Potential Sources of Heavy Metals in Sediments of an Urban‒Agricultural Watershed and Relationship with Land Use Using a Statistical Approach

Round 1

Reviewer 1 Report

The article examines the level of heavy metals pollution in the Yeongsan River watershed, located in South Korea, using different criteria (SQGs, PLI, and PERI). An interesting result of the work is the finding of a relationship between levels of metals in river bottom sediments and land use. Overall, the article is written concisely and contextually. However, the Conclusion is very extensive and overloaded with information. It is not necessary to describe the results of research in such detail in the Conclusion.  So it is recommended to reduce it by at least half. Consider this in more detail:

In the first paragraph of the Conclusion, the third sentence (These concentrations were low...) is redundant. It is sufficient to specify the general trend of the spatial distribution of metals (Pb, Zn, Cu, Cd, and Hg concentrations were highest in the mid–upstream of YR; As, Cr, and Ni concentrations were similar at most sites).

The criteria of contamination level and ecological risk (SQGs, PLI, and PERI) are complementary and demonstrate the general trend of metal pollution at several sites in the mid–upstream of the Yeongsan River basin. This should be specified, as well as the fact that these sites are close to urban areas (fifth sentence of second paragraph). No need to re-describe the result of each index! 

Also describe the general tendency of the statistical analysis in a few sentences: Zn, Cu, Cd, Pb, Hg are related to urban areas; Cr and Ni - geological influences; As - agriculture.

The last paragraph ("In conclusion, high concentrations...") is most similar to the Conclusion section. Use it as a basis and expand on it. 

 

Minor revision:

Lines 35, 38.  "Flow" is not a suitable verb to describe the process of pollutant delivery. Flow usually means the movement of water, e.g. More suitable verbs would be "input" or "inflow". Check the English style throughout the text.

Line 39. May mining and mining industry be the same thing?

Line 63. Reference to these minimal studies is needed. Or you've compared metal pollution of river sediments with land use at the first time? 

Lines 92-94. It is necessary to divide the sentence into two short ones.

Line 126. Which device is used to heat the samples?

Lines 352-355. Divide the sentence into two short ones. "The results are shown..." is a new sentence.

Lines 413-417. Is this sentence about arsenic? In that case, remove the phrase "heavy metal" at the beginning of the sentence and start the sentence with the full name of the element, rather than the symbol: "Arsenic, which is known..."

Lines 420-422. Rewrite the sentence as follows: "The mean concentrations of eight heavy metals in bottom sediments collected from the mainstream and tributaries of the Yeongsan River basin located in South Korea decreased in the order of Zn > Cr > Cu ≈ Pb > Ni > As > Cd > Hg.

 

Author Response

Comment 1: 
The article examines the level of heavy metals pollution in the Yeongsan River watershed, located in South Korea, using different criteria (SQGs, PLI, and PERI). An interesting result of the work is the finding of a relationship between levels of metals in river bottom sediments and land use. Overall, the article is written concisely and contextually. However, the Conclusion is very extensive and overloaded with information. It is not necessary to describe the results of research in such detail in the Conclusion.  So it is recommended to reduce it by at least half. Consider this in more detail:
In the first paragraph of the Conclusion, the third sentence (These concentrations were low...) is redundant. It is sufficient to specify the general trend of the spatial distribution of metals (Pb, Zn, Cu, Cd, and Hg concentrations were highest in the mid–upstream of YR; As, Cr, and Ni concentrations were similar at most sites). The criteria of contamination level and ecological risk (SQGs, PLI, and PERI) are complementary and demonstrate the general trend of metal pollution at several sites in the mid–upstream of the Yeongsan River basin. This should be specified, as well as the fact that these sites are close to urban areas (fifth sentence of second paragraph). No need to re-describe the result of each index! Also describe the general tendency of the statistical analysis in a few sentences: Zn, Cu, Cd, Pb, Hg are related to urban areas; Cr and Ni - geological influences; As - agriculture. The last paragraph ("In conclusion, high concentrations...") is most similar to the Conclusion section. Use it as a basis and expand on it.
<Response> 
We appreciate your suggestions and comments.
We have incorporated most of your suggestions into the ‘Conclusions’ section. Based on your suggestions and comments, we have tried to minimize the content in the 'Conclusions' section as much as possible. Then, we have revised the meaning of the content of the ‘Conclusion’ so that it does not change (Lines 418-450).

Comment 2: Lines 35, 38
"Flow" is not a suitable verb to describe the process of pollutant delivery. Flow usually means the movement of water, e.g. More suitable verbs would be "input" or "inflow". Check the English style throughout the text.
<Response> 
Thank for your suggestion.
Thus, we believe that there is no problem with the ‘revised manuscript’ because we have carefully re-edited the English proofreading. Therefore, we have decided to keep it in the ‘revised manuscript’.

Comment 3: Line 39
May mining and mining industry be the same thing?
<Response> 
We decided to delete "mining" to avoid confusion. In the revised manuscript (Lines 42-44):

However, heavy metals generated by anthropogenic activities flow into rivers through various routes, including fossil fuel combustion, industrial wastewater, traffic, mining industry, manufacturing, and use of fertilizers and pesticides [4,5].

