Application of Drifted Pumice Stone as a Sand-Capping Material
Round 1
Reviewer 1 Report
1) Please define the source of equation 1. How was this equation obtained?
2) Why was the DO monitoring started after half a day of acclimation?
3) How was equation (2) for nutrient release rate obtained?
4) What do you mean by artificial seawater?
5) Why was the 46% pumice weight ratio maintained?
6) How was the 100% pumice weight ratio checked?
7) According to Fig. 4, why is the sedimentary oxygen demand for CORE1 and CORE 2 very close?
8) In Fig. 7, put all three curves in a single graph.
9) Define condition index.
10) What do you mean by p<0.05?
11) Provide the source of Eq. (3).
12) All the observations displayed in all the graphs are not technically explained. Why are the trends increasing or decreasing?
Author Response
Detailed comments to the Reviewer:
The reviewer’s suggestions/comments are presented in plain text, and our responses are included in BOLD.
Reviewer #1:Comments and Suggestions for Authors
1) Please define the source of equation 1. How was this equation obtained?
Response:
Thank you for your comment.
Generally, in the sealed core experiment, the DO decrease monotonously due to the SOD (see Figure R1) and the SOD value is estimated from the DO decreasing rate in the core:
(R1)
where V is the volume of overlying water in the core, A is the cross-sectional area of the sediment core, CDO is the DO concentration in the overlying water, and t is the elapsed time.
Figure R1 Schematic view of SOD formulation
A reference, which formulated the SOD calculation referring DO variations in CORES, has been added (Line 104 in the revised manuscript).
2) Why was the DO monitoring started after half a day of acclimation?
Response:
Generally, the DO in the overlying water is not stable and not reliable because it is affected by any disturbance during preparation works. Therefore, we avoided referring to the DO concentration immediately after the setup, and only used those values after half a day of acclimation.
3) How was equation (2) for nutrient release rate obtained?
Response:
The nutrient concentration increase monotonously due to the nutrient release from the sediment (see Figure R2). Similarly to equation (1), therefore, the nutrient release rate (NRR) value is estimated from the increasing rate of nutrient concentration in the core.
(R2)
where Cnut is the nutrient concentration in the overlying water.
Figure R2 Schematic view of nutrient release rate formulation
A reference, which formulated the NRR calculation referring to nutrient concentration variations in CORES, has been added (Lines 126 and 499-500 in the revised manuscript).
4) What do you mean by artificial seawater?
Response:
In this experiment, we used artificial seawater, which is a blended salt solution (Lines 84-85 in the revised manuscript), to adjust osmotic pressure and to avoid any biochemical reaction in the overlying water. This is a common method used in our research field.
5) Why was the 46% pumice weight ratio maintained?
Response:
Firstly, we configured two experimental conditions, that is, 0% and 100% of pumice weight ratio to study its potential as a sand-capping material. Next, we planned to prepare 50% as a third experimental condition, but subtle preparation of the sediment and pumice weight was difficult and resulted in a condition of only 46%.
6) How was the 100% pumice weight ratio checked?
Response:
We installed crushed pure pumice on the sediment surface with care not to disturb it. By using this method, it was relatively easy to visibly confirm that the placed pumice was not contaminated by sediment, because the colors of pumice and sediment were different from each other.
Further, we note that, if the crushed pumice was slightly contaminated by the sediment, the effect should be negligible.
7) According to Fig. 4, why is the sedimentary oxygen demand for CORE1 and CORE 2 very close?
Response:
SOD is controlled not only by the biochemical process such as oxygen consumption in the sediment but also by the physical process such as a diffusion in the diffusive boundary layer. Therefore, it was comprehensible that SOD was not proportional to the mixture ratio of the sediment and the pumice.
Additionally, we understand that an 11% reduction of SOD was certainly significant and thus the values were not considered close to each other.
8) In Fig. 7, put all three curves in a single graph.
Response:
Thank you for your comment. The separate curves have been replaced by one graph (Line 289 in the revised manuscript).
9) Define condition index.
Response:
Thank you for your comment. The definition has been added at Lines 209-214 in the revised manuscript.
In addition, as the measurements were taken after the experiment, the description was modified accordingly.
10) What do you mean by p<0.05?
Response:
In this case, “p<0.05” indicates that the null hypothesis is rejected at 5% significance. In the exposure experiment, there were no significant differences among the groups. We believe that the statement is important to confirm the reliability of the experiment.
11) Provide the source of Eq. (3).
Response:
A reference, which formulated the phosphate adsorption as a single-layer model, has been added (Lines 343 and 503-504 in the revised manuscript).
12) All the observations displayed in all the graphs are not technically explained. Why are the trends increasing or decreasing?
Response:
Thank you for your comment. An explanation for Figure 3 has been added at Lines 221-224 in the revised manuscript. Please refer to Lines 241-243 and 280-287 for Figures 5 and 7, respectively.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Manuscript entitled "Application of drifted pumice stone as a sand-capping material“ submitted by authors Inoue and Fujita represents valuable scientific paper, worthy of investigations and within the scope of MDPI Water Journal – SI Sediment-Water Interface: Implications for Understanding, Assessment, Remediation of Eutrophicated and Contaminated Sediment.
Altogether, interesting, excellent written and very useful study for possible application of drifted pumice stone as a sand-capping material for eutrophic sediments. Authors in this study evaluated pumice stone generated by local submarine volcanic eruption by well designed experiments for determination of : Sedimentary oxygen demand; Sedimentary nutrient release; Nutrient adsorption; and bivalve R. philippinarum mortality using crushed pumice and Kaolin suspended material.
