Analysis of Environmental Purification Effect of Riparian Forest with Poplar Trees for Ecological Watershed Management: A Case Study in the Floodplain of the Dam Reservoir in Korea

Round 1

Reviewer 1 Report

Introduction

Line 44-Typhoons, droughts and floods are not “abnormal” events. The frequency and/or intensity of these events has increased in recent decades due to climate change.

Line 47-What do you mean by accumulate on the surface? In surficial sediments? P adsorbed to soil particles and can accumulate in riparian areas.

Line 50-Talking about the “land” in general is very broad in scope. Different soils and different crops will have differ level of nutrient deficiency or need. I think it would be better to make a statement more along the lines that there is a wide body of literature demonstrating the use of fertilizers for significant areas of agricultural land (you could use the current N review paper, #2, and cite a few others).

Lines 57-58-Briefly explain integrated nutrient management and what is meant by “appropriate fertilization management”.

Line 59-Use full name for Organization for Economic Co-operation and Development at first use.

Line 60-What do you mean by N “balance”? Do you mean the load exported from the watershed? Is this an average of annual loads?

Line 70-Riparian buffers are capable of removing pollutants from runoff, but they are then also areas where these pollutants can accumulate in sediments and for P in particular, when water levels and thus chemical conditions change, these pollutants can be desorbed and re-enter streamflow. I think you need to clarify if you are referring to pollutant filtration or phytoremediation as discussed in Lines 74-78.

Lines 82-88-You have done a good job explaining why poplar is a good species for a forested buffer, but you haven’t given an indication of how widespread poplar species are in temperate climates. You also need to compare its effectiveness to other quickly growing, tolerant, robust, riparian buffer species such as willow (genus Salix) for example.

Line 103-I would recommend rewording part of this sentence from “and tackle following three questions” to “to address the following three questions”.

Lines 110-112. I would remove “likely” from the sentence. These results would also add important validation data for SWAT-REMM.

Materials and Methods

Study Scope and Area

You need to provide a better description of the physical/environmental conditions at the study sites. What is the climate (mean annual temperature, maximum and minimum temperature, annual rainfall, how is rainfall weighted seasonally, soil classification, soil depth).

Line 119-Typo in purification.

Line 120-The trees were planted 5 years prior to the start of the 2013 study period? What do you mean by “sufficiently grown”? Did you use a minimum diameter-at-breast-height value or some other measure? Did you use field observations or remotely sensed data?

Planting Poplar for Test

Why were these particular species of poplar selected for the case study? Why use poplars in a floodplain setting that required drainage to facilitate root growth? Why not use other flood tolerant vegetated riparian buffer species?

Line 131-Replace “digged” with “dug”.

Research Method

Research Framework

Line 148-What is the land cultivated for? What is the size area under cultivation? What constitutes uncultivated land, what is the land cover?

Analysis of T-N and T-P content of the soil

When were these samples collected? Were they collected in one year only, in successive years?

Lines 170- What type of container was the homogenized soil stored in? What surface was used to air dry the samples? What was the concentration of the sulphuric acid solution? What was the concentration of the perchloric acid? What device was used for the colorimetry?

Analysis of T-N and T-P content of the plants in the riparian forests

When were these samples collected?

Lines 184-185-How many trees were selected?

Line 186-How was the xylem isolated?

Line 187-What exact quantity is “part by part”?

Comparison of environmental purification effect according to environmental conditions and tree growth rate

Lines 193-194-What do you mean by “environmental conditions”, what was actually recorded and how? Are you referring to the discussion Lines 206-236—which is really study site description and should be placed in that section rather than in the results.

T-test analysis

Without having a better understanding of the initial chemistry of the soil pre-planting, how can the lowest T-P or T-N contents be attributed to purification by poplars rather than perhaps low initial concentrations of T-P or T-N?

Why use sequential t-test analyses and compound errors rather than use an ANOVA?

T-N and T-P content in poplar biomass

Lines 318-336-This discussion should be in the Methods section.

Discussion

How do your study results compare to other studies?

If T-N and T-P was measured during one sampling season/year, what kind of changes can you expect with T-N and T-P seasonally or in different years?

Author Response

Thank you very much for your kind and accurate evaluations, and our responses to your comments can be found below. We reflected your opinion and marked the revised sentence in red.

