The importance of hydrology in routing terrestrial carbon to the atmosphere via global streams and rivers
Edited by Jonathan Cole, Cary Institute of Ecosystem Studies, Avon, NC; received April 3, 2021; accepted January 12, 2022
Significance
Stream/river carbon dioxide (CO2) emission has significant spatial and seasonal variations critical for understanding its macroecosystem controls and plumbing of the terrestrial carbon budget. We relied on direct fluvial CO2 partial pressure measurements and seasonally varying gas transfer velocity and river network surface area estimates to resolve reach-level seasonal variations of the flux at the global scale. The percentage of terrestrial primary production (GPP) shunted into rivers that ultimately contributes to CO2 evasion increases with discharge across regions, due to a stronger response in fluvial CO2 evasion to discharge than GPP. This highlights the importance of hydrology, in particular water throughput, in terrestrial–fluvial carbon transfers and the need to account for this effect in plumbing the terrestrial carbon budget.
Abstract
The magnitude of stream and river carbon dioxide (CO2) emission is affected by seasonal changes in watershed biogeochemistry and hydrology. Global estimates of this flux are, however, uncertain, relying on calculated values for CO2 and lacking spatial accuracy or seasonal variations critical for understanding macroecosystem controls of the flux. Here, we compiled 5,910 direct measurements of fluvial CO2 partial pressure and modeled them against watershed properties to resolve reach-scale monthly variations of the flux. The direct measurements were then combined with seasonally resolved gas transfer velocity and river surface area estimates from a recent global hydrography dataset to constrain the flux at the monthly scale. Globally, fluvial CO2 emission varies between 112 and 209 Tg of carbon per month. The monthly flux varies much more in Arctic and northern temperate rivers than in tropical and southern temperate rivers (coefficient of variation: 46 to 95 vs. 6 to 12%). Annual fluvial CO2 emission to terrestrial gross primary production (GPP) ratio is highly variable across regions, ranging from negligible (<0.2%) to 18%. Nonlinear regressions suggest a saturating increase in GPP and a nonsaturating, steeper increase in fluvial CO2 emission with discharge across regions, which leads to higher percentages of GPP being shunted into rivers for evasion in wetter regions. This highlights the importance of hydrology, in particular water throughput, in routing terrestrial carbon to the atmosphere via the global drainage networks. Our results suggest the need to account for the differential hydrological responses of terrestrial–atmospheric vs. fluvial–atmospheric carbon exchanges in plumbing the terrestrial carbon budget.
Data Availability
The direct pCO2 measurement dataset is included as Dataset S1. The monthly pCO2, k, and CO2 efflux estimates for the GRADES river networks are available at Dryad (https://datadryad.org/stash/dataset/doi:10.5061/dryad.d7wm37pz9). Code related to global stream and river CO2 emission estimates is available at GitHub (https://github.com/lsdeel/globalRiverCO2emission).
Acknowledgments
We thank Simone R. Alin, Loris Deirmendjian, Travis Drake, Audrey Marescaux, Denise Müller-Dum, Sveta Serikova, Xiaofeng Wang, Zhongjie Yu, Dongqi Wang, Åsa Horgby, Tom Battin, and Anne Conover for providing pCO2 data and Dr. Shuang Zhang for providing assistance with the RF model. The research was funded by NASA Project NNX17AI74G. S.L. was supported by Fundamental Research Funds for the Central Universities Project 2020NTST13. D.E.B. was supported by NASA Terrestrial Ecology Program Arctic and Boreal Vulnerability Experiment Project 80NSSC19M0104. X.X. was supported by National Natural Science Foundation of China Projects 52039001 and 92047303.
Supporting Information
Materials/Methods, Supplementary Text, Tables, Figures, and/or References
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Dataset S01 (XLSX)
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Copyright © 2022 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Data Availability
The direct pCO2 measurement dataset is included as Dataset S1. The monthly pCO2, k, and CO2 efflux estimates for the GRADES river networks are available at Dryad (https://datadryad.org/stash/dataset/doi:10.5061/dryad.d7wm37pz9). Code related to global stream and river CO2 emission estimates is available at GitHub (https://github.com/lsdeel/globalRiverCO2emission).
Submission history
Received: April 3, 2021
Accepted: January 12, 2022
Published online: March 7, 2022
Published in issue: March 15, 2022
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Acknowledgments
We thank Simone R. Alin, Loris Deirmendjian, Travis Drake, Audrey Marescaux, Denise Müller-Dum, Sveta Serikova, Xiaofeng Wang, Zhongjie Yu, Dongqi Wang, Åsa Horgby, Tom Battin, and Anne Conover for providing pCO2 data and Dr. Shuang Zhang for providing assistance with the RF model. The research was funded by NASA Project NNX17AI74G. S.L. was supported by Fundamental Research Funds for the Central Universities Project 2020NTST13. D.E.B. was supported by NASA Terrestrial Ecology Program Arctic and Boreal Vulnerability Experiment Project 80NSSC19M0104. X.X. was supported by National Natural Science Foundation of China Projects 52039001 and 92047303.
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This article is a PNAS Direct Submission.
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The authors declare no competing interest.
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The importance of hydrology in routing terrestrial carbon to the atmosphere via global streams and rivers, Proc. Natl. Acad. Sci. U.S.A.
119 (11) e2106322119,
https://doi.org/10.1073/pnas.2106322119
(2022).
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