The Effect of Monsoon Rainfall Patterns on Epilithic Diatom Communities in the Hantangang River, Korea
Round 1
Reviewer 1 Report
GENERAL COMMENTS
This manuscript addresses the effect of Monsoon rainfall patterns on Benthic diatom communities in the Hantangang River (Korea). This is an interesting study that may be useful to local managers/scientists but lacks however some broader scope. For example, you should outline here why your study is important for other context, i.e. what implications from my study that can be useful to others. There is a lack of details on M&M, but most importantly I really have doubts about the index (DIDC) you supposedly created. It lacks support and/or references which is rather unfortunate. Therefore, the authors need to explain the basis and fundamentals (how it works, input variables, etc.) of this index. Details are also missing on the PCA, how it was constructed, input variables. There is also some speculation on the Discussion that should be removed (if you don’t know, or do not have support, better remove it). Below is a list of specific comments for further suggestions.
SPECIFIC COMMENTS
Line 12 – You should first provide a short background (2-3 lines) on how your study is important.
Line 14 – Country for Hantangang River?
Line 18 – What do you mean, in terms of water quality parameters, by “the cleanest”?
Line 21-22- “The major species, Nitzschia fonticola and N. palea, of total abundance showed different tendencies before and after rainfall”. Remove “the major” and “of total abundance”. You mean the most abundant? Or the most dominant? Report %.
Line 23 – What about the other 3 years?
Line 24 – This is an unfortunate way to end your abstract, which highlights its local character. To increase the scope of the paper, you should outline here why your study is important for other context, i.e. what implications from my study that can be useful to others.
Line 40 – in disturbed (agricultural) landscapes, but not in all landscapes, such as pristine or undisturbed rivers.
Line 55-58 – you should clearly outline your specific goals here, for example in the form of questions/hypotheses. This would better clarify the readers.
Line 61 – What was the criteria for site selection? Habitat representativeness? Access? Other?
Line 62 – Sampling of what? I suppose is water and epilithic diatoms…How did you sample? Provide details of the sampling process (equipment, procedures, etc.).
Line 75 – “twice”. A day? A month? A year? Please be specific. Same on line 76.
Line 79 – What statistical test was conducted? Test statistic?
Line 82 – What do you mean by the “first”, “second” “investigation”? Each “investigation” is a different year? Clarify.
Line 82-84 – You calculated the rainfall? I thought this was measured. Please clarify (also how was the calculation performed).
Line 64-77 – This section is “Study Area” and should be the first sub-chapter within Material and Methods.
Line 93 – Forgot the caption for the small table within the figure.
Line 94 and throughout the manuscript – I would call “water quality parameters” (as you have in the abstract) instead of “environmental factors”.
Line 99-102 – Provide references for all these methods.
Line 121 – What were the input variables in the pca? How were they measured? Were the variables transformed? If so, what transformation was employed? What was the threshold for eigenvalue retainment?
Line 121 – How can you develop an index through a pca? Is this index applicable only here or can be extended to other regions? Clearly need to provide details on this.
Line 127 – What do you mean by the distance?
Line 128 – Further explanations should be given about this index that the authors created without giving any further details. Is there any reference to support the index? It seems not, to me. How was the index validated? What does it measure in practice? What does it mean the values of the index? (i.e. what does it mean a value of 1??, etc.).
Line 132 and throughout the manuscript – This sentence is unclear. You mean abundance data?? Please remove the term “standing crop” from the manuscript, as this applied mainly to plants/macrophytes. You mean abundance? Relative abundance? This is key and must be clarified.
Line 135 – What groups?
Line 137 – Remove the underline from precipitation.
Line 141 – What are these “eight investigations”? I haven´t seen further dates on M&M.
Line 144 – “appearance characteristics of the epilithic diatom communities”. Remove “appearance characteristics”, Results of cluster analysis were based on species presence or abundance, correct? Please clarify this.
Line 146 – “upstream, downstream, and tributary”. These are not stream orders. Suggest instead, stream position within the catchment.
Line 152 – once again these words “standing crops” should be removed from the manuscript.
Line 154-157 – Provide relative abundances (%) of these species.
Line 158 – What do you mean by “the major”? The largest ones? The most abundant?
Table 1 – Provide units for variables in Table 1.
Line 161-164 – provide relative abundance (%) for species.
Line 167-169 – provide the r and p-values for all your correlations.
Line 176 – These tests were not mentioned in M&M and must be. So, what does it mean different letters on each of the variables? That values are significant different? This must be said also.
Line 184 – What do you mean by “major” here? The 11 most abundant species?
Line 186 and throughout the manuscript – “dominant”. You need to clarify if you are presenting data base on abundance and dominance. A species may be dominant in a group cluster (i.e. in that it appears in all sites of that cluster) but may not be the most abundant of that group. Two different concepts, therefore, abundance and dominance.
Line 196, 240 and 259 – “All pollution indices, including electrical conductivity, turbidity, BOD, and nutrients…”. Conductivity, turbidity, BOD,…are pollution indices ??????? Perhaps you mean “water quality parameters”….
Line 202 – Provide the test statistics.
Line 213 – There are variables for which significance was not provided in the caption: DI =? H=? J=? ….What are the units for “abundance”?
Line 214 – This subtitle does not sound good. What do you want to show here?
Line 215 – “appearance characteristics (the number of appeared species, standing crop)”. Once again, this should be rephrased.
Line 217-218 – I could not find evidence of such result. Where is this shown?
Line 219-220 – Richness and number of species are not shown in Figure 6. Where is this shown?
Line 221 – As I pointed out in the M&M, the authors need to better explain and support this index. As it is, I c
Line 223 – 11.2% is a very low amount of variance explained.
Line 222-224 – Once again, there was no explanation on how the PCA was constructed. What were the input variables? The authors should provide the loadings of each variable and this was not shown. This is very important to see what variable are more relevant in each principal component.
Line 226-233 – This analysis, mixing an index that apparently the authors developed without giving further explanations/support and the PCA, for which the input variables and variable loadings are missing is a mess. Please provide the necessary information so this can be readily understood by the readers (see comment above).
Line 246 – These are not indices but parameters.
Line 268-269 – There seems to be some speculation here. Can you support this with data?
Line 281-282 – It seems this is methodology and should be moved accordingly. Why did you not show the results? If you don’t show them, it is better to remove this from the text.
Line 284-288 – Once again, I have serious reserves with this index which lacks supports and explanation (see comments above).
Line 288-289- Please avoid speculation.
Line 290 – “heavy rainfall had heavily impacted water quality”. Should not be the contrary (i.e. rainfall has a dilution effect on water pollutants)? Further, where is this shown on the results?
Line 299 – “Water quality had improved following rainfall”. You say the opposite on line 290. Change accordingly.
Line 301 – What were the tendencies?
Author Response
Point-by-point responses to Reviewers’ Comments
#1
This manuscript addresses the effect of Monsoon rainfall patterns on Benthic diatom communities in the Hantangang River (Korea). This is an interesting study that may be useful to local managers/scientists but lacks however some broader scope. For example, you should outline here why your study is important for other context, i.e. what implications from my study that can be useful to others. There is a lack of details on M&M, but most importantly I really have doubts about the index (DIDC) you supposedly created. It lacks support and/or references which is rather unfortunate. Therefore, the authors need to explain the basis and fundamentals (how it works, input variables, etc.) of this index. Details are also missing on the PCA, how it was constructed, input variables n. There is also some speculation on the Discussion that should be removed (if you don’t know, or do not have support, better remove it).
Response: We acknowledge the reviewer’s comment and hope our results can be accepted to publish by your valuable comments. We have carefully revised the old version of manuscript according to your recommendations.
Below is a list of specific comments for further suggestions.
SPECIFIC COMMENTS
Line 12 – You should first provide a short background (2-3 lines) on how your study is important.
Response: According to the reviewer’s recommendation, we added the sentence as “Due to an intense rainfall has been concentrated mainly in the Asian-Monsoon period in Korea peninsula, most of river and lake ecosystem has been strongly influenced”
Line 14 – Country for Hantangang River?
Response: According to the reviewer’s recommendation, we added “, South Korea” after Hantangang River.
Line 18 – What do you mean, in terms of water quality parameters, by “the cleanest”?
Response: According to the reviewer’s recommendation, we rewrote abstract as described below.
Line 21-22- “The major species, Nitzschia fonticola and N. palea, of total abundance showed different tendencies before and after rainfall”. Remove “the major” and “of total abundance”. You mean the most abundant? Or the most dominant? Report %.
Response: According to the reviewer’s recommendation, we rewrote abstract as described below.
Line 23 – What about the other 3 years?
Response: According to the reviewer’s recommendation, we rewrote abstract as described below.
Line 24 – This is an unfortunate way to end your abstract, which highlights its local character. To increase the scope of the paper, you should outline here why your study is important for other context, i.e. what implications from my study that can be useful to others.
