Dissolved Organic Matter (DOM) in a Warm-Temperate Forested Watershed—A Possibility of Ultraviolet Absorbance as an Indicator of DOM
Round 1
Reviewer 1 Report
Water soluble (dissolved) organic matter mater is a mixture of many compounds and it or dissolved organic carbon are measured with many methods for different purposes.
This paper presents that in different forest waters the dissolved organic carbon (DIC) and UV-absorbance at 254 nm correlate well with each other’s and thus, UV245 could be one method to estimate dissolved organic carbon in water. The idea is not very new; see Vogt, R.D., Akkanen, J., Andersen, D.O., Brüggerman, R., Chatterjee, B., Gjessing, E., Kukkonen, J. V. K., Larsen, H. E., Luster, J.,Paul, A., Pflugmacher, S., Starr, M., Steinberg, C. E. W., Schmitt-Koppling, P., Zsolnay, Á., 2004: Key site variables governing the functional characteristics of Dissolved Natural Organic Matter (DNOM) in Nordic forested catchments, Aquatic Sciences 66: 195–210.
The experiment is done in points of a deciduous forest near Kyoto during some three years analyzing rainwater, water flowing on tree trunks, and surface water and soil leaching water in different layers.
Nitrogen fallout is not high. You mention that one tree is Alnus. Does it have symbiotic nitrogen fixation with Frankia? What about the other biological nitrogen fixation?
The reading of this paper is not easy since there are many abbreviations that are not explained in the abbreviation list. You often present both the important and less important data together instead of helping the reader to find the most important data.
Explain O-layer (line 110). How many months or years old can be the leaf matter in the O layer? How thick is this layer?
In line 124 you mention the Oe layer. What is it?
What is Meiji period (line 96)?
In line 95 you promise to have Table A1 and Table A2, but there are only Tables 1 and 2. Don’t mislead!
The reader must return to the text to see what are Sta, STb, STc, STw, SPa, and SPb (and all the others) which are shown in Fig 1. In addition, there are lines that look like contours, but there should be more values showings the heights and the readers could estimate the direction of water flow. Improve the captions of this figure so that the reader can understand everything! Present here all abbreviations and then later in Figs 4 and 5 write: See the abbreviation in Fig. 1!
Be more specific! You use “sample type” in many places as in title 3.2. The sample types in this paper are water samples. Do you simply mean water samples or water sampled from different sites? For instance, in Fig 6 you have only water samples but the results of these waters are from different water sites.
In Fig 4 how many samplings did you have together during different samplings?
In Table 1: what is amount? of which compound? Improve the caption!
Think about the order in Table 1! Don’t hide the most important results! Start therefore from UV254 and SUVA254!
Do you have correlation coefficients between water flow and different water parameters sampled in different sampling sites? What is YMS (1)? In Table 2 you have YMS (2). I had to think about this for a long time but I guess there was only one YMS, and tables 1 and 2 present different correlation coefficients for different parameters sampled from the same sites in the same YMS. For the reader, it would be easier to have only one table having the same caption and in part A some physical and chemical parameters and B some ions. One solution is that the less important data in Table 2 would be given in the supplementary table.
Text in lines 238-262 is the same which is presented in Table 1. Please, trust that the reader can see the table! It is not necessary to tell the same again in the text. Reduce this highly!
Fig 6. omit this figure but present the equations and R2-values as a table!
Fig 7. Please, do you censor any data!
Omit the Fig 8. Now the font is so small that the reader cannot see anything. If somebody would take a print, this figure would not be useful. Omit it! It seems that the season did not have any clear effect. It might be that the time was too short and the variation between summer and winter is not so clear as it is in many other areas and the rains are always coming as water (newer as snow). If you have no important information about the season, please omit totally the text in lines 263-279! Or say that the effect of the season remained unclear in this study.
In line 303 you mention fir. Please, concentrate only on deciduous trees and omit those conifers!
In some cases, your references are not the original ones. For instance, phenolic compounds have been measured at 280 nm already in the 1960s which is much earlier than your references in line 55.
Correct the reference system from alphabet one to the order so that the first one is at the beginning of the introduction and the last one in conclusions or the end of discussion. See the guidance of this journal given to authors.
Author Response
Response to Reviewer 1 Comments
We wish to express our strong appreciation for the reviewer’s insightful comments on our paper. The comments were a great help in improving our manuscript. We wrote the answer to the comments, so please check it.
Comments and Suggestions for Authors
Water soluble (dissolved) organic matter mater is a mixture of many compounds and it or dissolved organic carbon are measured with many methods for different purposes.
