Mineral Composition and Environmental Importance of Fe–Mn Nodules in Soils in Karst Areas of Guangxi, China
, Rongrong Ying 1,2,* and Zhongfang Yang 3,*
Round 1
Reviewer 1 Report
The paper entitled ‘Mineral composition and environmental importance of Fe–Mn nodules in soils of high geological background areas of Guangxi, China’ by Wenbing Ji and co-authors for Sustainability provides insight into the chemical and mineralogical characteristics of FMNs sampled in a China karst region.
General comments:
Introduction is too long and contains repeats. What was the scientific hypothesis checked during the research? Some key parameters of methodology are described insufficiently. I did not catch the influence of “high geological background areas” on the elemental or/and mineralogical composition of FMNs. I did not find deep description of the results obtained and comparing the data on the two key area. Please, add this information. Conclusion is too descriptive and repeats the results obtained. I suggest it should be rewritten.
Specific comments:
I suggest replace some key words (Fe–Mn Nodules; Karst Area; Mineral composition) that are already in abstract.
L.48 ‘and corresponding soils’. They are not reported yet.
In introduction the manuscripts by Yu. N.Vodyanitskiy (Scopus ID https://www.scopus.com/authid/detail.uri?authorId=6701620566 and https://www.scopus.com/authid/detail.uri?authorId=6603434318) should be cited.
L.71 replace ‘soil heavy metals pollution’ with ‘soil heavy metals contamination’
Section 2.1. Please, indicate the soils and soil horizons that were sampled. How FMNs were taken from the soils?
L.156 – 158. It should be in acknowledgements.
Section 2.2. Did you use the Rietveld full-pattern fitting method?
Table 1. Please, transfer it to Supplementary.
l.244 – 248 ‘Minerals in FMNs can be classified into primary 244 and secondary minerals according to their sources. Primary 245 minerals are derived directly from the parent rock, while 246 secondary minerals are formed through the decomposition and 247 transformation of primary minerals [2,17-18]’ and ‘The characteristic data of FMNs in typical soils 251 worldwide revealed in different published studies over the last 252 20 years were summarized and reported in Table 3.’can be omitted.
L. 248 – 250 ‘In karst areas, the 248 parent rocks consist generally of carbonate rocks, specifically 249 limestone and dolomite, with small quantities of other rock types 250 [3,8,10-12].’ should be in the previous section or can be omitted.
L.264 – 266, 279 – 281 can be omitted.
L. 290 ‘sub-surface and core soil’. What do you mean?
Author Response
Response to Reviewer 1 Comments
Comments and Suggestions for Authors
The paper entitled ‘Mineral composition and environmental importance of Fe–Mn nodules in soils of high geological background areas of Guangxi, China’ by Wenbing Ji and co-authors for Sustainability provides insight into the chemical and mineralogical characteristics of FMNs sampled in a China karst region.
General comments:
Point 1: Introduction is too long and contains repeats. What was the scientific hypothes is checked during the research? Some key parameters of methodology are described insufficiently. I did not catch the influence of “high geological background areas” on the elemental or/and mineralogical composition of FMNs. I did not find deep description of the results obtained and comparing the data on the two key area. Please, add this information. Conclusion is too descriptive and repeats the results obtained. I suggest it should be rewritten.
Response 1: Repetitive introduction has been streamlined. We think main the main objective of the current study is to assess the mineral composition of FMNs in soils with high geological backgrounds and to understand the environmental conditions. In this article the concept of “high geological background areas” context is basically the same as “karst area”. The title of this article is somewhat related to other related studies in our project group[1-4], so this concept of “high geological background areas” is used. We apologize for this grammatical problem and have corrected it based on your suggestions. Some key parameters of methodology have been added and improved. We add and improve the abstract content. Conclusion has been rewritten.