Response: According to the reviewer’s recommendation, we rewrote abstract as follows;
ABSTRACT: Due to an intense rainfall has been concentrated mainly in the Asian-Monsoon period, most of rivers and lakes in Korea peninsula has been strongly disturbed. To examine the influence of rainfall on epilithic diatom communities, we measured the diatom distribution and river water quality at 29 sites along the mainstream and tributaries of the Hantangang River, South Korea. Water quality in the polluted sites had improved following rainfall, but the abundance of dominant species was varied with water quality; Nitzschia fonticola decreased in all sampling sites, and Nitzschia palea in the clean sites and Achnanthidium minutissima in the polluted sites increased after rainfall, respectively. The community dynamic index of epilithic diatom (CDI) results using a PCA ordination, indicate that the most dynamic shift of diatom community in the mid-polluted sites in the year of highest rainfall, among groups. These results collectively indicate that the monsoon rainfall strongly influenced water quality and diatom community, but our findings are limited to the water system of the small stream. Therefore, more study needs to generalize the effects of monsoon rainfall on water quality and epilithic diatom communities, considering various rivers with different water qualities, and rainfalls with different magnitudes and exposure times of precipitation
Line 40 – in disturbed (agricultural) landscapes, but not in all landscapes, such as pristine or undisturbed rivers.
Response: According to the reviewer’s recommendation, we revised as “Rainfall has a profound effect on the disturbed river ecosystems as such as pristine or undisturbed rivers; in particular, river biochemical oxygen demand (BOD), turbidity, electrical conductivity, and N-P nutrients were found to markedly increase following rainfall due to an influx of nutrients from the surrounding environment [6]”.
Line 55-58 – you should clearly outline your specific goals here, for example in the form of questions/hypotheses. This would better clarify the readers.
Response: According to the reviewer’s recommendation. Introduction has been revised mainly why we selected the DIDC method using a ordination method tools. Additionally, the purpose of this study is obviously presented in the last part of Introduction.
Inserted sentence is follows;
Our team has been reported several times the impacts of monsoon rainfall on the river diatom community (Kim et al. 20xx, Kim et al., 20xx, Cho et al. 20xx). As the impact or its magnitude of rainfall, we often calculated the difference in physico-chemical and biological parameters before and after monsoon using a simple statistical methods as analysis of variance (ANOVA), and the relationship between water quality parameters and biological index (dominance, diversity, eveness and richness) using a canonical correspondence analysis (CCA). In this study, for the pursuit of more visible performance on the shift of diatom community, we first introduced the community dynamic index of epilithic diatom (CDI) based on the ordination method (i.e. Principal component analysis) of biological data, and presented as the magnitude of change with the distance measured between two communities before and after Monsoon rainfall . For the simpler ordination method if possible, we previously tried to test various ordination methods, whether easy to approach the biological data, as small in quantity, no null data, no repetitive field data. And we also tested the ordination analysis, not further required environmental data as water quality parameters.
This is to study the impacts of Asian monsoon rainfall patterns on the river environment and the epilithic diatom communities, with an investigation of the water characteristics and epilithic diatom communities of the Hantangang River in the central Korean peninsula before and after the monsoon season from 2012~2015, including the year of highest rainfall.
Line 61 – What was the criteria for site selection? Habitat representativeness? Access? Other?
Response: According to the reviewer’s recommendation. We revised as “ To collect epilithic diatoms and river water samples, a total of 29 sites was selected within the mainstream and tributaries of the Hantangang River (Fig. 1). Since 2007, the study sites have been continuously monitored the stream organism and water quality with land-use under the project of NIER (National Institute of Environmental Research, Korea), and the sampling sites or total number of sites were already limited to this river. We conducted a total eight times of sampling, twice a year, in May (pre-monsoon) and September (post-monsoon) between 2012 and 2015. The sampling and analysis method of epilithic diatoms and river water is described in the separate section.
Line 62 – Sampling of what? I suppose is water and epilithic diatoms…How did you sample? Provide details of the sampling process (equipment, procedures, etc.).
Response: We acknowledge the reviewer’s comment, we added a sentence as” A total eight times of sampling was conducted twice a year, in May (pre-monsoon) and September (post-monsoon) between 2012 and 2015. The sampling method of epilithic diatoms and river water is described in the separate section.”
Line 75 – “twice”. A day? A month? A year? Please be specific. Same on line 76.
Response: We acknowledge the reviewer’s comment, we added a “a year” line 75 and 76.
Line 79 – What statistical test was conducted? Test statistic?
Response: We acknowledge the reviewer’s comment. To compare the rainfalls between 1st and 2nd samplings or among survey years, we calculated the quantity of total precipitation using a data of rainfall measured by a weather center of South Korea (http://www.kma.go.kr/index.jsp). The 1st sampling’s rainfall or precipitation before Monsoon (PBM) means the sum of all precipitation during the cold and dry season from the late autumn to the late spring, while the 2nd rainfall or precipitation after Monsoon (PAM) is the sum of all precipitation during the warm season from late spring to the late autumn. In Hantan River Basin, average of rainfalls during the Monsoon period for 4 years was about 2.5 times higher than that of non-Monsoon periods (average of 283.4±76.2 for PBM and 727.0±264.5 for PAM, t-test, P<0.001, Fig. 2).
Line 82 – What do you mean by the “first”, “second” “investigation”? Each “investigation” is a different year? Clarify.
Response: We acknowledge the reviewer’s comment. We exchanged the terms “first or second” or “investigation” in material and Method as “ 1st sampling of diatom and river water is for before Monsoon and 2nd samplings is those after Monsoon. However, the measurement of rainfall is differed from the sampling event. Like line 79, we revised as “to compare the rainfalls between 1st and 2nd samplings or among survey years, we calculated the quantity of total precipitation using a data of rainfall measured by a weather center of South Korea (http://www.kma.go.kr/index.jsp). The 1st sampling’s rainfall or precipitation before Monsoon (PBM) means the sum of all precipitation during the cold and dry season from the late autumn to the late spring, while the 2nd rainfall or precipitation after Monsoon (PAM) is the sum of all precipitation during the warm season from late spring to the late autumn”.
Line 82-84 – You calculated the rainfall? I thought this was measured. Please clarify (also how was the calculation performed).
Response: We acknowledge the reviewer’s comment. We mentioned above ;ine 79 and 82.
Line 64-77 – This section is “Study Area” and should be the first sub-chapter within Material and Methods.
Response: According to the reviewer’s recommendation, we made the subsection as “ 2.1 Study area”, so the old subtitle was divided into two section.
Line 93 – Forgot the caption for the small table within the figure.
Response: According to the reviewer’s recommendation, we added the caption of the table in figure 2, as follows; A small table in the figure showed the total precipitation for the periods of before (PBM) and after monsoon (PAM); PBM in 2012 indicate the sum of daily precipitation from 10 September to 3 May, while PAM or the latter is those from 4 May to 6 September of 2012, respectively.
Line 94 and throughout the manuscript – I would call “water quality parameters” (as you have in the abstract) instead of “environmental factors”.
Response: According to the reviewer’s recommendation, we revised as water quality parameters, instead of environmental factors.
Line 99-102 – Provide references for all these methods.
Response: According to the reviewer’s recommendation, we added a related reference; [26] APHA. Standard Methods for the Examination of Water and Waste Water. American Public Health Association: New York, NY, USA. 2001.
Line 121 – What were the input variables in the pca? How were they measured? Were the variables transformed? If so, what transformation was employed? What was the threshold for eigenvalue retainment?
Response: We acknowledge the reviewer’s comment. We revised 2.4. Dynamic index of diatom community (DIDC) as below.
Line 121 – How can you develop an index through a pca? Is this index applicable only here or can be extended to other regions? Clearly need to provide details on this.
Response: We acknowledge the reviewer’s comment. We revised 2.4. Dynamic index of diatom community (DIDC) as below.
Line 127 – What do you mean by the distance?
Response: We acknowledge the reviewer’s comment. We revised 2.4. Dynamic index of diatom community (DIDC) as below
Line 128 – Further explanations should be given about this index that the authors created without giving any further details. Is there any reference to support the index? It seems not, to me. How was the index validated? What does it measure in practice? What does it mean the values of the index? (i.e. what does it mean a value of 1??, etc.).
Response: We acknowledge the reviewer’s comment. We revised 2.4. Dynamic index of diatom community (DIDC) as below;
2.4 Measurement of diatom community changes
As above mentioned in Introduction, we first introduced the numerical method to measure the shift of diatom community before and after monsoon rainfall. Briefly, as an ordination method for the understanding the characteristics of a biological community or ecosystem, many statistical methods such as Principal Component Analysis (PCA), Multidimensional Scaling (MDS), Principal Coordinatie Analysis (PCoA), Extended Correspondence Analysis (DCA), Correspondence Analysis (CA), and Redundancy Analysis (RDA), CCA (Canonical Correspondence Analysis) have been often adopted. Of these, PCA which uses the Euclidean distance method, is the most commonly used model, which minimizes data loss and is easy to visualize or presnet even with a small amount of principal component variables (Ko et al. 2015). In this study, due to the identification of the changes in biological communities, RDA, DCA, and CCA, which required separate environmental variables, were excluded, while the correction models such as MDS and PCoA were not included due to null data. This study did not include null data. In the previous test, we calculated the distance in the PCA dimension before and after monsoon rainfall showed higher eigenvalue (Eigenvalue, 22.498) and variance (11.193) than DCA and CA. These characteristics are also consistent with the study of Ko et al (2015), which conducted with data of spider harvested by Ter Braak (1986).