Point 1: This paper presents that in different forest waters the dissolved organic carbon (DIC) and UV-absorbance at 254 nm correlate well with each other’s and thus, UV245 could be one method to estimate dissolved organic carbon in water. The idea is not very new; see Vogt, R.D., Akkanen, J., Andersen, D.O., Brüggerman, R., Chatterjee, B., Gjessing, E., Kukkonen, J. V. K., Larsen, H. E., Luster, J.,Paul, A., Pflugmacher, S., Starr, M., Steinberg, C. E. W., Schmitt-Koppling, P., Zsolnay, Á., 2004: Key site variables governing the functional characteristics of Dissolved Natural Organic Matter (DNOM) in Nordic forested catchments, Aquatic Sciences 66: 195–210.
Response 1: We appreciate that you introduced a valuable article. In the Introduction, we added the phrase of “except in rivers and lakes in forest catchment area (Vogt et al. 2004)” in L.72 in the revised manuscript.
Point 2: The experiment is done in points of a deciduous forest near Kyoto during some three years analyzing rainwater, water flowing on tree trunks, and surface water and soil leaching water in different layers. Nitrogen fallout is not high. You mention that one treeis Alnus. Does it have symbiotic nitrogen fixation with Frankia? What about the other biological nitrogen fixation?
Response 2: As tree speciess with the ability of nitrogen fixation, Alnus pendula and Robinia pseudoacacia sieboldiana also exist but not so many in the YMS. They and Alnus sieboldiana were planted in the rehabilitation about 100 years ago. We added the followimg sentence in L.95-96 in the revised manuscript: “The growth of Alnus pendula and Robinia pseudoacacian is also found in the understory as tree species with nitrogen-fixing ability (Goto et al. 2003).”
Point 3: The reading of this paper is not easy since there are many abbreviations that are not explained in the abbreviation list. You often present both the important and less important data together instead of helping the reader to find the most important data.
Response 3: We apologize for the dificulty for reading the manuscript because we used a lot of abbreviations. We added the meaning of the abbreviation: bulk rains, throughfall, stemflow, O layer leachate, soil-precolating waters, seepage waters and streamwaters to the caption of Figure 1. We wrote in the footnote in Figure 1 what means each abbreviations. Moreover, when we used the abbreviations for the other figures and tables, we would add “See the Figure 1 for the meaning of the abbreviations” to the title of figures and the footnote of tables.
Point 4: Explain O-layer (line 110). How many months or years old can be the leaf matter in the O layer? How thick is this layer?
In line 124 you mention the Oe layer. What is it?
Response 4: O layer of the YHS is composed of Oi layer and Oe layer and the depth of O layer is 6 cm, so we replaced "the Oe layer " with "the O layer (thickness 6 cm) " because the meaning of the point you pointed out is understood by O layer. The decomposition rate in YHS has not been investigated, but it is considered to be about the same as 0.45 yr-1, 0.60 yr-1 in Japanese deciduous broad-leaved forests and evergreen broad-leaved forests, respectively (Kawahara 1985).
Point 5: What is Meiji period (line 96)?
Response 5: “Meiji” is the name of era in Japan. Thus, we changed the ‘Meiji Period’ to ‘Meiji Period (AD 1968-1912)’ in L.89 in the revise manuscript.
Point 6: In line 95 you promise to have Table A1 and Table A2, but there are only Tables 1 and 2. Don’t mislead!
Response 6: Table A1 and Table A2 in the previous manuscript were supplementary tables. The description of "Supplementary Materials" was missing in the previous manuscript, so we added it and changed the initials related to Supplementary Materials from A to S, like ‘Table S1’ and ‘Table S2’
Point 7:The reader must return to the text to see what are Sta, STb, STc, STw, SPa, and SPb (and all the others) which are shown in Fig 1. In addition, there are lines that look like contours, but there should be more values showings the heights and the readers could estimate the direction of water flow. Improve the captions of this figure so that the reader can understand everything! Present here all abbreviations and then later in Figs 4 and 5 write: See the abbreviation in Fig. 1!
Response 7: In the Figure 1, we added an arrow and "water flow" indicating the direction of stream water flow, and added　the altitude (above sea level) of the contour line. We also added the following explanation to the caption of the figure; "Rv, Rr, Rd, bulk rain in a closed valley, on a ridge, and in the southwest of the watershed; TF, SF, SW, throughfall, stemflow, and soil-percolating waters at depth of 10 cm, 30 cm, and 70cm (So10, So30, and So70); SPa, SPb, seepage water at each point; STa, STb, STc, STw, stream water at each point and upstream side of the weir; O layer, soil O layer leachate. The area enclosed by a square dotted line indicates sampling points of TF, SF, and SW."
