Biological Restoration of Urban Soils after De-Sealing Interventions

Round 1

Reviewer 1 Report

Review of Biological restoration of urban soils after de-sealing interventions

Summary: The authors compare de-sealed soils with a topsoil intervention at three urban sites over a time period of three years. They observed no overall clear differences from the topsoil intervention compared to the de-sealed soil without adding topsoil. From their results they conclude that the intervention with topsoil from agricultural fields are not needed. The fertility of the de-sealed soil per se was enough for the growth of these ornamental plants. Furthermore, since sealed soils can be contaminated with heavy metals they have measured soil and leaf elemental content. But although they observed a metal enrichment over time in the soil, it seems not to be very bioavailable, since the plant leaves showed low levels of these tested heavy metals.

Comments:
I have one problem with the use of “no intervention”. In the conclusion you base the argumentation on the growth and performance of the plants growing in these plots. And these plants were planted there. So there was an intervention of adding ornamental plants. I recommend to be more specific and always talk about topsoil-intervention or something similar. For me no intervention would be, let nature take back the free spot by colonization.

And I miss in the introduction some explanation on the measure values in the context of increasing soil fertility… regarding the sentence from the conclusion: “chemical fertility, in terms of bulk density, pH values and nutrient content, and the increasing of microbial activity and faunal colonization over time.” For me nutrient content and increased microbial activity is clear, but why can you conclude from bulk density and pH value that the soil would increase in fertility. Also and more importantly you don´t show the pH and bulk density over time, only for T0. Could you add this data or otherwise please carefully rephrase this sentence in the conclusion.

Abstract: why do you call it pilot trials? That does not sound good.

Abstract: different font size at the end?

48 allowing, allow

51 context?

63 from pilot trials (use instead from field experiments or experimental plots)

71 strange sentence

78 respectively

90 “was done” maybe use instead: layed open

128 from each experimental plot? And how deep? Did you used soil cores to sample the soil?

132 which acid was used for the soil element analysis of Zn, Cd and Cu?

Table 2 remove the star. Group. Remove the dot.

Table 4 legend- something does not work in these sentences, please check. Top soil or Topsoil, one or two words?

Discussion: why were Zn, Cd and Cu so variable? Did you sample at the same time in the year?? Was maybe the weather very different from year to year?

214 a higher??

231 two times de-sealed

Fig3 legend, add information what T1 is (after one year?)

Fig3 I think the design for the graphs could be improved: please use letters for each graph, or add column titles: enzyme activity, urease, … and use one legend for all graphs with grey as top soil and white for de-sealed soil, plus use abbreviation (DS, TS) as axis labels. Add marks on the y-axis. Reduce some space and then make letters bigger if possible.

238 between de-sealed and topsoil 2x

245 and are

Figure 4, use same colour code as figure 3

Figure 5, please, use same design and colour code as figure 3, and put letters next to the columns

Table 5, after two years…at T1??

Table 5, maybe show it as a graph? Barplots or radar charts to visualize these numbers.

282 in terms in terms, and there was another misplaced “and “ before in the text

291 why specifically low metal concentration confirms… all of the measurements together pointed out that de-sealing soils could sustain plant growth with no topsoil-intervention.

306 plant colonization did not occur (without comma?): do you mean that they have not planted anything and nothing was colonizing yet the bare soil… after how much time?

You do not say anything about the performance of the plants at these sides. Did they show any signs of stress? Any more stress on de-sealed soil compared to topsoil? And are there other studies on how well seeds could develop on these soils? Because the question is what to do with de-sealed bare soil... is planting something there needed? Would that cost more than adding topsoil from agricultural field (which probably contain seeds). Or could plants easily colonize over time. I think this needs to go to the discussion.

 

Author Response

Dear ,

we really appreciate the referee works that have improved our paper.

We substantially reviewed the abstract and reorganizing the results presentation according to the reviewer suggestions, moreover we have also insert data relating the 3-year monitoring for soil biological quality, deleted any redundant data and transformed table into a graph. We delete all speculative sentences in discussion and conclusion sections.

Here we attach  the specific responses to comments

Author Response File: Author Response.docx

Reviewer 2 Report

This paper aims to test whether de-sealed soil without adding topsoil can recover the soil fertility and biological quality. The authors sampled soil properties in three trials of paired treatments in Italy over 3 years. The paired treatments include de-sealed soil, and de-sealed soil with added top-soil. This research topic is very important and the results can be useful for urban de-sealing practices. The manuscript is well-written with clear logic flow. The authors sampled and measured various soil indicators and I appreciate their huge efforts.

