The Impact of Cascade Large Deep Reservoir on the Migration and Deposition of Cadmium in Lancang River
Round 1
Reviewer 1 Report
The data presented may present importance for further ecological studies. Please see some comments below:
Line 14: Metal pollution is a global environmental. I do not understand what it means.
Line 17: the meaning of NZD and XW has to be defined before they appear in the text for the first time.
Line 116: Please, specify the frozen temperature.
Line 116: Please, specify units of mesh size, and the specifications of the used sieve.
Line 117: It should be clarified how the sediments prior to their measurement are digested. Indicate at least one reference.
Line 121: Please, specify the concentration and the used reagent. This comment is general for the rest of the reagents used.
Line 125 and 126: “ML” must be change for “mL”. “HNO3” must be change for “HNO3” (with subscript). The meaning of SWI has to be defined before it appears in the text for the first time (as line 165).
Line 128: the number of replicas musty be indicate.
Figure 2: Is there an explanation for the large variability in pH for the NZD-A sample point?
Line 195: table header 2 does not appear
Table 2: Specify, for each row, which data corresponds to water and which data corresponds to sediment, the number of replicas (n) and the +/-
Figure 3: Figure 3 and its legends must be arranged. It is not possible to understand it, so I cannot evaluate the statements that appear between lines 197 to 206.
Figure 4 and Fig 6: The quality of the figures need to be improved. Please, provide figures with higher resolution (at least 300 dpi). This is especially important in the small square of fig 6.
Figure 5: Please, explain in more detail what this figure contributes. Why was it only done for S? What about Mn and Fe?
Line 266: “The consistency of the distribution trends of the diffusion fluxes of labile Fe, Mn and S in the surface sediments of the six sampling points with Cd indicates a synchronous release mechanism between labile Cd and other elements in the surface sediments of different sampling points (Figure 6b).” I think you need to support that argument better. To me, it is not clear that this conclusion is derived from the figure.
Line 319: “1%level” must be change for “1% level”.
Figure 8: It must be clarified if the figure is of your own manufacture, otherwise indicate the references.
Other:
-The methodology is confusing, be specific as to which data were analyzed by which tests. Also include this data in the graphs / tables.
-Application of proper quality assurance/quality control (QA/QC) procedures is vital for the measurement results to be treated as a source of reliable analytical information. Consequently, I suggest that a separate section devoted to QA/QC be added to the manuscript. Special attention should be paid to the description of the validation procedure for the applied analytical protocols, especially in the case of Cd measurements, element present at the trace level and the main object of the work.
- The following sections need the previous revisions to be evaluated.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript “The impact of cascade large deep reservoir on the migration and deposition of cadmium in Lancang River” is devoted to a very important topic: Cd migration and deposition in surface sediments of large deep reservoirs. However there are several remarks on the manuscript. First of all there are a lot of grammar issues in the text of the manuscript that makes it difficult to understand (for more details look into list of minor remarks).
Secondly, authors stated that “The Lancang-Mekong River is the largest international river in Southeast Asia” and Xiaowan and Nuozadu are “large deep reservoirs, both with a storage capacity of over 10 billion”. And for such enormous water bodies only 6 sampling points have been arranged with snapshot observations. On what basis did the authors consider such a sampling scheme representative? It is also not clear why do you have any spread of values on the figure 2 for dissolved oxygen, pH, conductivity and temperature if different water parameters have been measured only once at each of six sampling points? If sampling and water parameters measurements were carried out in several replicates, then this should be described in the methods section of the manuscript. In addition, please, indicate the quantity of samples/measurements (in total and per each sampling point).
Third issue is that is not clear from the Materials and Methods section how was the core samples prepared for the ICP-MS? What is “a 100 mesh sieve”? Is it a frame diameter – 100 mm? What was the mesh size? What instrument was used for the ICP-MS (company, manufacturer: add this information to lines 117 and 128 please)? Please clarify the method: the DGT was inserted into the sediment at a water temperature of 25°C. Where did the water come from? What gel was cut as described on line 125? Is it the same resin gel that is mentioned on line 133? Was the DGT method used to analyze sediment pore water? If yes, it is not clear from the manuscript, please clarify.
The forth remark is about calculation process. It is not clear why did the authors take the value of the elution factor fe equal to 0.8? Please add units to all parameters in equations. What is t in equation (2)? Please add multiplication sign to formulas. For now it is not clear if it symbol “At” or “A·t” in equation (2), and the same for other equations. What is the slope of the change in DGT? Why was the porosity of the top 10 mm layer equal to 0.9? Did you measure it? Why there is the condition μ > 0.7 in the equation (4)?
Fifth issue is connected to the Conclusions section: I suggest shortening conclusions by reducing the repetition of the results and keeping only main research findings with very short explanations.
Further you can find the list of specific minor remarks:
Line 14: Metal pollution is a global environmental -> Looks like the predicate is missing. Did you mean “Metal pollution is a global environmental issue” or “problem”?
