Study of CO2 Flow and Energy Balance in a Transition Forest in Southwestern Amazonia by the Modified Bowen Ratio Methods and Eddy Covariance

Abstract

Background: The study of CO2 fluxes and energy between the surface and the atmosphere, contribute to investigate natural or anthropic effects on ecosystems. Meteorological and micrometeorological stations are usually equipped with instruments capable of measuring these flows directly or indirectly, using Eddy Covariance (EC) and Modified Bowen Ratio (MBR) methods, respectively. The coefficients of turbulent diffusivity are physical quantities directly correlated to magnitudes of flows, and difficult to measure. Objective: The objective of this work was to evaluate the use of turbulent diffusivity coefficients in CO2 flux estimates for the (MBR) method. Methods: The experiment was conducted in Amazonia / Cerrado transition forest, where a meteorological tower was installed. The fluxes of CO2, latent and sensitive heat obtained by the EC and MBR methods were compared by the Scheirer-Ray-Hare statistical test to detect possible differences between flows, seasons, and methods. The CO2 flux, estimated by the Modified Bowen Ratio method, was tested as a function of turbulent diffusion coefficients of sensible and latent heat. Results: In both Bowen ratio and Eddy Covariance methods, available net energy prioritized the latent heat flux during the dry season. The energy balance by Eddy Covariance method was underestimated in 30% in the humid season and 5% in the dry season. The energy balance by the Bowen ratio method closed at 100% during the dry season, but during the wet season it was underestimated at 4%. Conclusion: The CO2 fluxes measured by the Eddy Covariance method and estimated by the Modified Bowen Ratio method as a function of the latent heat turbulent diffusion coefficient, did not show significant differences between their estimates, between the seasons and between the methods. The sensible heat flux showed significant difference between the methods of Bowen ratio and Eddy Covariance, and between the seasons.