Grain Size and Pollen of Sediments in Wanghu Lake (Central China) Linked to Hydro-Environmental Changes
Round 1
Reviewer 1 Report
General comments
Dear Authors,
the manuscript (ms) is well-structured and provide information about pollen and the sediment grain size changes in Wanghu Lake in Central China. The aim was to “utilize a multiproxy approach to identify the historical hydrology of Wanghu Lake and investigate the impacts of lake system conversion from an overflowing lake to a closed basin and of land cover changes on the physical properties of sediments based on determination of the pollen deposition sequence, grain size, and comparison with 90-year synchronous climate observation data”. In my opinion your ms did not achieve this goal for several reasons. First of all, your research do not include sedimentation rate what is a crucial variable when talking about the conversion of the lake system. The lack of the sedimentation rate implies problems with pollen data. In my opionion it would be much more accurate to present pollen data as a flux (including sedimentation rate) rather than percentage contribution. The sedimentation rate might have changed after the dam construction and thus, the pollen data should be presented in annual concentration. Second, there is a crucial information missing (see below). Third, you didn't present climatic data - there is only a precipitation graph. Last, your results interpretarion is rather vague and limits only to the local conditions. In that case, there is no sufficient knowledge extension.
The title should be changed. The presented research aims at the recounstruction of the hydro-environmental changes over the last 90 years, thus it cannot be considered as a modern processes.
“Grain size” therm maybe confusing when discussed next to pollen data. Please add info that you use grain size analysis applied on sediment.
I provided comments, questions and suggestions in all parts of the ms and hope that they will help Authors to improve the ms. Please note, that comments to Figures are described separately.
Abstract
Authors wrote: ‘”Grain size of lake sediments is often measured in paleolimnological studies, especially investigations of past paleoclimatic and paleohydrologic changes. The implications of such measures, however, remain unclear, since watershed hydrology and the related transfer of materials to the lake are affected by local climate variables, hydrological shifts, and vegetation cover variables”. It is unclear to me, why do Authors think that the implications of grain size measurements are unclear? There is a lot of literature on this topic (i.e. grain size analysis). Please explain.
Introdcution
The introduction part is well-structured and well-written. However, I recommend adding a few information to give readers, who are not familliar with the local history, background why the dam was built. It would be also beneficial to add info about the Yangtze River i.e. what kind of material does it carry, what amount etc.
Line 46: Change “earth surface processes” into “landscape processes”.
Line 65: What about the wind? I understand that the majority of pollen enters the depositional basin via water but I think wind is also important agent here.
Lines 64-72: The sentence is far too long. Please rephrase it.
Methods
Overall, this part is well-written but several info is missing here. Please add info about the meteorological station and how the precipitation data was collected. This part of methods is not even mentioned. I am also not sure what is the purpose of correlation pollen data with the grain size. They have different units. For more details, please see bellow.
Site description: add info about the geomorphological and geological settings of the study site. This kind of information is crucial when discussing the material delivery from the catchment. What is the depth of the lake?
Line 78: Add ”air” in “annual temperature”.
Line 89: Change the wording, please. It is impossible to take 4 cores in the same place. What is the water depth in the spot where cores were taken? What is their location (slope, littoral zone, deepest point)? Why WHD was chosen for futher analysis? The length was the only reason? Please add missing info.
Line 98: There is a double brakets at the end of the sentence.
Subchapter 2.4: Please add more info about 210Pb dating. According to my knowledge gamma measurements are usually not used for assesement of 210Pb in the sediments becasue of the detection limits of gamma spectrometers. Please explain. Also, please add information why CIC model was used.
Line 115: What about the depth of 0-1 cm?
Line 120: Please add info what was the purpose of using scalling.
Results:
This part is well-written but information is missing:
Line 168: Authors write that there is a decreasing trend in pollen data but Pinus contribution is increasing at the top of the sediment! As mentioned at the very beginning, the pollen data should be rather presented as a flux or in the age scale.
What kind of correlation was used?
Line 212: Please add the values of the correlation between precipitation and the grain size.
Precipitation data was not mentioned in this part at all! Please add this info.
