the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Regulating effects of mixed cultivated grasslands in surface water conservation and soil erosion reduction along with restoration of alpine degraded hillsides
Yulei Ma
Jesús Rodrigo-Comino
Manuel López-Vicente
Gao-Lin Wu
Abstract. Vegetation restoration is one of the most effective measures to control runoff and sediment by human management. Nevertheless, few studies have been undertaken to objectively analyze the effectiveness of the effects of plant restoration on regional water availability, especially, in mixed-cultivated grasslands in alpine degraded hillsides. In this research, we carried out in situ monitoring using micro-plots to investigate the impact of three strategies, combining two grass species per plot (three species in total), in a 20-degree slope on the activation and volume of surface runoff and soil loss in alpine degraded hillsides for three years (2019, 2020 and 2022). A bare-soil plot was used as control. The findings indicated that mixed-cultivated grasslands can effectively conserve water and decrease soil loss along the increasing planting ages. Grass community of Deschampsia cespitosa and Poa pratensis L.cv. Qinghai was the most effective in reducing soil erosion. From 2019 to 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 soil erosion reduction ratio of the cultivated grass communities increased from -184.8 % to 18.0 % (in DE), from -231.5 % to 24.3 % (in PE), and from -139.3 % to 31.9 % (in PD), respectively, from 2019 to 2022; and the corresponding mean values of sediment concentration reduction ratio also 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 implied that protection measures should be considered a priority during the initial planting stage of cultivated grassland 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 grasslands.
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Yulei Ma et al.
Status: final response (author comments only)
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CC1: 'Comment on hess-2023-42', Qianjin Liu, 07 Mar 2023
This manuscript presented an important information on the change of soil and water loss in the mixed-cultivated grass land in alpine degraded hillsides, and the influencing factors were identified and interpreted in a detail. A minor revision needs to be performed before acceptance.
The detailed comments and suggestions are listed as follows:
Line 45: Please add the main human activities.
Line 59: considered may be better than viewed.
Line 76: Please use promote instead of active.
Line 82: Please delete solid.
Line 104: Please provide a statement on mixed artificial grasslands and on temporal variations in soil and water loss after planning or seeding at other regimes.
Line 125-126,: Please move these kind of contents to the instruction section.
Line 154: solely?
Line 355: please give the temporal change of soil and water loss and the main reason.
Fig. 2b: Please have a check the capital letter for PE.
Citation: https://doi.org/10.5194/hess-2023-42-CC1 - AC1: 'Reply on CC1', Gao-Lin Wu, 22 Sep 2023
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RC1: 'Comment on hess-2023-42', Corinna Gall, 14 Mar 2023
In this study, surface runoff and soil erosion are measured for three different combinations of grass species and a bare soil control sample in degraded alpine hillsides on the Qinghai-Tibetan Plateau, using runoff plots under natural rainfall. The goal is to find a grass mixture for grassland restoration that is best adapted to the needs of the ecosystem. This is a very important approach to grassland restoration that has not been sufficiently studied. Therefore, I consider this study worth publishing within the scope of HESS, however, it needs to be considerably revised in terms of comprehensibility.
Unfortunately, it is difficult to follow the structure in the introduction and in some parts to understand the reasoning in the discussion. In the introduction, it is challenging to find a common thread. In general, the introduction needs to be modified in order to lead the reader specifically to the goal or hypotheses of the study. I propose to explain the problems regarding surface runoff and soil erosion in this alpine grassland ecosystem in more detail at the beginning before pointing out the specific research gaps. Also, it would be good to end the introduction with hypotheses that you will answer throughout the manuscript. In the discussion, it is not always clear how the conclusions are reached. Some statements are too strong on the basis of the data presented and should be considered in a more differentiated way.
Additionally, I have the following comments and questions for the authors to consider:
Abstract
Line 19: Please rephrase “effectiveness of the effects”.
Lines 21-22: Are you sure the size is still micro-runoff plots?
Lines 21-24: If you measured surface runoff and soil loss, what can you say about the regional water availability mentioned above? It seems to me here that the representation of the knowledge gap and the research objective do not fit together properly.
Line 25: What is meant here by “conserve water”?
Lines 30-35: There are too much values for the abstract section. Maybe only list significant changes.
Introduction
Line 58: What do you mean with “maintaining runoff” here? Wouldn't it be desirable to reduce runoff and promote water retention in the soil?
Line 59: I recommend “considered” instead of “viewed”.
Line 61: I recommend “plant species” instead of “plant types”.
Line 68: This reference deals with tree restoration. Does this statement also apply to grasslands? Please provide a reference.
Line 70: Please change to “Grass communities … are …”.
Lines 70-72: What do you mean with “conserve water” in this context? Maybe use “retain” instead?
Line 73: Please rephrase “biomass grasses plant and litter cover”.
