The Evaluation of the Phytoremediation Potential of the Energy Crops in Acid Soil by Sewage Sludge Fertilization
, Gintaras Šiaudinis 1, Danutė Karčauskienė 1,*, Regina Repšienė 1, Karolina Barčauskaitė 1 and Olga Anne 2
Round 1
Reviewer 1 Report
Introduction:
The introduction should provide more specific information regarding the objectives of the study. It is not clear whether the sewage sludge is used for phytoremediation purposes or for fertility purposes. If it is used for phytoremediation, the specific mechanisms by which sewage sludge enhances phytoremediation should be highlighted with references to support the claim.
(Lines 83-95) Additionally, a clear numbering system could help organize the objectives and make them easier to understand.
Materials and Methods:
(Line 111) The term "agricultural parameters" should be replaced with "soil properties" to provide a more accurate description of the variables being measured.
Table 1:
The extraction methods for the macronutrients should be provided in Table 1. Furthermore, P and K concentrations should be better expressed as such rather than as oxides. Moreover, it is unclear whether Cr, Ni, Pb, Cu, and Zn refer to the total amounts of these elements or not. This information should be explicitly stated to avoid confusion. The above Table should be placed in the Results section.
Results:
Figures:
Error bars should be provided in all figures to provide a clearer representation of the data and to help readers assess the statistical significance of the results.
(Lines 281-284): these limit values should be presented in an additional table to provide a more organized and comprehensive view of the data.
(Line 430): Bioconcentration factor:
The bioconcentration factor is mentioned in the materials and methods section, but no information is provided regarding the analysis of heavy metal concentrations in plant tissues. If the heavy metal concentrations were determined in the plant tissues, a table should be provided with the respective concentration values. It is strongly recommended to clarify this issue and discuss it thoroughly in the revised version of the manuscript, since in my opinion it is the most important part that can support the findings of your work.
Moreover, it is recommended that the translocation factor between the aboveground and belowground biomass concentrations of respective heavy metals should be provided to obtain a more comprehensive understanding of the ability of respective plant species to be used as hyperaccumulators.
Author Response
Manuscript Land-2300919
Response to Reviewers
Dear reviewer,
Thank you for giving us the opportunity to submit a revised draft of the manuscript “The evaluation of the phytoremediation potential of the energy crops in acid soil by sewage sludge fertilization” for publication in the Land journal. We appreciate the time and effort that you and other reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated most of the suggestions made by the reviewers. Those changes are highlighted within the manuscript. Please see below, in blue, for a point-by-point response to the reviewers’ comments and concerns.
Comment: Introduction:The introduction should provide more specific information regarding the objectives of the study. It is not clear whether the sewage sludge is used for phytoremediation purposes or for fertility purposes. If it is used for phytoremediation, the specific mechanisms by which sewage sludge enhances phytoremediation should be highlighted with references to support the claim.
Author response: Thank you for the remark. The sewage sludge was used for both purposes: for fertility increasing and for phytoremediation purposes. The main aim was to evaluate the effect and possibilities of different energy crops on the removal of heavy metals from sewage sludge and soil seeking to improve sludge and soil quality in more economical and environmentally friendly approach. As phytomanagement of sewage sludge is a feasible and promising option, it is very important to select the right plant species to obtain „good candidates“ to for phytoremediation of different heavy metals.
We have added information highlighting remediation of heavy metals from contaminated sludge and selected energy crops functionality in the remediation process.
Comment:Lines 83-95) Additionally, a clear numbering system could help organize the objectives and make them easier to understand.
Author response: Thank you for pointing this out. We corrected this. The objectives were numbered.
Materials and Methods:
Comment: (Line 111) The term "agricultural parameters" should be replaced with "soil properties" to provide a more accurate description of the variables being measured.
Author response: Thank you for this suggestion. It was corrected.
Comment: Table 1:The extraction methods for the macronutrients should be provided in Table 1. Furthermore, P and K concentrations should be better expressed as such rather than as oxides. Moreover, it is unclear whether Cr, Ni, Pb, Cu, and Zn refer to the total amounts of these elements or not. This information should be explicitly stated to avoid confusion. The above Table should be placed in the Results section.
Author response: Thank you for pointing this out. The extraction methods were added in the Table 1. The heavy metals content is expressed as total amounts of these elements. Regarding P and K concentration it is expressed as plant available P and K compounds. In Lithuania, P and K data are often presented in this form. Unfortunately, P and K data in other forms were not conducted in this study, so we cannot provide them. But thank you very much for your comment, we will definitely take it into account when planning future research.
Comment: Results:Error bars should be provided in all figures to provide a clearer representation of the data and to help readers assess the statistical significance of the results.
Author response: We agree with the reviewer’s assessment. The error bars were added for clearer representation of the data.
Comment: (Lines 281-284): these limit values should be presented in an additional table to provide a more organized and comprehensive view of the data.
Author response: Thank you for this suggestion. We added the additional table with the the maximum permissible concentration of heavy metals (MPC) in soil after fertilization with sewage sludge according to the Lithuanian law.