Discussion
This part of the manuscript requires extensive work. The discussion should have a broader contex i.e. should be not limited only to the local changes. In this part Authors repeat the results instead discussiong them. As for the moment, the subchapters don’t sound convincing to me and do not bring any relevant or new knowledge. There is not much about the lake evolution itself. The human impact is only briefly mentioned. What are the other possible reasons of lake evolution? Can changes be related to the climatic shifts?
Line 218: Why authors write about 130 years? Where does it come form?
Line 220: What kind of evolution signals?
Line 222: What natural resources? Please specify.
Line 238: Add a space between 23 and cm (applies to next lines as well).
Line 238: Please change the wording “Sampling date” is unclear.
Line 246: It is unclear how the dam construction casued the decrease in the vegetation cover and its degradation. Please elaborate.
Line 257: Please change “organisms” into “plants”.
Line 264: Please change “lake” into “Lake”.
Figures:
Figure 1: What are specific colors and blue dots? Please add the legend.
Figure 4: How Authors will explain the change in the grain size? There is a clear upward increasing trend for the whole record.
Figures 5 and 6: Please add the letters on the pictures, i.e. a, b, c, and d.
Author Response
Dear reviewer,
We have studied the valuable comments from you, and tried our best to revise the manuscript. The point to point responds to your comments are listed as following:
Point 1: The manuscript (ms) is well-structured and provide information about pollen and the sediment grain size changes in Wanghu Lake in Central China. The aim was to “utilize a multiproxy approach to identify the historical hydrology of Wanghu Lake and investigate the impacts of lake system conversion from an overflowing lake to a closed basin and of land cover changes on the physical properties of sediments based on determination of the pollen deposition sequence, grain size, and comparison with 90-year synchronous climate observation data”. In my opinion your ms did not achieve this goal for several reasons. First of all, your research do not include sedimentation rate what is a crucial variable when talking about the conversion of the lake system. The lack of the sedimentation rate implies problems with pollen data. In my opionion it would be much more accurate to present pollen data as a flux (including sedimentation rate) rather than percentage contribution. The sedimentation rate might have changed after the dam construction and thus, the pollen data should be presented in annual concentration. Second, there is a crucial information missing (see below). Third, you didn't present climatic data - there is only a precipitation graph. Last, your results interpretarion is rather vague and limits only to the local conditions. In that case, there is no sufficient knowledge extension.
Response 1: Thank you for your careful work. According to your comment, we have added the pollen concentration and sedimentation rate in Figure 4. Crucial information has been added according to your comment and results interpretarion have been discussed in discussion section (see the revised manuscript).
Point 2: The title should be changed. The presented research aims at the recounstruction of the hydro-environmental changes over the last 90 years, thus it cannot be considered as a modern processes.
Response 2:We change the title to “Grain Size And Pollen Of Sediments In Wanghu Lake（Central China）Linked to Hydro-Environmental Changes”.
Point 3: “Grain size” therm maybe confusing when discussed next to pollen data. Please add info that you use grain size analysis applied on sediment.
Response 3: In our study, pollen data are used as the proxies for land cover changes in the lake catchment. We analyze the relationship between pollen and grain size to investigate how the land cover changes affected the grain size in the sediment. (see discussion section in the revised manuscript).
Point 4: Authors wrote: “Grain size of lake sediments is often measured in paleolimnological studies, especially investigations of past paleoclimatic and paleohydrologic changes. The implications of such measures, however, remain unclear, since watershed hydrology and the related transfer of materials to the lake are affected by local climate variables, hydrological shifts, and vegetation cover variables”. It is unclear to me, why do Authors think that the implications of grain size measurements are unclear? There is a lot of literature on this topic (i.e. grain size analysis). Please explain.
Response 4: Indeed, the grain size is among the most convenient proxy for reconstructing past hydrological and climate conditions. However, watershed hydrology and the related transfer of materials from terrestrial to aquatic systems are a function of several factors, including local climate variables, hydrological shifts, and vegetation cover variables. For example, the removal of vegetation can increase water and material transfer to a lake. Without the vegetation information, grain size alone, sometimes can not explain how the paleohydrologic changed.
Point 5: The introduction part is well-structured and well-written. However, I recommend adding a few information to give readers, who are not familliar with the local history, background why the dam was built. It would be also beneficial to add info about the Yangtze River i.e. what kind of material does it carry, what amount etc.
Response 5: Background why the dam was built and info about the Yangtze River have been added to the revised manuscript.