References:
[1]Ji, W.B.; Yang, Z.F.; Yu, T.; Yang, Q.; Wen, Y.B.; Wu, T.S.;Potential ecological risk assessment of heavy metals in the Fe–Mn nodules in the karst area of Guangxi, Southwestern China. Bulletin of Environmental Contamination and Toxicology. 2021a,106, 51-56.
[2]Ji WB, Yang ZF, Yin AJ, Lu YY, Ying RR, Yang Q, Liu X, Li B, Duan YR, Wang J, Wang YZ, Yu T, Wu TS, Zhang QZ.; Geochemical characteristics of Fe-Mn nodules with different sizes in soils of high geological background areas. Chinese Journal of Ecology. 2021b, 40, 2289-2301.
[3]Ji, W.B., Yang, Z.F., Yin, A.J., Lu, Y.Y., Ying, R.R., Yang, Q., Liu, X., Li, B., Duan, Y.R., Wang, J., Wang, Y.Z., Yu, T., Wu, T.S., Zhang, Q.Z.; Study on the formation mechanism of iron-manganese nodules in soils with high geological background-taking the central part of Guangxi as an example. Chinese Journal of Ecology. 2021c, 40, 2302-2314.
[4]Wen, Y.B., Yang, Z.F., Zhuo, X.X., Guan, D.X., Song, Y.X., Guo, C., Ji, J.F., Evaluation of various approaches to predict cadmium bioavailability to rice grown in soils with high geochemical background in the karst region, Southwestern China. Environmental Pollution. 2020a. https://doi.org/10.1016/j.envpol.2019.113645.
Point 2: I suggest replace some key words (Fe–Mn Nodules; Karst Area; Mineral composition) that are already in abstract.
Response 2: Some key words have been replaced in abstract.
Point 3: L.48 ‘and corresponding soils’. They are not reported yet.
Response 3: We apologize for this error and have corrected it based on your suggestions. We deleted the word ‘corresponding’. Iron (Fe) and manganese (Mn) is the main element of rocks and soil is formed by weathering of rocks. And therefore, iron (Fe) and manganese (Mn) is the main element of soils.
Point 4: In introduction the manuscripts by Yu. N.Vodyanitskiy (Scopus ID https://www.scopus.com/authid/detail.uri?authorId=6701620566 and https://www.scopus.com/authid/detail.uri?authorId=6603434318) should be cited.
Response 4: The two manuscripts by Yu. N.Vodyanitskiy above have been cited.
Point 5: L.71 replace ‘soil heavy metals pollution’ with ‘soil heavy metals contamination’.
Response 5: Thank you for your constructive suggestion. We have replaced ‘soil heavy metals pollution’ with ‘soil heavy metals contamination’.
Point 6: Section 2.1. Please, indicate the soils and soil horizons that were sampled. How FMNs were taken from the soils?
Response 6: The surface soil samples (0–20 cm) were collected. Each soil sample was collected about 2kg, stored in polyethylene bags, air-dried for about 5 days, and sieving through 2-mm nylon sieves. During sieving, FMNs larger than 2-mm were manually collected, washed with deionized (DI) water (18.25 MΩ), and dried. They were mainly elliptical.
Point 7: L.156 – 158. It should be in acknowledgements.
Response 7: Thank you for your suggestion. But we think L.156 – 158 is better suited to the original chapter.
Point 8: Section 2.2. Did you use the Rietveld full-pattern fitting method?
Response 8: Yes. We did. XRD patterns were analyzed using Jade 6.0 software using the Rietveld Full-pattern Fitting Method.
Point 9: Table 1. Please, transfer it to Supplementary.
Response 9: Thank you for your suggestion. We have transferred Table 1 to Supplementary.
Point 10: L.244 – 248 ‘Minerals in FMNs can be classified into primary and secondary minerals according to their sources. Primary minerals are derived directly from the parent rock, while secondary minerals are formed through the decomposition and transformation of primary minerals [2,17-18]’ and ‘The characteristic data of FMNs in typical soils worldwide revealed in different published studies over the last 20 years were summarized and reported in Table 3.’can be omitted.
