Molybdenum Isotopic Fingerprints in Taiwan Rivers: Natural versus Anthropogenic Sources

Round 1

Reviewer 1 Report

The paper is devoted the Mo isotopes in two rivers of Taiwan. The authors consider Mo as one of the main pollutant of the Danshuei river, the most polluted river inTaiwan. Another river -  Liwu -is pristine one. In the text I see that Mo concentrations in the polluted river is in a range 0.5-38 nM (without samples D4,  D5 with mixture of sea water with 105 nM Mo) 0.5-16.4nM, while in the clean river Mo= 22.7-65.1 nM (about 5nM in global river water).  The situation is very strange - in pristine river Mo concentration is almost 5 times higher that in polluted river. Some heavy metals - Cu, Zn, NI  (but not Fe as erroneously  marked in paper) are high in the polluted river, but In this river  Mo is not very high. The authors must give the understandable explanations of this strange situation.

Fig.1,b is badly readable, please impruve it.

 

Author Response

• The paper is devoted the Mo isotopes in two rivers of Taiwan. The authors consider Mo as one of the main pollutant of the Danshuei river, the most polluted river in Taiwan. Another river -  Liwu -is pristine one. In the text I see that Mo concentrations in the polluted river is in a range 0.5-38 nM (without samples D4, D5 with mixture of sea water with 105 nM Mo) 0.5-16.4nM, while in the clean river Mo= 22.7-65.1 nM (about 5nM in global river water).  The situation is very strange - in pristine river Mo concentration is almost 5 times higher that in polluted river. Some heavy metals - Cu, Zn, NI  (but not Fe as erroneously  marked in paper) are high in the polluted river, but In this river Mo is not very high. The authors must give the understandable explanations of this strange situation.

Reply: In polluted Danshuei river, the heavy metal concentration is high, but low Mo concentration is observed. While, in clean Liwu river, the Mo concentration is high ranging from 22.7 to 65.1 nM. This strange situation observed in Liwu river catchment is because of the sulfuric-acid induced oxidative weathering of pyrites and carbonates. As shown in Figure 2, samples from Danshuei river lie closer to the silicate end-member, due to weathering of Na-rich plagioclase and/or Na-bearing minerals. While samples from Liwu river lie close to the carbonate end-members and has more Ca²⁺ ions released relative to Na⁺. The disseminated calcites present in these low grade sedimentary and metamorphic terrane dissolves 350 times faster than plagioclase. Furthermore, sulfide-rich minerals such as pyrites are abundant in Liwu catchment [1,2] and sulfuric-acid weathering is significant in Liwu catchment as observed from previous studies. The coupled oxidative weathering of sulfides/pyrites and carbonates play an important role here. Mo is hosted in sulfide-rich rocks due to its similar chalcophile tendency and can contain Mo content as high as ~250μg/g [3]. The relative importance of sulphuric acid-mediated weathering also depends on the presence and weathering of pyrites in exposed lithologes. In addition, Liwu river has the highest denudation rate of 18 t km⁻² yr⁻¹, and the presence of fractured bedrocks increases the particle surface area to grain size ratio, and helps promotes deep chemical rock-water interaction. Thus, coupled oxidative weathering of carbonates and pyrites releases high Mo content in Liwu river as well as high Ca²⁺ and SO₄^2- content (Table 1-4).

 

• 1,b is badly readable, please impruve it.

Reply: The Figure 1 (including Fig. 1b) has been improved in the revised manuscript (page no. 3)

Reviewer 2 Report

Dear authors,

the submitted manuscript (Molybdenum isotopic fractionation in polluted and non-polluted rivers in Taiwan: Natural and anthropogenic sources) is interesting and could be published in Water with minor revisions.

1. Please state the e-mail of the corresponding author along with the tel and fax numbers, not only in the supplementary material.

2. Introduction" L53: unnecessary repetition.

3. Materials and methods, p 4: Please 

4. Please use the SI for the expression of the results - tables 1-4, S1 and S2. and in text. Stick to mg/L, for example.

5. Explain [Mo] when used for the first time in the text. Although used to express molar concentration, in my opinion [Mo] should be replaced with "Mo concentration" or "concentration of Mo" in the MS.

Author Response

Dear authors,

the submitted manuscript (Molybdenum isotopic fractionation in polluted and non-polluted rivers in Taiwan: Natural and anthropogenic sources) is interesting and could be published in Water with minor revisions.

