Abstract ID: 293

Interaction of micrometeorology and surface fluxes confounding the interpretation of CO2 fluxes in central Amazonia

The landscape of central Amazonia is composed of plateaus and valleys. Previous observations have shown preferential pooling of CO2 in the valleys, suggesting that the change in CO2 storage in the canopy air space (S) will be spatially variable at the scale of the topography. This may affect the interpretation of the net ecosystem exchange (NEE) rates measured on the plateaus if they have used one single atmospheric CO2 concentration ([CO2]) vertical profile measurement system. We have measured the diurnal and seasonal variation of S along the topography by using a set of [CO2] vertical profile measurement systems. In addition, NEE, the above-canopy turbulent exchange of CO2 (Fc) and meteorological variables were also measured by micrometeorological towers located on the plateau and in the valley. The nocturnal accumulation of CO2 was larger on the slopes and in the valleys than on the plateau, and was also larger in the dry season than in the wet season. In addition, the release of this CO2 occurred later in the day on the slopes and in the valleys than on the plateau. Differences in the flow regime above the canopy on the plateau and in the valley, the pattern of destruction of the nocturnal boundary layer in the valley, lateral drainage of respired CO2 downslope, and the temporal, spatial and seasonal variability of soil respiration are thought to have contributed to this. These conditions cause S to be lower on the slopes and in the valleys than on the plateau during midmorning hours. It is very likely that the interpretation of NEE measured on both plateau and valley may be biased by S being lower in the valley than on the plateau. We were not able to distinguish which term of the mass balance equation (either Fc or S) for the plateau was more susceptible to the CO2 released from the valley during the period after dawn. We have demonstrated that the temporal and spatial variability of S along a gentle slope may confound the interpretation of NEE. As many of the flux measurement towers are set over non-flat terrain, care must be taken when using the NEE for determining the carbon balance.

Session:  Carbon - The role of seasonality in carbon and water balance.

Presentation Type:  Poster