Point 8: Be more specific! You use “sample type” in many places as in title 3.2. The sample types in this paper are water samples. Do you simply mean water samples or water sampled from different sites? For instance, in Fig 6 you have only water samples but the results of these waters are from different water sites.
Response 8: The "sample type" in this paper means the types of observation targets: rainfall, throughfall, stem flow, O-layer passing water, soil infiltration water, spring water, and mountain stream water. Therefore, we replaced ‘all sample types’ with ‘all sample types of observation target’ in the Abstract (L.13), and replaced "each water sample type" with "each water sample type of observation target (hereinafter referred to as sample type)" in Introduction (L.80).
Point 9: In Fig 4 how many samplings did you have together during different samplings?
Response 9: The number of measured samples in Figure 4 is the same as that shown in Table S3. We added the following sentence in the caption in Figure 4. "The number of measured samples is the same as that shown in Table S3."
Point 10: In Table 1: what is amount? of which compound? Improve the caption!
Response 10: In response to your suggestions, we have significantly revised Table 1 and Table 2 in the previous manuscript, and their explanations in the manuscript. We reduced the number of items in the tables, combined the two tables into one as a new Table 1 in the revised manuscript, and arranged the items in order of importance from the left of the table. In the new Table 1, the following sentence was added to the footnote: "The unit of data used for the analysis is the same as that shown in the Table S3 and S4."
Point 11: Think about the order in Table 1! Don’t hide the most important results! Start therefore from UV254 and SUVA254!
Response 11:　Thank you for valuable comments. We answered in Response 10.
Point 12: Do you have correlation coefficients between water flow and different water parameters sampled in different sampling sites? What is YMS (1)? In Table 2 you have YMS (2). I had to think about this for a long time but I guess there was only one YMS, and tables 1 and 2 present different correlation coefficients for different parameters sampled from the same sites in the same YMS. For the reader, it would be easier to have only one table having the same caption and in part A some physical and chemical parameters and B some ions. One solution is that the less important data in Table 2 would be given in the supplementary table.
Response 12: We are sorry to confuse you about Tables 1 and 2 in the previous manuscript. The columns are sorted in descending order of DOC, and the items that are not related to DOC are deleted to make one new table as Table 1 in the revised manuscript, as explained in the Response 10. The explanation of the table has also been revised in the revised manuscript according to your advice.
Point 13: Text in lines 238-262 is the same which is presented in Table 1. Please, trust that the reader can see the table! It is not necessary to tell the same again in the text. Reduce this highly!
Response 13: We agreed your comments. We answered in the Response 10.
Point 14: Fig 6. omit this figure but present the equations and R2-values as a table!
Response 14: You have suggested to remove Figure 6 to make a new table with the correlation equations and coefficients of determination. However, we would like to keep the Figure 6 because it is necessary for visually understanding the different slopes and relationships between DOC and UV among sample types in rainfall, spring water, and mountain stream water. Therefore, we added the following sentences in the revised manuscript: "In order to visually understand the relationship with different slopes between DOC concentration and UV254, the relationship between the two was shown in the Figure 6." (L.248-263) and "For bulk rain (Rv, Rr, and Rd), the seepage waters (SPa, SPb) and the stream waters (STa, STb, STc, and STw), there were some data that deviate considerably from the approximate line. In contrast, no such data are found in TF, SF, the O leachate and the soil-percolating waters (So10, So30, and So70)."(L.258-261).
Point 15: Fig 7. Please, do you censor any data!
Response 15: You probably did not understand the necessity of Figure 7 because there was no explanation of the purpose the Figure in the previous manuscript. In addition, Reviewer 2 pointed out why the mean value is so different from that of the median value for the SUVA254 in bulk rain (Rv) in Figure 7. In response to these comments, the following sentences have been added to L.258-261: ”To further clarify the characteristics of SUVA254, SUVA254 for each sample was shown in a box plot (Figure 7). The difference between the average SUVA254 and the median SUVA254 are somewhat large in bulk rains (Rv, Rr, and Rd) due to the large variability of the data.”
Point 16: Omit the Fig 8. Now the font is so small that the reader cannot see anything. If somebody would take a print, this figure would not be useful. Omit it! It seems that the season did not have any clear effect. It might be that the time was too short and the variation between summer and winter is not so clear as it is in many other areas and the rains are always coming as water (newer as snow). If you have no important information about the season, please omit totally the text in lines 263-279! Or say that the effect of the season remained unclear in this study.