1. Introduction

Line 44-Typhoons, droughts and floods are not “abnormal” events. The frequency and/or intensity of these events has increased in recent decades due to climate change.

→ Global climate change has increased the frequency or intensity of typhoons, floods, and droughts in recent decades.

2. Line 47- What do you mean by accumulate on the surface? In surficial sediments?

P adsorbed to soil particles and can accumulate in riparian areas.

As runoff makes its way to rivers, lakes, and estuaries after rainfall, high concentrations of nutrients such as nitrogen and phosphorous that have accumulated on the surface or in the groundwater worsen water quality and weaken the health of watershed ecosystems.

→ As runoff makes its way to rivers, lakes, and estuaries after rainfall, high concentrations of nutrients such as nitrogen and phosphorous that have accumulated in surficial sediments or in the groundwater worsen water quality and weaken the health of watershed ecosystems.

3. Line 50- Talking about the “land” in general is very broad in scope. Different soils and different crops will have differ level of nutrient deficiency or need. I think it would be better to make a statement more along the lines that there is a wide body of literature demonstrating the use of fertilizers for significant areas of agricultural land (you could use the current N review paper, #2, and cite a few others).

→ Food and energy production from agriculture, combined with industrial and energy sources, have more than doubled the amount of reactive nitrogen circulating annually on land [00].

* The number of references is to be revised in a lump sum.

4. Lines 57-58- Briefly explain integrated nutrient management and what is meant by “appropriate fertilization management”.

→ Integrated nutrient management (INM), which precisely manages the input and output of nutrients to balance crops while minimizing environmental loads, was introduced in the 1980s, and since then, chemical fertilizer use has improved through appropriate fertilization management in cultivated land

5. Line 59- Use full name for Organization for Economic Co-operation and Development at first use.

→ Organization for Economic Co-operation and Development(OECD)

6. Line 60- What do you mean by N “balance”? Do you mean the load exported from the watershed? Is this an average of annual loads?

→ Nitrogen balance is a common term in agricultural systems, which means the difference and balance of nitrogen and emissions.

7. Line 70- Riparian buffers are capable of removing pollutants from runoff, but they are then also areas where these pollutants can accumulate in sediments and for P in particular, when water levels and thus chemical conditions change, these pollutants can be desorbed and re-enter stream flow. I think you need to clarify if you are referring to pollutant filtration or phyto remediation as discussed in Lines 74-78.

→ I agree with you. Nitrogen This is a statement that introduces the general function of the Riparian foists.

Therefore, we do not think that cleanup actions based on exceptional parts of the pollutant or various conditions are necessarily necessary in the context of the whole context. The following sentence describes the purification mechanism of the Riparian Forests.

8. Lines 82-88- You have done a good job explaining why poplar is a good species for a forested buffer, but you haven’t given an indication of how widespread poplar species are in temperate climates. You also need to compare its effectiveness to other quickly growing, tolerant, robust, riparian buffer species such as willow (genus Salix) for example.

→ We added references to poplars.

Poplar is a common name called all species belonging to “Genus Populus”. Poplars can be found anywhere in the world except for the tropics, and have shorter generations and easier asexual growth than other species. Therefore, Poplar is widely used as a model breed of traditional breeding or biotechnology in the forest field [00]

[00] FAO (1980) Poplars and willows in wood production and land use. FAO Forestry Series No. 10, p. 328.

[00] Dickmann EI (2001) An overview of the genus Populus. In Dickmann EI, Isebrands JG, Eckenwalder JE, Richardson R (eds) Poplar Culture in North America. NCR Research Press, Ottawa, p. 397.

* The number of references is to be revised in a lump sum.

9. Line 103- I would recommend rewording part of this sentence from “and tackle following three questions” to “to address the following three questions”.

→ Therefore, to verify the environmental purification effect of riparian forests with poplar trees in cultivated land in waterside regions, this study chose a waterside area of the Yongdam dam reservoir in Jinan-gun, Jeollabuk-do as a case study site, to address the following three questions:

10. Lines 110-112. I would remove “likely” from the sentence. These results would also add important validation data for SWAT-REMM.

→ We accept your opinion.

