Abstract ID: 471

CH₄ flux in an upland tropical forest derived from direct measurements of 222Rn

We propose to investigate the mechanisms controlling trace gases and methane (CH₄) fluxes in an upland tropical forest at Flona Tapajós (Belterra-Pará) using an especial system to measure Radon-222 (²²²Rn) activity and CH₄ concentration. ²²²Rn flux was calculated (15 min interval basis) in a vertical tower profile (65m). ²²²Rn ground flux measurements were provided by using a portable detector coupled to installed ground PVC collars in a suitable interval of 60 minutes. During sampling period (2002) the ²²²Rn ground flux (monthly average) varied from 5.42 to 35.78 mBq m^-2 s^-1, this variation is phase with soil moisture oscillation, which in turn, was in a range of 0.18 e 0.36 m³ m^-3. The ²²²Rn activity varied in the tower profile from 2.54 to 21.33 Bq m^-3. For CH₄ concentration amospheric air samples were collected in a vertical profile (0.2, 7.0, 15.0, 22.0, 35.0, and 45.0 m) in different times of the day (4:00, 16:00, 22:00, and 24:00h). The air samples were pulled through tubes by a battery-operated pump and then stored into glass flasks. The CH₄ concentration was determined by gas chromatography. The concentration varied from 1.87 to 2.62 ppm. This variation is in the range for values found for atmospheric methane. The heights near the ground showed higher amplitude of variation than the heights above canopy. This characteristic occurs due a combination of the effect of proximity of the main ²²²Rn source and the effect caused by the changes in ventilation along the profile

Session:  Carbon - Scaling carbon fluxes to the region from measurements in plots, towers, and aircraft.

Presentation Type:  Poster