.: Divergent shift of normal alpine meadow exacerbated soil loss of hillslope alpine meadows based on field experiments. Int. Soil Water Conse. Res., In Press, https://doi.org/10.1016/j.iswcr.2023.11.007, 2023.
Shang, Z.H., Ma, Y.S., Long, R.J., and Ding, L.M.: Effect of fencing, artificial seeding and abandonment on vegetation composition and dynamics of ‘black soil land’ in the headwaters of the Yangtze and the Yellow Rivers of the Qinghai-Tibetan Plateau, Land Degrad. Dev., 19(5), 554–563, https://doi.org/10.1002/ldr.861, 2008.
Wu, G.L., Liu, Z.H., Zhang, L., Hu, T., and Chen, J.: Effects of artificial grassland establishment on soil nutrients and carbon properties in a black-soil-type degraded grassland, Plant Soil, 333(1–2), 469–479, https://doi.org/10.1007/s11104-010-0363-9, 2010.
Zhao, X.N., Huang, J., Wu, P.T., Gao, X.D.: The dynamic effects of pastures and crop on runoff and sediments reduction at loess slopes under simulated rainfall conditions, Catena, 119, 1–7, http://dx.doi.org/10.1016/j.catena.2014.03.001, 2014.
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AC2: 'Reply on RC2', Gao-Lin Wu, 20 Feb 2024
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