11. You need to provide a better description of the physical/environmental conditions at the study sites. What is the climate (mean annual temperature, maximum and minimum temperature, annual rainfall, how is rainfall weighted seasonally, soil classification, soil depth).

→ The study area is located in the mountainous region of the southern inland area of the Korean Peninsula, with large temperature range and heavy snowfall and rainfall. The annual temperature is -17.7~32.5˚C, the average annual temperature is 11.2˚C, and the average annual precipitation is 1,298mm during the last 5 years.

12. Line 119-Typo in purification.

→ Corrected a typo

13. Line 120- The trees were planted 5 years prior to the start of the 2013 study period? What do you mean by “sufficiently grown”? Did you use a minimum diameter-at-breast-height value or some other measure? Did you use field observations or remotely sensed data?

→ The reason we chose the poplar we planted five years ago, this is because poplars are short-lived, and if they are more than three to five years old, they can be harvested and used for wood production and biomass.

In Korea, the "Enforcement Decree of the Forest Resources Development and Management Act" stipulates that poplars earn three years. In this regard, poplars that have been over five years have been selected as materials for this study.

14. Why were these particular species of poplar selected for the case study? Why use poplars in a floodplain setting that required drainage to facilitate root growth?

Why not use other flood tolerant vegetated riparian buffer species?

→ The poplar type showed strong cross-species phenomenon, and various attempts have been made to develop excellent breeds by hybridization around the world.

The varieties applied to this study have been proven to have excellent growth and ability to absorb pollutants in various places.

15. Line 131-Replace “digged” with “dug”

→ We corrected the wrong words.

16. Line 148- What is the land cultivated for? What is the size area under cultivation? What constitutes uncultivated land, what is the land cover?

→ The contents of this question are well described in the study results.

17. When were these samples collected? Were they collected in one year only, in successive years?

→ The collection time and duration of soil samples are from October 2019 to May 2020.

The choice of this period is to include the spring season, when fertilizer is sprayed for growing crops, and the autumn season, which is the harvest season.

18. Lines 170- What type of container was the homogenized soil stored in? What surface was used to air dry the samples? What was the concentration of the sulphuric acid solution? What was the concentration of the perchloric acid? What device was used for the colorimetry?

→ The homogenized soil collected at the site was stored in a polyethylene vinyl bag and transferred to the laboratory. Spread polyethylene vinyl, thinly spread the soil over it, and dry it in the air. The concentration of sulfuric acid solution was 8M H2SO4. The concentration of perchloric acid (HClO4) was 60% and UV/VIS Spectrophotometer was used for the colorimetry.

19. When were these samples collected?

→ Tree samples were collected in October, before the leaves fell. The reason is that trees lose nutrients, including nitrogen, when fallen leaves fall, so they were collected before falling leaves to determine the proportion of nutrients in the stems, branches, and leaves of the trees. However, in general, trees have a mechanism to transfer large amounts of nutrients from leaves to branches before falling leaves. Therefore, it is necessary to consider these mechanisms in the measurement results, and in the future, further research is needed on the purification efficiency in consideration of the mechanism of nutrient migration within trees due to seasonal changes.

20. Lines 184-185- How many trees were selected?

→ The contents of this question are well described in the study results.

21. Line 186- How was the xylem isolated?

→ The samples collected for each stem, branch, and leaf parts were dried and crushed to pass through a 40 mesh sieve, and then T-N and T-P were analyzed.

22. Line 187-What exact quantity is “part by part”?

→ The contents of this question are well described in the study results.

23. Lines 193-194- What do you mean by “environmental conditions”, what was actually recorded and how? Are you referring to the discussion Lines 206-236—which is really study site description and should be placed in that section rather than in the results.

→ In this study, the purification effects of poplar trees were compared according to environmental conditions

(pre-plant cultivation form and soil, topographical conditions, land use, etc.).

In the discussion and results, we mentioned the growth and purification effects of poplar according to the environment of the three target areas.

24. Without having a better understanding of the initial chemistry of the soil pre-planting, how can the lowest T-P or T-N contents be attributed to purification by poplars rather than perhaps low initial concentrations of T-P or T-N?

→ Although there is no data on soil T-N and T-P in the study site five years ago, considering the cultivation patterns of villages over the years and the use of nearby land, it is fully believed to be similar to the condition before planting the poplar.

