the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Impacts of anthropogenic water regulation on global riverine dissolved organic carbon transport
Yanbin You
Binghao Jia
Yan Wang
Longhuan Wang
Ruichao Li
Heng Yan
Yuhang Tian
Si Chen
Abstract. Anthropogenic water regulation activities, including reservoir interception, surface water withdrawal, and groundwater extraction, alter riverine hydrologic processes and affect dissolved organic carbon (DOC) export from land to rivers and oceans. In this study, schemes describing soil DOC leaching, riverine DOC transport, and anthropogenic water regulation were developed and incorporated into the Community Land Model 5.0 (CLM 5.0) and the River Transport Model (RTM). Three simulations by the developed model were conducted on a global scale from 1981 to 2013 to investigate the impacts of anthropogenic water regulation on riverine DOC transport. The validation results showed that DOC exports simulated by the developed model were in good agreement with global river observations. The simulations showed that DOC transport in most rivers was mainly influenced by reservoir interception and surface water withdrawal, especially in central North America and eastern China. Four major rivers, including the Danube, Yangtze, Mississippi, and Ganges Rivers, have experienced reduced riverine DOC flows due to intense water management, with the largest effect occurring in winter and early spring. In the Danube and Yangtze River basins, the impact in 2013 was four to five times greater than in 1981, with a retention efficiency of over 50 %. The Ob River basin was almost unaffected. The total impact of anthropogenic water regulation reduced global annual riverine DOC exports to the ocean by approximately 13.36 Tg C yr−1, and this effect increased from 4.83 % to 6.20 % during 1981–2013, particularly in the Pacific and Atlantic Oceans.
Yanbin You et al.
Status: final response (author comments only)
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RC1: 'Comment on esd-2023-2', Anonymous Referee #1, 20 Mar 2023
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.
- Equation (2): Please denote the unit of DOC leaching flux.
- Line 176: “Riverine DOC is mainly derived from organic carbon leaching processes in soil”; some literature support is required here.
- Line 189-190: where is the reference for choosing this weighting coefficient?
- Section 3.1: I suggest adding a table to show the main datasets used for model running and validation in this study.
- Line 221: Please introduce the details for the human water use activity dataset. A description of what data sources were used?
- Line 205: Only the fluxes into the soil carbon pool after surface water extraction are described. What about groundwater extraction?
- In Section 2.1, the parameters mentioned in the developed soil and river carbon dynamics parameterization scheme are uniform or spatially varying?
- Line 252: Figures 3a and 3c seem to underestimate. Please check carefully and modify.
- Line 273: Are constants (0.3 and 0.7) in equations the same for the whole world?
- 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.
- Line 354-355: The authors state that the three rivers were affected by minor groundwater regulation. Please briefly explain the impact and the reasons.
- In section 5, some words about future work are needed.
Citation: https://doi.org/10.5194/esd-2023-2-RC1 -
AC1: 'Reply on RC1', Zhenghui Xie, 29 Mar 2023
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.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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RC2: 'Comment on esd-2023-2', Anonymous Referee #2, 20 Mar 2023
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:
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.
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.
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).
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?
Line 292: “alpine” should be “arctic”
Citation: https://doi.org/10.5194/esd-2023-2-RC2 -
AC2: 'Reply on RC2', Zhenghui Xie, 29 Mar 2023
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.
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AC2: 'Reply on RC2', Zhenghui Xie, 29 Mar 2023
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RC3: 'Comment on esd-2023-2', Anonymous Referee #3, 05 Apr 2023
This paper introduces a novel approach to study the effects of surface and subsurface water regulation on dissolved organic carbon (DOC) transport. The authors combine a DOC model with the CLM/MOSART model to simulate the DOC dynamics in both surface water and groundwater systems. This is an innovative contribution because most previous studies and models have neglected the role of water extraction in DOC dynamics and the interaction between DOC and groundwater. However, the paper needs to improve in several aspects before it can be accepted. First, the paper does not clearly quantify the relationship between DOC concentration and water flux in different processes. For instance, how much DOC is removed by surface water and groundwater extraction? Second, the paper does not present the model results in an effective way. Some maps have poorly designed color bars and do not show the spatial patterns clearly. Since the main focus of the paper is on DOC export, some results are not relevant and should be moved to the supplementary information.
Page 2
Line 30:
Rivers are a pipe linking the two major carbon pools of terrestrial and ocean ecosystems.
Maybe “aquatic ecosystems”? Since the river also connects to the lake, etc.
Line 31:
IPCC AR5, full name if it is the first-time usage
Line 34:
“This”, what this is referred to?
Line 35-37:
Higher than what? Consider breaking this long sentence to shorter ones.
Line 45
May define DOC leaching before use? Also, consider breaking this sentence into shorter ones.
Line 61:
There are at least some time series DOC measurements in some datasets, even if they are not long-term measurements.
Line 90:
Why not use the same resolution, such as 0.5 degrees, for land and river?
Line 103:
What do you mean by linear RTM? More details are needed.
Line 124:
What are upstream and downstream, can you link these processes in Figure 1 so readers can understand what Equation 1 is illustrating in Figure 1?
Line 132:
The unit of DOC is inconsistent from Line 127. Normally, DOC concentration is expressed as mg C / L. Based on Equation 3, [DOC] is unitless.
Again in Line 139, you used another unit for [DOC] as mg g soil-1.
Please unify the DOC units.
Since you mentioned both adsorption and desorption, you should describe both processes and their equations.
Line 153:
I assume that Equation (7) DOC_leached is the LDOC? If so, you can make them the same.
How about RDOC? How is it modeled?
Line 188:
How are these coefficients obtained? Please provide some details or references.
Besides, how sw and gw are linked to DOC? For example, if there is SW extraction, then shouldn’t it be included in Equation (8), such as a term to describe DOC extraction?
Line 214:
The land component is not 1 degree by 1 degree, so there is some inconsistency.
Line 220:
Is it ok to have spatial interplate dam/reservoir data? Maybe more details are needed to show how it was conducted.
Line 245:
Use scientific notation for large numbers.
Line 247:
Which was generally consistent? If they are consistent, then it should be “which is consistent”. There is no need to use the past sense.
There are a few hotspots in the high latitudes, where they are permafrost regions, why are DOC losses relatively higher there?
Line 252:
How about a time series evaluation? For example, the DOC concentration at a large river outlet?
Line 254:
What do you mean by overestimated or underestimated? Compared with what?
In Figure 3d, the color represents both magnitude and over/underestimate. This can be confusing. Since you have a color bar, readers will assume the color represents values based on the color bar.
Line 260:
This simulation is already a global-scale DOC export study.
Figure 4
The positive/negative of latent heat/sensible heat need to be checked. Also, the color bar should match the actual ranges.
I am not sure why a multi-year temperature average is needed. If surface water regulation has an impact, then maybe comparing the differences with or without regulation is more meaningful.
Soil moisture cannot be negative, so the color bar needs revision.
The same applies to runoff.
Figure 7, what is the reference of the change?
Citation: https://doi.org/10.5194/esd-2023-2-RC3 - AC3: 'Reply on RC3', Zhenghui Xie, 12 Apr 2023
Yanbin You et al.
Yanbin You et al.
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