What’s pity to me, is that the biological properties were sampled only in time T1 (~8 months after the treatment), with no sampling in T0 (in the beginning of the treatment) and T2 (~3 year after the treatment). Therefore, it is not valid to claim that biological activity is restored with time, without knowing the initial condition of the de-sealed soil.

The only results addressing the research question are the chemical properties, which were sampled in all three time points. But I would strongly encourage the authors to visualize the data by converting the data table into graphs (time as the x-axis). With this approach, the readers can see clearly the temporal trends in soil fertility, as well as the difference between de-sealed and topsoil treatments.  

Finally, I suggest the authors to revise speculative sentences throughout the manuscript, especially “The results demonstrate that de-sealed urban soils

rapidly restore their biological quality and fertility even with no

intervention”.  

For the above reasons, I suggest a major revision of this manuscript. See the detailed comments below.

Abstract

In the abstract, there is a lack of information on trial period, sampling time (month after treatment installation), and trial plot size. To know the temporal and scale scales of this trial help to assess the effect of the treatments.

Line 20-21

Consider to rephrase this sentence for more clarity. For example, “We assessed three paired treatments with de-sealed soil with top soils, and de-sealed soil without top soils. Both treatments have two ornamental shrub species.”

 

Line 21-23

I am not sure if the authors could claim that “the de-sealed soils rapidly restore their biological quality and fertility”. As there is only one time-point (T1) for biological measurement without baseline values (T0) to compare with.

 

For chemical properties, the authors measured three time points. Soil organic carbon is the only properties that increase over time, but only for plot 3. Therefore, the claim “de-sealed soils restore the fertility over time” is not a general pattern observed in this study. The authors could consider revising to “One of three trials shows an increase in soil organic carbon for both top-soil and de-sealed soil treatments.”

Introduction

 Line 48

Delete “allowing”

Methods

Figure 1

It would be interesting to know where the top soils were taken for each trial plots on the map.

Line 91

Consider to add a sentence to summarize the categories of the soil assessment. For example, “We sampled 1) soil chemical, physical, and biological properties, 2) chemical properties of topsoil, and 3) Trace elements of plant leaves.”

Line 94:

Consider to give the information on month for T0.

Line 100-105

Consider to write explicitly whether biological data of T0 or T2 were sampled.

Results

From what I understand, the only analyses addressing on the research question are in Table 3 and Table 4. The authors can compare the treatment effect with a baseline (T0). From Figure 3 onward, the soil properties were sampled at only one time-point (T1). It is not valid to claim that de-sealed treatment performed as well as the topsoil treatment, unless de-sealed treatment has less biological activities than the top-soil at T0.

Page 7

Except for soil texture, there is no difference in pH, bulk density, and total carbon between top soil and de-sealed soils. Additionally, TOC is lower in top-soil at site 3. If I understand correctly, the top-soil and de-sealed soil are very similar, while top-soil may even be less fertile given a lower TOC at site 3. Could these data explain why the authors did not find a significant benefit of adding top soil?

In contrast, if the de-sealed soils have apparently poorer soil fertility than top soil in some other cases, would adding top-soil beneficial? If it is more likely, whether to add top-soil or not seems to depend on the difference in the fertility of de-sealed soil and the added top soil. The authors may consider to elaborate this point a bit in the Discussion, and to state whether the findings in this study can be applied in different soil conditions.

Table 4

Is it possible to convert the table into graphs here? For example, X-axis being sampling points (time), Y axis being different soil properties, point color being top soil vs de-sealed soil. In this case, it is much easier to compare the paired treatments, and to see the temporal trends.

Discussion

1. The authors can address the caveats as mentioned above.
2. The wording of the main conclusion should be more conservative and avoid speculation (for example, Line 278-279).

Author Response

Dear ,

We really appreciate the referee works that have improved our paper.

We substantially reviewed the abstract and reorganizing the results presentation according to the reviewer suggestion, moreover we have also insert data relating the 3-year monitoring for soil biological quality, deleted any redundant data and transformed table into a graph. We delete all speculative sentences in discussion and conclusion sections.

Here are the specific responses to referee's comment

Author Response File: Author Response.docx

Reviewer 3 Report

Broad comments:

Because of the heterogeneous nature of the soils, even more in urban soils much more samples should be investigated when the de-sealing project start in the practice.

