A Detailed Insight into the Detrital and Diagenetic Mineralogy of Metal(oid)s: Their Origin, Distribution and Associations within Hypersaline Sediments

Round 1

Reviewer 1 Report

Abstract:

The abstract is not easy to understand. It has to be revised completely. I think it would be good to elaborate a bit about the role of heavy metals in soils, trace metals, and metalloids in soils and their bioavailability. I would recommend checking the latest international literature on mineralogy and geochemistry of alluvium contaminated by metal mining. There are studies that lead to interesting comparisons.

M&M:

Sites: You should explain more explicitly that you took your samples on the Adriatic coast. So, uptake of elements from seawater by ferromanganese crusts: may be exceptionally long under solid-phase associations and sea-water speciation. You should sell this fact much better e.g. in the title of the paragraph. Please make it a nice story of the detrital and diagenetic mineralogy. Isn’t there any information about the history (management, use, disturbance) of metal accumulation within salt marsh environments? What can be said about the seasonal effects?
               

Results:

Table 2: Please give the absolute mineralogical composition of investigated sample contents. You mention this in the text but the table is not reflecting this information. The ratios don’t help a lot in understanding.

Figure 4: It would be interesting to relate the patterns of rhizo-sediment samples. Is there any information on that?

Figure 12: Only now I am to realize what you did. Can you integrate the sites into the PCA graph? Can you reduce this information to one form of multivariate assessment? I don’t see the added values of the relationship between heavy metal contents and clay mineral properties in surface sediments. You mentioned that: “PCA explained for 84.63% of the data variance in the first two ordination axes, highlighting significant positive correlations between the samples from crystallization basin and Poslužnica due to their higher heavy metal(oid) and Sr concentrations. The samples from Piccia clearly have lower heavy metal(oid) and Sr concentrations. A pattern of individual correlations between heavy metal(oid) and Sr distribution is also recognized”. But I can notice a lot of negative relations. How to interpret it? You must discuss implications for metal pollution assessment.

Discussion:

There are many studies but this area (see below) of research is underrepresented compared to the for example adsorption of zinc and copper ions on calcite and aragonite and its influence on the transformation of aragonite to calcite, I agree. But I would love to see your emphasis changing to the history o estuary salt marshes' feedback to sea level rise over a long period.

The general impression on the discussion your discussion is touching the principle roles of insights from the application of geochemical indices and metal(oid) mobility in a hypersaline salt marsh sediment. This is ok and nice and correct. This information is somewhat general potential bioaccumulation of trace metals from salt marshes. What makes your study unique is the sequential extraction procedure for the speciation of particulate trace metals. So, I would strongly recommend including more of management, geochemistry of iron ochres and mine waters in your discussion. It would make your study more colorful and interesting. Please provide relevant references.

Detailed comments:

The manuscript entitled "Detailed insight into detrital and diagenetic mineralogy of 2 metal(oid)s: their origin, distribution and associations within hypersaline sediments" is interesting. Various techniques were used to characterize the effects of sediment geochemical properties on heavy metal bioavailability. Remarks are listed below.

1. Please revise the Abstract to keep consistent with the research contents of this work.

2. It will be better to provide some key data in the abstract, for better elucidating the results of this study.

3. Please check and revise the English language, since there are a number of grammar mistakes and badly constructed sentences.

4. Lines 537-543 Accordingly, detrital particles from the geological hinterland, e.g. the type of rock fragments and minerals, the various anthropogenic sources, the particle size relative to the number of clay minerals, the abundance of organic matter, and early diagenetic precipitates significantly affect the heavy metal accumulation and retention. However, given the physical conditions currently prevailing in the sediments, the release of metal(oid)s and their further transfer within the system will be closely related. This part must be modified.

5. Please add some evidence to support the conclusion that "The studied elements were mainly associated with Fe/Mn oxides and oxyhydroxides (As, Cr, Ni, Pb, Zn), incorporated into or adsorbed onto the crystal lattices of clay minerals (As, Cr, Pb, Sn, Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr, Zn) and associated with organic matter (Cu, Pb and Zn)". Please revise. Additionally, mechanisms of regional background concentrations of heavy metals and pore-filling effect, and hydrogen bond interaction actually were not mentioned and discussed in the main text in this study.

6. Please compare the major chemical composition of sediment samples between this work and other studies with similar samples.

Constructive feedback:

The research output, in terms of novelty, scores good uniqueness in terms of data. The level of clarity is above the threshold of acceptability, as well as the state of the art and the comparative discussion. It adopts up-to-date methodologies with respect to the object of research. However, the paper does not fully discuss the limitations of the approach and potential biases due to the assumptions made. The complete raw database is not yet made completely available in an authigenic clay mineral in continental evaporitic environments in this study. Data sharing is the practice of making data used for scholarly research available to other investigators. Many funding agencies, institutions, and publication venues have policies regarding data sharing because transparency and openness are considered by many to be part of the scientific method. The article does not adhere to appropriate reporting guidelines and community standards for data availability. How to use your results in practice?