Lines 74-78: This sentence is difficult to understand. Please consider rephrasing.
Line 83: Please specify “changing” here.
Lines 84-86: A dense root system is more effective than what? Please clarify.
Line 87: I would suggest referring to alpine grassland as an ecosystem or landscape unit rather than a plant type.
Lines 94-96: This sentence explains my question in Line 58. This explanation must be given earlier.
Methods
Line 110: It is unclear what the term "representative area" refers to.
Line 112: What means “Three Rivers” here? Is it a landscape unit or a district?
Lines 113-118: Please be more specific here. Perhaps provide additional averages for temperature and precipitation per season to illustrate the differences between warm and cold seasons.
Line 129: Please use “climate” instead of “climatic”.
Lines 129-130: I would suggest to change the wording to “…have complementary morphological characteristics and habits”.
Line 149: Figure 1 shows that the control plot is not completely bare, but is degraded grassland. Please mention this in the text as well.
Line 154: Please use “runoff plot” instead of “runoff area”.
Lines 93 +113 + 152 + 157: Please make clear which part of Figure 1 you are referring to (a, b, c, or d).
Line 169: Does this mean that all precipitation events outside the growing season were snow and therefore measurements were only taken during the growing season? How did you deal with melt water erosion in the time between the growing seasons?
Lines 174-175: How did you ensure that the water and sediment in the tank were evenly mixed in order to collect two representative 500-ml samples?
Lines 178-179: I think there is an incorrect description of the drying of the sediment here. Air drying to a constant weight at 105°C does not fit together.
Line 184-188: In my opinion, scaling to km² is not appropriate for such small runoff plots. I would recommend expressing soil erosion in kg / g m-2. Moreover, it is confusing to extrapolate only soil erosion and not surface runoff within the same sample.
Lines 191-193: It is not clear how and when vegetation cover and plant litter biomass were obtained. Was the vegetation coverage estimated for August 2022 only or after each rainfall event? What do you mean by "collection techniques" in the context of plant litter biomass? Was the plant litter biomass determined randomly in the 50x50cm frames or for the entire plot? Please specify and provide references for your methods.
Line 202: Please provide the primary source for these indices. They were also used in Zhao et al. 2014The dynamic effects of pastures and crop on runoff and sediments reduction at loess slopes under simulated rainfall conditions.
Lines 207-210: Be sure to use a consistent spelling of "mixed cultivated grassland". Sometimes you use it with a dash, sometimes without.
Line 215: I suggest the expression “to test for significant differences between”.
Figure 1: Please use your abbreviations for the treatments also in Figure 1. The runoff plots appear a bit distorted and of different sizes in the illustration, perhaps a simple top view would be more appropriate here. Please check the spelling and punctuation in the figure caption again (line 541-546).
Results
Line 225: Please be consistent with the designation of your treatments. Usually you have used the term "bare land" or the abbreviation "BL".
Lines 221-234: It would be very valuable here to additionally provide a diagram with the values of vegetation cover per year and plot. Especially, it would be good to know the vegetation cover of the bare land treatment, as it was not completely bare. In addition, information is needed on how you managed the bare land treatment during the three-year experiment. If there were no human impacts as described in the methods, surely the vegetation cover on the bare land was lower in 2019 than in 2022?
Figure 2 and 3: In general, the illustrations are a bit overloaded with information. Therefore, I suggest to remove the jitter points and instead indicate the number of measurements per year, which should be the same for all treatments. Furthermore, I would remove the written mean values because they are already mentioned in the text. It would also be a good idea to choose different colours for your treatments, as they are indistinguishable to readers with colour vision deficiencies. Please also explain your boxplots in more detail in the figure caption, e.g., the line inside boxplots sometimes refers to median, sometimes to mean values, which is not explained here.
Figure 3: Please change the y-axis label of part (d) to “RRSR”.
Lines 232-234: Please explain how you came to this conclusion based on the results.
Lines 244-245: This sentence rather belongs to the discussion section.
Line 247: Space is missing between “were” and “PD”.
Lines 251-252: This was only the case in 2022. From 2019 to 2020 the RRSR was higher than 1, is this right?
Lines 254-264: Instead of listing all the values of the path analysis, it would be more comprehensible to list only the values of the most important parameters.
Table 1: Please include the explanation of “*” in Table 1 instead of Table 2.
Table 1 and 2: Sometimes the description of parameters in the caption is not clear, e.g., “ARI is average intensity” should be average rainfall intensity. Please check and clarify.
Line 265: Please change to “with R being the most relevant”.
Line 271: In Table 2 the indirect path coefficient of LB is -0.02, in the text it is -0.03. Please check again.
Discussion
Lines 275-276: What do you mean by "conserve water"? Perhaps retaining or storing water? Also, it is not clear to me how you conclude that soil loss was minimized, since soil erosion on bare land was lower than on grassland in 2019 and 2020 after all, and in 2022 the difference was not significant (Figure 2b).