De-sealed soils may contain organic contaminants which can pollute the air and may have hazardous to people or animal pets, therefore analyses for possible contaminants (e.g. PAH’s) should not be neglected.

 

Specific comments:

The De-sealed soils were also filled to reach the necessary level with de-sealed soils. Where does this material come from? Please, add it to the description.

In this experimental design soil fauna elements can easily move from the Topsoil to De-sealed soil. Was it an isolation used to prevent this movement?  

Soil biological quality was evaluated using the QBS index is not widely used. Please give some more details about using this index in the introduction.

L139 cellulase-activity instead of cellulose-activity.

L282 “in terms” in double.

L296 Do not use “low difference” please write simply if significantly different or not.

L313 Using the term “relative good values of the QBS” is ambiguous, please specify it more exactly.

Author Response

Dear,

We really appreciate the referee works that have improved our paper.

We substantially reviewed the abstract and reorganizing the results presentation according to the reviewer suggestion, moreover we have also insert data relating the 3-year monitoring for soil biological quality, deleted any redundant data and transformed table into a graph. We delete all speculative sentences in discussion and conclusion sections.

Here are the specific responses to your comment

Author Response File: Author Response.docx

Reviewer 4 Report

General Comments

            Maienza et al. performed a longitudinal study examining the management of de-sealed urban soils. They compared the physico-chemical and biological properties of de-sealed soils without any intervention to those where de-sealed soil was replaced with topsoil. Their study has clear value, and their experimental design was appropriate for their hypothesis. The authors also collected a fairly comprehensive set of data. However, there are major issues with the work as it is currently presented, and I cannot recommend it for publication.

Firstly, the authors need to make major improvements to the writing and presentation of data. The Results section does not present a clear case for how the authors tested their hypothesis. There is too much information presented and the evidence is muddled by arbitrary statistical contrasts among sites and soil properties which had no purpose for their hypothesis. What purpose is there to test whether copper concentrations are different between a random street in Carpi or Forli?

            Your study will attract readers who wish to know more about ways of managing the fertility of de-sealed soils. To that end, the authors could make more specific hypotheses. A general comparison is fine, but what are specific problems faced when planting in de-sealed soils? The problem of metal contamination was tested, but not included in the hypotheses. The compaction of sealed soils is another characteristic that might form part of their hypothesis. Refining and elaborating on the hypotheses will help the authors focus their results and provide a more structured and meaningful analysis.

            One major omission is information on plant growth which informed several of the conclusions the authors have made. The authors claim there were no differences in plant growth between treatments but provide no evidence of this. Did the authors observe any differences in growth, nutrition of susceptibility to disease of their shrubs? If this data is not available, the information in the study is still worth publishing, but several of their conclusions (including their major findings) need to be re-evaluated. There are other instances where the authors have made claims not supported by the data they provided (see Line 320 and Line 323).

            While less important, I would like to see the authors discuss their observation that metal concentrations increased in all sites across time. This observation poses a broader question about the risk of ‘greening’ urban spaces, if soils (and soil macrofauna / flora) accumulate toxic metals. It would be nice to see the author address this concern in greater length in the Discussion / Conclusions.

 

Comments on Tables & Figures

Figure 1 <- What information do the aerial views provide? I suggest removing them and consolidating the photographs of the sites (also labeled Figure 1).

Figure 2 <- This would be more informative if you made it into a schematic, which captures all of the steps performed in preparing your experiment. This is figure is good, as it clarifies exactly what your treatments are, but your study can also serve as a template for others when performing de-sealing. In this regard, you’d dramatically increase the impact of your work if you offered some kind of schematic that shows a ‘how-to’ as well as clarifies your treatments.

Table 2 <- This should be supplementary information. This is not a methods paper (i.e., your reader is not interested in this level of methodological detail). Also, do you have permission to reprint the Table from the journal that published Parisi et al. 2001? You should include this information, because your work needs to be reproducible, but it should not be displayed as one of your tables.

Table 4 present too much information. The authors need to do a better job highlighting key trends that they believe are important results. This should be made into a figure like Fig. 3. I am lost staring at all the widely spaced numbers and am not sure what differences matter for the hypothesis you’re testing. The full Table 4 can be included as Supplementary Table.

Figure 3 is an improvement on Table 4, but, again, there is no reason to show ALL your data. It is better to simply mention which biological properties did not significantly differ (i.e., urease activity) in your text and use your figure to highlight the key differences. Also, if qCO₂ is calculated from CO₂ and ATP, why show all of this information, especially given the qCO₂ value did not differ?