Biotic communities show a variety of different characteristics according to location and time. Therefore, this makes it difficult to determine the degree of the dynamic index in response to specific changes, such as rainfall. We therefore developed the community dynamic index of epilithic diatom (CDI) to accurately quantify the rainfall-driven changes in epilithic diatom communities. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. The input variables of PCA is two kinds of variables such as species appearance (number of species) and their biomass (often called an abundance) of epilithic diatom identified from each sampling site, which was expressed in PCA ordination. A principal component analysis (PCA) was to develop the CDI. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree, and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. Using this analysis, each site showing the appearance characteristics (species, density) of epilithic diatoms was expressed in ordination. Note that the distance is considered as a measure of shift in diatom community before and after monsoon rainfall over the text. Community dynamic index of epilithic diatom (CDI) was calculated by the following equation:
-----------------------------------------------------------(1)
d is the distance or dynamic index between two communities in PCA with different times at the specific site
before and after mon rainfall.
x1 and y1 is the first sampling in PCA dimension before monsoon rainfall
x2 and y2 is the second sampling in PCA dimension after monsoon rainfall
--------------------------------------------------------------------------(3)
CDI is the community dynamic index of epilithic diatom or the average of total distances between different times of groups or clusters before and after monsoon rainfall.
di is the distance between different times at the ith sampling site before and after monsoon rainfall.
n is the number of sampling sites or communities
Line 132 and throughout the manuscript – This sentence is unclear. You mean abundance data?? Please remove the term “standing crop” from the manuscript, as this applied mainly to plants/macrophytes. You mean abundance? Relative abundance? This is key and must be clarified.
Response: We acknowledge the reviewer’s comment. We revised the old sentence as follows; The total abundance of epilithic diatom species in each investigation site and the relative abundance of each species were multiplied to calculate the species density (cells/cm2). Based on these results such as the number and the total abundance of appeared species in each sampling site, the major species, dominance [29], diversity [30], richness [31], and evenness [32] were calculated.
Line 135 – What groups?
Response: We acknowledge the reviewer’s comment. In this study we used the term “group”, instead of cluster, based on a cluster analysis. The term “group” is the synonym of cluster.
Line 137 – Remove the underline from precipitation.
Response: Thank you very much. According the reviewer’s recommendation, we removed the underline.
Line 141 – What are these “eight investigations”? I haven´t seen further dates on M&M.
Response: We acknowledge the reviewer’s comment. Actually, eight investigations indicate total number of samplings twice a year from 2012 to 2015. We revised as the diatom samplings instead of the eight investigations.
Line 144 – “appearance characteristics of the epilithic diatom communities”. Remove “appearance characteristics”, Results of cluster analysis were based on species presence or abundance, correct? Please clarify this.
Response: According the reviewer’s recommendation, we revised as “Results of cluster analysis were based on species presence or abundance, divided into three groups (G1–3)”
Line 146 – “upstream, downstream, and tributary”. These are not stream orders. Suggest instead, stream position within the catchment.
Response: According the reviewer’s recommendation, we removed the stream order (upstream, downstream, and tributary).
Line 152 – once again these words “standing crops” should be removed from the manuscript.
Response: According the reviewer’s recommendation, we removed the term ”standing crops” over the text.
Line 154-157 – Provide relative abundances (%) of these species.
Response: According the reviewer’s recommendation, we added a relative abundance of dominant diatom species.
Line 158 – What do you mean by “the major”? The largest ones? The most abundant?
Response: According the reviewer’s recommendation, we revised as “most abundant”, instead of “major”
Table 1 – Provide units for variables in Table 1.
Response: According the reviewer’s recommendation, we added a units of variables in Table 1.
Line 161-164 – provide relative abundance (%) for species.
Response: According the reviewer’s recommendation, we added a relative abundance (%) of most abundant species.
Line 167-169 – provide the r and p-values for all your correlations.
Response: We acknowledge the reviewer’s comment. We revised the part of sentence as “…positively related with nutrients such as NH4, NO3, TN, PO4 and TP. In contrast, Nitzschia palea—the major species of G3—negatively related with the same nutrients (Table 3).
Line 176 – These tests were not mentioned in M&M and must be. So, what does it mean different letters on each of the variables? That values are significant different? This must be said also.
Response: We acknowledge the reviewer’s comment. We revised the part of sentence as “The ANOVA results on physico-chemical and biological parameters showed the obvious differences among three groups divided by a cluster analysis based on the distribution of epilithic diatoms (Table 1)” Most of water quality parameters including electrical conductivity, turbidity, BOD, and nutrients such as NH4, NO3, TN, PO4 and TP, showed lowest values in G1, indicating the highest water quality among groups.
Line 184 – What do you mean by “major” here? The 11 most abundant species?
Response: We acknowledge the reviewer’s comment. We replaced the term “major” with “most abundant” as the mean of diatom abundance over the text.
Line 186 and throughout the manuscript – “dominant”. You need to clarify if you a e presenting data base on abundance and dominance. A species may be dominant in a group cluster (i.e. in that it appears in all sites of that cluster) but may not be the most abundant of that group. Two different concepts, therefore, abundance and dominance.
Response: We acknowledge the reviewer’s comment. We replaced the term “major” with “most abundant” as the mean of diatom abundance over the text.
Line 196, 240 and 259 – “All pollution indices, including electrical conductivity, turbidity, BOD, and nutrients…”. Conductivity, turbidity, BOD,…are pollution indices ??????? Perhaps you mean “water quality parameters”….
Response: According the reviewer’s recommendation, we changed as “water quality parameters” instead of “All pollution indices“
Line 202 – Provide the test statistics.
Response: We acknowledge the reviewer’s comment. We removed the significant and replace with “obviously” because of figure-basis explanation.
Line 213 – There are variables for which significance was not provided in the caption: DI =? H=? J=? ….What are the units for “abundance”?
Response: According the reviewer’s recommendation, we added a caption of DI, H, J and e indices to the below of Fig. 5.
DI; Dominance index, H’; Diversity index, j; Richness index, e; Evenness index, 12-BF and 12-AF : the measurements before and after monsoon in 2012, respectively.
Line 214 – This subtitle does not sound good. What do you want to show here?
Response: According the reviewer’s recommendation, we moved the subtitle of 3.3. Dynamics of diatom communities, following the sentence relating Fig. 5.
Line 215 – “appearance characteristics (the number of appeared species, standing crop)”. Once again, this should be rephrased.
Response: We acknowledge the reviewer’s comment, we explained it on the next comments and revised.
Line 217-218 – I could not find evidence of such result. Where is this shown?
Response: According the reviewer’s recommendation, we rewrote the phrased as follow;
Figure 5 showed the variation of diatom community such as number and abundance of species, dominant index (DI), species diversity (H’), richness index (j) and evenness index (e) before and after Monsoon between 2012-2015. Throughout the four-year study period, the abundance of both G1 and G2 decreased after rainfall, whereas G3 showed no consistent trend (Fig. 5). The richness index and number of species were highest in G2 in all investigations and consistently increased after rainfall. In contrast, G1 and G3 showed no consistent trends. Except G1, DI and H’ in G2 and G3 showed the most obvious flux before and after Monsoon over the study, while the rainfall in Monsoon increased species diversity and decreased dominant index through all investigation.
Line 219-220 – Richness and number of species are not shown in Figure 6. Where is this shown?
Response: We acknowledge the reviewer’s comment. We revised the Fig. 6, that is mistake of Fig. 5.
We added a caption of DI, H, J and e indices to the below of Fig. 5. DI; Dominance index, H’; Diversity index, j; Richness index, e; Evenness index, 12-BF and 12-AF : the measurements before and after monsoon in 2012, respectively.
In addition, we revised Figure 6 as follows; Epilithic diatom community characteristics before and after Monsson in the Hantangang River from 2012 to 2015, including A) the PCA ordination and B) the average CDI distances of each group between the before (1-BF) and after monsoon (2-AF). Black circle is total annual precipitation during the Monsoon period every year. Example, G1-BF and G1-AF: the sampling sites of group 1(G1) before (red-closed circle) and after monsoon (red-open circle), respectively
Line 221 – As I pointed out in the M&M, the authors need to better explain and support this index. As it is, I c
Response: According the reviewer’s recommendation, we already inserted the explanation on CDI into material and method.
Line 223 – 11.2% is a very low amount of variance explained.