Response 10: Thank you for your suggestion. ‘The characteristic data of FMNs in typical soils worldwide revealed in different published studies over the last 20 years were summarized and reported in Table 3.’ has been deleted. But we think L.244 – 248 is necessary. Because the concept of primary and secondary minerals was first introduced in the article.
Point 11: L. 248 – 250 ‘In karst areas, the parent rocks consist generally of carbonate rocks, specifically limestone and dolomite, with small quantities of other rock types [3,8,10-12].’ should be in the previous section or can be omitted.
Response 11: We have put L. 248 – 250 in the introduction.
Point 12: L.264 – 266, 279 – 281 can be omitted.
Response 12: L.264 – 266 and L 279 – 281 have been deleted.
Point 13: L 290 ‘sub-surface and core soil’. What do you mean?
Response 13: The sub-surface layer is a soil layer of diagnostic significance formed by the leaching, migration, precipitation, or in situ enrichment of material below the surface layer of the soil. It is formed between the topsoil layer and the subsoil layer by bearing the material leached down from the topsoil, and is usually the soil layer below the topsoil layer to a depth of 50 cm, including the B layer (e.g., claying layer) and the E layer (bleaching layer) in the occurrence layer. The core layer is also known as the "raw soil layer". It is the middle layer of the soil profile. It is located between the topsoil layer and the subsoil layer. It is formed by the material that has been leached from the topsoil. It is usually the soil layer below the topsoil layer to a depth of 50 cm. Because of the movement and deposition of materials, the topsoil layer and the core soil layer best reflect the characteristics of the soil formation process. In cultivated soils, the core soil layer is generally less structured, has a lower nutrient content, and has fewer plant roots.
Author Response File: 
Author Response.doc
Reviewer 2 Report
Why karst soils have so low calcium and carbonate content?
The sum of Fe2O3 (30.06%) +SiO2 (19.72%) +Al2O3(17.93%) +TiO2(0.96%) +P2O5(0.78) +MnO2(0.64%) + MgO(0.21%) +CaO(0.13%) +K2O(0.12%) +Na2O(0.05%) = 71.14 %, but where are the rest 28.86 % ?
Please give more information about the soils – what type are they according to WRB or Soil Taxonomy?
Please give more information about soil properties such as - soil reaction, physico-chemical properties, soil texture and etc. This will help to understand Fe–Mn nodules genesis.
Author Response
Response to Reviewer 2 Comments
Point 1: Why karst soils have so low calcium and carbonate content?
Response 1: This is mainly due to the strong chemical weathering in the natural environment of the study area. Our object of study in this paper is Fe-Mn nodules in soil, which are formed in the soil after a long evolutionary history. Calcium is easily lost due to the leaching effect of natural rainwater.
Point 2: The sum of Fe2O3(30.06%) +SiO2(19.72%) +Al2O3(17.93%) +TiO2(0.96%) +P2O5(0.78%)+MnO2(0.64%)+MgO(0.21%)+CaO(0.13%)+K2O(0.12%)+Na2O(0.05%) = 71.14 %, but where are the rest 28.86 % ?
Response 2: The rest 28.86 % mainly includes organic matter, a small amount of water and weakly crystalline water molecules in the oxides.
Point 3: Please give more information about the soils – what type are they according to WRB or Soil Taxonomy?
Response 3: The major soil types have been identified as Ferric Acrisols following the World Reference Base (WRB) for Soil Resources (FAO, 2015).
References
Food and Agriculture Organization of the United Nations (FAO), 2015. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. FAO, Rome.
Point 4: Please give more information about soil properties such as - soil reaction, physico-chemical properties, soil texture and etc. This will help to understand Fe–Mn nodules genesis.
