Lagrangian dispersion of 222Rn, H2O and CO2 within Amazonian rain forest

The inverse solution for 222Rn source/sink distributions shows a high sensitivity to small measurement errors, especially for day-time conditions, when there is efficient turbulent mixing in the upper canopy and profile gradients are small. The inverse approach is also applied to CO2 and H2O profiles. The predicted net fluxes show a reasonable agreement with Eddy Covariance (EC) measurements made above the forest canopy, although the scatter is large and the day-time solutions for CO2 are very sensitive to measurement errors. However, this is not the case for typical night-time conditions, where the CO2 profile gradients in the upper canopy are large. The inverse approach predicts a mean CO2 emission flux of 7.5 μmol m−2 s−1 for the investigation period. This value is somewhat larger compared to estimates based on EC measurements, which are quite uncertain at night-time and thus reduces the upper bound of the estimated carbon sink strength for Amazonian rain forest.