Response: We acknowledge the reviewer’s comment. As you know, biotic data obtained from the field sampling, specially a benthic diatom, often showed the very low amount of variance in PCA, CCA and other models, below 6.5% in other organisms. We often identified the organism analysis by several persons, indicate an individual difference. Of course, if possible, all data should be harvested to the specific organism. There are numerous species of diatoms even at one sampling sites.
Line 222-224 – Once again, there was no explanation on how the PCA was constructed. What were the input variables? The authors should provide the loadings of each variable and this was not shown. This is very important to see what variable are more relevant in each principal component.
Response: According the reviewer’s recommendation, we already inserted the explanation on CDI into material and method.
Line 226-233 – This analysis, mixing an index that apparently the authors developed without giving further explanations/support and the PCA, for which the input variables and variable loadings are missing is a mess. Please provide the necessary information so this can be readily understood by the readers (see comment above).
Response: We acknowledge the reviewer’s comment. We already inserted the explanation on DIDC into material and method.
Table 4. The correlation coefficients between the community dynamic index of epilithic diatom (CDI) and biological indices in the Hantangang River from 2012 to 2015. ** p<0.01
|
Biological indices |
CDI |
|
Abundance |
-0.03 |
|
No. of species |
0.44** |
|
Dominant index |
-0.31** |
|
Diversity index |
0.35** |
|
Richness index |
0.41** |
|
Eveness index |
0.28** |
Line 246 – These are not indices but parameters.
Response: According the reviewer’s recommendation, we changed as “parameters”, instead of “indices”
Line 268-269 – There seems to be some speculation here. Can you support this with data?
Response: According the reviewer’s recommendation, we rewrote a sentence as “In this study, the cellular abundance of the clean-water diatom species, Ach. alteragracillima and Nit. fonticola, obviously decreased after rainfall, despite improved water quality. In other hand, Nit. palea as dominant species in the polluted water more increased after monsoon rainfall than that of the mid-polluted water (our data). It may suggest that the rainfall can strongly influence on the most abundant diatom species following to the stream condition with different water quality. However, we do not exactly explain whether water quality of stream or flow velocity by precipitation and its magnitude. In general, the epilithic diatom community is strongly influenced by the increased water flow and higher flow velocities after rainfall. In particular, pennate diatoms are pioneer species that stably attach to substrates immediately after the occurrence of floods that wash out most of the substrates [references]. They speculated that the monsoonal climate of South Korea likely influenced the appearance of the now common pioneer species Ach. minutissima. This result is consistent with this study, but still to explain the abrupt decrease of Ach. altergracillima after rainfall whether species-specific characteristics or physical effect like a washing out. In this study, not all pennate diatoms increased after rainfall, and thus further studies should investigate the introduction of pioneer species on substrates immediately following severe environmental disturbance like rainfall “.
Line 281-282 – It seems this is methodology and should be moved accordingly. Why did you not show the results? If you don’t show them, it is better to remove this from the text.
Response: According the reviewer’s recommendation, the sentences relating a study result were moved to Results.
Line 284-288 – Once again, I have serious reserves with this index which lacks supports and explanation (see comments above).
Response: We acknowledge the reviewer’s comment. We explained various biological indices in Material and Method.
Line 288-289- Please avoid speculation.
Response: We acknowledge the reviewer’s comment. We removed the specific demonstration from discussion.
Line 290 – “heavy rainfall had heavily impacted water quality”. Should not be the contrary (i.e. rainfall has a dilution effect on water pollutants)? Further, where is this shown on the results?
Line 299 – “Water quality had improved following rainfall”. You say the opposite on line 290. Change accordingly.
Line 301 – What were the tendencies?
Response: We acknowledge the reviewer’s comment. We revised the conclusion as follows;
An intense rainfall has been concentrated mainly in the Asia-Monsoon period in Korea peninsula. We examined the influence of rainfall before and after Monsoon rainfall on epilithic diatom communities and water quality parameters at the Hantangang River, South Korea from 2012–2015. Water quality in the polluted sites had improved following rainfall, but the abundance of dominant species was varied with water quality; Nitzschia fonticola decreased in all sampling sites, and Nitzschia palea in the clean sites and Achnanthidium minutissimum in the polluted sites increased after rainfall, respectively. CDI results using a PCA ordination, indicate that the shift of diatom community in the mid-polluted sites in 2013—the year of highest rainfall, was the most obvious among groups. This study results collectively indicate that the Monsoon rainfall strongly influenced water quality and diatom community, but our findings are limited to the water system of the small stream. Thus, further study need to generalize the effects of Monsoon rainfall on water quality and epilithic diatom communities, considering more rivers with different water qualities, and more rainfalls with different magnitudes, and more exposure times of precipitation.
#2
This manuscript measured the diatom distribution and river water quality at 29 sites along the Hantangang River from 2012-2015 to the effect of Monsoon Rainfall Patterns on Benthic Diatom Communities. The result presented that water quality of Hantangang River, especially the sites with serious pollution, were improved after rainfall, and the epilithic diatom communities of were significant controlled by the rainfall. This study proposed the effection of Asian monsoon rainfall on benthic diatoms, and also provided important data for the study of the relationship between diatoms and water environment. This study should be a valuable contribution to the literature. I could recommend this manuscript. The following Suggestions are for the author's reference when revising：
The study of the rainfall-impacts on phytoplankton and the epilithic diatom communities should be well introduced in the part of Introduction.
Response: Thank you so much. According the reviewer’s recommendation, we added a reference related with phytoplankton and diatom communities to the Introduction.
“2.3. Analysis of epilithic diatoms”, the detailed counting methods of diatom should be described, such as how many diatom valves were counted in each samples.
Response: According the reviewer’s recommendation, we revised the old sentence as” The total abundance of epilithic diatoms (cell/cm2) at each study site was quantified using an inverted microscope (Nikon E600, Tokyo, Japan), and their relative abundance (%) of each species appeared was calculated during the identification process. To calculate the real density or abundance of diatom (cells/cm2), the total abundance of diatom species in each investigation site and the relative abundance of each species were multiplied. Based on the number and total abundance of appeared species in each sampling site, we defined the most abundant species, and calculated dominance [29], diversity [30], richness [31], and evenness [32] of the epilithic diatom community.”
“3.1. Epilithic diatoms of the Hantangang River”: The authors presented only one dominant species of each group, the other dominant species should also be introduced to analyze the effect of rainfall on epilithic diatom.
Response: Thank you very much. As you know, we presented the major dominant species and its abundance (>2% of total abundance) throughout all sampling In Table 2 and Fig.4. Of course, other dominant species also important member of each community, although there were many kinds of species participating in each community. However, in this study, we wanted to appeal the dynamic of major dominant taxa after event as rainfall. If you want to see the raw data, we can attach the original sheet of data as supplement of this work. Diatoms with little or small amount of abundance is limited due to the space, however, we also believe that that is very important data.
Line 254: “and Ach. Minutissima in G2,” should be “and Ach. minutissima in G2,”; “and Nit. Plaea in G3 [37-39].”should be “and Nit. plaea in G3 [37-39].”
Response: According the reviewer’s recommendation, we revised the mistakes of species names, as small characters.
Line 268: “and Nit. Fonticola, significantly” should be “and Nit. fonticola, significantly”.
Response: According the reviewer’s recommendation, we revised the mistakes of species names, as small characters.
Reviewer 2 Report
This manuscript measured the diatom distribution and river water quality at 29 sites along the Hantangang River from 2012-2015 to the effect of Monsoon Rainfall Patterns on Benthic Diatom Communities. The result presented that water quality of Hantangang River, especially the sites with serious pollution, were improved after rainfall, and the epilithic diatom communities of were significant controlled by the rainfall. This study proposed the effection of Asian monsoon rainfall on benthic diatoms, and also provided important data for the study of the relationship between diatoms and water environment. This study should be a valuable contribution to the literature. I could recommend this manuscript. The following Suggestions are for the author's reference when revising：
- The study of the rainfall-impacts on phytoplankton and the epilithic diatom communities should be well introduced in the part of Introduction.
- “2.3. Analysis of epilithic diatoms”, the detailed counting methods of diatom should be described, such as how many diatom valves were counted in each samples.
- “3.1. Epilithic diatoms of the Hantangang River”: The authors presented only one dominant species of each group, the other dominant species should also be introduced to analyze the effect of rainfall on epilithic diatom.
- Line 254: “and Ach. Minutissima in G2,” should be “and Ach. minutissima in G2,”; “and Nit. Plaea in G3 [37-39].”should be “and Nit. plaea in G3 [37-39].”
- Line 268: “and Nit. Fonticola, significantly” should be “and Nit. fonticola, significantly”.