Response 4: The major soil types have been identified as Ferric Acrisols following the World Reference Base (WRB) for Soil Resources (FAO, 2015). Ferric Acrisol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Ferric Acrisol form on old landscapes that have an undulating topography and a humid tropical climate. Their natural vegetation is woodland, which in some areas has given way to tree savanna maintained by seasonal burning. The age, mineralogy, and extensive leaching of these soils have led to low levels of plant nutrients, excess aluminum, and high erodibility, all of which make agriculture problematic. Nevertheless, traditional shifting cultivation of acid-tolerant crops has adapted well to the conditions found in Ferric Acrisols. They occupy just under 8 percent of the continental land surface on Earth, covering most of Guangxi's land area. Ferric Acrisols are defined by the presence of a subsurface layer of accumulated kaolinitic clays where less than half of the ions available to plants are calcium, magnesium, sodium, or potassium and also by the lack of an extensively leached layer below the surface horizon (uppermost layer). Here are some available research information about the study area.
Ferric Acrisols, are generally characterized as soils gone through deep and intensive weathering, and have a residual accumulation of resistant minerals (e.g. quartz) and subsequently formed clay minerals (e.g. kaolinite and gibbsite)(Wen et al., 2020).
(a) A-CN-K diagram of the carbonate bedrocks, saprolites, terra rossa, and FeeMn concretions showing the degree of chemical weathering. (b) Correlation between Fe2O3T and Al2O3 contents in the samples from profiles(Wen et al., 2020)
Here are Soil main chemical properties of different soil types reported by (Wen et al., 2020). The data are presented as mean ± standard deviation. Manganese and iron concentrations are high, especially in the Ferralsols, with Mn and Fe contents 4.4 and 3.4 times higher than that in the Anthrosols, respectively.
References
Wen,Y.B., Li, W., Yang, Z.F., Zhang, Q.Z., Ji, J.F.; Enrichment and source identification of Cd and other heavy metals in soils with high geochemical background in the karst region, Southwestern China. Chemosphere.2020b, https://doi.org/10.1016/j.chemosphere.2019.125620.
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
The manuscript was corrected. But some my comments and questions were not solved:
What was the scientific hypothesis checked during the research?
I did not catch the influence of “high geological background areas” on the elemental or/and mineralogical composition of FMNs.
I did not find deep description of the results obtained and comparing the data on the two key area. Please, add this information.
‘sub-surface and core soil’. What do you mean?
Author Response
Response to Reviewer 1 Comments
（Round2）
The manuscript was corrected. But some my comments and questions were not solved:
General comments:
Point 1: What was the scientific hypothesis checked during the research?
Response 1: The main objective of the current study is to assess the mineral composition of FMNs in soils with high geological backgrounds and to understand the environmental conditions. In addition, the mineral composition of FMNs in the karst area was compared to those in non-karst areas and to reveal the relationship between mineral composition and its forming environment.
Point 2: I did not catch the influence of “high geological background areas” on the elemental or/and mineralogical composition of FMNs.
Response 2: In this article the concept of “high geological background areas” context is basically the same as “karst area”. The title of this article is related to other related studies in our project group, so this concept of “high geological background areas” is used. Literature review of the mineralogical composition of the FMNs in typical soils(Table 2) has shown that there is no difference in the mineral composition of Fe-Mn nodules in karst areas and non-karst areas. But there will be some differences in elemental composition.Publicly available research data show that there are some differences in the composition of the main elements of Fe-Mn nodules in karst and non-karst areas, the main difference is that the content of aluminum and iron elements in Fe-Mn nodules in karst areas is relatively high, the content of silicon elements is relatively low, and there is no significant difference in the content of other elements such as manganese elements and calcium elements(Table S2)
References:
[1]Ji, W.B.; Yang, Z.F.; Yu, T.; Yang, Q.; Wen, Y.B.; Wu, T.S.;Potential ecological risk assessment of heavy metals in the Fe–Mn nodules in the karst area of Guangxi, Southwestern China. Bulletin of Environmental Contamination and Toxicology. 2021a,106, 51-56.