Comment: (Line 430): Bioconcentration factor:The bioconcentration factor is mentioned in the materials and methods section, but no information is provided regarding the analysis of heavy metal concentrations in plant tissues. If the heavy metal concentrations were determined in the plant tissues, a table should be provided with the respective concentration values. It is strongly recommended to clarify this issue and discuss it thoroughly in the revised version of the manuscript, since in my opinion it is the most important part that can support the findings of your work.
Author response: Thank you for pointing this out. The analysis of heavy metals in the plants aboveground biomass was evaluated the same as for soil samples. We added the data about the heavy metals concentration in plant aboveground biomass under different contamination with sewage sludge levels by growing different energy plants (please, look at the Table 6) and discussed it in manuscript.
Comment:Moreover, it is recommended that the translocation factor between the aboveground and belowground biomass concentrations of respective heavy metals should be provided to obtain a more comprehensive understanding of the ability of respective plant species to be used as hyperaccumulators.
Author response: The analysis of heavy metals in the plant’s aboveground biomass in 2013 and 2017 was conducted in total in the entire above ground biomass, without dividing it into separate parts, so we do not have possibility to calculate the translocation factor in this study.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript evaluates of the phytoremediation potential of the energy crops in acid soil by sewage sludge fertilization. The research was interesting and possesses scientific soundness. However, the manuscript requires some amendments to enhance the quality of the manuscript. The comments are as follows:
Abstract:
1) Please provide a clearer research background and problem statement which lead to the use of phytoremediation using energy crops.
2) The methodology describing the field trial should be mentioned clearly.
3) The finding should also mention the effects of two energy crops on the changes in the selected heavy metals concentrations in soil.
4) Please indicate which heavy metal is significantly reduced by the energy crop, for example Cu and Ni were reduced by common osier while Pb and Zn were reduced by cup plant.
Introduction:
1) Please provide some reviews on how long the energy crops' phytoremediation process will take place to significantly absorb the heavy metals in soil.
2) Why the objective only focused on the status of heavy metals in soil after application with different sewage sludge contamination levels and to determine the potential risks to the environment that heavy metal pollution could pose? The objective should also mention the effects of two energy crops on the changes in the selected heavy metals concentrations in soil.
Materials and Methods:
1) Please provide reason on why 45 and 90 t/ha of sewage sludge were applied in the soil? Is there any reason why 45 and 90?
2) Please provide more clear elaboration on the land preparation, sewage sludge application and cultivation of the energy crops during the field trial. The methodology should also mention how long the cover crops will be cultivated and harvested.
3) Any reason why soil samples only being collected on the top soil layer only? There might be possibility of the mobilization of heavy metals into the lower part of the soil.
Results and Discussion:
1) Please revise the section title of Results to "Results and Discussion" .
2) Suggest performing a comparison between each heavy metal under cultivation of common osier and cup plant so that we can see clearly the effectiveness of which plant in bioremediating the particular heavy metal in Figure 2.
3) The discussion is generally sufficient. Suggest providing scientific discussion on the mechanisms and reasons on why Cu and Ni were significantly reduced under the cultivation of common osier, Pb and Zn under the cultivation of cup plant. This result is particularly essential because this is the main outcome every reader is interesting of.
Conclusion:
Please indicate which heavy metal is significantly reduced by the energy crop, for example Cu and Ni were reduced by common osier while Pb and Zn were reduced by cup plant.
Author Response
Manuscript Land-2300919
Response to Reviewers
Dear reviewer,
Thank you for giving us the opportunity to submit a revised draft of the manuscript “The evaluation of the phytoremediation potential of the energy crops in acid soil by sewage sludge fertilization” for publication in the Land journal. We appreciate the time and effort that you and other reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated most of the suggestions made by the reviewers. Those changes are highlighted within the manuscript. Please see below, in blue, for a point-by-point response to the reviewers’ comments and concerns.
Comment: Abstract:
1) Please provide a clearer research background and problem statement which lead to the use of phytoremediation using energy crops.
2) The methodology describing the field trial should be mentioned clearly.
3) The finding should also mention the effects of two energy crops on the changes in the selected heavy metals concentrations in soil.
4) Please indicate which heavy metal is significantly reduced by the energy crop, for example Cu and Ni were reduced by common osier while Pb and Zn were reduced by cup plant.
Author response: Thank you for pointing this out. As suggested by the reviewer, the abstract was re-written according to the reviewers’ comments.
Introduction:
Comment: Please provide some reviews on how long the energy crops' phytoremediation process will take place to significantly absorb the heavy metals in soil.
Author response: Thank you for this suggestion. We added some information about factors influencing energy crops' phytoremediation process.
Comment: Why the objective only focused on the status of heavy metals in soil after application with different sewage sludge contamination levels and to determine the potential risks to the environment that heavy metal pollution could pose? The objective should also mention the effects of two energy crops on the changes in the selected heavy metals concentrations in soil.
Author response: Thank you for the suggestion. We have added the additional objective about the effect of energy crops growing on the heavy metal’s concentration in soil.