Author Response
This manuscript measured the diatom distribution and river water quality at 29 sites along the Hantangang River from 2012-2015 to the effect of Monsoon Rainfall Patterns on Benthic Diatom Communities. The result presented that water quality of Hantangang River, especially the sites with serious pollution, were improved after rainfall, and the epilithic diatom communities of were significant controlled by the rainfall. This study proposed the effection of Asian monsoon rainfall on benthic diatoms, and also provided important data for the study of the relationship between diatoms and water environment. This study should be a valuable contribution to the literature. I could recommend this manuscript. The following Suggestions are for the author's reference when revising：
The study of the rainfall-impacts on phytoplankton and the epilithic diatom communities should be well introduced in the part of Introduction.
Response: Thank you so much. According the reviewer’s recommendation, we added a reference related with phytoplankton and diatom communities to the Introduction.
“2.3. Analysis of epilithic diatoms”, the detailed counting methods of diatom should be described, such as how many diatom valves were counted in each samples.
Response: According the reviewer’s recommendation, we revised the old sentence as” The total abundance of epilithic diatoms (cell/cm2) at each study site was quantified using an inverted microscope (Nikon E600, Tokyo, Japan), and their relative abundance (%) of each species appeared was calculated during the identification process. To calculate the real density or abundance of diatom (cells/cm2), the total abundance of diatom species in each investigation site and the relative abundance of each species were multiplied. Based on the number and total abundance of appeared species in each sampling site, we defined the most abundant species, and calculated dominance [29], diversity [30], richness [31], and evenness [32] of the epilithic diatom community.”
“3.1. Epilithic diatoms of the Hantangang River”: The authors presented only one dominant species of each group, the other dominant species should also be introduced to analyze the effect of rainfall on epilithic diatom.
Response: Thank you very much. As you know, we presented the major dominant species and its abundance (>2% of total abundance) throughout all sampling In Table 2 and Fig.4. Of course, other dominant species also important member of each community, although there were many kinds of species participating in each community. However, in this study, we wanted to appeal the dynamic of major dominant taxa after event as rainfall. If you want to see the raw data, we can attach the original sheet of data as supplement of this work. Diatoms with little or small amount of abundance is limited due to the space, however, we also believe that that is very important data.
Line 254: “and Ach. Minutissima in G2,” should be “and Ach. minutissima in G2,”; “and Nit. Plaea in G3 [37-39].”should be “and Nit. plaea in G3 [37-39].”
Response: According the reviewer’s recommendation, we revised the mistakes of species names, as small characters.
Line 268: “and Nit. Fonticola, significantly” should be “and Nit. fonticola, significantly”.
Response: According the reviewer’s recommendation, we revised the mistakes of species names, as small characters.
Reviewer 3 Report
General Comments:
This manuscript includes a valuable dataset in examining the effects of precipitation on benthic diatoms in a river influenced by monsoon climate. However, the manuscript needs to be improved before the acceptance. First of all, it is difficult to follow the manuscript since figure and table citations in the text do not match and are neither in their appearance in the text. Authors also need to explain better for the mechanism behind the difference between the periods before and after monsoon. For instance, temperature also appears to control the spatial and temporal variations of diatom community based on their results. Finally I recommend authors add hypothesis of their study and highlight the significance of their study more clearly in the section of conclusion.
Specific Comments:
Abstract
Line 14: I recommend adding “, S. Korea” after “Hantangang River”
Line 18: Do you mean clearest?
- Introduction
The manuscript can be improved by adding hypothesis of the study.
- Materials and Methods
Line 61-63: Authors need to describe more details on water sampling here, such as water depth, protocol of water sampling they used, and how the sampling dates were selected relevant to rainfall and why a single survey was conducted etc. I can expect that daily variations are also high depending on rainfall.
Line 75-81: The sentences can be included in the section of results. Instead, description on rainfall for several days before the sampling dates is more useful here to interpret the data because the effect of rainfall can be maintained for a few days depending on the systems.
Line 81-84: I do not understand this sentence. Also why did you include 3 months rainfall?
Line 121: (PCA) was used?
Line 130: (n+1) => (x+1)?
Line 137: Please check the precipitation.
- Results
Line 152: Table 1 includes water quality data and then community characteristics. I recommend the explanation matching with the order in the table. Numbering of figures should be based on appearance in the text; Fig. 4 should be here instead of Fig. 5.
Line 159: What is MS? Please check the number of cell counts (x106).
Line 166: Do you mean Table 3 here?
Line 166-169: Their correlation with nutrients may be due to autocorrelation with water temperature.
Line 215: Figure 6? or 5? It is not easy to follow the text due to this kind of errors. Please check the typo also (“6shows”). The results of this study focus primarily on the spatial difference and I do not see the apparent or statistical results on the difference between pre-monsoon and post-monsoon.
Line 221-231: The results are very nice and essential in this study. However, water temperature also appears important in controlling the diatom community based on the results in Tables 1 and 2. Authors need to validate the difference is mainly due to rainfall in their results.
4. Discussion
Line 292-294: The last sentence does not help in highlighting this study although the study includes valuable data. I recommend rewriting this sentence.
5. Conclusion
Line 303-305: I recommend rewriting this.
Figures
Figure 1. I recommend changing the color of station symbols in accordance to G1, G2, and G3 in Figs. 5 & 6.
Figure 5. Authors need to describe what Di, H’, j and e represent.
Author Response
This manuscript includes a valuable dataset in examining the effects of precipitation on benthic diatoms in a river influenced by monsoon climate. However, the manuscript needs to be improved before the acceptance.
First of all, it is difficult to follow the manuscript since figure and table citations in the text do not match and are neither in their appearance in the text.
Response: According the reviewer’s recommendation, we revised the captions of figures and tables, and matched with the text.
Authors also need to explain better for the mechanism behind the difference between the periods before and after monsoon. For instance, temperature also appears to control the spatial and temporal variations of diatom community based on their results.
Finally I recommend authors add hypothesis of their study and highlight the significance of their study more clearly in the section of conclusion.
Response: According the reviewer’s recommendation, we revised a conclusion focused on the purpose and highlight of this study.
Specific Comments:
Abstract
Line 14: I recommend adding “, S. Korea” after “Hantangang River”
Response: According the reviewer’s recommendation, we added “, S. Korea” after “Hantangang River” .
Line 18: Do you mean clearest?
Response: Thank you. You are right. According the reviewer’s recommendation, we rewrote ABSTRACT.
Introduction
The manuscript can be improved by adding hypothesis of the study.
Response: According the reviewer’s recommendation, we added a new sentence on the purpose and process of the study
Materials and Methods
Line 61-63: Authors need to describe more details on water sampling here, such as water depth, protocol of water sampling they used, and how the sampling dates were selected relevant to rainfall and why a single survey was conducted etc. I can expect that daily variations are also high depending on rainfall.
Response: We acknowledge the reviewer’s comment. The procedures and methods of water sampling was inserted, although this study has been partly conducted under the National Biomonitoring Project of Rivers. The sampling dates has been selected based on the annual average of precipitation in Hantangang river basin from National Weather Center. The rainfall should be affected the daily variation of diatom community. However, we wanted to understand, in this study, the impacts of total annual precipitation before and after the Asia-Monsoon. Further study is that a short-term or spike of rainfall’s impacts on the river system in laboratory and field conditions. If possible, we will first conduct in a laboratory and move to the field condition.
Line 75-81: The sentences can be included in the section of results. Instead, description on rainfall for several days before the sampling dates is more useful here to interpret the data because the effect of rainfall can be maintained for a few days depending on the systems.
Response: We acknowledge the reviewer’s comment. So, we revised a sentence as “To compare the rainfalls between 1st and 2nd samplings or among survey years, we calculated the quantity of total precipitation using a data of rainfall measured by a weather center of South Korea (http://www.kma.go.kr/index.jsp). The 1st sampling’s rainfall or precipitation before Monsoon (PBM) means the sum of all precipitation during the cold and dry season from the late autumn to the late spring, while the 2nd rainfall or precipitation after Monsoon (PAM) is the sum of all precipitation during the warm season from late spring to the late autumn. In Hantan River Basin, average of rainfalls during the Monsoon period for 4 years was about 2.5 times higher than that of non-Monsoon periods”. Actually, the data of rainfall is not our measurement, just we used for the understand the rainfall’s pattern during the study period. Therefore, we removed the part on the analysis of t-test and its significance from the old version.
Line 81-84: I do not understand this sentence. Also why did you include 3 months rainfall?
Response: According the reviewer’s recommendation, we revised a sentence as above mentioned response in Line 75-81.
Line 121: (PCA) was used?
