Vegetation Determines Lake Sediment Carbon Accumulation during Holocene in the Forest–Steppe Ecotone in Northern China
and Hailong Wang 4,5Round 1
Reviewer 1 Report
The study is well designed, well reported, and interesting from many perspectives.
This reviewer has some remarks the Authors might consider.
Not all abbreviations have been defined; this reviewer has been unable to find out the meaning of GPP.
A broader review of watershead sedimentation studies might be in place.
The text on lines 103-105 and 200-201 is not easy to understand.
The integer multiplier in Eq. (2) is probably incorrect.
There is a sharp decline in CAR in the vicinity of 2300 BP. Why is that? This observation should be mentioned around line 198.
Figure 3 caption (N) -> (TN).
There is a significant increment in CAR from 6000 BP to 5000 BP. Why is that?
Human activity increases CAR in lake sediments. Is the net effect of this human activity positive or negative? Maybe more carbon is immobilized than sequestered?
Author Response
Point 1: The study is well designed, well reported, and interesting from many perspectives.
Response: Thanks for your positive comments.
Point 2: This reviewer has some remarks the Authors might consider.
Response: We have carefully revised our manuscript accordingly.
Point 3: Not all abbreviations have been defined; this reviewer has been unable to find out the meaning of GPP.
Response: Thank you. We have added the definition for GPP in Line 28 and 270.
Point 4: A broader review of watershed sedimentation studies might be in place.
Response: Thank you. We have added more review in the discussion. For example, “The lakes in China showed high carbon sequestration potential (1.98 Tg OC yr-1) [10]” (Line 45-46) and “Especially during the mid-Holocene and late Holocene, the carbon storage was relatively high [12, 13] because of the changes of CARs and lake sizes.” (Line 47-49)
Point 5: The text on lines 103-105 and 200-201 is not easy to understand.
Response: We have revised these two sentences. “As the measured age of the 0 cm for the core was 1511 cal yr BP (before 1950), we suggested 1573 years as a possible reservoir effect (sum of 1511 years and the difference between 2012 and 1950) assuming that the lake surface was the drilling age (2012 A.D.).” (Line 108-111); “During the period from 2100 cal yr BP to present, the TIC, TOC and TN contents decreased compared with those of the previous period, but these drops were smaller compared with SAR and CAR, which showed a sharp decline. After 400 cal yr BP, the CAR increased a little due to the increase of TOC.” (Line 207-210)
Point 6: The integer multiplier in Eq. (2) is probably incorrect.
Response: We have examined this equation and added the units of these variables.
Point 7: There is a sharp decline in CAR in the vicinity of 2300 BP. Why is that? This observation should be mentioned around line 198.
Response: Thank you. We have added this result description in the Line 207. “During the period from 2100 cal yr BP to present, the TIC, TOC and TN contents decreased compared with those of the previous period, but these drops were smaller compared with SAR and CAR, which showed a sharp decline. After 400 cal yr BP, the CAR increased a little due to the increase of TOC.”; “The sharp decline of CAR since about 2100 cal yr BP was also consistent with the decreased broadleaved tee ratio and vegetation coverage (Figure 6).” (Line 284-285)
Point 8: Figure 3 caption (N) -> (TN).
Response: We have modified this to TN.
Point 9: There is a significant increment in CAR from 6000 BP to 5000 BP. Why is that?
Response: We thought this mainly because of the vegetation change and soil erosion (Figure 6). After 6000 cal yr BP, the trees ratios increased significantly. At the same time, the grain size increased, which indicated the enhanced soil erosion. We also added this in the manuscript: “The significant increment in CAR from about 6000 to 5000 cal yr BP was consistent with the increased arboreal ratios and grain size (Figure 6).” (Line 267-268)
Point 10: Human activity increases CAR in lake sediments. Is the net effect of this human activity positive or negative? Maybe more carbon is immobilized than sequestered?
Response: The human activities had positive effects on CAR based on our data and the previous studies. We have added this in the manuscript: “In this study, the human activities show closely positive relationships with CAR in our study by Pearson’s correlation (Table 2), demonstrating that human activities have positive effects on CAR in lake sediments.” (Line 320-322)
Author Response File: 
Author Response.docx
Reviewer 2 Report
The subject of this paper is interesting and fulfils the scope of Forests.
This manuscript is overally properly organized, however some information needs to be completed or changed.
The references are mostly relevant and cover mainly the last 10 years.
The authors present clear objectives and the conclusions well correspond with them.
Specific comments:
- Please strictly describe how the total organic carbon, total nitrogen and dry bulk density were determined.
- In my opinion the presentation all: the Table 2, Figure 4 and Figure 5 is unnecessary. Based on the its data, we receive similar conclusions.
Author Response
Response to Reviewer 2 Comments
Point 1: The subject of this paper is interesting and fulfils the scope of Forests.
This manuscript is overall properly organized; however, some information needs to be completed or changed.
The references are mostly relevant and cover mainly the last 10 years.
The authors present clear objectives and the conclusions well correspond with them.
Response: Thanks for your positive and constructive comments. We have carefully revised our manuscript accordingly.
Point 2: Specific comments:
Please strictly describe how the total organic carbon, total nitrogen and dry bulk density were determined.
Response: Thank you for your suggestions. We have added the detailed method description in the Part 2.2.3. “Total carbon (TC) and total nitrogen (TN) were measured using an Elementar Vario EL (Elementar Analysensysteme GmbH, Hanau, Germany).” (Line 122-123); “The TOC was calculated by subtracting TIC from TC.” (Line 120-121); “The dry bulk density (DBD) was calculated with TOC based on the following formula (eq. 3, 4).” (Line 130-131)
Point 3: In my opinion the presentation all: the Table 2, Figure 4 and Figure 5 is unnecessary. Based on the its data, we receive similar conclusions.
Response: Thank you for your comment. The Table 2 showed the result of Pearson’s correlation, while Figure 5 was based on the result of RDA (redundancy analysis) and HP (hierarchical variation partitioning). At the same time, we tried to show the trends of these variables to make a visual comparison in Figure 4. Although these all tried to illustrate the changes of CAR and the main influencing factors, these were based on different methods and support our results. Thus, we didn’t delete these in our revised manuscript.
Author Response File: Author Response.docx