Comment 4: Line 63
Reference to these minimal studies is needed. Or you've compared metal pollution of river sediments with land use at the first time?
<Response> 
Thank you for your advice.
As your advice, our study was the first attempted on the relationship between heavy metals in sediments and land use in the Yeongsan River basin. Thus, we have corrected the revised manuscript as follows (Lines 66-67):

however, the effect of land use on sediment pollution has not yet been studies.

Comment 5: Lines 92-94
It is necessary to divide the sentence into two short ones.
<Response> 
We have divided the sentence you pointed out into two paragraphs as follows (Lines 95-98):

The land uses of the Yeongsan River basin were classified into seven types (bare land, agricultural, forest, water, wetland, urban, and grassland). Subsequently, the land uses for each site were calculated by considering the catchment area using the ArcGIS program (ver. 10.2.2).

Comment 6: Line 126
Which device is used to heat the samples?
<Response> 
We have added the device used for sample decomposition as follows (Lines 128-130):

subsequently, the samples were heated at 130 ℃ using a graphite heating block (ECOPPE- III, ODLAB, Korea) until they were completely decomposed.

Comment 7: Lines 352-355
Divide the sentence into two short ones. "The results are shown..." is a new sentence.
<Response> 
As you pointed, we have divided it into two paragraphs as follows (Lines 351-354):

CA and PCA were performed to verify the correlation between heavy metals and land use among the sediments of the mainstream and tributaries in the Yeongsan River basin. Figure 5 shows the CA and PCA results as a clustered heatmap and biplot, respectively.

Comment 8: Lines 413-417
Is this sentence about arsenic? In that case, remove the phrase "heavy metal" at the beginning of the sentence and start the sentence with the full name of the element, rather than the symbol: "Arsenic, which is known..."
<Response> 
Thank you for your opinion.
Thus, we have revised it by reflecting your opinion as follows (Lines 412-415):

Arsenic, known to be introduced into aquatic environments by the use of pesticides (insecticides and herbicides) in agriculture [60,61], was found to be related to the mid–downstream (YS14 and YS18–19) and the most downstream (YS20 and YS22–25) of the Yeongsan River basin with high agricultural land use.

Comment 9: Lines 420-422
Rewrite the sentence as follows: "The mean concentrations of eight heavy metals in bottom sediments collected from the mainstream and tributaries of the Yeongsan River basin located in South Korea decreased in the order of Zn > Cr > Cu ≈ Pb > Ni > As > Cd > Hg.
<Response> 
Thanks for your suggestion.
However, we have divided the sentence you pointed out into two paragraphs to make it easier to understand. Thus, we rewritten the revised manuscript as follows:

We analyzed the mean concentrations of the eight heavy metals in the sediments collected from the Yeongsan River basin in South Korea. The concentrations decreased in the order of Zn > Cr > Cu ≈ Pb > Ni > As > Cd > Hg.

 

Author Response File: Author Response.docx

Reviewer 2 Report

The division of sections needs to be explained again. Why?  Does the relationship between land use and urban land use correspond?  It just looks like a difference in space. 

What is the basis for the selection of pollution assessment methods? Need to give some reasons.

The conclusions are too long and not generalizable enough.

Author Response

Comment 1: 
The division of sections needs to be explained again. Why?  Does the relationship between land use and urban land use correspond?  It just looks like a difference in space.
<Response> 
Thanks for your opinion.
In fact, we evaluated the distribution of heavy metal concentrations in the sediments for all sites in the Yeongsan River basin, regardless of section division. However, as explained in ‘Distribution of heavy metal concentrations’ of ‘Results and Discussion’, some heavy metal concentrations could not be well reflected the spatial distribution characteristics considering land use. Thus, we needed an evaluation of the distribution of heavy metal concentrations according to the sections that reflected the spatial characteristics of land use. Then, the spatial distribution of heavy metal concentrations could be assessed more clearly understandable (presented in ‘Results and Discussion’, Lines 250-251). Although land use and urban land may appear to be spatially different, it was confirmed that they are consistent through calculations considering the catchment area of each site using ArcGIS.

Comment 2: 
What is the basis for the selection of pollution assessment methods? Need to give some reasons.
<Response> 
We appreciate your advice.
The sediment pollution assessment method is generally most widely used in comparison with Sediment Quality Guidelines (SQGs). In addition, Contamination Factor (CF), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI) methods are widely used to evaluate anthropogenic pollutions of heavy metals in sediments. Approaches such as SQGs, CF, PLI and PERI have been cited in the literature as methods for assessing sediment pollution. SQGs are one of the framework factors for assessing sediment quality and are often used as the first step in assessing the potential risk of sediment pollutant. In general, SQGs are well-known as recommended criteria for sediment management policies in each country. Therefore, SQGs have different recommendation criteria in each country, and were developed as national sediment monitoring began in Korea. Thus, we used SQGs from Korea as the first framework to evaluate the quality of all sediments in this study. For the second framework, anthropogenic heavy metal pollution was evaluated using the widely used PLI and PERI in sediments. We believe that the approaches used in this study would have been appropriate to assess sediment pollution.