[2]Ji WB, Yang ZF, Yin AJ, Lu YY, Ying RR, Yang Q, Liu X, Li B, Duan YR, Wang J, Wang YZ, Yu T, Wu TS, Zhang QZ.; Geochemical characteristics of Fe-Mn nodules with different sizes in soils of high geological background areas. Chinese Journal of Ecology. 2021b, 40, 2289-2301.
[3]Ji, W.B., Yang, Z.F., Yin, A.J., Lu, Y.Y., Ying, R.R., Yang, Q., Liu, X., Li, B., Duan, Y.R., Wang, J., Wang, Y.Z., Yu, T., Wu, T.S., Zhang, Q.Z.; Study on the formation mechanism of iron-manganese nodules in soils with high geological background-taking the central part of Guangxi as an example. Chinese Journal of Ecology. 2021c, 40, 2302-2314.
[4]Wen, Y.B., Yang, Z.F., Zhuo, X.X., Guan, D.X., Song, Y.X., Guo, C., Ji, J.F., Evaluation of various approaches to predict cadmium bioavailability to rice grown in soils with high geochemical background in the karst region, Southwestern China. Environmental Pollution. 2020a. https://doi.org/10.1016/j.envpol.2019.113645.
Point 3: I did not find deep description of the results obtained and comparing the data on the two key area. Please, add this information.
Response 3: Concentrations of major elements in the FMNs in karst areas and no-karst areas were shown in Table S2. Publicly available research data show that there are some differences in the composition of the main elements of Fe-Mn nodules in karst and non-karst areas, the main difference is that the content of aluminum and iron elements in Fe-Mn nodules in karst areas is relatively high, the content of silicon elements is relatively low, and there is no significant difference in the content of other elements such as manganese elements and calcium elements(Table S2). Due to the special soil-forming parent material and special climatic conditions leading to a large loss of other elements and a large accumulation of iron and aluminum, a portion of the other elements will be lost. Both the A-CN-K diagram and correlation between Fe2O3T and Al2O3 contents in the samples from profiles in karst areas illustrates the same perspectives. Fe-Mn nodules in karst areas represent the product of the late stage of weathering but not in other non-karst areas.
Table S2. Concentrations of major elements in the FMNs in karst areas and no-karst areas
|
Sample |
Al |
Fe |
Si |
Mn |
Ca |
Reference |
|
% |
% |
% |
% |
% |
||
|
Fe-Mn nodules(n=15) in karst areas |
9.49 |
20.99 |
9.22 |
0.50 |
0.09 |
This study |
|
Fe-Mn nodules(n=20) in karst areas |
10.21 |
19.69 |
10.10 |
2.41 |
0.82 |
Wen et al., 2020 |
|
Fe-Mn nodules(n=2) in no-karst areas |
2.8 |
8.11 |
29.6 |
6.4 |
1.46 |
Ettler et al., 2017 |
|
Fe-Mn nodules(n=40) in no-karst areas |
6.85 |
12.17 |
25.55 |
6.83 |
0.64 |
Liu et al., 2002 |
|
Fe-Mn nodules(n=9) in no-karst areas |
6.54 |
9.61 |
20.20 |
7.67 |
0.64 |
Tan et al., 2006 |
|
Fe-Mn nodules in no-karst areas |
4.47 |
17.65 |
28.80 |
0.73 |
0.19 |
Sun et al., 2018 |
|
Fe-Mn nodules(n=4) in no-karst areas |
7.61 |
36.15 |
- |
0.54 |
0.98 |
Gao et al., 2018 |
(a) A-CN-K diagram of the carbonate bedrocks, saprolites, terra rossa, and FeeMn concretions showing the degree of chemical weathering. (b) Correlation between Fe2O3T and Al2O3 contents in the samples from profiles in karst areas(Wen et al., 2020).