Summary:

The article is presented in an intelligible manner. This work is extremely interesting, it has a sufficient impact and does add some novelties to the knowledge base. Potentially, its potential impact upon the international scientific community of reference is well done. The study presents the results of primary scientific research, while the comparison with other types should be the toughest section, although not well exploited in the Discussion section. Experiments, statistics, and other analyses are performed to a sound technical standard and are described in detail. However, conclusions, as they presented, are not new.

Author Response

Abstract:

The abstract is not easy to understand. It has to be revised completely. I think it would be good to elaborate a bit about the role of heavy metals in soils, trace metals, and metalloids in soils and their bioavailability. I would recommend checking the latest international literature on mineralogy and geochemistry of alluvium contaminated by metal mining. There are studies that lead to interesting comparisons.

The manuscript has been written for the Special Issue “Metal(loid)s Mobility in Hypersaline Environments and Salt Marshes” and the research is dealing with a precise mineralogical and geochemical characteristics of hypersaline sediment and rhizo-sediment. As far as bioavailability is concerned, you require a good understanding of where and how metal(oid)s occur (are incorporated) within hypersaline sediment (solid components) - that is, whether they are bound to mineral components (and which mineral components) or to organic matter. This is a must and a first step for comprehensive understanding of metal(oid)s bioavailability and transfer in the system - because of this facts we conducted a proposed study. And please, there is no mine in the direct geological background of the research area. For a more precise understanding of the area in question, we added an Environmental setting description into the Materials and Method section.

Abstract has been revised into:

Hypersaline environments are among the most vulnerable coastal ecosystems and, are extremely noteworthy for a variety of ecological reasons. Comprehensive assessment of metal(oid) contamination in hypersaline sediments from Sečovlje (Northern Adriatic, Slovenia) was addressed by highlighting the detrital and diagenetic mineralogy and geochemical properties within the solid sediment material. Close associations between Fe/Mn oxides and oxyhydroxides with As, Cr, Ni, Pb and Zn, and between organic matter with Cu, Pb and Zn were confirmed using X-ray powder diffraction, SEM-EDS and ICP emission spectrometry analysis. Possible incorporation or adsorption on the crystal lattices of clay minerals (As, Cr, Pb, Sn and Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr and Zn) were also detected. All presented correlations were introduced by various statistical analyses. The enrichment factor (EF) values showed a low degree of anthropogenic burden for As, Bi, Hg and Zn, while Cd, Cr, Cu, Ni, Pb, Sn and Sr originated from the geological background. These results emphasise that a detailed mineralogical and geochemical characterisation of solid (especially detrital and diagenetic) sediment particles is crucial in further understanding the metal(oid) translocation within the hypersaline ecosystems.

M&M:

Sites: You should explain more explicitly that you took your samples on the Adriatic coast. So, uptake of elements from seawater by ferromanganese crusts: may be exceptionally long under solid-phase associations and sea-water speciation. You should sell this fact much better e.g. in the title of the paragraph. Please make it a nice story of the detrital and diagenetic mineralogy. Isn’t there any information about the history (management, use, disturbance) of metal accumulation within salt marsh environments? What can be said about the seasonal effects?

1. As already mentioned, due to the Special Issue dealing with Hypersaline environments, we arrange samples from Sečovlje salina, a hypersaline environment in the Gulf of Trieste, located along the Adriatic coast. Unfortunately, there are no ferromanganese crusts found nearby the research area.
2. One of the most valuable natural and cultural heritage sites in Slovenia, the Sečovlje Salina Nature Park (KPSS) is an important tourist attraction on the Slovenian coast. While providing a home for numerous indigenous species of flora and fauna (Kaligarič and Škornik, 2006; Sovinc, 2012; Škornik, 2008), the KPSS also preserves the tradition of salt production. With written references dating back to the second half of the 13th century, the area has contributed to the traditional manual harvesting of salt in crystallization basins, and thus to other products produced in the area, including those within the food, cosmetics, and therapeutic purposes.
3. The research area was already presented in the Glavas, 2013; Glavas et al., 2015; Glavas et al., 2017; Glavas et al., 2018 and Kovač et al., 2018 – in the studies we investigated the upper part of the surface sediment (up to 5 cm), petola and salt production, and yes, the season affects the mobility of elements due to precipitation processes in the upper part of the surficial sediments (2-3 cm) (in crystallization basin). Now, the aim was different: the sediments depth was 15 cm and we wanted to precisely define the mineralogy and geochemistry of hypersaline sediment and rhizo-sediment (all sediment solid components) on the sub-micron level in relation to metal(oid)s presence.

