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Increased mobilization of aged carbon to rivers by human disturbance

Nature Geoscience volume 8, pages 112116 (2015) | Download Citation

Abstract

Approximately 8% of anthropogenic carbon dioxide emissions are estimated to come from land-use change1, but this estimate excludes fluxes of terrestrial carbon to aquatic ecosystems from human disturbance. Carbon fluxes from land to rivers have probably increased by 0.1 to 0.2 petagrams of carbon per year as a result of disturbances such as deforestation, agricultural intensification and the injection of human wastewater2. Most dissolved organic carbon in rivers originates from young organic carbon from soils and vegetation3, but aged carbon removed from the modern carbon cycle is also exported in many systems. Here we analyse a global data set of radiocarbon ages of riverine dissolved organic carbon and spatial data on land cover, population and environmental variables. We find that the age of dissolved organic carbon in rivers increases with population density and the proportion of human-dominated landscapes within a watershed, and decreases with annual precipitation. We reason that disturbance reintroduces aged soil organic matter into the modern carbon cycle, although fossil carbon in fertilizer or petroleum products may also be a source of aged carbon in disturbed watersheds. The total export from the terrestrial environment to freshwater systems remains unknown; nevertheless, our results suggest that 3–9% of dissolved organic carbon in rivers is aged carbon mobilized by human disturbance.

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Acknowledgements

We want to thank C. Lawrence (U.S.G.S.) for important comments regarding soil carbon dynamics, and P. Neubauer (Dragonfly Science, Wellington Australia) and O. Jensen (Rutgers) for guidance on the MixSIAR modelling approach. Financial support for this analysis was provided by a Yale Institute for Biospheric Studies Environmental Fellowship awarded to H.F.W., an E.P.A. STAR grant (FP-91637501-1) awarded to R.T.B., and a NASA Earth and Space Science Fellowship (NNX07AN83h) awarded to D.E.B. and postdoctoral support provided by the US Geological Survey Land Carbon program (D.E.B.). We also thank the Natural Sciences and Engineering Research Council of Canada for supporting field sampling, and the numerous scientists and research organizations that provided the data summarized here on 14C-DOC.

Author information

Affiliations

  1. University of Washington, School of Environmental and Forest Sciences, Box 352100, Seattle, Washington 98195, USA

    • David E. Butman
  2. Brandon Research Centre, Agriculture and Agri-Food Canada, Brandon, Manitoba R7A 5Y3, Canada

    • Henry F. Wilson
  3. Environmental Program, Colorado College, Colorado Springs, Colorado 80903, USA

    • Rebecca T. Barnes
  4. Department of Biology, Trent University, Peterborough, Ontario K9J 7B8, Canada

    • Marguerite A. Xenopoulos
  5. Yale School of Forestry and Environmental Studies, 195 Prospect Street New Haven, Connecticut 06115, USA

    • Peter A. Raymond

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Contributions

D.E.B., H.F.W. and R.T.B. equally contributed to the conceptual development of the project, writing, data compilation, field sampling for unpublished data sets provided herein, and data synthesis. P.A.R. provide logistical support, contributed data to the analysis, contributed to conceptual presentation within the manuscript and edited manuscript drafts. M.A.X. coordinated and supported collection of targeted samples in Ontario streams, was involved with conceptual discussions and edited manuscript drafts.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to David E. Butman.

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DOI

https://doi.org/10.1038/ngeo2322

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