Comment 3:
The conclusions are too long and not generalizable enough.
<Response> 
As your advice, we tried to keep the content as short as possible in the ‘Conclusion’ section. Thus, we have deleted some of the contents that overlaps with the ‘Results and Discussion’ section, but we have decided to keep the main contents to highlight in this manuscript. Then, we rearranged the ‘revised manuscript’ (Lines 418-450).

Author Response File: Author Response.docx

Reviewer 3 Report

Hae Jong Yang and colleagues evaluated heavy metal pollution levels in the Yeongsan River basin sediments. They assessed pollution levels using pollution load indexes (PLI) and potential ecological risk indexes (PERI). Heavy metal pollution was found to be caused by intensive anthropogenic activities along the river stretch. I believe this manuscript should be published in Sustainability, but with some revisions.

Below are a few comments I would like to make:

Abstract

Line no 19: change the word "Fair stages"

Introduction

Lines 34 and 35: Rephrase the sentences

Line no 44: It would be better if the authors specified aquatic sediments rather than river sediments

The introduction should be improved. This section can be improved by adding the following relevant studies:

DOI: 10.1016/j.scitotenv.2011.09.025

doi.org/10.1080/15320383.2020.1835822

doi.org/10.1016/j.jhydrol.2005.01.021

Why didn't the authors discuss sediment physical and chemical variables?

Metal concentrations should be noted on a dry weight basis or appropriate in the results and discussion.

 

Author Response

Comment 1: Line 19
Change the word "Fair stages"
<Response> 
Thank you for your advice.
The “Fair stages” that you pointed out refer to the sediment pollution status by SQGs comparison, and the additional meaning is included in the ‘Abstract’. Nevertheless, we have revised it as follows to avoid confusion (Lines 19-20).

The polluted sites, which showed the potential toxicity toward benthic organisms in comparison to SQGs, were most frequently observed at mid–upstream.

Comment 2: Lines 34 and 35
Rephrase the sentences
<Response> 
Thanks for your comment. 
Thus, we have rewritten some sentence, and the comments you pointed out here will be explained in Comment 4.

Comment 3: Line 44
It would be better if the authors specified aquatic sediments rather than river sediments
<Response> 
We have changed from ‘river sediments’ to ‘aquatic sediments’ in the ‘revised manuscript’. Then, we have simplified this sentence for better readability as follows (Lines 48-50):

Aquatic sediments are very important for assessing anthropogenic pollution because they act as the carrier of pollutants and also as potential secondary pollution sources [9].

Comment 4:
The introduction should be improved. This section can be improved by adding the following relevant studies:
doi.org/10.1016/j.scitotenv.2011.09.025
doi.org/10.1080/15320383.2020.1835822
doi.org/10.1016/j.jhydrol.2005.01.021
<Response> 
We appreciate your advice to improve the quality of the manuscript.
In particular, we are very impressed that you have provided references related to our research. Therefore, we have rewritten or added some sentences by citing the references you have provided to improve the introduction. Then we have added a citation in the reference list (Lines 478-484), and also have corrected all citation numbers in the ‘revised manuscript’. Here, we have rewritten to include Comment 2 as follows (Lines 33-40):

Heavy metals are major pollutants of the aquatic environment [1,2]. They flow into rivers through various routes and accumulate in sediments. Sediments play an important role in the management of aquatic ecosystems as they reflect the pollution history of rivers and act as sinks in the aquatic environment [2]. Pollution caused by recent industrial development and population increases pose serious irreversible damage to all environments and are continuously affecting the global environment. Pollutants such as heavy metals have adverse effects on aquatic ecosystems, owing to their long persistence in the environment [3].

Comment 5:
Why didn't the authors discuss sediment physical and chemical variables?
<Response>

As your advice, physical and chemical variables such as particle size, organic matter, and nutrients in sediments are very closely related to the behavior of heavy metals. However, we focused on assessing the impact of land-use environmental conditions around the watershed rather than the behavioral mechanisms related to the adsorption and elution of heavy metals in the aquatic environment. Thus, we could not consider the physical and chemical variables of the sediment in this study. Nevertheless, we believe that the results of this study on the relationship between heavy metal concentration in sediments and land-use would not have been affected.

Comment 6:
Metal concentrations should be noted on a dry weight basis or appropriate in the results and discussion.
<Response> 
We agree with your opinion.
The concentrations of all heavy metals should be expressed on a dry weight basis, and it is also appropriate to reflect this in the ‘Results and Discussion’. However, we presented in ‘sampling and pretreatment of sediments’ of ‘Materials and Methods’ that sediment samples were analyzed for heavy metal concentrations after drying. Moreover, many citations related to sediments generally omit dry weight basis, and as in this study, only ‘Materials and Methods’ suggest pretreatment methods for heavy metal analysis. Therefore, we believe that the heavy metal concentrations presented in this study should not be a problem.

Author Response File: Author Response.docx