Point 6: Line 46: Change “earth surface processes” into “landscape processes”.
Response 6: We have Changed “earth surface processes” into “landscape processes” in the revised manuscript.
Point 7: Lines 64-72: The sentence is far too long. Please rephrase it.
Response 7: We have rephrased the sentence (see the revised manuscript).
Point 8: Site description: add info about the geomorphological and geological settings of the study site. This kind of information is crucial when discussing the material delivery from the catchment. What is the depth of the lake?
Response 8: The information about the geomorphological and geological settings of the study site has been added to the revised manuscript.
Point 9: Line 78: Add ”air” in “annual temperature”.
Response 9: We have Changed “annual temperature” into “annual air temperature” in the revised manuscript.
Point 10: Line 89: Change the wording, please. It is impossible to take 4 cores in the same place. What is the water depth in the spot where cores were taken? What is their location (slope, littoral zone, deepest point)? Why WHD was chosen for futher analysis? The length was the only reason? Please add missing info.
Response 10: We have changed the wording and added more information to the revised manuscript.
Point 11: Line 98: There is a double brakets at the end of the sentence.
Response 11: We have deleted one of them.
Point 12: Subchapter 2.4: Please add more info about 210Pb dating. According to my knowledge gamma measurements are usually not used for assesement of 210Pb in the sediments becasue of the detection limits of gamma spectrometers. Please explain. Also, please add information why CIC model was used.
Response 12: More information has been added about 210Pb dating (see the revised manuscript).
Point 13: Line 115: What about the depth of 0-1 cm?
We have changed “23-1 cm” to “23-0 cm” (see the revised manuscript).
Point 14: Line 120: Please add info what was the purpose of using scalling.
Response 14: The scalling is used to see how the grain size changed with rainfall clearly.
Point 15: This part is well-written but information is missing: Line 168: Authors write that there is a decreasing trend in pollen data but Pinus contribution is increasing at the top of the sediment! As mentioned at the very beginning, the pollen data should be rather presented as a flux or in the age scale. What kind of correlation was used?
Response 15: The flux (pollen concentration and sedimentation rate) have been added to Figure 4. The pollen concentration seems to related to the sedimentation rate. Percentage contribution of pollen with both pollen concentration and sedimentation rate can help to explain the results clearly (see discussion section in the revised manuscript).
Point 16: Line 212: Please add the values of the correlation between precipitation and the grain size. Precipitation data was not mentioned in this part at all! Please add this info.
Response 16: Because the sediment date is not annual, that means 1 cm sediment represents 2-3 years. So we just present the precipitation and grain size data to see the trend, and don’t analyze the correlation.
Point 17: This part of the manuscript requires extensive work. The discussion should have a broader contex i.e. should be not limited only to the local changes. In this part Authors repeat the results instead discussiong them. As for the moment, the subchapters don’t sound convincing to me and do not bring any relevant or new knowledge. There is not much about the lake evolution itself. The human impact is only briefly mentioned. What are the other possible reasons of lake evolution? Can changes be related to the climatic shifts?
Response 17: We have reorganized the discussion section (see discussion section in the revised manuscript).
Point 18: Line 218: Why authors write about 130 years? Where does it come form?
Response 18: We have changed it to 90 years.
Point 19: Line 220: What kind of evolution signals?
Response 19: The changes of grain size and pollen in the sediment (see discussion section in the revised manuscript).
Point 20 :Line 222: What natural resources? Please specify.
Response 20: Here, we mean natural forest. We have reorganized the discussion section (see discussion section in the revised manuscript).
Point 21 :Line 238: Add a space between 23 and cm (applies to next lines as well).
Response 21: We have changed it.
Point 22 :Line 238: Please change the wording “Sampling date” is unclear.
Response 22: We deleted it, because it has been mentioned in the results section. We have reorganized the discussion section (see discussion section in the revised manuscript).
Point 23 :Line 246: It is unclear how the dam construction casued the decrease in the vegetation cover and its degradation. Please elaborate.
Response 23: Dam construction didn’t cause the decrease in the vegetation cover and its degradation. The decrease in the vegetation cover and its degradation cause the increasing in grain size.
Point 24 :Line 257: Please change “organisms” into “plants”.
Response 24: We have changed it.
Point 25 : Line 264: Please change “lake” into “Lake”.
Response 25: We have changed it.
Point 26: Figure 1: What are specific colors and blue dots? Please add the legend.
Response 26: This is the country name. I seems not necessary. We delete the dots.
Point 27: Figure 4: How Authors will explain the change in the grain size? There is a clear upward increasing trend for the whole record.
Response 27: This may be related to the erosion, because the sediment rate seems to increase for the whole record. I do believe that this point could be discussed in the Discussion section.
Point 28: Figures 5 and 6: Please add the letters on the pictures, i.e. a, b, c, and d.
Response 28: a, b, c, and d is in the pictures at the left bottom of the pictures.
Reviewer 2 Report
The manuscript "Grain Size And Pollen Of Sediments In Wanghu Lake（Central 2 China）Linked to Modern Hydro-Environmental Changes" presents grain-size and pollen data obtained for a core drilled in Wanghu Lake deposits. The theme is appealing and the results seem to me reliable. In general, interpretations and main conclusions are supported by data, although the section “Discussion and Conclusions” has some repetitions that should be removed and phrases that are not clear.
My main problem with the manuscript concerns the dating approach. Besided the 137Cs and 210Pb data, it is necessary to explain well why an age of 1916 is proposed for the bottom of the core. In addition, note that the authors present only two ages and do interpretations based on the grain size along a core. If the particle size varies sedimentation rates should also change.
Other things that deserve attention are indicated in the annotated manuscript. Some are listed below:
194-196 and 204-205: Correlations can be significant, but they are weak. Given the very high scatter in the figure, please double-check the levels of significance. 209: Don't start a chapter with a figure. 2012-213 and a few more highlighted in annotated manuscript: Phrases unclear
Figures 5 and 6: a, b, c and d not shown in the figure. Indicate 1-23 and 24-50 depths to make reading easier
Taking into consideration these issues, I suggest something between major and minor revision. I hope that this review will help to improve the manuscript.
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer,
We have studied the valuable comments from you, and tried our best to revise the manuscript. The point to point responds to your comments are listed as following:
Point 1: The manuscript "Grain Size And Pollen Of Sediments In Wanghu Lake（Central 2 China）Linked to Modern Hydro-Environmental Changes" presents grain-size and pollen data obtained for a core drilled in Wanghu Lake deposits. The theme is appealing and the results seem to me reliable. In general, interpretations and main conclusions are supported by data, although the section “Discussion and Conclusions” has some repetitions that should be removed and phrases that are not clear.
Response 1: Thank you for your careful work. According to your comment, we have reorganized the discussion section (see discussion section in the revised manuscript).
Point 2: My main problem with the manuscript concerns the dating approach. Besided the 137Cs and 210Pb data, it is necessary to explain well why an age of 1916 is proposed for the bottom of the core. In addition, note that the authors present only two ages and do interpretations based on the grain size along a core. If the particle size varies sedimentation rates should also change. Other things that deserve attention are indicated in the annotated manuscript. Some are listed below:
Response 2: Indeed, the dating approach based on 137Cs and 210Pb data has its weakness. It can’t produce annual resolution date. However, it is the standard method to calculated the sediment date when lack of other information in centennial scale. We add more information about the dating approach in the “chronological framework” section (see discussion section in the revised manuscript).
Point 3:194-196 and 204-205: Correlations can be significant, but they are weak. Given the very high scatter in the figure, please double-check the levels of significance.
Response 3: We have check the level significance using R software.
Point 4:209: Don't start a chapter with a figure. 2012-213 and a few more highlighted in annotated manuscript: Phrases unclear
Response 4: We have changed according to your comment.
Point 5: Figures 5 and 6: a, b, c and d not shown in the figure. Indicate 1-23 and 24-50 depths to make reading easier
Response 5: We add a, b, c, and d at the left bottom of the pictures.
Round 2
Reviewer 1 Report
Dear Authors,
Thank you for incorporating my suggestions into your manuscript. However, there are still a few instances that have to be taken into consideration. Please find my comments below:
Line 561: Authors wrote about synchronous climate observation data but, in fact, they discuss only precipitation. Thus, I recommend changing wording into synchronous precipitation measurement (or observation).
Lines 576-582: The information is mixed. Please structure as follow first geology and later soil cover.
