Trace Elements in Sediments of Two Lakes in the Valley of the Middle Courses of the Ob River (Western Siberia)

Round 1

Reviewer 1 Report

Presented manuscript has significant value for environmental geochemistry and paleolimnology. New data about lakes of Siberia and their modern sediments are studied. All approaches and methods used by the authors are corresponding to new days. Results are described clearly. However discussion should be more wide with using references on studies around the world, not only local Siberian researches. In this section many ideas and statements request proof (references) and more clear explanations. Besides, I think authors should change the title of own article, so the main focus out their study of different trace elements in sediments of lakes, but in the current title significance of heavy metals highlights only. But in general, I believe it is a very good study and this article can be published after But in general, I believe it is a very good study and this article can be published after some revision. All my comments and suggestions are in edited text of the manuscript I attached.

Comments for author File: Comments.pdf

Author Response

Thank you for valuable comments. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript, the authors focus on resolving spatial variation of trace element concentration in sediments and quantifying the rate of sediment accumulation of two lakes. The topic is timely and relevant and the manuscript is written clearly and concisely. However, a number of issues/questions need to be clarified and addressed in a revised manuscript before publication. These are summarised here and described in more detail below.

 

General comments

 

 (1)  The authors argued that the bottom sediments of Schuchie Lake are depleted in REE due to the high content of organic matter, and they also proposed the bottom sediments of the two lakes belong to different types according to the content of organic matter. However, they did not analyze the total organic contents of bottom sediments in this study.

 

(2)  The calcium concentrations in bottom sediments are variable, and the authors think it was probably due to the precipitation of carbonates. I think it makes sense. The variations of some major and trace element concentrations of bottom sediments are attributed to the precipitation of minerals in the lakes. It will be helpful if the authors could analyze the mineralogical compositions of the bottom sediments using XRD if possible.

 

(3)  In Figure 3 and 6, the increasing Cd concentration in Sch should be attributed to the anthropogenic input. However, it seems the Ink got fewer influences from human beings. Why?

 

(4)  The pattern of many major and trace elements in the bottom sediments in two lakes is quite different, indicating different mechanisms control the accumulation process of elements in bottom sediments in two lakes. However, the pattern of REE is similar in the two lakes. It is better to discuss in more detail the mechanism governing the accumulation of elements in sediments.

 

(5)  The introduction should be largely improved.

 

 

Detailed comments

 

Figure 1: It seems a more detailed geological map (smaller scale) in two lake catchments contributes to reflecting the geological environment around the lake area.

 

Figure 2 and 3 : Different colors should be used to distinguish the curves of the two lakes.

 

Figure 2 and 3 : It is better to show the age of sediments in the figures.

 

Line 75: The first occurrence of the word “Inkino” and “Shchuchie” is in lines 63 and 66 in the main text.

 

Line 149: Replace “North American shale NASC” with “North American shale (NASC)”.

 

Line 154. NASC should subscript

 

Line 425: “(Cfi)” superscript and subscript？

 

Line 442: Delete the space

Author Response

Thank you for valuable comments. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

GENERAL REMARK

The article provides a wealth of data on the concentration and distribution of trace and some major elements in the bottom sediments of fresh water lakes in boreal environment. The aim of the research is interesting and most of the targets are achieved. The methods used for sampling and analysis are fine. However, the work lacks mineral analysis of these sediments which would have provided valuable information as well as support to some of the conclusions on elements–mineral associations instead of driving conclusions based on statistical results which are not conclusive. Some of the statements are not supported by any evidence. Redox conditions are not discussed in term of geochemical behavior of the analysed elements, especially REE and Mn. The pH of the water as well as sediments was not measured. The English is fine. A few typing mistakes were corrected on the annotated text and contradictions in some statements were also outlined.

 

SPECIFIC REMARKS

Line 61: In your methods of work you should have done some XRD analysis and heavy mineral analysis to show the mineralogy of these sediments.

Line 82: Concretions by definition are usually larger than 1mm. May be nodules or peloids are better terminologies. You need to observe the internal structure of these grains to give them a name.

Line 151: Methods used in the calculations of REE data need references.

Line 185: some RSD values need checking and correction.

Line 266: Mineral analysis is missing in this work. Geochemistry cannot be explained or discussed without mineral analysis. Statements based on statistics are not conclusive.

Line 337: The positive correlation between Ti-Mn-P needs explanation in term of mineralogy.  

