LBA-ECO CD-04 Meteorological and Flux Data, km 83 Tower Site, Tapajos National Forest

In contrast, the magnitude of the annual integral was highly sensitive to the treatment of calm nights, changing by over 4 Mg C(.)ha(-1.)yr(-1) when a filter was used to replace the net ecosystem exchange (NEE) during nocturnal periods with u* < 0.2 m/s. Analyses of the relationship between nocturnal NEE and u* confirmed that the annual sum needs to be corrected for the effect of calm nights, which resulted in our best estimate of the annual flux (+0.4 Mg C(.)ha(-1.)yr(-1)).

The observed sensitivity of the annual sum to the u* filter is far greater than has been previously reported for temperate and boreal forests. The annual carbon balance determined by eddy covariance is therefore less certain for tropical than temperate forests. Nonetheless, the biometric and micrometeorological measurements in tandem provide strong evidence that the forest was not a strong, persistent carbon sink during the study interval.