Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO2


Terrestrial ecosystems in the humid tropics play a potentially important but presently ambiguous role in the global carbon cycle. Whereas global estimates of atmospheric CO2 exchange indicate that the tropics are near equilibrium or are a source with respect to carbon1,2, ground-based estimates indicate that the amount of carbon that is being absorbed by mature rainforests is similar to or greater than that being released by tropical deforestation3,4 (about 1.6 Gt C yr-1). Estimates of the magnitude of carbon sequestration are uncertain, however, depending on whether they are derived from measurements of gas fluxes above forests5,6 or of biomass accumulation in vegetation and soils3,7. It is also possible that methodological errors may overestimate rates of carbon uptake or that other loss processes have yet to be identified3. Here we demonstrate that outgassing (evasion) of CO2 from rivers and wetlands of the central Amazon basin constitutes an important carbon loss process, equal to 1.2 ± 0.3 Mg C ha-1 yr-1. This carbon probably originates from organic matter transported from upland and flooded forests, which is then respired and outgassed downstream. Extrapolated across the entire basin, this flux—at 0.5 Gt C yr-1—is an order of magnitude greater than fluvial export of organic carbon to the ocean8. From these findings, we suggest that the overall carbon budget of rainforests, summed across terrestrial and aquatic environments, appears closer to being in balance than would be inferred from studies of uplands alone3,5,6.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Flooded area of the central Amazon basin at high water, as mapped from the Japanese Earth Resources Satellite radar data (May–June 1996).
Figure 2: Spatially integrated annual sequences of surface water area for hydrographic environments as determined from JERS-1 radar data and multi-year hydrographic records.
Figure 3: Seasonal distributions of carbon dioxide dissolved in rivers of the central Amazon basin.
Figure 4: Spatially integrated sequences of monthly carbon dioxide evasion for the respective hydrographic environments (identified in Fig. 2).

Similar content being viewed by others


  1. Schimel, D. S. et al. Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems. Nature 414, 169–172 (2001).

    Article  ADS  CAS  Google Scholar 

  2. Gurney, K. R. et al. Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models. Nature 415, 626–630 (2002).

    Article  ADS  Google Scholar 

  3. Malhi, Y. & Grace, J. Tropical forests and atmospheric carbon dioxide. Trends Ecol. Evol. 15, 332–337 (2000).

    Article  CAS  Google Scholar 

  4. Houghton, R. A. A new estimate of global sources and sinks of carbon from land-use change. Eos 81(Suppl.), S281 (2000).

    Google Scholar 

  5. Grace, J. et al. Carbon dioxide uptake by an undisturbed tropical rain forest in Southwest Amazônia, 1992 to 1993. Science 270, 778–780 (1995).

    Article  ADS  CAS  Google Scholar 

  6. Malhi, Y. et al. Carbon dioxide transfer over a central Amazonian rain forest. J. Geophys. Res. 103, 31593–31612 (1998).

    Article  ADS  CAS  Google Scholar 

  7. Phillips, O. L. et al. Changes in the carbon balance of tropical forests: Evidence from long-term plots. Science 282, 439–442 (1998).

    Article  ADS  CAS  Google Scholar 

  8. Richey, J. E. et al. Biogeochemistry of carbon in the Amazon River. Limnol. Oceanogr. 35, 352–371 (1990).

    Article  ADS  CAS  Google Scholar 

  9. Degens, E. T., Kempe, S. & Richey, J. E. (eds) Biogeochemistry of Major World Rivers 323–397 (Wiley, Chichester, 1991).

    Google Scholar 

  10. Sarmiento, J. L. & Sundquist, E. T. Revised budget for the oceanic uptake of anthropogenic carbon dioxide. Nature 356, 589–593 (1992).

    Article  ADS  CAS  Google Scholar 

  11. Richey, J. E., Brock, J. T., Naiman, R. J., Wissmar, R. C. & Stallard, R. F. Organic carbon: oxidation and transport in the Amazon River. Science 207, 1348–1351 (1980).

    Article  ADS  CAS  Google Scholar 

  12. Cole, J. J. & Caraco, N. F. Carbon in catchments: Connecting terrestrial carbon losses with aquatic metabolism. Mar. Freshwat. Res. 52, 101–110 (2001).

    Article  CAS  Google Scholar 

  13. Kling, G. W., Kipphut, G. W. & Miller, M. C. Arctic lakes and streams and gas conduits to the atmosphere: implications for tundra carbon budgets. Science 251, 298–301 (1991).

    Article  ADS  CAS  Google Scholar 

  14. Hope, D., Palmer, S. M., Billett, M. F. & Dawson, J. J. Carbon dioxide and methane evasion from a temperate peatland stream. Limnol. Oceanogr. 46, 847–857 (2001).

    Article  ADS  CAS  Google Scholar 

  15. Telmer, K. & Veizer, J. Carbon fluxes, pCO2 and substrate weathering in a large northern river basin, Canada: carbon isotope perspectives. Chem. Geol. 159, 61–86 (1999).