Response: According the reviewer’s recommendation, we revised the related sentence related with the reason why we adopted PCA and measurement process of CDI of each sites and group. Inserted sentence is follows;
2.4 Measurement of diatom community changes
As above mentioned in Introduction, we first introduced the numerical method to measure the shift of diatom community before and after monsoon rainfall. Briefly, as an ordination method for the understanding the characteristics of a biological community or ecosystem, many statistical methods such as Principal Component Analysis (PCA), Multidimensional Scaling (MDS), Principal Coordinatie Analysis (PCoA), Extended Correspondence Analysis (DCA), Correspondence Analysis (CA), and Redundancy Analysis (RDA), CCA (Canonical Correspondence Analysis) have been often adopted. Of these, PCA which uses the Euclidean distance method, is the most commonly used model, which minimizes data loss and is easy to visualize or presnet even with a small amount of principal component variables (Ko et al. 2015). In this study, due to the identification of the changes in biological communities, RDA, DCA, and CCA, which required separate environmental variables, were excluded, while the correction models such as MDS and PCoA were not included due to null data. This study did not include null data. In the previous test, we calculated the distance in the PCA dimension before and after monsoon rainfall showed higher eigenvalue (Eigenvalue, 22.498) and variance (11.193) than DCA and CA. These characteristics are also consistent with the study of Ko et al (2015), which conducted with data of spider harvested by Ter Braak (1986).
Biotic communities show a variety of different characteristics according to location and time. Therefore, this makes it difficult to determine the degree of the dynamic index in response to specific changes, such as rainfall. We therefore developed the community dynamic index of epilithic diatom (CDI) to accurately quantify the rainfall-driven changes in epilithic diatom communities. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. The input variables of PCA is two kinds of variables such as species appearance (number of species) and their biomass (often called an abundance) of epilithic diatom identified from each sampling site, which was expressed in PCA ordination. A principal component analysis (PCA) was to develop the CDI. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree, and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. Using this analysis, each site showing the appearance characteristics (species, density) of epilithic diatoms was expressed in ordination. Note that the distance is considered as a measure of shift in diatom community before and after monsoon rainfall over the text. Community dynamic index of epilithic diatom (CDI) was calculated by the following equation:
-----------------------------------------------------------(1)
d is the distance or dynamic index between two communities in PCA with different times at the specific site
before and after mon rainfall.
x1 and y1 is the first sampling in PCA dimension before monsoon rainfall
x2 and y2 is the second sampling in PCA dimension after monsoon rainfall
--------------------------------------------------------------------------(3)
CDI is the community dynamic index of epilithic diatom or the average of total distances between different times of groups or clusters before and after monsoon rainfall.
di is the distance between different times at the ith sampling site before and after monsoon rainfall.
n is the number of sampling sites or communities
Line 130: (n+1) => (x+1)?
Response: According the reviewer’s recommendation, we revised as “The abundance of epilithic diatom measured from each sites were converted to log10(x+1) to reduce the population variation”.
Line 137: Please check the precipitation.
Response: Thank you so much. We corrected the word.
Results
Line 152: Table 1 includes water quality data and then community characteristics. I recommend the explanation matching with the order in the table. Numbering of figures should be based on appearance in the text; Fig. 4 should be here instead of Fig. 5.
Response: According the reviewer’s recommendation, we rearranged the numbering of figures and tables.
We revised as “The community characteristics of the epilithic diatoms in this study are shown in Table 1 & 2 and Figs. 4 & 5”
Line 159: What is MS? Please check the number of cell counts (x106).
Response: According the reviewer’s recommendation, we revised as “In addition, the most abundant species in the Hantangang River were Nitzschia fonticola (before monsoon, BF: 8.3 cells/cm2, after monsoon, AF: 0.7x106 cells/cm2), Nitzschia palea (BF: 3.8 x106cells/cm2, AF: 4.9x106cells/cm2), and Achnanthes convergens (BF: 3.5 x106 cells/cm2, AF: 2.6 x106 cells/cm2) (Fig. 4)”.
Line 166: Do you mean Table 3 here?
Response: According the reviewer’s recommendation, we changed as Table 3.
Line 166-169: Their correlation with nutrients may be due to autocorrelation with water temperature.
Response: According the reviewer’s recommendation, we revised as a caption of Table 3, as “The correlation coefficients between the dominant diatom species (DS) and environmental variables before and after the monsoon in the Hantangang River from 2012 to 2015.”
Line 215: Figure 6? or 5? It is not easy to follow the text due to this kind of errors. Please check the typo also (“6shows”). The results of this study focus primarily on the spatial difference and I do not see the apparent or statistical results on the difference between pre-monsoon and post-monsoon.
Response: We acknowledge the reviewer’s comment. We revised a sentence as “3.3. Shift in of diatom communities before and after monsoon.
The variation of diatom community such as number and abundance of species, dominant index (DI), species diversity (H’), richness index (j) and evenness index (e) before and after monsoon rainfall obviously appeared throughout the study period (Fig. 5). The abundance of both G1 and G2 decreased after rainfall, whereas G3 showed no consistent trend. The richness index and number of species were highest in G2 in all investigations and consistently increased after rainfall. In contrast, G1 and G3 did not consistent. Indices of dominance and diversity in G2 and G3 indicated the obvious change of epilithic diatom community before and after monsoon rainfall, such as increase of species diversity, converse to dominant index. T-test results also supported the distinct changes of biological index as dominance and diversity after rainfall (P<0.01 for two, data not shown).
In PCA ordination, all diatom community clearly showed the obvious change before and after monsoon rainfall from 2012- 2015 without sampling sites (Fig. 6A). The eigenvalues of axis 1 and 2 were 14.1 and 8.4, respectively, and together they explain 11.2% of the total variance (significance level of p<0.001). In addition, the correlations between axis 1 and 2 with rainfall were -0.23 (p<0.01) and -0.32 (p<0.01). The positive and negative regions on axis 1 in the PCA ordination correspond to the before and after monsoon rainfall data, respectively. Meanwhile, the positive region on axis 2 is divided into the before rainfall G1 and G2 data and the after rainfall G2 and G3 data. The negative region on axis 2 is divided into the after rainfall G1 and before rainfall G2 data. These results of the PCA ordination therefore demonstrate clear differences between groups with different water quality and investigation.
The shift in diatom community or community dynamic index of epilithic diatom (CDI) of three groups before and after monsoon rainfall from 2012-2015 were calculated (Fig. 6B). The CDI in G2, the mid-polluted river, was the highest among three groups without the study period, indicating a relative higher fluctuation of diatom species, compare to the clean or polluted water. These trends did not consistent with water quality parameter. Previously, the G3, the polluted sites highly improved water quality after rainfall among sites. It may suggest that the effect of rainfalls on water quality and diatom community is slightly different. ANOVA results found that G2 showed the highest CDI throughout the investigation period. However, the group showed significant differences only in 2013 in response to the highest annual rainfall during the study period (p<0.001).
Line 221-231: The results are very nice and essential in this study. However, water temperature also appears important in controlling the diatom community based on the results in Tables 1 and 2. Authors need to validate the difference is mainly due to rainfall in their results.
Response: Thank you so much. We acknowledge the reviewer’s comment. Of course, temperature also is most important factors can control the diatom community. However, we did not fail to understand the role of temperature on diatom community during the monsoon, due to the reason why the relationship between rainfall and temperature is not obvious. In my opinion, the impacts of rainfall on water temperature is not large, rather the increased turbidity via a heavy rainfall often influenced the diatom community.
- Discussion
Line 292-294: The last sentence does not help in highlighting this study although the study includes valuable data. I recommend rewriting this sentence.
Response: Thank you so much. According the reviewer’s recommendation, we rewrite a last sentence.
- Conclusion
Line 303-305: I recommend rewriting this.
Response: Thank you very much. According the reviewer’s recommendation, we rewrote a conclusion as” An intense rainfall has been concentrated mainly in the Asia-Monsoon period in Korea peninsula. We examined the influence of rainfall before and after Monsoon rainfall on epilithic diatom communities and water quality parameters at the Hantangang River, South Korea from 2012–2015. Water quality in the polluted sites had improved following rainfall, but the abundance of dominant species was varied with water quality; Nitzschia fonticola decreased in all sampling sites, and Nitzschia palea in the clean sites and Achnanthidium minutissima in the polluted sites increased after rainfall, respectively. CDI results using a PCA ordination, indicate that the shift of diatom community in the mid-polluted sites in 2013—the year of highest rainfall, was the most obvious among groups. These results collectively indicate that the Monsoon rainfall strongly influenced water quality and diatom community, but our findings are limited to the water system of the small stream. Therefore, more study need to generalize the effects of Monsoon rainfall on water quality and epilithic diatom communities, considering many rivers with different water qualities, and rainfalls with different magnitudes and exposure times of precipitation.”
Figures
Figure 1. I recommend changing the color of station symbols in accordance to G1, G2, and G3 in Figs. 5 & 6.
Response: Thank you so much. According the reviewer’s recommendation, we redraw the figures with changed color and symbols.
Figure 5. Authors need to describe what Di, H’, j and e represent.
Response: Thank you so much. According the reviewer’s recommendation, we added a full name of DI, H’, J and E index.
Reviewer 4 Report
Review on: The Effect of Monsoon Rainfall Patterns on Benthic Diatom Communities in the Hantangang River, Korea
First of all, I'd like to highlight that the article is well written in a very consistent way. The methods and statistical analyses are adequate to answer the scientific questions raised by the study.
I have only minor comments to improve the manuscript.
L91. Figure 2. -There is no explanation on the inner table, this should be excluded from the figure and could be included as a separate table.