Lines 39-41: Please rephrase the sentence “Sediments have a strong tendency to accumulate trace metals, are the main storage site for natural and man-made interference metals and are an important medium for evaluating the pollution level of aquatic ecosystems.”
Line 61: focus -> focused?
Lines 72-74: The bioavailability of trace metals is related to not only the concentration of their in sediment but also the migration speed of these metals in the sediment -> The bioavailability of trace metals is related not only to their concentration in sediment but also to the migration speed of these metals in it.
Line 74: a new approach with which to determine the concentration of trace metals in sediments -> new approach to the determination of trace metals concentrations in sediments.
Line 90: is form -> is formed.
Lines 109-111: Column B seals the ends of the plastic tubing with rubber plugs, then keeps the sediment core upright to minimize disturbance and transports it immediately to the laboratory. -> Please rephrase, did you mean “Column B was sealed at the ends, … was kept upright, and … was transported immediately”?
Lines 111-113: there is no predicate (no verb) in the sentence, please rephrase.
Line 125: What is SWI? This abbreviation was not introduced earlier in the text. It is mentioned for the first time only on line 165. Please move decoding of this abbreviation to the place where you mentioned this term in the first time.
Line 126: HNO3 -> HNO3
Lines 125-126: 1.5 ML centrifuge tube -> did you mean 1.5 mL (milliliter)? 1 ML -> did you mean 1 mL (milliliter)?
Line 141: Dcd -> DCd.
Line 186: what is “concentration of the reservoir sediments”?
Table 2 (if it is indeed table 2) does not have any title (page 6).
Figure 3: it is not clear why only data for depth of 12 cm is shown on this figure if the sediment sampler of 100 cm was used? And why “(b) distribution characteristics of labile Cd and other elements in water” if this data is obtained from sediment column B? Are they concentrations in sediment pore water? In this case, please clarify the method section describing DGT analysis.
Line 235: a large number of reducing active bacteria and S coexist -> please rephrase. I am not sure that it is grammatically correct to say that S as a chemical element “coexist” with something/someone.
Figure 5: it is not clear why data for depth of 110 cm is shown on this figure if the sediment sampler of 100 cm was used?
Lines 281-284: Please rephrase and clarify the sentence “Because the ability of the sediment to adsorb and carry metals at this point is stronger than that at other sampling points, the metal ions Cd, Fe, Mn and S in the overlying water at NZD-C similarly tend to converge in surface sediments.”
Figure 7, lines 318-319: There are notes with asterisks in the Figure caption: “Significant correlation at the 5% level; ** Significant correlation at the 1%level”. Where are those asterisks on the Figure itself? Please, check.
Line 359: te upstream -> upstream.
Line 399: Sediments in the downstream area flow into the NZD reservoir -> how could sediments flow?
However I believe that this research lies within the scope of Sustainability Journal and will make a good contribution to it. The manuscript can be improved after major revisions.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
-Line 118: “HNO3” must be change for “HNO3 (with subscript)”.
In addition, Please, specify the concentration, quality and other information of used reagent (for example: pro analysis or Suprapur grade, supplied by Merck (Darmstadt, Germany) or Sigma–Aldrich (Steinhein, Germany)).
This comment is general for the rest of the reagents used.
-Table 2: Specify, for each row, the +/-
-Figure 3: You should review this figure. Some figures appear above others and the legend hides part of the first graphs.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript “The impact of cascade large deep reservoir on the migration and deposition of cadmium in Lancang River” is devoted to a very important topic: Cd migration and deposition in surface sediments of large deep reservoirs. Authors did good job in improving the manuscript. However there are still some issues left.
(1) The authors did not substantiate the sufficiency of 6 sampling points. I understand that these are typical positions (pre-reservoir, mid-reservoir and aft-reservoir), but 6 sampling points are difficult to consider as a representative sample selection in regards of statistical data processing. Even two sediment cores taken from one sampling station but at a distance of 2 meters from each other will differ. On what basis did the authors consider such a sampling amount representative?
(2) Thank you for clarification about 7 sensor ports that can measure DO, pH, conductivity and temperature and other physicochemical indicators of the overlying water simultaneously every 2-3 seconds, but it is still not clear how many measurements have you done? If you know the multi-parameter water quality meter speed (1 measurement per each 2-3 seconds) and total time during which it measured you should be able to calculate amount of measurements. Anyway you have some database on the basis of which the box-with-whiskers plots were built (Figure 2). So please indicate the quantity of samples/measurements (in total and per each sampling point)! Please add the number of measurements to the Table 2 as well.
(3) What are (a) and (b) in footer of the Table 2 (Lines 204 – 207)? Do they belong to the Figure 2? Anyway, lines 204 – 205 sounds confusing please check the grammar.
Line 246: these -> These
Line 300: previous -> Previous
However I believe that this research lies within the scope of Sustainability Journal and will make a good contribution to it.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Authors did fix all issues. There is one minor (but important) correction. Clarify please in Table 2 +- what value did you use? Was it standard error of mean or standard deviation?