Reference
- Ettler,, Chren,M., Mihaljevič, M., Drahota, P., Kříbek, B., Veselovský, F., Sracek, O., Vaněk, A., Penížek, V., Komárek, M., Mapani, B., Kamona, F.; Characterization of Fe–Mn concentric nodules from Luvisol irrigated by mine water in a semi–arid agricultural area. Geoderma, 2017, 299: 32–42.
- Wen,Y.B., Li, W., Yang, Z.F., Zhang, Q.Z., Ji, J.; Enrichment and source identification of Cd and other heavy metals in soils with high geochemical background in the karst region, Southwestern China. Chemosphere.2020b, https://doi.org/10.1016/j.chemosphere.2019.125620.
- Liu,, Colombo,C., Adamo, P., He, J.Z., Violante, A.; Trace elements in manganese–iron nodules from a Chinese alfisol. Soil Science Society of America Journal. 2002, 66(2): 661–670.
- Tan,W.F., Liu, F., Li, Y.H., Hu, H.Q,. Huang, Q.Y,; Elemental composition and geochemical characteristics of iron–manganese nodules in main soils of China. Pedosphere. 2006, 16:72–81.
- Gao,T., Ke, S., Wang, S.J., Li, F.B., Liu, C.S., Lei, J., Liao, C.Z., Wu, F., Contrasting Mg isotopic compositions between Fe–Mn nodules and surrounding soils: Accumulation of light Mg isotopes by Mg–depleted clay minerals and Fe oxides. Geochimica et Cosmochimica Acta. 2018, 237:205–222.
- Sun Z., Jiang Y.Y., Wang, Q.B., Owens, P.R.;Fe–Mn nodules in a Southern Indiana loess with a fragipan and their soil forming significance. Geoderma. 2018, 313: 92–111.
Point 4: ‘sub-surface and core soil’. What do you mean?
Response 4: They are the two layers in the soil respectively. The sub-surface soil layer is a soil layer formed between the topsoil layer and the subsoil layer by bearing the material leached down from the topsoil, with depth range of 20-50cm. The core soil layer, is also known as the "raw soil layer". It is the middle layer of the soil profile. It is located between the topsoil layer and the subsoil layer, with depth range of 20-50cm. However, core soil layer is a term used in Chinese soil genesis and may be easily misunderstood, so it was deleted in the new manuscript.
Author Response File: Author Response.doc
Round 3
Reviewer 1 Report
Response 1. Please, add this information in the text.
Point 2. As the term “high geological background areas” is not used to solve the aim of the research, please, remove it.
Response 3. Initially, in the text the locations of sampling sites was presented in Figure 1. There were two key sites located in NanNing and DaXing. Please, provide information separately for each key site. Moreover, add information how many samples were collected during this research in section 2.1. And the map mentioned should be in the text. Otherwise, provide GPS coordinates of sampling sites.
Response 4. OK. Please, add this information in the text.
Author Response
Response to Reviewer 1 Comments
（Round3）
Response 1. Please, add this information in the text.
Response 1: We have added the following information in the new manuscript.
“The main objective of the current study is to assess the mineral composition of FMNs in soils with high geological backgrounds and to understand the environmental conditions. In addition, the mineral composition of FMNs in the karst area was compared to those in non-karst areas and to reveal the relationship between mineral composition and its forming environment.”.
Point 2. As the term “high geological background areas” is not used to solve the aim of the research, please, remove it.
Response 2: We have replaced “high geological background areas” with“karst areas”in the new manuscript.
Response 3. Initially, in the text the locations of sampling sites was presented in Figure 1. There were two key sites located in NanNing and DaXing. Please, provide information separately for each key site. Moreover, add information how many samples were collected during this research in section 2.1. And the map mentioned should be in the text. Otherwise, provide GPS coordinates of sampling sites.
Response 3: We have provided GPS coordinates of sampling sites in Table S1 in the supplementary materials.
Response 4. OK. Please, add this information in the text.
Response 4: We have added that information in the new manuscript.
Author Response File: Author Response.doc
