Dear Referee #1,

Thank you very much for your time involved in reviewing the manuscript and your constructive suggestions. To facilitate this discussion, we first retype your comments in bold font and then present our responses to the comments. An annotated version of the revised manuscripts is attached.

This manuscript incorporated a riverine dissolved organic carbon transport scheme to the land surface model CLM5.0 to evaluate the impacts of anthropogenic water regulation on riverine DOC discharges and transport. The paper is well written, presenting an interesting work in a clear and organized way. I have a few minor comments below.

Response: We appreciate your very encouraging comments on the merits, and hope that the response has fully addressed all your concerns.

1. Equation (2): Please denote the unit of DOC leaching flux.

Response: We will add the unit of DOC leaching flux (g C m^–2 s^–1).

1. Line 176: “Riverine DOC is mainly derived from organic carbon leaching processes in soil”; some literature support is required here.

Response: We will add corresponding references as suggested.

1. Line 189-190: where is the reference for choosing this weighting coefficient?

Response: We chose this coefficient according to the previous studies (Liu et al., 2019; Zou et al., 2014), and we will add corresponding references at the same time.

1. Section 3.1: I suggest adding a table to show the main datasets used for model running and validation in this study.

Response: Thanks for your valuable suggestion. We will add a table to summarize the main datasets used in this study.

1. Line 221: Please introduce the details for the human water use activity dataset. A description of what data sources were used?

Response: Based on the comment, we will revise the manuscript. The human water use activity dataset was derived based on five datasets: the water use dataset from the Food and Agricultural Organization (FAO), a shape file data of national boundaries, the Global Map of Irrigation Areas, version 5 (GAMIP5; Siebert et al., 2013), the historical monthly soil moisture levels and saturated soil moisture levels(Zeng et al., 2017), and the FAO water information system for 2010, which contained the agricultural, industrial, and municipal water withdrawals.

1. Line 205: Only the fluxes into the soil carbon pool after surface water extraction are described. What about groundwater extraction?

Response: Because groundwater extraction usually occurs in situ and will pass through the filtering effect of the soil layer, we hypothesized the part of DOC that returned to soil with groundwater extraction was ignored in our parameterization scheme.

1. In Section 2.1, the parameters mentioned in the developed soil and river carbon dynamics parameterization scheme are uniform or spatially varying?

Response: The parameters mentioned in our developed schemes are uniform. In fact, it does not correspond to spatial heterogeneity, and we will further refine and modify the parameterization scheme in our future work. The current parameterization scheme has reasonable accuracy in the simulation results, so we believe that our model can be applied to global-scale riverine DOC transport simulation studies.

1. Line 252: Figures 3a and 3c seem to underestimate. Please check carefully and modify.

Response: Thank you so much for your careful check. We will modify it in our manuscript.

1. Line 273: Are constants (0.3 and 0.7) in equations the same for the whole world?

Response: Yes, we set the constant due to the limitation of data.

1. This study developed a model to describe the soil carbon leaching and riverine carbon transport processes, which are not well described in previous land surface models. But the discussion of current uncertainties and limitations in modeling is missing. It should be discussed more.

Response: Thank you for your advice. We will add some discussion of current uncertainties and limitations in our manuscript.

1. Line 354-355: The authors state that the three rivers were affected by minor groundwater regulation. Please briefly explain the impact and the reasons.

Response: In our selected rivers, only the Mississippi, Yangtze, and Ganges rivers were affected by minor groundwater regulation, which usually occurred during the dry period, where DOC export increased slightly in the Mississippi and Ganges rivers because of higher soil leaching due to irrigation, while DOC export decreased in the Yangtze River due to a significant reduction in river discharge. This also corresponds to the results in Section 4.3.

1. In section 5, some words about future work are needed.

Response: Thank you for your suggestion. We will add some discussion about future work in our manuscript.

Once again, thank you very much for your comments and suggestions.

Sincerely,

Yanbin You, Zhenghui Xie, Binghao Jia, et al.

Dear Referee #2,

Thank you very much for your helpful comments and suggestions to improve our manuscript. To facilitate this discussion, we first retype your comments in bold font and then present our responses to the comments. 

This study aims to assess the effects of anthropogenic regulation of waters on the global transport of DOC by rivers. Given the importance of DOC in the carbon cycle and the potential of human activities to alter its cycling, this is a very important aim. I find the paper generally interesting, but have a few concerns:

Response: We appreciate your clear and detailed feedback, and hope that the response has fully addressed all your concerns.

The presentation can be made clearer. The authors should make an effort to make it more accessible to non-modelers (like me), and to readers who want to take home the message without detailed reading of the methods. For example, the different simulations of control conditions and different parts of water regulation considered (CTL, EXPA, EXPB) are in several of the figures presented without explanation or spelling out.

Response: Thank you very much for your suggestion. We will modify the subtitle and legend of Fig. 4~12 to make it easier for the reader to understand.

Is there some way to add (or more carefully discuss) uncertainty ranges around the various estimates and graphs?  The current version presents and compares several numbers with 3-4 significant digits, with no confidence intervals.

Response: Based on your comment, we will add a standard deviation after the estimated value to indicate its uncertainty range (mean±std).

Table 2 could be expanded, it appears incomplete. There are several additional estimates of DOC export (possible resulting in a higher median than presented in the manuscript). Some (but not all) are cited in Drake et al. 2018 (Limnol Oceanogr Letters).

Response: Thanks for your detailed comment. We have read the article you mentioned and found that most of the carbon flux which export to the ocean is estimated to be 0.95 Pg C yr^-1, but it includes all forms of carbon in rivers. We set the organic carbon (OC) / inorganic carbon (IC) ratio to 0.4/0.5, in which 55% of OC flux is dissolved (DOC). Finally, we calculated that the riverine DOC export flux was 232.22 Tg C yr^-1. We will add this result to the table at the same time. Besides, we will also add another result from van Hoek et al. (2021, Environ. Sci. Technol.).

I do not understand how transformations in the regulated and unregulated waters are treated. The methods (line 196) say that “migration transformation” is ignored in the model, and loss rate is assumed equal in reservoirs and rivers. In contrast, one of the model results (line 287) is suggested to be due to increased residence time by the construction of reservoirs, causing increased DOC removal. How is this compatible?

Response: Thank you so much for your careful check. We will revise this sentence to “This may be related to the fact that the reservoir adjusting the river discharge and intercepting the riverine DOC.”

Line 292: “alpine” should be “arctic”

Response: We will revise it in our manuscript.

Thank you again for your detailed and precious comments on our manuscript.

Sincerely,

Yanbin You, Zhenghui Xie, Binghao Jia, et al.

Thanks for your comments. Please find our reply on the attached PDF.