Spatial-Temporal Changes of Carbon Source/Sink in Terrestrial Vegetation Ecosystem and Response to Meteorological Factors in Yangtze River Delta Region (China)

Round 1

Reviewer 1 Report

The manuscript dels with NEP and its spatial and temporal distribution in the Yangtze River Delta Region (China). However the authors try to relate it with carbon sink/source and trading market in China. There are no scientific references and profs or discussion how NEP could be seen in carbon sink/source balance modeling. It should be improved or the article should be simplified and analyze NEP distribution in the region. 

The quality of the figures, titles ad agendas should be improved.
Maybe temperature and precipitation also could be from remote sensing data. How NEP correlates with landscape types is not clear. How carbon trading market is related to natural environment?
The manuscript should be carefully revised by the authors. More details and comments in manuscript text.

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This study was designed to investigate the spatial and temporal variations of NEP in the Yangtze River Region over the past 20 years. The authors downloaded the MODIS NPP and estimated Rh using a simple regression model, then calculated the NEP. They showed a trend of NEP changes over the years and the spatial distribution of NEP.

This study has some merits as the Yangtze River delta is an important region in term of economic development and environments. The authors generated some useful results. However, I have some serious concerns with the current version of the manuscript. First, English and presentation should be significantly improved. It is unacceptable in the current version. There are many long run-on sentences that dramatically hinder readers’ understanding. Second, the logic in the material and methods section is not clear. The authors did not provide a general approach of the methods and I don’t know the purpose of some of the methods. Third, the discussion part needs to be improved. The authors provided the results, but there is a lack of explanation of the results. Based on the above reasons, I recommend Major revision.

Specific comments:

L14-18: This sentence is too long and is a run-on sentence. Please revise it.

L18: change Through to Using a

L18-23: This sentence is not clear. I’m not sure if NPP from MODIS is use, why CASA model is needed.

L22: interannual and spatial dynamics of NEP

L28, 31: change is to was: Please use past tense to describe the results from this study.

L34: delete were, delete respectively.

L44: State President? “Peak carbon dioxide emissions”: I don’t understand this part.

L58: change severe to major

L71-81: One sentence?

L83-84: I don’t see these as shortcomings.

L90-99: This sentence is very long and should be separated into several sentences.

L139-140: I don’t understand this sentence. Did the authors say that the NPP data were generated using the BIOME-BGC model?

L176-179: It is not clear why this equation 2 was used for soil heterotrophic respiration calculation. Under which condition was this equation developed? Did the authors verify the accuracy of this equation and whether this model can be applied to the study area?

L185-188: 11 years (2000-2010) or 20 years (2000-2019)?

L193-224: What’s the purpose of this NPP calculation? It is not clear here.  

L202: R or r is for annual precipitation?

L225, 2.4 Did I miss something here? I don’t understand the purpose of this subsection. Please describe why list this method here.

The authors mentioned CASA model but I did not see it in the method section.

Table 1: As there is no value for built-up lands (?) or unused lands, why considered it C source?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript deals with very important issue of carbon inland sink/source changes in recent world. The authors focus only on green and natural ecosystems, which provides only part of the source/sink information in Yangtze River Delta Region (China), which has highly urbanized and densely populated area. However, NEP (net ecosystem productivity of vegetation) provides full picture of current situation of productivity, as well as, changes during recent 20 years (from 200 to 2019).

The presented methodology is clear and concise. It could be used in different parts of the world for the same or different purposes. The authors combine remote sensing and in situ data. However, it could be more efficient to use only remote sensing data for all the parameters, it would provide the method to worldwide scale. The discussion about remote sensing and ground station data is still an open question. It could be nice to use not only meteorological data, but also NPP and NEP data from small experiments provided in different types of landscapes and parts of the Delta region. All the approximations for such a big area is not giving full answer about real state of carbon sink/source balance. Therefore, the most recent studies try to focus on local scale to understand the whole mechanism for bigger terrestrial parts. It is just a suggestion for further research in this field for authors.

It is obvious that inter-annual change of meteorological conditions impact NPP more that changes landscape types. From climatological perspective, year-by year fluctuations are not so important as mean values of the 20 years’ period. Therefore, for the healthy state of ecosystems, the landscape stability is crucial point.  However, the importance of increasing vegetation (woodlands and natural grasslands) percentage in Delta region should be more discussed facing climate change effects.

A couple of mistakes, which I noticed in manuscript (should be fixed before the publishing):

Line 478: “Rn is the annual net radiation (mm)“, Rn cannot be measured in mm, maybe  MJ m−2?

Line 977: the quality (contrast) of Figure 9, is low. There is no possibility to distinguish pixel colors. Maybe Fig.9 could be enlarged?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have made great effort and addressed my concerns in the revised manuscript. They also provided their detailed responses. I think the manuscript has been improved. But there are still a few minor issues in the abstract and introduction that need to be addressed.

L17: the length sequenced variation: I don’t understand this part.

L18: NEP of terrestrial ecosystems?

L17-21: I don’t understand this sentence. Please revise.

L21-22: This statement needs to be move to the end or deleted.

L39: their own changes?

L43: This is a lack of conclusion statement.

L106: future forms?

L126. Separate into another paragraph.

Usually in the last paragraph of Introduction, the authors briefly describe the goal and objectives of the study. I would like to see the specific objectives or hypotheses of this study here.

Author Response

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Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.