L104 -In "Analysis of epilithic diatoms" Indicate the valve number counted.
L 119 "A principal component analysis (PCA) was to develop the DIDC" - This is not clear why to calculate PCa first if only a distance needed several indices could be used as Jaccard, Euclidean Bray Curtis etc. The authors should describe why to choose PCA. After the making of PCA, I assume that the 1st and 2nnd Axis values were used to calculate the distance of each site in pre and postmonsun period but this should be clearly written here.
L131 cluster analysis (CA) indicate the grouping algorithm (Ward, UPGMA?)
L 136 "the Pearson's correlation analysis" here again identify which parameter of epilithic diatoms were used in the calculation (dominant diatom species abundance?)
L 155 Check current scientific names ex. Achnanthidium minutissimum (Kützing) is the valid name of Achnanthes minutissima.
L190 What was used for dominant diatom species abundance or relative abundance?
Author Response
#4
First of all, I'd like to highlight that the article is well written in a very consistent way. The methods and statistical analyses are adequate to answer the scientific questions raised by the study.
I have only minor comments to improve the manuscript.
L91. Figure 2. -There is no explanation on the inner table, this should be excluded from the figure and could be included as a separate table.
Response: According to the reviewer’s recommendation, we added the caption of the table in figure 2, as follows; A small table in the figure showed the total precipitation for the periods of before (PBM) and after monsoon (PAM); PBM in 2012 indicate the sum of daily precipitation from 10 September to 3 May, while PAM or the latter is those from 4 May to 6 September of 2012, respectively.”
L104 -In "Analysis of epilithic diatoms" Indicate the valve number counted.
Response: According to the reviewer’s recommendation, we revised as “The total abundance of epilithic diatoms (cell/cm2) at each study site was quantified using an inverted microscope (Nikon E600, Tokyo, Japan), and their relative abundance (%) of each species appeared was calculated during the identification process. To calculate the real density or abundance of diatom (cells/cm2), the total abundance of diatom species in each investigation site and the relative abundance of each species were multiplied. Based on the number and total abundance of appeared species in each sampling site, we defined the most abundant species, and calculated dominance [29], diversity [30], richness [31], and evenness [32] of the epilithic diatom community”.
L 119 "A principal component analysis (PCA) was to develop the DIDC" - This is not clear why to calculate PCa first if only a distance needed several indices could be used as Jaccard, Euclidean Bray Curtis etc. The authors should describe why to choose PCA. After the making of PCA, I assume that the 1st and 2nnd Axis values were used to calculate the distance of each site in pre and postmonsun period but this should be clearly written here.
Response: According to the reviewer’s recommendation, we revised as follows;
2.4 Measurement of diatom community changes
As above mentioned in Introduction, we first introduced the numerical method to measure the shift of diatom community before and after monsoon rainfall. Briefly, as an ordination method for the understanding the characteristics of a biological community or ecosystem, many statistical methods such as Principal Component Analysis (PCA), Multidimensional Scaling (MDS), Principal Coordinatie Analysis (PCoA), Extended Correspondence Analysis (DCA), Correspondence Analysis (CA), and Redundancy Analysis (RDA), CCA (Canonical Correspondence Analysis) have been often adopted. Of these, PCA which uses the Euclidean distance method, is the most commonly used model, which minimizes data loss and is easy to visualize or presnet even with a small amount of principal component variables (Ko et al. 2015). In this study, due to the identification of the changes in biological communities, RDA, DCA, and CCA, which required separate environmental variables, were excluded, while the correction models such as MDS and PCoA were not included due to null data. This study did not include null data. In the previous test, we calculated the distance in the PCA dimension before and after monsoon rainfall showed higher eigenvalue (Eigenvalue, 22.498) and variance (11.193) than DCA and CA. These characteristics are also consistent with the study of Ko et al (2015), which conducted with data of spider harvested by Ter Braak (1986).
Biotic communities show a variety of different characteristics according to location and time. Therefore, this makes it difficult to determine the degree of the dynamic index in response to specific changes, such as rainfall. We therefore developed the community dynamic index of epilithic diatom (CDI) to accurately quantify the rainfall-driven changes in epilithic diatom communities. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. The input variables of PCA is two kinds of variables such as species appearance (number of species) and their biomass (often called an abundance) of epilithic diatom identified from each sampling site, which was expressed in PCA ordination. A principal component analysis (PCA) was to develop the CDI. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree, and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. Using this analysis, each site showing the appearance characteristics (species, density) of epilithic diatoms was expressed in ordination. Note that the distance is considered as a measure of shift in diatom community before and after monsoon rainfall over the text. Community dynamic index of epilithic diatom (CDI) was calculated by the following equation:
-----------------------------------------------------------(1)
d is the distance or dynamic index between two communities in PCA with different times at the specific site
before and after mon rainfall.
x1 and y1 is the first sampling in PCA dimension before monsoon rainfall
x2 and y2 is the second sampling in PCA dimension after monsoon rainfall
--------------------------------------------------------------------------(3)
CDI is the community dynamic index of epilithic diatom or the average of total distances between different times of groups or clusters before and after monsoon rainfall.
di is the distance between different times at the ith sampling site before and after monsoon rainfall.
n is the number of sampling sites or communities
L131 cluster analysis (CA) indicate the grouping algorithm (Ward, UPGMA?)
Response: According to the reviewer’s recommendation, we revised as follows;
The abundance of epilithic diatom measured from each sites were converted to log10(x+1) to reduce the population variation. As a first step, to understand the characteristics of epilithic diatoms, we performed a cluster analysis (Ward’s methods) based on the number and abundance of species of epilithic diatoms identified from each site. We also conducted an Analysis of Variance (ANOVA) to compare the differences in biological characteristics (number and abundance of appeared species), community indices (dominant species and index, diversity, eveness and richness), and water quality between each group. In addition, we applied the Pearson's correlation analysis to determine the associations between epilithic diatoms, water quality, and the precipitation during monsoon. In a second step, we performed a principal component analysis (PCA) to calculate the community dynamic index (CDA), the distance between two communities before and after monsoon rainfall. Meanwhile, for the generalization and validation of the CDI to other organisms or communities, we examined the relationship between CDI and the above community indices using a correlation coefficient analysis. The statistical analyses were performed using PC-ORD (ver. 4.25. MjM Software, Gleneden Beach, OR, USA) and SPSS software (ver. 23. SPSS Inc. Korea).
L 136 "the Pearson's correlation analysis" here again identify which parameter of epilithic diatoms were used in the calculation (dominant diatom species abundance?)
Response: According to the reviewer’s recommendation, we revised as above L13.
L 155 Check current scientific names ex. Achnanthidium minutissimum (Kützing) is the valid name of Achnanthes minutissima.
Response: According to the reviewer’s recommendation, we changed as Achnanthidium minutissimum over the text.
L190 What was used for dominant diatom species abundance or relative abundance?
Response: Thank you so much. We acknowledge the reviewer’s comment. We defined a dominant species that having a high relative abundance at the specific sampling site, while major dominant species is above 2% of total abundance at each community in Figure 4. In a community, we can measure the dominant index (DI), is that the relative abundance (%) of first and second dominant species, DI= (sum of 1st DS+ 2nd DS)*100/2
Reviewer 5 Report
The authors present an interesting work. They use extensive data collected in the field and perform adequate statistics to support their arguments. The manuscript is well written with good structure.
There are a few errors in the text that require a minor language revision. The presentation of the results and the figures are of high quality and add value to the overall quality of the paper.
I recommend to accept the submitted article for publication after a minor revision that considers for a careful check for small language errors and a few comments below.
L12-14: In my opinion this part needs editing. In addition I think is more correct to say that that quantified or investigated the distribution of diatom communities and not measured.
L46: Here you mean that the studies on diatoms are limited but you actually state that effects are limited. You should rephrase.
L121: Here, a verb is missing. Possibly a PCA “was used”?
L141: You mean 201 total different taxa? Using groups here may confuse the readers with the cluster groups discriminated with the statistical analysis
L240: There are environmental characteristics of the water and I would avoid using the term pollution indices. You could just state that water characteristics showed higher values that may indicate signs of pollution.
Author Response
The authors present an interesting work. They use extensive data collected in the field and perform adequate statistics to support their arguments. The manuscript is well written with good structure. There are a few errors in the text that require a minor language revision. The presentation of the results and the figures are of high quality and add value to the overall quality of the paper. I recommend to accept the submitted article for publication after a minor revision that considers for a careful check for small language errors and a few comments below.
L12-14: In my opinion this part needs editing. In addition, I think is more correct to say that that quantified or investigated the distribution of diatom communities and not measured.
Response: Thank you very much. According to the reviewer’s recommendation, we changed as “investigated” instead of “measured”.
L46: Here you mean that the studies on diatoms are limited but you actually state that effects are limited. You should rephrase.
Response: According to the reviewer’s recommendation, we changed as “the study on the effects of rainfall on epilithic diatom communities are currently limited”.