The Environmental setting description was added into the Materials and Method section:

The catchment area is basically a much closed geological area mainly towards the inland and thus we cannot find any anthropogenic sources from inland direction. The only possible pollution path from the inland could be through the air particles deposition – like this we can justify the presence of cinnabar or mercury particles originated from Idrija historical mine, which is almost 70 km by air from the Sečovlje salina. Cinnabar or mercury small particles (e.g. μm-nm size) emitted into the air can travel thousands of miles in the atmosphere before they settle into the ground.

Conversely, we could trace the pollution from the sea side much more clearly. There are two large ports near the Sečovlje salina: (1) Koper at the air distance of 14 km with cargo traffic and (2) Trieste at the air distance of 23 km with cargo and passenger traffic. On the other side of the Gulf of Trieste bay at the air distance of 28 km, is the mouth of the Soča/Isonzo River, which transports/transported different geogenic and anthropogenic material from inland, including the material from now long closed Idrija Hg mine and several small Cu deposits. However, the inflow of presented material into Sečovlje salina area is strongly dependent on the currents in the Gulf of Trieste bay. In general, the currents are clock-wise (up along the Adriatic coast and down along the Italian coast), but it could be more complex, meaning that the currents could also bring the dispersed geogenic and anthropogenic material from Soča/Isonzo River, Trieste and Koper port.

Within the research area there are also many vineyards and orchards where CuSO₄ was used as a pesticide spray.

Results:

Table 2: Please give the absolute mineralogical composition of investigated sample contents. You mention this in the text but the table is not reflecting this information. The ratios don’t help a lot in understanding.

The % are absolute but not relative! It would be relative if we worked semi-quantitatively, but we did/applied Rietveld, which also takes crystallinity into account. We added the GOF (goodness-of-fit value - Rwp (weighted R)/Rexp (expected R) value for each sample. It is a statistical hypothesis test used to see how closely observed XRD data mirrors expected fitted XRD data.

Figure 4: It would be interesting to relate the patterns of rhizo-sediment samples. Is there any information on that?

Yes, we did that - Figure 4: XRD patterns of the studied samples. Grey patterns represent the sediment samples and red patterns represent the rhizo-sediment samples. The uppercase letters describe the mineral composition of the samples.

In the text: Main mineral phases are presented in the integrated diffractograms (Figure 4) for all samples. The mineral composition of the sediments studied consists of high quantities of quartz, calcite and illite/muscovite, followed by albite, aragonite, clinochlore, goethite, pyrite and halite (Table 2). The clay mineral phases revealed with XRD analysis (oriented preparation) are kaolinite (Figure 5, Table 2) and low quantities of chlorite, interstratified layers of illite/smectite (I/S), illite and smectite.

In principle, the mineral composition between sediments and rhizo-sediments is very similar, but minor differences can be observed, which are primarily related to the sampling locations. The rhizo-sediments from the Piccia area show an inversely proportional relationship between illite/muscovite, kaolinite and quartz, i.e. lower amounts of illite/muscovite and kaolinite with higher amounts of quartz.

The Piccia area is located closer to the sea and is not part of the salt processing crystallization area with crystallization basins and Poslužnica: the Piccia area is therefore very intact and the sediments have not been redeposited such as in the active crystallization area. The occurrence of halite minerals is also slightly higher in the sediments from active crystallization basin and Poslužnica area. Higher quantities of aragonite (from 6.1% to 9.8%) and consequently lower quantities of calcite (from 18.3% to 20.6%) were determined only in sediment and rhizo-sediment samples from crystallization basin and Poslužnica area. This is due to the mineral differences of the biogenic particles: in the crystallization basin and in Poslužnica area there are more aragonite skeletons, while in Piccia calcite residues predominate.

Figure 12: Only now I am to realize what you did. Can you integrate the sites into the PCA graph? Can you reduce this information to one form of multivariate assessment? I don’t see the added values of the relationship between heavy metal contents and clay mineral properties in surface sediments. You mentioned that: “PCA explained for 84.63% of the data variance in the first two ordination axes, highlighting significant positive correlations between the samples from crystallization basin and Poslužnica due to their higher heavy metal(oid) and Sr concentrations. The samples from Piccia clearly have lower heavy metal(oid) and Sr concentrations. A pattern of individual correlations between heavy metal(oid) and Sr distribution is also recognized”. But I can notice a lot of negative relations. How to interpret it? You must discuss implications for metal pollution assessment.

Yes, we did as you suggested and rewrite:

PCA (Figure 12) explained 84.63% of the data variance in the first two ordination axes, highlighting significant positive correlations between the samples from the crystallisation basin and Poslužnica due to their higher metal(oid) and Sr content. A pattern of individual correlations among metal(oid) and Sr distribution between the samples from crystallisation basin and Poslužnica is also recognised. Samples from Piccia (S1, RS1, S2, RS2, S3 and RS3) clearly show lower metal(oid) and Sr content, thus we can track down negative connections or no connections with the samples from crystallisation basin (S4, RS4, S5 and RS5) and Poslužnica area (S6 and RS6).

Discussion:

There are many studies but this area (see below) of research is underrepresented compared to the for example adsorption of zinc and copper ions on calcite and aragonite and its influence on the transformation of aragonite to calcite, I agree.