Lines 291-293: Are these percentages based on the average values from Table 3? If this is the case, I assume, the percentages are not correct.
Lines 301-302: I do not really understand what is meant by this sentence.
Line 321: Please correct the spelling of Poa pratensis here and in the whole paragraph.
Lines 322-323: It is unclear to me how you come to this conclusion, since there were no significant differences between the grass mixtures.
Lines 348-352: This part rather belongs to the introduction section to underline the importance of this study.
Line 353-354: I suggest deleting the term “Overland flow turbidity” here, as this is the first time it has been used and it is confusing when new terms are introduced at the end of the discussion.
Conclusions
Lines 356-359 + 361-364: These are too strong statements for the data you presented in your manuscript.
Corinna Gall
Citation: https://doi.org/10.5194/hess-2023-42-RC1 - AC2: 'Reply on RC1', Gao-Lin Wu, 22 Sep 2023
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RC2: 'Comment on hess-2023-42', Veerle Vanacker, 28 Aug 2023
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.
Given a longstanding interest in soil and water conservation measures, and their effectiveness and efficiency, there exists a vast amount of literature on the topic. It includes not only empirical work on e.g. runoff or Wishmeier plots, but also regional synthesis on the effectiveness of conservation measures. This manuscript would be strengthened by embedding it better in the international literature, using e.g. the terminology that was established in soil erosion research, and using standardised methods for measuring the effectiveness of treatments.
Four major points caught my attention, and they might guide the revisions. Besides these points, I have some detailed comments that are listed below.
1-The methodological aspects need to be better explained to the reader as to avoid confusion. The effect of the measures is quantified through "reduction ratios" of runoff, soil erosion and sediment concentration. Is it not entirely clear why the authors have chosen to focus on the "reduction ratios" rather than the absolute values of runoff quantity, and soil erosion rate? What is the added value of introducing such ratios? What is the difference between the effect on soil erosion, and the effect on the "sediment concentration" if both are quantified based on measurements from the sediment that is eroded from the plots, and captured in the tank? Given that the size of the plots is the same, the "sediment concentration" measure would be redundant if the "runoff depth" and "soil erosion rate" were given. Can you explain why you keep "concentration" as an indicator?
I can see that the authors want to compare treatments, with the "control" of bare land, but are the experimental plots in a comparable initial state? From the text, one might have the impression that the "control" site is left untouched while the other plots have been prepared for seeding, including ploughing of the site. Ploughing might have a strong impact on the soil physical properties, and change surface roughness, break up soil crusts and enhance infiltration. As such, there is an effect of ploughing and then of the vegetation. If the "control" plot is not ploughed, how do you differentiate between the effect of mechanical ploughing (and breaking up soil crusts) and the effect of vegetation?
2-There is some confusion in the text with regard to vegetation restoration as a measure to control water runoff and soil erosion. This can be due to the framing of the research, and the use of terminology. For example, the authors often refer to "control runoff and sediment" but it would be good to have more precise use of the terminology that is commonly used in soil erosion studies. Are the authors referring to "in-situ runoff" and "soil erosion"? or "sediment mobilisation and lateral transport"? In the methods (L184 and following), the authors also introduce another term to express the soil loss rate, which is the "soil erosion modulus". It is not clear to me why a new term is introduced.
3-The authors describe the soil and water conservation treatments in different ways, which is somehow confusing for the reader. A clear description of the vegetation composition of the alpine grasslands would be helpful, as well as an explanation of the human alterations of these grasslands. What are "artificial grasslands", "mixed artificial grasslands", mixed cultivated grasslands"? What are the differences between them in plant species composition?, How are "artificial grassland restoration" projects (L106) done? In the methods, the experiments are rather well described, but it remains unclear if the grasses that are used in the restoration project are native grasses if they are common/abundant in the region, and if the plant composition (two grass species) is common in the region.
Also, it is necessary to describe the initial state of the plots (see comment above). What are the soil physical properties of the plots before running the experiments? Do you have information on bulk density, soil crusts, and topographic roughness? Are these properties similar between the plots?
4-In the description of the results, there is a tendency to overstate the results (and the effect of the treatments). The authors have realised an ANOVA analysis (with posthoc comparison->?) to verify if the treatments lead to different runoff or soil erosion rates (or different ratios). As there are no replicate plots/samples, the authors take the response to individual events as their observations. Wouldn't you expect that the response to these events is somehow autocorrelated? Is there a way to deal with this? It also makes the analyses very sensitive to the definition of the events, which makes me wonder how events were defined/delimited in time. This would merit further explanation in the methods, including a discussion of how consecutive events are used as independent observations.