 

Line Comments

Line 14: “Most of the urban greening interventions need soil de-sealing and induction of fertility in…” <- Try: “Most urban greening interventions involve soil de-sealing and management to enhance fertility. Management typically involves translocating fertile topsoil to the site, which comes at great environmental costs.” The authors’ writing is mostly clear but would really benefit from a polishing service.

Line 18: “soil enzyme” <- “soil enzyme activity”

Lines 17-20: “Physico-chemical properties, soil enzyme, soil microbial biomass and respiration rate, and biological quality based on the arthropod community were studied on three de-sealed soils in three municipalities of Northern Italy.” <- Avoid providing long lists at the start of a sentence – a list should follow the subject of the sentence.

Line 20: “Three pilot trials were assessed with de-sealed soil vegetated with two ornamental…” <- This statement confused me. It appears to suggest that the ornamentals were not planted in the agricultural soil. It had me confused until Figure 2.

For lines 17-21, try re-ordering as follows: “We compared the fertility of de-sealed soils treated with high intensity management, involving infilling with exogenous agricultural soil, and no intervention in three municipalities of Northern Italy. Soil fertility was determined based on the growth of two species of ornamental shrub and on changes in physico-chemical and biological properties of de-sealed soils, according to elemental analysis and measures of microbial biomass, respiration, soil enzyme activity and biological quality (QBS-ar).”

Line 48: “allowing allow”

Line 57: “could undergo” <- technically ‘would undergo’ since a hypothesis is an affirmative statement of expectation.

Line 85: Please state which site shown in the picture.

Line 88-91: I am fairly certain there is one hole per site, but please state this explicitly.

Line 89: In several places in the introduction the authors say ‘minimum  or no intervention’ is adding agricultural soil the ‘minimum’ intervention? Based on earlier descriptions (lines 58-60), this does not strike me as ‘minimum’ given the cost to the agricultural ecosystem as well as te transport of soil. Please change ‘minimum’ or ‘standard’ or ‘conventional.’

Line 90: “done” <- “dug”, as in a hole was dug, correct?

Line 94: Can you please provide more details on how the de-sealed soil was treated? Was it piled next to the hole, then shoveled back in to fill the appropriate depth? I’d like to know more about how the physical structure of the soil was affected during set up. Were there any interventions to prepare the soil prior to infilling?

Line 95: Why were these species chosen? Are they particularly tolerant to metal pollution, or undeveloped / nutrient poor soils?

Line 98: How many soil replicates per year? You mention three replicates were taken for T1. What about other timepoints?

Line 118: In Figure 2, there are four dark colored ‘shrubs’ and two light colored. Does this mean there were 4 of one variety and 2 of the other? If so, please specify which color corresponds with which shrub. If not, even out the coloring.

Lines 134-140: Please summarize your methods and provide further details in a Supplementary Methods document. It is important that your reader be able to know roughly what was done without digging through the literature. I also find it unlikely that the methods were followed exactly as described in past research.

Line 185: This is one of my common complaints, so bear with me. It is much more effective to frame the presentation of your results based on your hypothesis, rather than as a list of information. Consider starting your Results with a statement that conjures your hypothesis: “After each site was prepared (T0), there were few significant differences between the de-sealed soil and exogenous top-soil. Characteristics that differed were…”

Line 187: Bulk density of sealed soils is consistently lower. It is worth mentioning this, as it reflects one of the main challenges in reclaiming urban soils which are typically compacted.

Line 187: I may have missed it, but I couldn’t find how many replicates (n = ?) were used in your calculation. Please clarify here and in the text. It doesn’t hurt to provide the information twice.

Line 198: “variable values” <- not true. Metals consistently increased over time. This is very apparent (and worrying) and also forms the basis of one of the authors’ discussion points (line 289). Please correct and appropriately highlight this result.

Line 235: What is the y-axis of the “enzyme activities” bar plots? “mg PNP-P” is not defined anywhere. How did the authors normalize the activity across enzymes? More importantly, why did they do this? What value is there in contrasting the activity of enzyme when their hypothesis is about soil reclamation?

Line 224: Try: “…significantly higher (p < 0.001) abundances were observed in topsoil (6.7 x 10^3) compared to the no intervention treatment (3.5 x 10^3).

Line 226: “show differences” <- “show significant differences”

Line 229: “Number of taxa (NT)” <- Use more appropriate terminology, such as ‘species richness’ or ‘alpha-diversity’. Also, why is this being abbreviated? I couldn’t find any other uses.