But I would love to see your emphasis changing to the history of estuary salt marshes' feedback to sea level rise over a long period:

Unfortunately, this is not the aim of the proposed study, we are working on the proposed subject now as part of a project covering the Slovenian part of the Gulf of Trieste.

The general impression on the discussion your discussion is touching the principle roles of insights from the application of geochemical indices and metal(oid) mobility in a hypersaline salt marsh sediment. This is ok and nice and correct. This information is somewhat general potential bioaccumulation of trace metals from salt marshes. What makes your study unique is the sequential extraction procedure for the speciation of particulate trace metals.

So, I would strongly recommend including more of management, geochemistry of iron ochres and mine waters in your discussion. It would make your study more colorful and interesting. Please provide relevant references:

There is not direct historical and active mining activities in the geological background of the research area – and therefore no iron ochres and mine waters.

Detailed comments:

The manuscript entitled "Detailed insight into detrital and diagenetic mineralogy of 2 metal(oid)s: their origin, distribution and associations within hypersaline sediments" is interesting. Various techniques were used to characterize the effects of sediment geochemical properties on heavy metal bioavailability. Remarks are listed below.

1. Please revise the Abstract to keep consistent with the research contents of this work.

We correct and revise the abstract.

2. It will be better to provide some key data in the abstract, for better elucidating the results of this study.

We correct and revise the abstract.

3. Please check and revise the English language, since there are a number of grammar mistakes and badly constructed sentences.

It has been already revised before the submission of the article. For review, we arrange the English proof reading again.

4. Lines 537-543 Accordingly, detrital particles from the geological hinterland, e.g. the type of rock fragments and minerals, the various anthropogenic sources, the particle size relative to the number of clay minerals, the abundance of organic matter, and early diagenetic precipitates significantly affect the heavy metal accumulation and retention. However, given the physical conditions currently prevailing in the sediments, the release of metal(oid)s and their further transfer within the system will be closely related. This part must be modified.

Yes, the conclusion was rewritten:

This study demonstrates that understanding the origin and incorporation of metal(oid)s within different solid sediment particles (such as detrital particles, anthropogenic particles, clay minerals, organic matter and diagenetic minerals) is critical to identify their distribution, accumulation, retention and further transfer into a vulnerable and ecologically important ecosystem such as salt marshes.

The results suggest that the detrital particles from the geological hinterland, e.g. the type of rock fragments and minerals, the various anthropogenic sources, the particle size relative to the amount of clay minerals, the abundance of organic matter and early diagenetic precipitates, significantly affect the metal(oid) accumulation and current retention in corresponding sediment and rhizo-sediment content of the Sečovlje salina. The metal(oid)s, e.g. As, Bi, Cd, Cr, Cu, Hg, Ni, Pb, Sn, Sr, Pb and Zn display many differences in the origin, distribution and association within the sediment components.

According to the results of XRD, ICP-ES, SEM-EDS and various statistical analyses, the studied elements were mainly associated with Fe/Mn oxides and oxyhydroxides (As, Cr, Ni, Pb, Zn), incorporated into or adsorbed onto the crystal lattices of clay minerals (As, Cr, Pb, Sn, Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr, Zn) and associated with organic matter (Cu, Pb and Zn). Only As, Bi, Hg and Zn were recognised as anthropogenic, although it would be difficult to determine anthropogenic sources for As and Zn, as their abundance is more likely due to processes occurring in the sedimentary basin. Traces of As were found in halite minerals, while Zn is an essential element for all living beings and is therefore also present in larger quantities. BiO industrial compounds are very common cargo found in the nearby ports and Hg presence is the result of almost 500 years of historical mining activity in Idrija.

5. Please add some evidence to support the conclusion that "The studied elements were mainly associated with Fe/Mn oxides and oxyhydroxides (As, Cr, Ni, Pb, Zn), incorporated into or adsorbed onto the crystal lattices of clay minerals (As, Cr, Pb, Sn, Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr, Zn) and associated with organic matter (Cu, Pb and Zn)". Please revise.

Of course, the conclusions were rewritten.

Additionally, mechanisms of regional background concentrations of heavy metals and pore-filling effect, and hydrogen bond interaction actually were not mentioned and discussed in the main text in this study.

The detrital particles are by nature part of the regional geological background and we have presented them in sub-micron detail. We added the following text in the discussion:

The geological background with the associated flysch rocks represents the primary source for the sediments and the detrital particles trapped within the sedimentary material represents the particles of the background rocks. Further on, primary and secondary clay minerals tend to bind free ions from the solution. The properties of the deposited mineral particles have a tremendous influence on the binding ability of metal(oid)s to mineral surfaces or incorporation into the crystalline structure of newly formed authigenic minerals [46,85,86,87,88].

Please compare the major chemical composition of sediment samples between this work and other studies with similar samples.