Lines 622-650: Add references.
No meteorological data in results ie. there is a correlation of participation with other proxy but it would be beneficial to add info about precipitation data itself.
Lines 701-707: This part is confusing because of an unclear structure (mixed info). Please rewrite the paragraph to make it easier to follow.
Line 800: Change „lakes” into „Lake”
Line 811: Sedimentation rate cannot be caused by rainfall. It can be affected or influenced by rain.
The hydrological aspect of the changes has to be more highlighted. The authors captured interesting shift in the hydrological regime in the lake, but I have the impression that this aspect is too vague.
There is a lack of conclusions. Please add the chapter with corresponding info.
I would recommend working on the graphical side of the ms. In the current form, the figures are a bit boring.
Author Response
Dear reviewer,
We have studied the valuable comments from you, and tried our best to revise the manuscript. The point to point responds to your comments are listed as following:
Point 1: Line 561: Authors wrote about synchronous climate observation data but, in fact, they discuss only precipitation. Thus, I recommend changing wording into synchronous precipitation measurement (or observation).
Response 1: Thank you for your careful work. According to your comment, we have changed wording into “synchronous precipitation measurement” (see the revised manuscript).
Point 2: Lines 576-582: The information is mixed. Please structure as follow first geology and later soil cover.
Response 2: We have reorganized Lines 576-582.
Point 3: Lines 622-650: Add references. No meteorological data in results ie. there is a correlation of participation with other proxy but it would be beneficial to add info about precipitation data itself.
Response 3: We have added references and precipitation data itself. (see the revised manuscript).
Point 4: Lines 701-707: This part is confusing because of an unclear structure (mixed info). Please rewrite the paragraph to make it easier to follow.
Response 4: We have reorganized Lines 701-707.
Point 5: Line 800: Change „lakes” into „Lake”
Response 5: We have Changed “lake” into “Lake” in the revised manuscript.
Point 6: Line 811: Sedimentation rate cannot be caused by rainfall. It can be affected or influenced by rain.
Response 6: We have Changed “rainfall” into “rain” in the revised manuscript.
Point 7: The hydrological aspect of the changes has to be more highlighted. The authors captured interesting shift in the hydrological regime in the lake, but I have the impression that this aspect is too vague.
There is a lack of conclusions. Please add the chapter with corresponding info.
I would recommend working on the graphical side of the ms. In the current form, the figures are a bit boring.
Response 7: We have reorganized the Discussion section, added conclusions and changed the figures which are not suitable (see the revised manuscript).
Reviewer 2 Report
I noticed an effort to change the part about the age model. But the problem that I raised earlier about the possibility of changes in sedimentation rates, calling into question the age of the core bottom remains. The discussion has been completely reshaped and it seems to me a lot better that way.
There are a number of suggestions I made previously, but they were ignored. I leave other suggestions that authors and editors can treat as they see fit.
Comments for author File: Comments.pdf
Author Response
Dear reviewer,
We have studied the valuable comments from you, and tried our best to revise the manuscript. The point to point responds to your comments are listed as following:
Point 1: I noticed an effort to change the part about the age model. But the problem that I raised earlier about the possibility of changes in sedimentation rates, calling into question the age of the core bottom remains. The discussion has been completely reshaped and it seems to me a lot better that way.
Response 1: Indeed, age below 42 cm of the core bottom can not calculated by the dating approach based on 137Cs and 210Pb data. Because the 210Pb activity of the core decline to 0 below 42 cm. Multiple 210Pb-based dating models and the piecewise linear function base on 137Cs time mark were tested to establish the chronological framework for the sediment in the core. Generally, the results of all the models agreed with 137Cs time mark. So the ages below 42 cm were extrapolated based on the CIC model. Considering this problem, we just present the precipitation and grain size data to see the trend before and after 1967 and don’t analyze the correlation year to year between them.
Point 2: There are a number of suggestions I made previously, but they were ignored. I leave other suggestions that authors and editors can treat as they see fit.
Response 2: We have changed the wording according your suggestions highlight in the ms. We make the letters in figure 7 and figure 8 easy to see.
Round 3
Reviewer 1 Report
Dear Authors,
thank you for implementing my comments and suggestions. I have nothing more to add.
Best wishes,
Reviewer
