Dear Authors

I thank you for providing detailed responses to the comments and suggestions offered by two reviewers.

Both reviewers recognized the importance of your exploratory study in the Shaliu River on the Qinghai-Tibetan Plateau, an understudied region in the study of the global carbon cycle, and the novelty of your findings on the seasonal shift in the hydrologically driven export of soil organic carbon. However, the reviewers also raised several critical issues including articulating key messages and structuring the Results and Discussion sections. While your responses well addressed most reviewer comments, I add additional suggestions below to facilitate your revision. I envisage that the manuscript would require a substantial revision to address all raised issues and suggestions. Therefore, I have to recommend ‘reconsider after major revisions’ and might need to ask the reviewers to reevaluate the revised manuscript.

- Definition of headwater streams: Headwater streams have often been restricted to the first- to third-order streams in the literature. Please define your use of “headwater streams” and explain how you can consider the main stem and tributaries of the Shaliu River based on specific stream order information for the river system.
- Study objectives: It appears that you wanted to focus on the unique hydro-biogeochemistry of the Shaliu River as an “headwater” system. On the other hand, you gave less priority in linking your findings (and citing latest publications) to the growing interest in the carbon export from the permafrost of the Qinghai-Tibetan Plateau. Please articulate your primary objectives in the last paragraph of Introduction and the abstract (“To assess these aspects”?).
- The hydrology during the thawing period (snowmelts): As your new description of the thawing-induced hydrologic changes nicely explain (“Thawing frozen soils and deepening of active layers can strongly affect catchment hydrology, including creating vertical and lateral flow paths, increasing soil filtration, enhancing groundwater-surface water exchange and baseflow”), “lateral flow paths” would also bring substantial amounts of carbon from the surface soil horizons (this has been observed in many systems including even temperate systems). However, you tend to contrast (in a simplifying way) the dominance of deep paths during the thawing period and the surface flows during the monsoon storm events. I wondered if the rising water table during thawing or snowmelt events would not flush carbon from the surface horizons rich in carbon. Please provide some discussion of the relative importance of the lateral and vertical flow (or deep vs. shallow) paths during thawing or snowmelt events.
- L274-275 (response to the first reviewer comment): Can’t you find precipitation data at a nearby site, like in some weather stations near the Lake Tsinghai? You talked about the carbon export “peaking in the summer due to high discharge brought by the monsoon”, but it’s really challenging to follow up this without resorting to rainfall data.
- Geological information: Given the quantitative importance of DIC, it would help readers if you provide some information (and discussion) on the distribution of bedrocks in the basin.
- Details on sampling and analysis: Given the importance of carbon analysis in this study, you need to provide more details on sampling bottles (glass or plastic? Acid-washed?), SPE, TOC analyzer (high-temperature oxidation? Accuracy?), QC,,,

I would like to ask you to make all the changes easily identifiable in a marked-up manuscript based on your point-by-point responses to the comments offered by the reviewers and myself. Please also specify the line numbers of the marked-up manuscript in your responses to comments.

Sincerely,

Ji-Hyung Park
Associate Editor, Biogeosciences

Dear Authors,

I thank you for your comprehensive revision integrating all the comments and suggestions from the first review round.

A reviewer involved in the first review round has kindly provided another set of very considerate and constructive comments. This reviewer, like myself, thought that your careful revision would further improve the manuscript while reducing some lingering uncertainties that are detailed in the attached reviewer report. Regarding the issue of the term “headwater streams”, your perusal of the hydrology literature, in addition to the reviewer comment, would fix the nonsense in sentences like “The Shaliu River is composed of first- to third-order streams (Figure 1a) and hence a typical headwater stream”: in other words, a headwater stream consists of headwater streams.

As you did well during the first revision, please make all the changes easily identifiable in a marked-up manuscript and specify the line numbers of the marked-up manuscript in your responses to the reviewer comments:

Sincerely,

Ji-Hyung Park
Associate Editor, Biogeosciences

Dear Authors

I thank you for incorporating the very constructive reviewer comments in your second revision.

I am pleased to let you know that your manuscript can be published in Biogeosciences, after some technical corrections as follows:

- Consistent use of headwater streams and catchments: While you tried to limit the use of headwater streams to small-order streams that could not be identified easily on the coarse-resolution map in Fig. 1, there are still some confusing statements including,
- 1. Title: “an alpine headwater catchment” is Shaliu River, so the phase needs to be rewritten (like “an alpine catchment”) to avoid any confusion.
- 2. Abstract: “an alpine small stream (the Shaliu River capturing headwaters within its catchment)” can be changed to something like “the Shaliu River, an alpine small river receiving many headwater streams”
- 3. Main text (lines 71, 84, 91-92,,,): Please use the terms “river” and “headwater streams” consistently. For instance, the lines 91-92 can be rewritten (The Shaliu River is a small river integrating headwater streams of orders of 1−3). To reflect these changes, you may need to change the Fig. 1 legend that still allocates 1-3 orders to the entire reaches. Please refer again to the reviewer comment.

It has been a great pleasure for me to take part in the review process where you and the reviewers have done excellent jobs in improving the presentation and interpretation of invaluable data obtained from a hard-to-access alpine river system. In particular, I would like to express my sincere thanks to the anonymous reviewer who offered two detailed reports containing very constructive comments, which is rare in this age of “quick reviews”, and thereby warranting authors’ acknowledgement.

Sincerely,

Ji-Hyung Park
Associate Editor, Biogeosciences