It was already done and written in the text: The values of investigated elements were consistent with those measured in surface sediments from central Adriatic Sea [61], Piran Bay [62], and Koper Bay [63] and in two saltmarshes located in the Marano and Grado lagoon [64]. In contrast, salts marsh sediments from Tijuana Estuary [65], Rosario Estuary [66] and Northern Europe [67] carried much higher values of Cd, Cu, Pb and Zn.

Constructive feedback:

The research output, in terms of novelty, scores good uniqueness in terms of data. The level of clarity is above the threshold of acceptability, as well as the state of the art and the comparative discussion. It adopts up-to-date methodologies with respect to the object of research. However, the paper does not fully discuss the limitations of the approach and potential biases due to the assumptions made. The complete raw database is not yet made completely available in an authigenic clay mineral in continental evaporitic environments in this study. Data sharing is the practice of making data used for scholarly research available to other investigators. Many funding agencies, institutions, and publication venues have policies regarding data sharing because transparency and openness are considered by many to be part of the scientific method. The article does not adhere to appropriate reporting guidelines and community standards for data availability. How to use your results in practice?

The data are deposited by the authors and they could be available to editors and peer reviewers if requested: authors could make data available on request and could provide an explanation, data and details on request.

Reviewer 2 Report

The manuscript presents and discuss original data concerning the geochemistry and mineralogy of two type of hypersaline sediments. From this point of view, the idea of analyzing such systems sounds good and original. Manuscript is accompanied by a rich list of references.

Before recommending for publication, I have made some remarks concerning the terms used (meta(oid}, concentration, etc.) which are not in accordance with IUPAC recommendation. 

I have never seen the analysis of TOC with respect with major and trace elements. This should be done.

Also, I would recommend to add to each experimental value provided in Tables the corresponding total uncertainty (statistic +calibration).

All my remarks can be found as sticky noted on the attached .pdf. file. 

Therefore, I do not recommend the manuscript to be published in its present for, but after a thoroughly revision.

Comments for author File: Comments.pdf

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Referee report:

Manuscript: “Detailed insight into detrital and diagenetic mineralogy of metal(oid)s: their origin, distribution and associations within hypersaline sediments”

Authors: Nastja Rogan Šmuc, Nives Kovač, Žan Hauptman, Andrej Šmuc, Matej Dolenec, Aleš Šoster

The manuscript is interesting, well written and fits the scopes of Minerals journal. I appreciate the amount effort that went into the development of this work. Unfortunately, it presents low scientific significance and the scientific goals stated in the Introduction have not been achieved (goals no. 2 and 3).

- The distribution of metals and metaloids has not been fully documented. Comprehensive analysis of the translocation processes into S. fruticose plants were omitted, the content of analytes in seawater and water-sediment transport of elements were not taken into account.

- The authors did not indicate the potential anthropogenic sources of sediment contamination with particular metals/metalloids (only the source of Hg, Bi, Sn and Zn was mentioned). Is the studied area significantly exposed to anthropogenic pollution at all? If not, taking into account the references cited, the work does not bring any new information.

From the analytical point of view, the section 2 needs to be deeply revised, extended and rewritten. The above-mentioned description of potential anthropogenic sources is missing.

- In line 107 it was stated that 45 samples were taken (45 of sediment, 45 of rhizo-sediment and 45 of plant, or 15 samples of each type - 45 in total?). 12 samples are further discussed (Figs. 4 and 6, Tables 2 and 3a,b).

- A map with the location of all sampling sites or a table with GPS data of all sites and detailed information on the type of samples collected (sediment, rhizo-sediment, plant) and their symbols must be attached.

- Line 119 – “Samples of S. fruticosa plant (…) were also packed” - have the plants been analyzed?

- Lines 121-123 “A representative sample of underlying sediment and rhizo-sediment for each sampling site consisted of 3 samples of underlying sediments and 3 samples of rhizo-sediment, which were mixed and quartered.” – is not clear; how many samples were analyzed?

- Line 141 – 2 mm or < 2 mm?

- Please use micron or mm – lines 137, 141,143.

- Please complete the description of the granulometric analysis - the type and dimensions of the laboratory vessel.

- Line 142 – “The entire procedure was repeated” - what procedure, mixing the same sub-sample, or preparing another sub-sample?

- Lines 162-168 and 193 - the paragraph on quality assurance/quality control should include complete information on CRM and standards (for pH and TOC).

- Lines 194-195 - was the validation performed for only 2 sub-samples? Please add a table with the results of the CRM analysis in the supplementary materials.

- Lines 197-203 - explain if PCA and CA have been caried out on standardized data.

Moreover, interpretation of analytical results is in question.

- Section 3.1. – instead of Table 1, please add in the supplementary materials the results of the granulometric analysis of all samples and their classification.

- Section 3.2. - please add in the supplementary materials the results of the pH and TOC analyses of all samples.

- Fig. 4 - illegible upper symbols of minerals.

