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Resolving systematic errors in estimates of net ecosystem exchange of CO2 and ecosystem respiration in a tall-stature forest: application to a tropical forest biome

Lucy R Hutyra, Harvard University, University of Washington, (Presenting)
James W. Munger, Harvard University,
Elizabeth Hammond-Pyle, Harvard University,
Scott R Saleska, University of Arizona,
Natalia Restrepo-Coupe, University of Arizona,
Plinio B de Camargo, USP-CENA,
Steven C Wofsy, Harvard University,

The controls on tropical rainforest CO2 exchange and the likely future responses to a changing climate are among the largest uncertainties in global climate change models. Eddy-covariance measurements potentially provide detailed data on CO2 exchange in these forests, but accurate estimates of the net ecosystem exchange of CO2 (NEE) and ecosystem respiration (R) require careful analysis of data representativity and treatment of data gaps. This study discusses the biases in NEE and R potentially associated with two sources of systematic error in eddy-covariance data, lost nighttime flux and missing canopy storage measurements, and we propose robust approaches to correct for theses biases. Multiple independent estimates for the net carbon balance and ecosystem respiration are presented to validate the analyses, including a carefully constructed bottom-up budget for respiration and extrapolation of daytime data to zero light. We found that lost nocturnal flux can produce a significant bias and, where appropriate, a site-specific u* threshold should be evaluated to avoid systematic bias in estimates of carbon exchange. The inclusion of canopy storage is essential to accurate assessments of net carbon exchange, due to day-night asymmetry in storage and turbulence. We found that short-term measurements of storage may be adequate to accurately model storage for use in obtaining ecosystem carbon balance. The analytical framework utilized in this study could be applied to any eddy-covariance site for validation of methodological techniques.

Science Theme:  CD (Carbon Dynamics)

Session:  3B: Carbon and Energy Fluxes

Presentation Type:  Oral (view presentation (3657 KB))

Abstract ID: 1

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