Reply: Thank you for your valuable comments to improve our manuscript. The primary modifications in the paper and the responses to your comments are as follows.

 

1. Please state the e-mail of the corresponding author along with the tel and fax numbers, not only in the supplementary material.

Reply: The email address of the corresponding author along with the telephone and fax numbers have been provided in the revised manuscript.

 

 

2. Introduction" L53: unnecessary repetition.

Reply: Thank you for your suggestion. L53 has been removed in the revised manuscript to avoid unnecessary repetition.

 

 

3. Materials and methods, p 4: Please 

Reply: This comment has been discussed below.

 

4. Please use the SI for the expression of the results - tables 1-4, S1 and S2. and in text. Stick to mg/L, for example.

Reply: In this study, the Mo concentration in the dissolved load are expressed in (nM), while Mo concentration in the bedload sediments are expressed in (ppm), which has been the accepted norm in Mo isotope studies as reported in previous literature [4-7]. While the major ion (Na⁺, Mg²⁺, K⁺, Ca²⁺, SO₄^2-, Cl^-, NO₃^- and Si) concentrations have been reported in (mM), Sr concentration in (μM) and trace element (Fe, Zn, Cu, Ni) concentrations are reported in (nM). This convention is widely accepted and is helpful in comparing the results from this study with previously reported literatures. Moreover, the same has been observed in other isotope system like Sr, U, B etc., [8-11]. Hence, we stick to this norm of reporting concentration data in our study, thus making subsequent changes wherever necessary including tables 1-4, S1 and S2, and in text throughout. Furthermore, we also provide the concentration data in mg/L for major ions and in μg/L for Mo and trace elements in the supplementary material for reference.

 

5. Explain [Mo] when used for the first time in the text. Although used to express molar concentration, in my opinion [Mo] should be replaced with "Mo concentration" or "concentration of Mo" in the MS.

Reply: We thank the reviewer for this suggestion. The [Mo] has been replaced either with “Mo concentration” or “concentration of Mo” in the revised manuscript.

Reviewer 3 Report

I went ahead and read the Shail Vijeta Ekka et al. article with the title ``Molybdenum isotopic fractionation in polluted and non-polluted rivers in Taiwan: Natural and anthropogenic sources ". In terms of the findings, the paper presents intriguing possibilities. Overall, based on the research and the data, it is appropriate for publication. However, there is a minor issue that has to be fixed that I found.

 

Please make the title more catchy.

Please add numerical results in abstract.

Please concern some recent papers for introduction such as Water 13 (19), 2660 and Water 13 (7), 905.

Please improve the quality of figures specially figure 1.

Please improve the quality of language of the full article.

Need to check the full article in terms of typo error, spelling error etc such as in table 4 "dry season" and many more.

Please rewrite the conclusion in concise way.

Author Response

I went ahead and read the Shail Vijeta Ekka et al. article with the title ``Molybdenum isotopic fractionation in polluted and non-polluted rivers in Taiwan: Natural and anthropogenic sources ". In terms of the findings, the paper presents intriguing possibilities. Overall, based on the research and the data, it is appropriate for publication. However, there is a minor issue that has to be fixed that I found.

Reply: Thank you for your valuable comments to improve our manuscript. The primary modifications in the manuscript and the responses to your comments are as follows.

 

1. Please make the title more catchy. 

Reply: The title has been modified to make it more interesting and engaging. The title has been changed to “Molybdenum isotopic fingerprints in Taiwan rivers: Natural versus anthropogenic sources”.

2. Please add numerical results in abstract.

Reply: The numerical results from the MixSIAR model have been added in the abstract of revised manuscript.

 

3. Please concern some recent papers for introduction such as Water 13 (19), 2660and Water 13 (7), 905.

Reply: Thank you, the above mentioned papers have been cited in the introduction.

 

4. Please improve the quality of figures specially figure 1.

Reply: The quality of figures have been improved specially figure 1.

 

5. Please improve the quality of language of the full article.

Reply: The quality of the language of the full article has been improved.

 

6. Need to check the full article in terms of typo error, spelling error etc such as in table 4 "dry season" and many more.

Reply: Thanks, the full article in terms of typo error, spelling errors etc., have been re-checked.

 

7. Please rewrite the conclusion in concise way.

Reply: The conclusion is re-written in a concise way.