    Article  ADS  CAS  Google Scholar 

  16. McClain, M. E. & Richey, J. E. Regional-scale linkages of terrestrial and lotic ecosystems in the Amazon basin: A conceptual model for organic matter. Arch. Hydrobiol. 113 (Suppl.), 111–125 (1996).

    CAS  Google Scholar 

  17. Davidson, E. A. & Trumbore, S. E. Gas diffusivity and production of CO2 in deep soils of the eastern Amazon. Tellus B 47, 550–565 (1995).

    Article  ADS  Google Scholar 

  18. Richey, J. E., Victoria, R. L., Mayorga, E., Martinelli, L. A. & Meade, R. H. in Biospheric Feedbacks in Climate and the Hydrological Cycle (ed. Kabat, P.) (Springer, in the press).

  19. McClain, M. E., Richey, J. E., Brandes, J. A. & Pimentel, T. P. Dissolved organic matter and terrestrial-lotic linkages in the central Amazon Basin, Brazil. Glob. Biogeochem. Cycles 11, 295–311 (1997).

    Article  ADS  Google Scholar 

  20. Melack, J. M. & Forsberg, B. R. in The Biogeochemistry of the Amazon Basin (eds McClain, M. E., Victoria, R. L. & Richey, J. E.) 235–274 (Oxford Univ. Press, New York, 2001).

    Google Scholar 

  21. Chambers, J. Q., dos Santons, J., Ribeiro, R. J. & Higuichi, N. Tree damage, allometric relationships, and above-ground net primary production in central Amazon forest. Forest Ecol. Management 5348, 1–12 (2000).

    Google Scholar 

  22. Devol, A. H., Forsberg, B. R., Richey, J. E. & Pimentel, T. P. Seasonal variation in chemical distributions in the Amazon (Solimões) River: a multiyear time series. Glob. Biogeochem. Cycles 9, 307–328 (1995).

    Article  ADS  CAS  Google Scholar 

  23. Siqueira, P. et al. A continental-scale mosaic of the Amazon Basin using JERS-1 SAR. IEEE Trans. Geosci. Remote Sensing 38, 2638–2644 (2000).

    Article  ADS  Google Scholar 

  24. Barbosa, C., Hess, L., Melack, J. & Novo, E. Mapping Amazon Basin wetlands through region-growing segmentation and segmented-based classification of JERS-1 data. IX Latin Am. Symp. Remote Sensing (6–10 November 2000) 1168–1176 (Universidad Nacional de Lujan, Puerto Iguazu, Argentina, 2000); see also 〈〉.

  25. Hess, L. L. et al. Geocoded digital videography for validation of land cover mapping in the Amazon Basin. Int. J. Remote Sensing (in the press).

  26. Sippel, S. J., Hamilton, S. K., Melack, J. M. & Novo, E. M. Passive microwave observations of inundation area and the area/stage relation in the Amazon River floodplain. Int. J. Remote Sensing 19, 3055–3074 (1998).

    Article  ADS  Google Scholar 

  27. Richey, J. E., Devol, A. H., Wofsy, S. C., Victoria, R. & Ribeiro, M. N. G. Biogenic gases and the oxidation and reduction of carbon in the Amazon River and floodplain waters. Limnol. Oceanogr. 33, 551–561 (1988).

    Article  ADS  CAS  Google Scholar 

  28. Devol, A. H., Quay, P. D., Richey, J. E. & Martinelli, L. A. The role of gas exchange in the inorganic carbon, oxygen and 222 radon budgets of the Amazon River. Limnol. Oceanogr. 32, 235–248 (1987).

    Article  ADS  CAS  Google Scholar 

  29. Clark, J. F., Wanninkhof, R., Schlosser, P. & Simpson, H. J. Gas exchange rates in the tidal Hudson River using a dual tracer technique. Tellus B 46, 264–285 (1994).

    Article  ADS  Google Scholar 

  30. MacIntyre, S., Eugster, W. & Kling, G. W. in Gas Transfer at Water Surfaces (eds Donelan, M. A., Drennan, W. M., Saltzman, E. S. & Wanninkhof, R.) 135–139 (American Geophysical Union, Washington, 2001).

    Google Scholar 

Download references


We thank E. Mayorga, S. Denning, M. Gastil, D. Montgomery, R. Victoria, A. Krusche, A. Devol, P. Quay and J. Hedges for technical assistance and discussions, B. Forsberg and T. Pimental for fieldwork, and the Global Rain Forest Mapping Project of the National Space Development Agency of Japan for providing the JERS-1 radar data. This work was supported by the US NSF and NASA EOS and LBA projects, and by the Brazilian FAPESP programme.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Jeffrey E. Richey.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests

Rights and permissions

Reprints and permissions

About this article

Cite this article

Richey, J., Melack, J., Aufdenkampe, A. et al. Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO2. Nature 416, 617–620 (2002).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing