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United States Department of Agriculture

Agricultural Research Service

Research Project: Ecohydrological Processes, Scale, Climate Variability, and Watershed Management

Location: Southwest Watershed Research

Title: Data-driven diagnostics of terrestrial carbon dynamics over North America

Authors
item Xiao, J. -
item Ollinger, S.V, -
item Frolking, S. -
item Hurtt, G.C. -
item Hollinger, D.Y. -
item Davis, K.J. -
item Pan, Y. -
item Zhang, X. -
item Deng, F. -
item Chen, J. -
item Baldocchi, A.D. -
item Law, B.E. -
item Arain, M.A. -
item Desai, A.R. -
item Richardson, A.D. -
item Sun, G. -
item Amiro, B. -
item Margolis, H. -
item Gu, L. -
item Scott, Russell
item Blaken, P.D. -
item Suyker, A.E. -

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 29, 2014
Publication Date: July 19, 2014
Citation: Xiao, J., Ollinger, S., Frolking, S., Hurtt, G., Hollinger, D., Davis, K., Pan, Y., Zhang, X., Deng, F., Chen, J., Baldocchi, A., Law, B., Arain, M., Desai, A., Richardson, A., Sun, G., Amiro, B., Margolis, H., Gu, L., Scott, R.L., Blaken, P., Suyker, A. 2014. Data-driven diagnostics of terrestrial carbon dynamics over North America. Agricultural and Forest Meteorology. 197:142-157. DOI: 75110.1016/j.agrformet.2014.06.013.

Interpretive Summary: Despite the general agreement that the terrestrial ecosystems in North America provide a sizeable carbon sink, the size and distribution of the sink remain uncertain. We use a data-driven approach to determine the carbon dioxide exchanges between the land and the atmosphere over the North American continent by integrating flux observations, meteorology, stand age, aboveground biomass, and a proxy for canopy nitrogen concentrations. We then use the resulting flux estimates from March 2000 to December 2012 to assess the magnitude, distribution, and interannual variability of carbon fluxes for the U.S. and Canada. The average annual gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of the U.S. over the period 2001–2012 were 6.84, 5.31, and 1.10 Pg C yr-1, respectively; the mean annual GPP, ER, and NEP of Canada over the same 12-year period were 3.91, 3.26, and 0.60 Pg C yr-1, respectively. The mean nationwide annual NEP of natural ecosystems over the period 2001–2012 was 0.53 Pg C yr-1 for the U.S. and 0.49 Pg C yr-1 for the conterminous U.S. Our estimate of the carbon sink for the conterminous U.S. was almost identical with the estimate of the First State of the Carbon Cycle Report (SOCCR). The carbon fluxes exhibited relatively large interannual variability over the study period. The main sources of the interannual variability in carbon fluxes included drought and disturbance. The annual GPP and NEP were strongly related to annual evapotranspiration (ET) for both the U.S. and Canada, showing that the carbon and water cycles were closely coupled. Our gridded flux estimates provided an independent, alternative perspective on ecosystem carbon exchange over North America.

Technical Abstract: The exchange of carbon dioxide is a key measure of ecosystem metabolism and a critical intersection between the terrestrial biosphere and the Earth's climate. Despite the general agreement that the terrestrial ecosystems in North America provide a sizeable carbon sink, the size and distribution of the sink remain uncertain. We use a data-driven approach to upscale eddy covariance flux observations from towers to the continental scale by integrating flux observations, meteorology, stand age, aboveground biomass, and a proxy for canopy nitrogen concentrations from AmeriFlux and Fluxnet-Canada Research Network as well as a variety of satellite data streams from the MODIS sensors. We then use the resulting gridded flux estimates from March 2000 to December 2012 to assess the magnitude, distribution, and interannual variability of carbon fluxes for the U.S. and Canada. The mean annual gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of the U.S. over the period 2001–2012 were 6.84, 5.31, and 1.10 Pg C yr-1, respectively; the mean annual GPP, ER, and NEP of Canada over the same 12-year period were 3.91, 3.26, and 0.60 Pg C yr-1, respectively. The mean nationwide annual NEP of natural ecosystems over the period 2001–2012 was 0.53 Pg C yr-1 for the U.S. and 0.49 Pg C yr-1 for the conterminous U.S. Our estimate of the carbon sink for the conterminous U.S. was almost identical with the estimate of the First State of the Carbon Cycle Report (SOCCR). The carbon fluxes exhibited relatively large interannual variability over the study period. The main sources of the interannual variability in carbon fluxes included drought and disturbance. The annual GPP and NEP were strongly related to annual evapotranspiration (ET) for both the U.S. and Canada, showing that the carbon and water cycles were closely coupled. Our gridded flux estimates provided an independent, alternative perspective on ecosystem carbon exchange over North America.

Last Modified: 12/20/2014
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