Distribution Characteristics and Influencing Factors of Uranium Isotopes in Saline Lake Waters in the Northeast of Qaidam Basin

Round 1

Reviewer 1 Report

The paper presents the distribution characteristics and influencing factors of uranium isotopes in saline lake waters in the Northeast of Qaidam Basin. The Introduction clearly presents background information on the study, problem statement and objectives of the study, and it is supported by recent literature. 

The section on Materials and Methods could be better presented, by using Tables to clearly indicate the location, type, and/or depth of the samples, as well as the period of sampling. Analytical methods should be more elaborate.

The results, discussion and conclusion clearly responded to the set objectives of the paper.

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors obtained unique analytical data on the distribution of uranium isotope values in lake waters. But, unfortunately, the work does not provide information about the values of the amount of organic carbon, hydrogen carbonate ion (based on the pH values - this is the hydrogen carbonate ion). When discussing the results of the work, the authors using the literature data on the basis of these values make the main conclusions, but not arguing the values for specific studied lakes. The authors show the dependence of the change in the values of uranium on the pH. Therefore authors must be explain why the pH change. In addition, the authors compare the values of TDS and salinity, but again do not give an explanation of what is due to the differences or similarities of these values. The proposed conclusions on the dependence of changes in the values of uranium isotopes should be justified and analyzed on the example of specific lakes studied, of course, using the literature data.

The fact is that the mobility of uranium species is determined not only by the redox conditions and pH of water but also by biogeochemical processes (i.e., the presence of organic matter (OM) and its interaction with iron and manganese oxides/hydroxides) (Andersson et al., 2001; Fredrickson et al., 2002; Koch-Steindl and Pröhl, 2001). Sorption of uranium complexes on iron hydroxides is significantly reduced in the presence of organic matter and/or competing cations, such as Ca2+ and Mg2+ (Belli et al., 2015). Other studies showed that the concentration of U(VI) in the aqueous phase drastically decreases during bacterial processes because of the formation of insoluble U(IV) compounds (Newsome et al., 2014, 2015).

 

There are a number of comments on the article:

1)It is unclear why the literature review did not include data on lakes in Mongolia with high uranium content in the waters. For example (B. S. Linhoff, P. Bennett, T. Puntsag, and O. Gerel, “Geochemical Evolution of Uraniferous Soda Lakes in Eastern Mongolia,” Env. Earth Sci. (2010); DOI: 10.1007/s12665-010-0512-8.; V. P. Isupov, A. G. Vladimirov, N. Z. Lyakhov, S. L. Shvartsev, S. Ariunbileg, M. N. Kolpakova, S. S. Shatskaya, L. E. Chupakhina, L. V. Kuibida & E. N. Moroz Uranium in saline lakes of Northwestern Mongolia //Doklady Earth Sciences volume 437, pages352–356(2011))

2) Methods of investigation of uranium isotopes should be briefly described

3) A Piper diagram is a graphical representation of the chemistry of a water samples. Why was the basic anions carbonate plus hydrogen carbonate replaced with nitrogen in the Piper diagram? It's not a Piper diagram. The apexes of the anion plot are sulfate, chloride and carbonate plus hydrogen carbonate anions. 

4) Why build the same charts, TDS and salinity is in this case the same thing. Or it is necessary to explain what factors determine the differences between TDS and salinity.

5) It is also necessary to justify changes in pH in lakes. What is the reason for such an alkaline pH, chloride and sulfate ions can not provide it.

6) From the above it is not clear, so what determines the differences in the values of 234U/238U in different lakes studied in this work. Clearly there is a lack of data on the forms of finding uranium: suspension, true solutions.

6) In the discussion the authors show the dependence of the distribution of uranium isotope values in lake waters from the carbonate and bicarbonate anion, and as has been shown in measurements for some reason this ions are absent. It is necessary to make and carry out studies of pH changes from its values. It is also necessary to consider the dependence of uranium isotope ratios on the concentration of hydrogen carbonate ion, such information is practically absent in the articles, and this material can be shown.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

All necessary changes have been made. Only the reasons for the formation of high pH in chloride and sulphate waters remained unexplained. I hope the authors will be interested in this important point and they will continue their research. Since this is what can be associated with the accumulation of uranium in chloride waters.