Crushed pumice as a sand cover material effectively reduced the sedimentary oxygen consumption rate. Nutrient release from sediment showed a similar trend, with ~25% and 82% reduction in NH4-N and PO4-P release rates. The bivalve exposure experiments using crushed pumice suspended in seawater showed no adverse effects specific to pumice and lower bivalve mortality than that using kaolin at the same concentration.
The methodology and data analysis are up to date. Results are clearly presented, conclusions are supported by the data, with adequate discussion, consistent with the objectives.
Minor comments and corrections:
Page 2
Line 45
- Sort cited literature references according year of publication
Page 7
Line 227
- “for 168 h (7 days) and…”
Page 9 – 13
- The size of Figure 4, 5, 6 and 7 can be reduced
Page 16 and 17
- The equation formulas should be aligned according Instructions for authors
Page 19
- “Therefore, the results of this study represent an important finding for the possible application and formulation of countermeasures against drifting pumice.”
Author Response
Reviewer #2:Comments and Suggestions for Authors
Manuscript entitled "Application of drifted pumice stone as a sand-capping material“ submitted by authors Inoue and Fujita represents valuable scientific paper, worthy of investigations and within the scope of MDPI Water Journal – SI Sediment-Water Interface: Implications for Understanding, Assessment, Remediation of Eutrophicated and Contaminated Sediment.
Altogether, interesting, excellent written and very useful study for possible application of drifted pumice stone as a sand-capping material for eutrophic sediments. Authors in this study evaluated pumice stone generated by local submarine volcanic eruption by well designed experiments for determination of : Sedimentary oxygen demand; Sedimentary nutrient release; Nutrient adsorption; and bivalve R. philippinarum mortality using crushed pumice and Kaolin suspended material.
Crushed pumice as a sand cover material effectively reduced the sedimentary oxygen consumption rate. Nutrient release from sediment showed a similar trend, with ~25% and 82% reduction in NH4-N and PO4-P release rates. The bivalve exposure experiments using crushed pumice suspended in seawater showed no adverse effects specific to pumice and lower bivalve mortality than that using kaolin at the same concentration.
The methodology and data analysis are up to date. Results are clearly presented, conclusions are supported by the data, with adequate discussion, consistent with the objectives.
Response:
Thank you for your comments.
Minor comments and corrections:
Page 2, Line 45
- Sort cited literature references according year of publication
Response:
Thank you for your comment. References have revised to be numbered and indicated by numerals in square brackets.
Page 7, Line 227
- “for 168 h (7 days) and…”
Response:
Thank you for your comment. A revision has been conducted accordingly, at Line 197 in the revised manuscript.
Page 9 – 13
- The size of Figure 4, 5, 6 and 7 can be reduced
Response:
Thank you for your comment. All figures have been re-sized.
Page 16 and 17
- The equation formulas should be aligned according Instructions for authors
Response:
Thank you for your comment. Revisions have been conducted for all equations.
Page 19
- “Therefore, the results of this study represent an important finding for the possible application and formulation of countermeasures against drifting pumice.”
Response:
Thank you for your comment. A revision has been conducted accordingly, at Lines 448-449 in the revised manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Please show Figure R1 (Schematic view of SOD formulation) in the revised manuscript.
As shown in Figure 1, on what basis, a 5 cm gap was given?
In Figures 3, 5, and 7, how were all three curvatures plotted? How many data were taken?
In Figure 10, how was curvature for the single layer model plotted?
Author Response
Detailed comments to the Reviewer:
The reviewer’s suggestions/comments are presented in plain text, and our responses are included in BOLD.
Reviewer #1:Comments and Suggestions for Authors
1) Please show Figure R1 (Schematic view of SOD formulation) in the revised manuscript.
Response:
Thank you for your comment.
Equation (1) is well-known and is frequently used in previous studies related to this field, such as Inoue and Nakamura (2009). Therefore, we would not like to insert Figure R1 in the manuscript.
2) As shown in Figure 1, on what basis, a 5 cm gap was given?
Response:
A certain gap between the inlet of the sampling tube and the sediment surface is required to prevent the disturbance of sediment surface by water sampling operation. Although there is no authorized value for the gap, it was set as 5 cm in this experiment, which was considered to be enough. As a result, no disturbance was observed at the sediment surface throughout the experiment.
3) In Figures 3, 5, and 7, how were all three curvatures plotted? How many data were taken?
Response:
For Figure 3, the DO concentration of the overlying water was measured at 10-min intervals, and the total number of DO measurements were 85 for each CORE. A description of the sampling interval was added in the revised manuscript (Lines 96-97).
For Figure 5, the curvatures were plotted due to three water samples (Line 116). Symbols have been added to Figure 5 to clarify the number of samples.
For Figure 7, the nutrient concentration was measured before and immediately after, 1, 2, 5, 10, 20, and 30 min, and 1, 2, 3, and 6 h after the crushed pumice stone was added (Lines 154-155). Symbols have been added to Figure 7 to clarify the number of samples.
4) In Figure 10, how was curvature for the single layer model plotted?
Response:
The theoretical time series of PO4-P concentration was numerically calculated based on Equation (5) referring to the measured initial PO4-P concentration and assuming Ceq = 0.060 (mg L-1) and k = 2.0 × 10-3 (L g-1 min-1) (Lines 355-359 in the revised manuscript).
Author Response File: Author Response.docx