Line 233: “showed” <- “shown”

Line 249 – 251: This information is provided in Figure 5. There is no reason to report the values here. Please remove.

Line 258: It is still not clear why you are bothering to test between sites? How does this fit into your hypothesis? This is echoing previous criticism about Figure 3, where the authors test differences among enzyme activities with no apparent relevance to their hypothesis. Please remove this information. Note: the cross-study comparison was not made in Figure 4 (which is good!).

Line 272: Could the authors explain why Pb was below detection in site 1 at T2, when the plants had significantly higher levels? This data point goes against the trends in other sites where Pb accumulated with time. Is it possible to re-analyze this soil?

Line 293: The authors have not provided any evidence of growth, though the plants clearly can survive in de-sealed soil for that long.

Line 295: “…plant growth explains…” <- Again, no measurements of growth have been provided. Plants can die very slowly. Were there any signs of stress, malnourishment or disease? Was any fertilizer provided at any point?

Line 297-298: This trend was not highlighted in the Results. How was the variation between the two treatments compared? Was the difference in variation significant? This is the only time the word variation is used in the manuscript.

Line 298: “small differences” <- Try: “broad similarity”

Line 301 & Line 307: The total carbon and total organic carbon values largely decreased with time. How are the authors drawing these conclusions? The Discussion needs to make direct reference to data presented in the Results. Any speculation should derive from specific results, not based wholly on speculation.

Line 305: “sealed soil” <- “de-sealed soil”

Line 305: “for as compared to” <- syntax error

Line 306: “…agricultural soils; in those observations plant colonization, did not occur.” <- This is an unnecessarily complex sentence structure.

Line 310: Could you please explain to me (and perhaps in your Methods) how this measure reflects stress? I am unfamiliar with this ratio.

Line 313: It strikes me that much of this information could be quantified. Why was so little attention paid to the growth, fitness and function of the plants?

Line 320: “De-sealing improved soil chemical fertility, microbial activity and micro-arthropod colonization.” <- Based on what evidence? The only way the authors could conclude this is if they saw improvements in biological activity over time. Figure 3 and 4 do not show any evidence of difference across time, nor is this information presented anywhere in the Results. Did the authors collect activity and arthropod data from all years?

Line 321: “growth” <- show evidence.

Line 323: ‘labile C’ <- Where did the authors measure labile C? This is only mentioned in the Discussion. Furthermore, the differences in TOC and TC reported do not follow any clear  trend suggesting this phenomenon. Please justify your conclusion.

Line 325: “de-sealed soils can improve their ecological functionality” <- awkward. De-sealed soils do not act on themselves. Also, you’ve planted shrubs which you cite has having an important effect. Thus, it is more accurate to speak about the management strategy you’ve performed, rather than suggesting that de-sealing, by itself, will magically improve fertility. Your study did not test this hypothesis.

Author Response

Dear r referee,

We would really appreciate the referee works that improving the paper.

We substantially reviewed the abstract and reorganizing the results presentation. We have also insert data relating the 3-year monitoring for soil biological quality, deleted any redundant data and transformed table into a graph. We delete all speculative sentences in discussion and conclusion sections.

Here are the specific responses to your comments

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

General Comments

            The authors have made the necessary changes. The authors should be applauded for their improvements. However, I strongly urge the editor to ask that the manuscript writing be polished. There are still many errors in syntax as well as awkwardly structured sentences. I have highlighted several below, but there are many more than I had time to note.

Line 22: “Since metal contamination is related to urban de-sealed soil, …” <- Try: “Since metal contamination is a concern where urban soils are de-sealed…”

Line 40: (first sentence of introduction) “The ever-growing urbanization with the related household and mobility infrastructure construction, jointly with past urban sprawl and industrialization, have consumed soil mainly by sealing, leading to soil loss and contamination” <- awkward sentence.

Line 47: “Main adverse effects of soil sealing are…” <- “The main adverse…”

Line 54: “… which generally require backfill soil to leveling and allowing the optimal plant rooting.” <- ???

Line 66: “We hypothesized that de-sealed urban soils, after shrubs planting…” <- syntax

Line 70: “If this is the case, the increase of fertility of de-sealed urban soils could avoid the movement of top-soils from …” <- syntax

Line 110: “Three samples replicate for undisturbed soil cores…” <- syntax

Line 110: What is an ‘undisturbed soil core’?

Line 282: Try: “…could restore their quality and fertility at a comparable level to amendment with exogenous topsoil.”