Therefore, the study was conducted through soil analysis results for adjacent arable land and closed land.

Rather than calculating the absolute amount of reduction through poplar vegetation, this study was intended to predict relative expected effects through comparison with arable land and closed land in similar environments and to present plans for creating precise and efficient waterside areas in the future.

25. Why use sequential t-test analyses and compound errors rather than use an ANOVA?

→ The reason for applying t-test is that it was more important to compare the area where poplar was planted w ith the area where the poplar was planted than to analyze by the number of sites.

First of all, t-test was applied because comparison before and after planting was needed to identify the function of poplar forest.

26. How do your study results comare to other studies?

→ Studies for reducing non-point pollution sources vary. However, there are few studies using poplar forests on arable land. The difference between the subjects and criteria of the study for reducing non-polluting sources is large, and I think simple comparison is very difficult.

However, the obvious fact is that it is more cost effective than wetlands or device-type facilities to reduce non-point pollutants.

Also, I think that reducing non-point pollutants through forest has the advantage of creating eco-friendly and diverse convergence values.

27. If T-N and T-P was measured during one sampling season/year, what kind of changes can you expect with T-N and T-P seasonally or in different years?

→ In this study, the site survey period was in the fall of the crop harvest season from the spring when fertilizer began. Soil samples were then collected from the standard distribution area and tested on poplars during the growth period.

It may vary depending on when the roots of the poplar are active and when they are dormant.

It may vary depending on when it rains heavily and when it is dry, and may vary depending on the type of crop. In addition, T-N and T-P will be affected as the area without cultivation increases.

We respect your opinion and thank you again more politely

Author Response File: Author Response.docx

Reviewer 2 Report

Page three lines 107-108. Question three seems almost similar to question two in the context. I would recommend rephrasing the question to avoid mixing it with question two.

Page three, line 119. The word “purificatgion” makes no sense and the correct word should be “purification”.

Page four, line 126. Fix figure 1.

Page four, line 126. Is it possible to add sub-watersheds to figure 2 to give an idea of how much water flows at each study site?

Page four, line 138. Fix figure 2.

Page five, line 159. Could you please explain why the field investigation was carried out during the fall of 2019, through winter of 2020, to early spring of 2020? It is expected that concentration of nutrients to peak during summer that could lead to drastic changes in the findings.

Page five, line 170. On what basis the soil sample was taken at 30cm depth?

Page six, line 205. SWAT model can simulate flow for watershed management. The simulated flow could better support the findings of the research, as flow varies from one site to another. There could be high flow variations form site 1 to site 2 to site 3 and that can impact the nutrients carried at each site. Please explain why such a simulation was not carried out and added to the findings of the research.    

Page six, line 208. Could you please explain what do you mean by “the total water storage capacity is 0.82 km²”? Water storage capacity is measured in unit-cube and not unit-square.

Page 7 line 221. Test site-2 is almost similar to Test site-1 regarding its topographical characteristics and in addition to its land-use/landcover. What are the reasons behind selecting such a site that is almost similar to another site of the study area?

Page 8, line 243. Please use the box-plot to compare the results.

Page 15, line 465. Future recommendations should be given instead of hope. What surrounding characteristics should be included in future studies to support the findings of this research; hydrology, sub-watershed vegetation, or channel morphology?

Comments for author File: Comments.pdf

Author Response

Thank you very much for your kind and accurate evaluations, and our responses to your comments can be found below. We reflected your opinion and marked the revised sentence in red.

1. Page three lines 107-108. Question three seems almost similar to question two in the context. I would recommend rephrasing the question to avoid mixing it with question two.

→ We agree with you. We would like to change the third question as follows.

Third, are there differences in the growth rate of riparian forests and in the removal of nitrogen and phosphorous from soils depending on the environmental conditions?

2. Page three, line 119. The word “purificatgion” makes no sense and the correct word should be “purification”.

→ Corrected a typo

3. Page four, line 126. Fix figure 1.

→ We modified Figure 2 to make the body of water stand out well.

And Figure 4, drawn up through drone shooting, provides information on the direction of water flow and the waters.

4. Page four, line 126. Is it possible to add sub-watersheds to figure 2 to give an idea of how much water flows at each study site? Page four, line 138. Fix figure 2.