Line 339: The positive correlation between Ca and Al is not explained or justified. The former is found in authigenic carbonates and the latter in detrital aluminosilicates, which usually leads to negative correlation between the two.

Lines 378–379: You have no direct evidence to conclude co-precipitation of Ba-Mo-Mn in the sediments.

Line 384: The variation in Ce-anomaly in sediments is mainly influenced by the redox conditions which are not discussed or mentioned here.

Line 395: The pH was not determined for lake water, yet you say it is acidic.

Line 400: These are merely speculations about mineralogy. You have no conclusive evidence to support your statement.

  

Comments for author File: Comments.pdf

Author Response

Thank you for valuable comments. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for good work with your manuscript.  I suggest it can be published as soon as editors can.

Author Response

Dear reviewer! Thank you for your hard work in reviewing and improving our article and for your valuable suggestions. Best regards!

Reviewer 2 Report

 The Authors have revised the manuscript thoroughly and carefully based on all the comments. The manuscript can be accepted with only minor editorial corrections.

 Line 442 replace "According to ref. [21]" with “According to Author‘s name et al. (year) [21]”

Author Response

Dear reviewer! Thank you for your hard work in reviewing and improving our article and for your valuable suggestions.

We replaced "According to ref. [21]" with “According to Strakhovenko et al. (2010) [11]”.

Best regards!

Reviewer 3 Report

Thank you for considering my comments. The article is better now although I still feel that some direct mineral analysis of the sediments would have provided solid evidence to support your conclusions.

Author Response

Dear reviewer! Thank you for your hard work in reviewing and improving our article and for your valuable suggestions.

We have a number of arguments that XRD analysis is not necessary and even might be misleading for the interpretation of obtained results. First of all, please note that the studied sediments are represented largely by particulate organic matter (detritus, sapropel) which is the main factor controlling the storage of trace metals and their vertical concentration pattern. Another significant part of trace metals is associated with amorphous Fe and Al hydroxides, allophones and imogolites, which cannot be resolved by XRD analysis. Second, some trace metals are certainly associated with crystalline or semi-crystalline clay minerals, both of primary origin, from the suspended matter of the Ob River (muscovite, chlorite) or formed in-situ, in lake sediments (illite, kaolinite, vermiculite). However, quantitative analysis of these minerals require structural XRD approach, with oriented samples treated according to conventional techniques. This clearly goes beyond the scope of the present study. We base this argument on results of our recent mineralogical analyses of the Ob River suspended particulate matter, sampled at the Kaibasovo station, right in between the two studied lakes. These results are included in another work of our group which is in preparation for submission to Minerals, and they are illustrated for convenience below.

Average mineral composition of the Ob River particulate matter measured on the base of XRD analysis of 28 samples (based on unpublished data of V.P. Shevchenko and I.V. Krickov) is follows:

Quartz – 34%±6%; Albite – 15.7%±3.4%; Potassium feldspar – 7.2%±1.6%; Pyroxene – 2.9%±0.9%; Muscovite – 5.2%±4.8%; Calcite – 10.1%±10.0%; Smectite – 7.0±3.7%; Illite – 11.7%±3.5%; Kaolinite – 3.5%±1.8%; Chlorite – 11.7%±3.1%; Vermiculite  – 6.8%±2.9%; Goethite – 4.0%±1.8%;

Crystalline minerals – quartz, feldspars, amphibole and pyroxenes – largely dominate the mineralogy of river sediments. However, as can be seen, the role of clay minerals is also high. Since many heavy metals (main toxicants (Zn, Cd, Pb))  may be present in sediments in a sorbed form on the surface of clay particles, mineral analysis will be of little information for us. Another possible mechanism of heavy metal concentration is the presence of ore carrier minerals, which most likely will not show up in the analysis due to their low abundance.

Third, simple XRD phase analysis can identify only these crystalline minerals, which will be of little use for understanding the behavior of trace metals. Moreover, in organic-rich lake sediments such as those investigated in the present work, the resolution of such analysis will be quite low and the signal can be strongly blurred by the presence of large amount (40-90%) of particulate organic matter. To overcome this, a digestion/thermal treatment would be necessary and this can create further artifacts on mineral distribution in the lake sediments.

Taken together, XRD phase analysis will add little insights into the behavior of trace metals, whereas conducting structural oriented XRD identification of clays and semi-amorphous materials can be highly challenging in the presence of large amount of organic matter, and this would require a study in its own.

 

Best regards!