From Figures 2 and 3, it is clear that the three interventions lead to responses that are often statistically different from the "control" bare land, but that there is rarely a statistical difference between the interventions (they are most of the time all part of the "a" group in Fig 2 and 3). The authors might need to revise the text (section 3.1, and section 3.2) to highlight only significant differences. Also, with regard to the ratios, the text needs to be revised after verifying that the responses are statistically different from 1.
The path analyses merit to be further explained in the method section. What are the variables that go into the path analyses, and what are the observations? In the results, the authors mention that "vegetation cover" and "litter biomass" are explanatory factors, but it is not clear to me how the authors compared the information that you collect at event basis with information that is collected at the start/end of the experiments (VC and LB). Also, some variables like the precipitation (P) would be automatically related to the runoff depth for a given treatment. This merits further explanation and development in the text to understand the results of the path analysis presented in section 3.3.
Detailed comments
L10: check "4" instead of "d"
L18: Please rephrase "control runoff and sediment (?)". Do you mean sediment transport?
L19: "objectively" is not the correct term. do you suggest that previous work was subjective?
L22: The effectiveness of measures is often scale-dependent. What is the size of the plots?
L25: What do you mean by "conserve water"?
L46: Can you rephrase this sentence? Do you mean that the highest population concentrations on earth are found in grassland ecosystems?
L51: Can you check the wording "analyse...root causes, .. impacts and restoration measures of grassland degradation" doesn't read very well.
L58: Efficiency or effectiveness? Please check.
L64: Can you clarify this sentence? What do you mean by "enhancement of soil characteristics with the growth of vegetation"? Which soil properties are improved after vegetation restoration?
L73: Please check the wording of this and the following sentence. The terminology is not always used in the correct way. What do you mean by "grasses below-ground"? Or with the "interaction of soil and rich grassroots"?
L83: What is the effect of the roots on the soil mass? Can you be more explicit here?
L87: Can you check the wording? "alpine grasslands" are not a plant type.
L90: What do you mean by "non-planned human activities"?
L87-98: Given the overall concern of increased soil loss in the alpine grasslands, can you give some quantitative data on soil loss rates in the area (and compare them with other regions)?
L114: Can you be more specific? What do you mean by "just cold and warm'?
L122: Can you give the species that were used in restoration efforts?
L127: Can you be more specific about the meaning of "concentration areas"?
L129: alpine climate (?)
L131: Can you reword "blending complementary grass species"?
L137: above-ground "biomass"? instead of "plants"
L150-154: Are there any replicate plots?
L170: In a conventional rain gauge, snow would also fall in the pluviometer. So, did you account/correct for that?
L172: Average intensity of the rain event? or of the 60-minute interval?
L178: Can you check the wording: what is "qualitative filter paper"?
L178-179: There is some inconsistency here: either air-dried or dried at 105°C. Please check.
L197: Please check the wording.
L217: Not entirely clear how this is conceived with 4 plots.
L223: Based on the observations, you cannot conclude that the vegetation restoration increased runoff. In fact, you compare 4 plots with different vegetation cover and different levels of soil roughness and sealing. To conclude that the vegetation restoration has increased the runoff, you would need to do a before/during/after evaluation of the effectiveness of the treatment.
L222 and following: This conclusion "grass communities dramatically influence runoff" is not fully supported. There is a difference between the runoff depth between the bare land and the restoration plots, in 4 out of 6 cases. No difference between the other treatments.
L238: Can you revise the wording of this sentence? What do you mean by "surface water conservation"?
L237-252: Based on the equations provided, the effectiveness is measured using ratios but in the text, the author refers to %. Please check for consistency.
L280 and the following: What do you mean by "soil erosion modulus"?
Section 4.3: The last section of the discussion deals with the "implications of grassland restoration", and discusses differences in surface runoff and soil loss between different treatments. Are the differences significant?
L356-359: Is this what you observe in your results when you compare the "treated" plots with the "control" plots?Figure1: Nice figure especially the pictures on the runoff plots. Is it possible to show the scalebar on all maps, and give some reference on the spatial scale of the pictures?
Figure 3: The reduction ratios are mentioned as fractions in the method sections, which should be the case for a "fraction", but they are then displayed as % in Figure 3. Please check.
Tables 1 &2: Some background info on the path analysis would be welcome. You could add a few sentences in the methods to explain the background of this stat analysis.Citation: https://doi.org/10.5194/hess-2023-42-RC2 -
AC3: 'Reply on RC2', Gao-Lin Wu, 22 Sep 2023
Dear Prof. Veerle Vanacker,
Thank you very much for your critical and constructive comments and suggestions on our manuscript. Please find our detailed answers to all of your comments in the supplement.
Kind regards,
Gao-Lin Wu on behalf of all co-authors
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AC3: 'Reply on RC2', Gao-Lin Wu, 22 Sep 2023
Yulei Ma et al.
Yulei Ma et al.
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