Response 16: We are sorry that the figure is too small. We have enlarged Figure 8.
Point 17: In line 303 you mention fir. Please, concentrate only on deciduous trees and omit those conifers!
Response 17: We would like to show that the DOC concentration of SF is higher in conifers than in hardwoods. Therefore, we will not delete the description about fir, but shorten the sentences described by Liu and Sheu (L.294-297 in the revised manuscript) as follows: “Liu and Sheu [11] reported that the DOC concentration of SF was higher in the Chinese fir (Cunninghamia lanceolata) plantation (30.8±17.3 mg L-1) than in the secondary and natural hardwood stands (7.2 ± 4.1–15.5 ± 11.6 mg L-1) in Guandaushi Forest in central Taiwan.”.
Point 18: In some cases, your references are not the original ones. For instance, phenolic compounds have been measured at 280 nm already in the 1960s which is much earlier than your references in line 55.
Response 18: We quoted the paper No.50 (Chin et al. 1994) because it states that specific UV absorbance (SUVA) is associated with aromatic carbon. If you know any older reports about the relationship between SUVA and aromatic carbon, could you please tell us?
Point 19:Correct the reference system from alphabet one to the order so that the first one is at the beginning of the introduction and the last one in conclusions or the end of discussion. See the guidance of this journal given to authors.
Response 19: Following your suggestions, we corrected the order of references in the revised manuscript according to the writing guidelines.
Correction of the manuscripts other than the above
We would like to inform you that we have made the following corrections because there were some errors other than the above in the manuscript.
- “Subsection 3-4 and all the text contained therein in the previous manuscript (L.280-291) was deleteted because it was a duplicated.
- “3.2. Relationships between DOC concentration and the other sample types” (L.237 in the previous manuscript (L.237) was replaced with “3.2. Relationships between DOC concentration and the other constituent of water samples”(L.229 in the new manuscript).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper, Shinji Kaneko et al researched the Dissolved organic matter (DOM) in a warm-temperate forested watershed. The paper is well-written. Below are my suggestions:
Major suggestions:
(1) Part of writing is similar to previous studies by the same author. The author may consider the rewrite. For example, in Line 144- Line 150, the paper states: "Inorganic cations and anions were determined using ion chromatography (IC 7000S; Yokogawa Analytical Systems, Tokyo, Japan). The concentrations of dissolved inorganic carbon (DIC) and DOC in all liquid samples were determined using a total organic carbon (TOC) analyzer (TOC 5000; Shimadzu, Kyoto, Japan)."
Shinji Kaneko et al (2007) Nitrogen budget of a rehabilitated forest on a degraded granitic hill. This paper states that
"Inorganic cations and anions were determined using ion chromatography (IC 7000S; Yokogawa Analytical Systems, Tokyo, Japan). The concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in stream water samples were determined using a total organic carbon (TOC) analyzer (TOC 5000; Shimadzu, Kyoto, Japan)."
(2) This study is taken place in Yamashiro Experimental Forest, Japan. Is it similar results compared to other places of the world (e.g., tropic area)? Please briefly discuss.
(3) DOC is easier to measure? Or say, UV254 is easier to measure? We normally hope to use a simple method to estimate the much more difficult method.
Minor suggestions:
(1) Line 167-Line 169. The author states UV254 was estimated by a specific method. The authors may provide the reference or the reason for this estimation.
(2) Line 262 Figure 7. Please check the data of the Rv group since the average is much higher than the median.
(3) Line 279 Figure 8. This figure and the fonts are too small. Please help to enlarge during publication.
This is a good paper and it is worthy to be published. Hope this paper to be published after some modifications and improvements.
Author Response
Response to Reviewer 2 Comments
We wish to express our deep appreciation of the reviewer's insightful comments on our article. These comments helped us a lot to improve our script. We wrote the answer to the comments, so please check it.
Comments and Suggestions for Authors
In this paper, Shinji Kaneko et al researched the Dissolved organic matter (DOM) in a warm-temperate forested watershed. The paper is well-written. Below are my suggestions:
Major suggestions:
Point 1: Major suggestion(1) Part of writing is similar to previous studies by the same author. The author may consider the rewrite. For example, in Line 144- Line 150, the paper states: "Inorganic cations and anions were determined using ion chromatography (IC 7000S; Yokogawa Analytical Systems, Tokyo, Japan). The concentrations of dissolved inorganic carbon (DIC) and DOC in all liquid samples were determined using a total organic carbon (TOC) analyzer (TOC 5000; Shimadzu, Kyoto, Japan)."