- Fig. 5 - identification based on a single peak (illite, smectite – no peak)?

- Fig. 6 – what method was used for the division into clusters and subclusters? What the signs (+ *) next to the sample symbols mean?

- Lines 294-298 and 497-498 - the authors indicate different levels of organic carbon and pH in individual samples, while previously found no significant differences (line 231)!

- Section 3.4. lines 309-310 – why sediment contamination was compared with soil and not the sediments?

- Lines 461-462 – Hg should be included, since the authors analyze its content; reference [81] is from 1980, has nothing changed in the study area since then? All EFs should be given in the supplementary materials.

- Conclusions: The author needs to clearly specify the novelty of this work in addition to the aims mentioned. Not all the results reported in the manuscript can be confirmed.

References - should be carefully corrected in accordance with the instructions for authors; I suggest to update the literature, only 35 references are from the last 10 years.

Author Response

- The distribution of metals and metaloids has not been fully documented.

The manuscript has been written for the Special Issue “Metal(loid)s Mobility in Hypersaline Environments and Salt Marshes” and the research is dealing with a precise mineralogical and geochemical characteristics of hypersaline sediment and rhizo-sediment. Therefore, the distribution of metal(oid)s was carried out in accordance with the set objectives (Discussion part).

Comprehensive analysis of the translocation processes into S. fruticose plants were omitted, the content of analytes in seawater and water-sediment transport of elements were not taken into account.

1. The comprehensive analysis of the translocation processes into S. fruticose plants were not omitted, because, as it is written in the MM part: Sediment and rhizo-sediment samples were collected for this study in order to comprehensively identify the mineralogical and geochemical characteristics and metal(oid)-bearing minerals in the samples studied.
2. As far as bioavailability (prerequisite for translocation processes) is concerned, you require a good understanding of where and how metal(oid)s occur (are incorporated) within hypersaline sediment (solid components) - that is, whether they are bound to mineral components (and which mineral components) or to organic matter. This is a must and a first step for a comprehensive understanding of metal(oid)s bioavailability and transfer/translocation in the system.

- The authors did not indicate the potential anthropogenic sources of sediment contamination with particular metals/metalloids (only the source of Hg, Bi, Sn and Zn was mentioned). Is the studied area significantly exposed to anthropogenic pollution at all? If not, taking into account the references cited, the work does not bring any new information.

We strongly disagree. As far as pollution is concerned, it can be geogenic or anthropogenic and understanding both sources is extremely very important. For a more precise understanding of the area in question, we added an Environmental setting description into the Materials and Method section.

From the analytical point of view, the section 2 needs to be deeply revised, extended and rewritten. The above-mentioned description of potential anthropogenic sources is missing.

Again, for a more precise understanding of the area in question, we added an Environmental setting description into the Materials and Method section:

The catchment area is basically a much closed geological area mainly towards the inland and thus we cannot find any anthropogenic sources from inland direction. The only possible pollution path from the inland could be through the air particles deposition – like this we can justify the presence of cinnabar or mercury particles originated from Idrija historical mine, which is almost 70 km by air from the Sečovlje salina. Cinnabar or mercury small particles (e.g. μm-nm size) emitted into the air can travel thousands of miles in the atmosphere before they settle into the ground.

Conversely, we could trace the pollution from the sea side much more clearly. There are two large ports near the Sečovlje salina: (1) Koper at the air distance of 14 km with cargo traffic and (2) Trieste at the air distance of 23 km with cargo and passenger traffic. On the other side of the Gulf of Trieste bay at the air distance of 28 km, is the mouth of the Soča/Isonzo River, which transports/transported different geogenic and anthropogenic material from inland, including the material from now long closed Idrija Hg mine and several small Cu deposits. However, the inflow of presented material into Sečovlje salina area is strongly dependent on the currents in the Gulf of Trieste bay. In general, the currents are clock-wise (up along the Adriatic coast and down along the Italian coast), but it could be more complex, meaning that the currents could also bring the dispersed geogenic and anthropogenic material from Soča/Isonzo River, Trieste and Koper port.

Within the research area there are also many vineyards and orchards where CuSO₄ was used as a pesticide spray.

- In line 107 it was stated that 45 samples were taken (45 of sediment, 45 of rhizo-sediment and 45 of plant, or 15 samples of each type - 45 in total?). 12 samples are further discussed (Figs. 4 and 6, Tables 2 and 3a, b).

Yes, I am sorry, it was a typo. In total, there were 54 samples, due to the fact that the representative sample of sediment, rhizo-sediment and plant for each location (altogether 6 locations, now presented in Figure 2) consisted of 3 subsamples. In the study, we thus presented 6 representative sediment samples and 6 representative rhizo-sediment samples.

- A map with the location of all sampling sites or a table with GPS data of all sites and detailed information on the type of samples collected (sediment, rhizo-sediment, plant) and their symbols must be attached.