L121: Here, a verb is missing. Possibly a PCA “was used”?
Response: Thank you so much. We acknowledge the reviewer’s comment.
2.4 Measurement of diatom community changes
As above mentioned in Introduction, we first introduced the numerical method to measure the shift of diatom community before and after monsoon rainfall. Briefly, as an ordination method for the understanding the characteristics of a biological community or ecosystem, many statistical methods such as Principal Component Analysis (PCA), Multidimensional Scaling (MDS), Principal Coordinatie Analysis (PCoA), Extended Correspondence Analysis (DCA), Correspondence Analysis (CA), and Redundancy Analysis (RDA), CCA (Canonical Correspondence Analysis) have been often adopted. Of these, PCA which uses the Euclidean distance method, is the most commonly used model, which minimizes data loss and is easy to visualize or presnet even with a small amount of principal component variables (Ko et al. 2015). In this study, due to the identification of the changes in biological communities, RDA, DCA, and CCA, which required separate environmental variables, were excluded, while the correction models such as MDS and PCoA were not included due to null data. This study did not include null data. In the previous test, we calculated the distance in the PCA dimension before and after monsoon rainfall showed higher eigenvalue (Eigenvalue, 22.498) and variance (11.193) than DCA and CA. These characteristics are also consistent with the study of Ko et al (2015), which conducted with data of spider harvested by Ter Braak (1986).
Biotic communities show a variety of different characteristics according to location and time. Therefore, this makes it difficult to determine the degree of the dynamic index in response to specific changes, such as rainfall. We therefore developed the community dynamic index of epilithic diatom (CDI) to accurately quantify the rainfall-driven changes in epilithic diatom communities. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. The input variables of PCA is two kinds of variables such as species appearance (number of species) and their biomass (often called an abundance) of epilithic diatom identified from each sampling site, which was expressed in PCA ordination. A principal component analysis (PCA) was to develop the CDI. The PCA finds the orthogonal axis while maintaining the variance of data to a maximum degree, and converts the variables in the higher-dimensional space into a lower-dimensional space with no linear correlation. Using this analysis, each site showing the appearance characteristics (species, density) of epilithic diatoms was expressed in ordination. Note that the distance is considered as a measure of shift in diatom community before and after monsoon rainfall over the text. Community dynamic index of epilithic diatom (CDI) was calculated by the following equation:
-----------------------------------------------------------(1)
d is the distance or dynamic index between two communities in PCA with different times at the specific site
before and after mon rainfall.
x1 and y1 is the first sampling in PCA dimension before monsoon rainfall
x2 and y2 is the second sampling in PCA dimension after monsoon rainfall
--------------------------------------------------------------------------(3)
CDI is the community dynamic index of epilithic diatom or the average of total distances between different times of groups or clusters before and after monsoon rainfall.
di is the distance between different times at the ith sampling site before and after monsoon rainfall.
n is the number of sampling sites or communities
L141: You mean 201 total different taxa? Using groups here may confuse the readers with the cluster groups discriminated with the statistical analysis
Response: According to the reviewer’s recommendation, we changed as “201 different taxa..” instead of “ 201 taxonomic groups”.
L240: There are environmental characteristics of the water and I would avoid using the term pollution indices. You could just state that water characteristics showed higher values that may indicate signs of pollution.
Response: Thank you very much. According to the reviewer’s recommendation, we changed as “water quality parameters”, instead of pollution indices.
Round 2
Reviewer 1 Report
The manuscript needs to be revised by a native English speaker. There are several sentences in which the grammar needs improving (starting with the first one on line 12, abstract) and is not correct.
L12-13 – The reason why several rivers and lakes in Korea have been disturbed is not surely due to the intense rainfall, a natural pattern. Perhaps you want to consider human disturbance such as damming, channelization, pollution,..
L30 – Provide full name for acronyms upon first citation.
L71-75- Please avoid writing on a personal form (avoid using “we”).
L72- Why are these references with no year? 20XX ???
L188 – Remove “above”.
L191-193- Provide adequate references.
L198-199 – Null data? What do you mean? With no precipitation?
L203 – Provide references.
L210 – Could you provide a reference for this index (CDI)? Same on line 221.
L211 - “may be a useful tool”. Is it or not? If you are not sure, should not use it at all.
L345 – Replace “Small” by “Superscripts”.
L350 – Suggest replacing 1st and 2nd by (BF) and (AF), while removing L351.
L412 – “without sampling sites”?
L464-467 – This comment should be moved to the Discussion.
L559 – I think this first sentence of the Conclusion should be removed. After all, intense rainfall during monsoon, is a perfectly common situation (no novelty at all).
Author Response
The manuscript needs to be revised by a native English speaker. There are several sentences in which the grammar needs improving (starting with the first one on line 12, abstract) and is not correct.
Response: Again thank you very much for lots of your valuable comments. According to the reviewer’s recommendation, we sent the manuscript for the English editing.
L12-13 – The reason why several rivers and lakes in Korea have been disturbed is not surely due to the intense rainfall, a natural pattern. Perhaps you want to consider human disturbance such as damming, channelization, pollution,..
Response: According to the reviewer’s recommendation, we rewrote as “Most of Korea's rivers and lakes are subject to physico-chemical disturbances such as increased quantity or flow rates and influx of nitrogen and phosphorus, due to intense rainfall concentrated in the Asian monsoon season”
L30 – Provide full name for acronyms upon first citation.
Response: According to the reviewer’s recommendation, we revised as “nitrogen-phosphorus (N-P)”
L71-75- Please avoid writing on a personal form (avoid using “we”).
Response: According to the reviewer’s recommendation, we changed as a passive form.
L72- Why are these references with no year? 20XX ???
Response: According to the reviewer’s recommendation, we inserted two references 21-22.
L188 – Remove “above”.
Response: According to the reviewer’s recommendation, we removed “above”.
L191-193- Provide adequate references.
Response: According to the reviewer’s recommendation, we inserted the references relating with models.
L198-199 – Null data? What do you mean? With no precipitation?
Response: According to the reviewer’s recommendation, we revised as “ …… not include null data that not measured “
L203 – Provide references.
Response: According to the reviewer’s recommendation, we inserted the references, and revised the sentence as “Biotic communities show different characteristics according to abiotic parameters such as rainfall; these characteristics can also significantly change with time (below). This makes it difficult to determine the degree of the numerical values in response to specific changes, such as a precipitation gradient”.
Hallett, L.M.; Hsu, J.S.; Cleland, E.E.; Collins, S.L. et al. Biotic mechanisms of community stability shift along a precipitation gradient. Ecology 2014, 95, 1693– 1700.
L210 – Could you provide a reference for this index (CDI)? Same on line 221.
Response: We acknowledge the reviewer’s comment. As you know, until now, the shift of diatom community has been not reported using an ordination or distance method. We tried to pre-test the change of diatom community in the x-y dimension (PCA, CCA, RCA etc.). This is the first introduction of ordination method to compare the numerical changes of diatom community before and after events (i.e. rainfall) to other sampling sites varying water quality. In this study, we temporarily present about the applicable potential of an ordination method having visual performance to the field of quantitative ecology.
L211 - “may be a useful tool”. Is it or not? If you are not sure, should not use it at all.
Response: According to the reviewer’s recommendation, we removed “may be a useful tool”.
L345 – Replace “Small” by “Superscripts”.
Response: According to the reviewer’s recommendation, we replaced “Small” by “Superscripts”.
L350 – Suggest replacing 1st and 2nd by (BF) and (AF), while removing L351.
Response: According to the reviewer’s recommendation, we revised as “The arrows are the sampling dates before (red color) and after the monsoon (blue color), respectively”.
L412 – “without sampling sites”?
Response: According to the reviewer’s recommendation, we revised as “regardless of sampling sites”
L464-467 – This comment should be moved to the Discussion.
Response: According to the reviewer’s recommendation, we revised and moved to the last part of Discussion, as “However, the community change of epilithic diatoms did not consistent with water quality parameter before and after monsoon rainfall. Previously, the polluted sites highly improved water quality after rainfall among sites, while the biotic community or CDI of the mid-polluted water heavily changed. It may suggest that the effect of rainfalls on water quality and diatom community is slightly different, thus, it is necessary to study the relationship between diatom community and water quality in more diverse conditions”.
L559 – I think this first sentence of the Conclusion should be removed. After all, intense rainfall during monsoon, is a perfectly common situation (no novelty at all).
Response: According to the reviewer’s recommendation, we removed “Intense rainfall is concentrated mainly in the Asia-monsoon period in the Korean peninsula.”.
Reviewer 3 Report
I appreciate the authors' attention to my comments in their revision of the manuscript. I suppose that the manuscript is acceptable to water after English editing.
Author Response
I appreciate the authors' attention to my comments in their revision of the manuscript. I suppose that the manuscript is acceptable to water after English editing.
Response: According to the reviewer’s recommendation, we sent the manuscript for the English editing. Again thank you very much for your valuable comments