Response 1: Thank you for your suggestions. We took carefully read whether the similar sentences with our previous paper of Kaneko et al. (2007). Then, the following corrections have been made:
We deleted the similar sentences in the previous manuscript (L.112-122, L.145-154) and added the following sentences in the revised manuscript:
(L.118-119) “The sampling method of bulk rain, TF and Sf was described in the previous paper of Kaneko et al. (2007).
(L.142-144) "The pH, electrical conductivity (EC), inorganic cations, inorganic anions, DOC, and dissolved inorganic carbon (DIC) were measured in the laboratory. The method was described in the previous paper (Kaneko et al. 2007)." .
Point 2: Major suggestion (2)This study is taken place in Yamashiro Experimental Forest, Japan. Is it similar results compared to other places of the world (e.g., tropic area)? Please briefly discuss.
Response 2: There is less DOM research in tropical forests than in temperate forests, so we added the following sentences in the session 4.1 (L.304-308): " Only a few studies on DOC in tropical forests have been reported compared to temperate forests. DOC flux in TF was reported to be 68.4-195 kg ha-1yr-1 in an Amazon tropical forest (Neu et.al 2016) and that in the O layer ranged from 4.2 to 5.4 Mg C ha-1 yr-1 in a forest of East Kalimantan, Indonesia (Fujii et.al 2009). These results suggest that the DOC flux in tropical forests has similar or slightly higher ranges than that in temperate forests.
Point3: Major suggestion (3)DOC is easier to measure? Or say, UV254 is easier to measure? We normally hope to use a simple method to estimate the much more difficult method.
Response 3: DOC measurement with a total carbon measuring instrument is time consuming and expensive. On the other hand, UV measurement can be performed by simply setting a water sample in a spectrophotometer and measuring the absorbances, so no analytical reagent or gas is required, and measurement can be performed in a short time. We wrote an explanation for this L.15-17 in the Abstract and L. 427-428 in the Conclusions, and added the following phrase in L.393-394 in the session 4.2;” because the measurement of DOC using a total carbon analyzer is both time-consuming and expensive ”.
Minor suggestions:
Point 4: Minor suggestion (1)Line 167-Line 169. The author states UV254 was estimated by a specific method. The authors may provide the reference or the reason for this estimation.
Response 4: A.23 Initially, we measured the absorbances at 240 nm and 260 nm for the purpose of estimating the DOC concentration. Other studies such as Inamdar et al. (2012) used the absorbance at 254 nm, so we decided to use the absorbance at 254 nm in this paper which was estimated from the wavelengths of 240 nm and 260 nm. We added the reference of spectrophotometer analysis in L.157-159.
Point 5: Minor suggestion (2) Line 262 Figure 7. Please check the data of the Rv group since the average is much higher than the median.
Response 5: We appreciate your valuable comments. The difference between the average SUVA254 and the median SUVA254 is somewhat large in the other bulk rains (Rr and Rd), so we considered that the reason why the difference between the two parameters is large in Rv is that data variation is large. As for the Figure 7, Reviewer 2 pointed out that the explanation is insufficient. Therefore, we added the following sentences in L.25-261 the revised manuscript:
“To further clarify the characteristics of SUVA254, SUVA254 for each sample was shown in a box plot (Figure 7). The difference between the average SUVA254 and the median SUVA254 are somewhat large in bulk rains (Rv, Rr, and Rd) due to the large variability of the data.”
Point6: Minor suggestion (3) Line 279 Figure 8. This figure and the fonts are too small. Please help to enlarge during publication.
Response 6: We are sorry that the figure is too small. Following your advice, we have enlarged the figure.
Correction of the manuscripts other than the above
We would like to inform you that we have made the following corrections because there were some errors other than the above in the manuscript.
- “Subsection 3-4 and all the text contained therein in the previous manuscript (L.280-291) was deleted because it was a duplicated.
- “3.2. Relationships between DOC concentration and the other sample types” (L.237 in the previous manuscript (L.237) was replaced with “3.2. Relationships between DOC concentration and the other constituent of water samples”(L.229 in the new manuscript).
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The Figure 1 is now as it should be. Similarly, the list of abbreviations is now clear.
Still the Figure 8 is not clear if you are not able to increase magnification.
Take a photocopy using grey paper or a machine which is not the best one. It will show that too small details are not easy to read. Think about still once if you should replace this figure with a table. The time is so short that the trend of the season hardly can be seen.
Think self if you like to correct this or not!
Author Response
please check the attachment.
Author Response File: 
Author Response.docx