We attached the table with GPS data and there is detailed information about sediment and rhizo-sediment samples in the text: A representative sample of underlying sediment and a representative samples of rhizo-sediment for each sampling site marked in Figure 2 consisted of 3 subsamples of underlying sediments and 3 subsamples of rhizo-sediment.

- Line 119 – “Samples of S. fruticosa plant (…) were also packed” - have the plants been analyzed?

Yes, but we did not include plant analysis in this study.

- Lines 121-123 “A representative sample of underlying sediment and rhizo-sediment for each sampling site consisted of 3 samples of underlying sediments and 3 samples of rhizo-sediment, which were mixed and quartered.” – is not clear; how many samples were analyzed?

Lines were rewritten: A representative sample of underlying sediment and a representative samples of rhizo-sediment for each sampling site marked in Figure 2 consisted of 3 subsamples of underlying sediments and 3 subsamples of rhizo-sediment.

- Line 141 – 2 mm or < 2 mm?

Corrected.

- Please use micron or mm – lines 137, 141,143.

Corrected into μm.

- Please complete the description of the granulometric analysis - the type and dimensions of the laboratory vessel.

Added in the text: …Particle sizer (laser granulometry) and dynamic image analyser Fritch Analysette 22-28 with measuring range from 40 nm to 2 mm (laser granolumetry) and 20 μm to 20 mm (dynamic image analyser). The sample was ultrasonically dispersed for 2 minutes before analysis.

- Line 142 – “The entire procedure was repeated” - what procedure, mixing the same sub-sample, or preparing another sub-sample?

No, “The entire procedure was repeated three times for each sample to decant almost the entire fraction below the 2 μm.”

- Lines 162-168 and 193 - the paragraph on quality assurance/quality control should include complete information on CRM and standards (for pH and TOC).

Corrected to: Sediment pH was measured in situ using a portable pH meter (EUTECH Instruments) and further premeasured in the laboratory according to ISO standard 10390:2005 (suspension of sediment in water). Total organic carbon (TOC) content was determined using an Elementar Vario Micro CHNS elemental analyser. Prior determination, freeze-dried powdered samples were acidified with 6 M HCl to remove inorganic carbon (Sieper et al., 2006). The precision of the method was 3%. To calibrate the analytical system the Calibration Standard sulfanylamide (with theoretical values N - 16.27%, C - 41.82%, H - 4.68%, O - 18.58%, S - 18.62%) was used.

- Lines 194-195 - was the validation performed for only 2 sub-samples? Please add a table with the results of the CRM analysis in the supplementary materials.

It was performed on one sample, number S6. We explained the validation again and added the table in the supplementary material. The accuracy of the analytical method, estimated by calculation of the relative systematic error between the measured and recommended values of the reference materials STD DS11 and STD OREA262, was in the range of 2-13% with a median value of 7%. The precision of the analytical method, expressed as the relative percentage difference (% RPD) between the sample S6 duplicate measurements was in the range of 0-7% with a median value of 3%.

- Lines 197-203 - explain if PCA and CA have been carried out on standardized data.

Yes, we worked with Statistica program and standardization of data is done every time before PCA and CA.

- Section 3.1. – Instead of Table 1, please add in the supplementary materials the results of the granulometric analysis of all samples and their classification.

According to reviewer 2, we arranged Ternary diagram in the text and other results in the supplementary material.

- Section 3.2. - Please add in the supplementary materials the results of the pH and TOC analyses of all samples.

The results were added into the supplementary materials.

- Fig. 4 - illegible upper symbols of minerals.

Corrected.

- Fig. 5 - identification based on a single peak (illite, smectite – no peak)?

There is a peak for smectite with an intensity of 100% at 17.0A, and as you can see, this peak has a very low intensity (350 counts), which means that the two peaks (8.35 and 5.57) in the EG samples are barely visible! But there is clearly a shift of the peak for smectite from 14.0 to 17.0 and also for mixed layers I/S! We mark the illite peak at 5.0, but now the figure looks too confusing. You can also see the peaks of illite (5) in Figure 4.

- Fig. 6 – what method was used for the division into clusters and sub clusters? What the signs (+ *) next to the sample symbols mean?

We used Fast profile Comparison with Position and Intensity type - with Distance Measure as Euclidian and the Linkage Method as Ward. The *** after some names indicate the most representative scan of a certain cluster. A + sign after a scan name indicates the two most different scans within one cluster. The colours indicate the actual clusters, datasets with names in black are unclustered.

- Lines 294-298 and 497-498 - the authors indicate different levels of organic carbon and pH in individual samples, while previously found no significant differences (line 231)!

Thank you, lines 231-232 “No significant differences were observed in pH values and total carbon content between samples and sampling locations” were rewritten to: “Highest pH values and total carbon contents were observed in samples from the crystallization basin and the Poslužnica area.”

- Section 3.4. Lines 309-310 – why sediment contamination was compared with soil and not the sediments?

