Eddy Covariance of Methane in Upland and Seasonally Flooded Forests in the Amazon Basin, Working Towards the Contribution of Tree Stems on Ecosystem Methane Fluxes

Authors

Joost van Haren¹* (jvanhare@ariona.edu), Raphael Tapajos², Rodrigo da Silva², Miércio Ferreira Jr.², Raimundo Cosme de Oliveira³, José Mauro S. de Moura,² Jhon del Aguila Pasquel¹, Scott Saleska¹

Institutions

¹University of Arizona, Tucson, AZ; ²Federal University of Western Pará (UFOPA), Santarém, Pará, Brazil; ³Brazilian Agricultural Research Corporation (Embrapa), Santarém, Pará, Brazil

Abstract

Methane emissions from tree stems have been gathering much attention (Barba et al. 2019; Pangala et al. 2017). However, in seasonally flooded (várzea) forests along the Amazon River, researchers have only scant measurements of the dynamics of tree stem emissions. The team is developing seasonal ecosystem and component methane flux measurements in both a várzea and an upland forest near Santarém, Brazil. The team will present preliminary eddy covariance and monthly tree and soil flux results from the upland tower site and a seasonally flooded site. These initial measurements were made as part of the measurement systems’ development and testing and the várzea forest site selection process. All discrete fluxes will be analyzed using the gasfluxes R package, which was modified to work the flux measurement data gathering methods. Eddy covariance analysis will be conducted with the openeddy R package.

Methane stem fluxes in the upland site appear to be higher in tree species with lower wood density and higher sap flux rates. Seasonal variability of stem fluxes in the upland forest is very small, suggesting that the source methane variability is much lower than in várzea forests. Várzea tree stem fluxes are several orders of magnitude higher in the wet (flooded) season relative to the dry season and the upland forest site. Tree stem flux measurements along vertical profiles show an exponential decay of methane emissions with height, and most methane is emitted within the first 2 m of height along the stem. Cylindrical diffusion of methane flux along tree stems best fits the measured flux data from the várzea forest sites.

References

Barba, J., et al. 2019. “Methane Emissions from Tree Stems: A New Frontier in the Global Carbon Cycle,” New Phytologist 222(1), 18–28. DOI:10.1111/nph.15582.

Pangala, S. R., et al. 2017. “Large Emissions from Floodplain Trees Close the Amazon Methane Budget,” Nature 552, 230–34. DOI:10.1038/nature24639.