→ In this study, the flow rate through each target site was not measured. Because the main focus of the study was on soil and poplar plants. However, after this study, we plan to conduct research on flow measurement and effect verification based on hydrology.

5. Page five, line 159. Could you please explain why the field investigation was carried out during the fall of 2019, through winter of 2020, to early spring of 2020? It is expected that concentration of nutrients to peak during summer that could lead to drastic changes in the findings.

→ The collection time and duration of soil samples are from October 2019 to May 2020.

The choice of this period is to include the spring season, when fertilizer is sprayed for growing crops, and the autumn season, which is the harvest season.

6. Page five, line 170. On what basis the soil sample was taken at 30cm depth?

→ The soil depth for investigating the physicality and chemical properties of common soil is based on 30 cm. Samples at one point of the test site are based on a mixture of three adjacent samples.

7. Page six, line 205. SWAT model can simulate flow for watershed management. The simulated flow could better support the findings of the research, as flow varies from one site to another. There could be high flow variations form site 1 to site 2 to site 3 and that can impact the nutrients carried at each site. Please explain why such a simulation was not carried out and added to the findings of the research.

→ I agree with you. The SWAT model is diverse and widely utilized, and the effect of water quality on the whole reservoir can be analyzed. However, in this study, we wanted to verify the effects of soil and arboreal biomass in the poplar forest through experiments.

We are going to do SWAT analysis on the further enlarged forest in the next study.

8. Page six, line 208. Could you please explain what do you mean by “the total water storage capacity is 0.82 km2”? Water storage capacity is measured in unit-cube and not unit-square.

→ The dam storage capacity unit was modified to 0.82 m3.

9. Page 7 line 221. Test site-2 is almost similar to Test site-1 regarding its topographical characteristics and in addition to its land-use/landcover. What are the reasons behind selecting such a site that is almost similar to another site of the study area?

→ We agree with you. Target sites 1 and 2 have geographical similarities. Both were optimal conditions for poplar plantation. However, there are differences in detailed environmental conditions and the results of the study show.

10. Page 15, line 465. Future recommendations should be given instead of hope.

→ We recommend that this study will lead to further research on different models of riparian forests for ecological watershed management in the future.

11. What surrounding characteristics should be included in future studies to support the findings of this research; hydrology, sub-watershed vegetation, or channel morphology?

→ We conducted a study of nitrogen and phosphorus in soil and poplar organisms.

In order to support the results of this study, hydraulic and hydrological verification is required, and further studies on pollutant purification mechanisms in plants and waterside forest functions in various floodplain environments will be conducted in the future.

We respect your opinion and thank you again more politely

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I appreciate that you responded to each of my comments. However, I have concerns that you have too limited a dataset both temporally and spatially to support a conclusion of effectiveness of the buffer in decreasing T-P and T-N.

Specific comments according to the question numbers:

#2. “sediments” is needed after surficial.

#6. I am aware of the term balance as it relates to nutrient cycles and in the agricultural research sector in particular. Balance, however, refers to inputs-outputs. The kg/ha is the mass per spatial area which would indicate land-based sources. The time from for this value needs to be included e.g. the export on annual/yearly basis.

#11. The timing and amount of rainfall is very important to note here. Especially, considering how rainfall affects soil moisture, redox conditions, microbial breakdown of organic matter. You need to indicate when most of this rainfall occurs. This is also important to know in relation to if you sampled during a wet/dry season (#17) and if the 2019-2020 year that you collected your samples was a wet or dry year in comparison to the 5 year average.

#13. Your explanation should be included in the manuscript.

#16. I understand that you placed some of this information in the results, but you need to clearly state this type of information in the study area description.

#18. This additional information needs to be in the manuscript.

#20, #22. Even though this information is in the results sections, it must be first in the methods.

#23. Environmental conditions must be explicitly stated, i.e. just state that you compared purification to these specific environmental factors: pre-plant cultivation form and soil, topography, land use type.

#24. It is unclear if you have pre-planting soil chemistry data for the surrounding land.

#26. If there are few studies. State the results of the few studies and make it clear that your study is providing results to add to the literature.

#27. Sampling only once in each season and not knowing if these were “typical” seasons makes it difficult to support the significance of your findings.

Author Response

Please see attachment.

Author Response File: Author Response.pdf