Slovenian legislation in regulations on critical, warning, and limit emission values of hazardous substances are defined only for soils and not for sediments. Now, we additionally introduced Sediment quality assessment guidelines (SQGs). We added:

Additionally, the obtained values were also compared to consensus-based sediment quality guidelines (SQGs) (Table 3b). The TEL value is a sediment metal(oid) content at which a toxic response has started to be observed in benthic organisms. The PEL value is the metal(oid) content at which a large percentage of the benthic population shows a toxic response. A comparison of sediment metal(oid) content with the consensus-based TEC and PEC values revealed that only Ni content is higher than both the TEC and PEC special values, while Cr content distinctly exceeds and Cu and As contents slightly exceed the proposed TEC values. 

- Lines 461-462 – Hg should be included, since the authors analyse its content; reference [81] is from 1980, has nothing changed in the study area since then?

Yes, as far as mercury sources are concerned, nothing has changed. Please see the Environmental setting.

All EFs should be given in the supplementary materials.

Table was added in the supplementary material.

- Conclusions: The author needs to clearly specify the novelty of this work in addition to the aims mentioned. Not all the results reported in the manuscript can be confirmed.

The conclusions were rewritten:

This study demonstrates that understanding the origin and incorporation of metal(oid)s within different solid sediment particles (such as detrital particles, anthropogenic particles, clay minerals, organic matter and diagenetic minerals) is critical to identify their distribution, accumulation, retention and further transfer into a vulnerable and ecologically important ecosystem such as salt marshes.

The results suggest that the detrital particles from the geological hinterland, e.g. the type of rock fragments and minerals, the various anthropogenic sources, the particle size relative to the amount of clay minerals, the abundance of organic matter and early diagenetic precipitates, significantly affect the metal(oid) accumulation and current retention in corresponding sediment and rhizo-sediment content of the Sečovlje salina. The metal(oid)s, e.g. As, Bi, Cd, Cr, Cu, Hg, Ni, Pb, Sn, Sr, Pb and Zn display many differences in the origin, distribution and association within the sediment components.

According to the results of XRD, ICP-ES, SEM-EDS and various statistical analyses, the studied elements were mainly associated with Fe/Mn oxides and oxyhydroxides (As, Cr, Ni, Pb, Zn), incorporated into or adsorbed onto the crystal lattices of clay minerals (As, Cr, Pb, Sn, Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr, Zn) and associated with organic matter (Cu, Pb and Zn). Only As, Bi, Hg and Zn were recognised as anthropogenic, although it would be difficult to determine anthropogenic sources for As and Zn, as their abundance is more likely due to processes occurring in the sedimentary basin. Traces of As were found in halite minerals, while Zn is an essential element for all living beings and is therefore also present in larger quantities. BiO industrial compounds are very common cargo found in the nearby ports and Hg presence is the result of almost 500 years of historical mining activity in Idrija.

References - should be carefully corrected in accordance with the instructions for authors; I suggest to update the literature, only 35 references are from the last 10 years.

Checked and updated.

Round 2

Reviewer 1 Report

Thank you for the revised and improved version.

Author Response

Thank you very much for the detailed review of the article.

The manuscript was sent to English proofreading for a second time.

Kind regards,

Nastja Rogan Šmuc 

Reviewer 2 Report

The present variant of the manuscript has o multitude of improvement with respect to initial one, but there are still two main issues which should be solved:

i. the absence of any uncertainty concerning the experimental data provided in Tables 2 to 6

ii. on the clay- sand - silt discriminating ternary diagram all experimental data, i.e.,s1-s6, rs1-rs6 should be represented.  

Please take these recommendations as mandatory.

These will significantly increase the manuscript/paper quality.

Therefore, I recommend: minor to moderate revisions. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have clarified a number of my doubts that have arisen in the previous version of the article. Thank you for taking into account some of my comments. However, it is a pity that some of the relevant responses to my review were only included in the letter and not in the manuscript.

There is only one Table with the pH and TOC values in the supplementary material. I don't see grain-size distribution, EF values and validation.

Author Response

The authors have clarified a number of my doubts that have arisen in the previous version of the article. Thank you for taking into account some of my comments.

However, it is a pity that some of the relevant responses to my review were only included in the letter and not in the manuscript.

We disagree, the majority of the text was added in the manuscript.

Now, we added the following response as well (Introduction part): In terms of bioavailability (a prerequisite for translocation processes), a thorough understanding of metal(oid) associations in sediment solid components is necessary - whether they are bound to mineral constituents (and which mineral constituents) or organic matter. This is the first step to a comprehensive understanding of bioavailability and the transfer of metal(oid) to the system.

There is only one Table with the pH and TOC values in the supplementary material. I don't see grain-size distribution, EF values and validation.

Materials were arranged and ready, but unfortunately, we had problems with uploading – therefore we sent all Supplementary files to Mrs. Rita Xu, an Assistant Editor – I'm so sorry you didn't get the files. All supplementary material has now been converted to a Zip file, I hope, you will get the file.