Materials and Methods:
Comment: Please provide reason on why 45 and 90 t/ha of sewage sludge were applied in the soil? Is there any reason why 45 and 90?
Author response: Thank you for pointing this out. We selected the sewage sludge (SS) rates for the following reasons. Firstly, we had study scientific articles of other research in order to set SS rates in our field experiments. As well, by selecting SS rates, we intended to apply enough nutrients (N (nitrogen), P (phosphorus) or K (potassium)) available for Salix viminalis growth and biomass yield at least for two successive rotations ahead (8 or more years). The same SS rates were applied and for Silphium perfoliatum.
Comment: Please provide more clear elaboration on the land preparation, sewage sludge application and cultivation of the energy crops during the field trial. The methodology should also mention how long the cover crops will be cultivated and harvested.
Author response: We agree with the reviewer’s assessment. We added additional information about the land preparation, sewage sludge application and cultivation of the energy crops during the field trial. Regarding the cultivation of cover crops, the experiment will continue at least for next few years. Our intention is to watch (monitor) the dynamics of agrochemical parameters (humus, nitrogen, phosphorus, potassium) and 1) how long the amount of these nutrients will be sufficient for the growth and productivity of both plant species; 2) how long time does it takes to clean enough the soil from heavy metals inserted with sewage sludge.
Comment: Any reason why soil samples only being collected on the top soil layer only? There might be possibility of the mobilization of heavy metals into the lower part of the soil.
Author response: Thank you for pointing this out. We know that the most rapid change of all chemical elements takes place precisely in the top layer of the soil. To monitor the processes in deeper soil layer requires even longer observation time. In this article, we have aimed to present only the transformations of heavy metals occurring in the upper soil layer.
Results and Discussion:
Comment: Please revise the section title of Results to "Results and Discussion" .
Author response: Thank you! We corrected it.
Comment: Suggest performing a comparison between each heavy metal under cultivation of common osier and cup plant so that we can see clearly the effectiveness of which plant in bioremediating the particular heavy metal in Figure 2.
Author response: We agree with the reviewer suggestion. We have added some sentences regarding the comparison between accumulation of heavy metal under cultivation of common osier and cup plant as it is described more detailed in Table 3.
Comment: The discussion is generally sufficient. Suggest providing scientific discussion on the mechanisms and reasons on why Cu and Ni were significantly reduced under the cultivation of common osier, Pb and Zn under the cultivation of cup plant. This result is particularly essential because this is the main outcome every reader is interesting of.
Author response: We agree with the reviewer’s assessment. The reasons on different metals accumulation growing different energy plants were discussed through all the discussion text.
Conclusion:
Comment: Please indicate which heavy metal is significantly reduced by the energy crop, for example Cu and Ni were reduced by common osier while Pb and Zn were reduced by cup plant.
Author response: Thank you for pointing this out. As suggested by the reviewer, we added the additional sentence indicating the differences of accumulation of heavy metals growing different energy crops.
Author Response File: Author Response.docx
Reviewer 3 Report
Total C and Total C should be express in the same unit.
Best to include C/N ratio as well.
Figure 2 need to be enlarged. You need to put in error bar, as well denotation of significant or non-significant differences in all of the bar charts
Author Response
Manuscript Sustainability- 1391715
Response to Reviewers
Dear reviewer,
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Heavy metal accumulation and ecological risk assessment in acid soil–energy crops systems with different sewage sludge contamination levels” for publication in the Sustainability journal.
Total C and Total C should be express in the same unit.
Now all the parameters are expressed in the same way in the same units.
Best to include C/N ratio as well.
C/N ratio is included now.
Figure 2 need to be enlarged. You need to put in error bar, as well denotation of significant or non-significant differences in all of the bar charts
We put error bars on each column in Figure 2.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The revised version of the ms has been extensively improved and the authors have complied with most of my suggestions. Therefore, I recommend the acceptance of this work. A minor comment is that concentration units are missing in Table 6.
Additionally, if you agree, the references provided below I believe could further enhance the strength of the Introduction and Discussion section:
https://doi.org/10.3390/environments9050061
https://doi.org/10.1007/s10653-021-01151-2
https://doi.org/10.15244/pjoes/68957
Author Response
Dear Reviewer,
We appreciate for your precious time in reviewing our paper and providing valuable comments. It was your valuable and insightful comments that led to possible improvements in the current version. The authors have carefully considered the comments and tried our best to address every one of them. We hope the manuscript after careful revisions meet the high standards of Land journal. The authors welcome further constructive comments if any.
We have considered and adjusted the article according to all the comments made. We have added the concentration units in Table 6. Some additional references were provided to strength the Discussion section. All modifications in the manuscript have been highlighted in red.
Reviewer 2 Report
The authors had amended and improved the manuscript according to the comments given by the reviewers previously. Hence, there is no further amendments are required.
Author Response
Dear Reviewer,
We appreciate for your precious time in reviewing our paper and providing valuable comments. It was your valuable and insightful comments that led to possible improvements in the current version. The authors have carefully considered the comments and tried our best to address every one of them. We hope the manuscript after careful revisions meet the high standards of Land journal.
