Tropical forest CH4 and N2O: from chamber fluxes to tower concentration measurements

Methane (CH₄) is the second most important long-lived anthropogenic atmospheric greenhouse gas. Despite its importance, natural sources of methane, such as tropical wetlands, are still not well understood and a large source of uncertainty to the global CH₄ budget. The Amazonian rain forest is estimated to hold 90-120 Pg of carbon, which is approximately 14-27% of the carbon stored in vegetation worldwide. The region is characterized by high precipitation rates and large wetlands, and it has been estimated that the Amazon basin emits 7% of the annual total CH₄ emissions. Due to its remote location, micro-meteorological measurements are rare and usually absent for other gases than CO₂.

The 50 m high K34 tower (field site ZF2) is located in a pristine `Terre Firme' tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH₄ production. In October 2018, in addition to the existing EC CO₂ system, an in-situ FTIR-analyzer (measuring CO₂, CO, CH₄, N₂O and δ¹³CO₂) was set up to measure tower profile concentrations, above and below the canopy, continuously. By analyses of vertical and temporal nighttime concentrations patterns, an emission estimate for all gases could be made, and an ecosystem emission of ~1 nmol CH₄ m^-2 s^-1 and ~0.5 nmol N₂O m^-2 s^-1 was estimated. In addition, by use of different types of flux chambers, possible N₂O and CH₄ sources such as soils, trees, water and termite mounds were measured. By combining tower and flux chamber measurements, the role and magnitude of different ecosystem sources could be assessed. In this presentation, an overview of the measured CH₄ and N₂O forest concentrations and fluxes will be given.