PROCEEDINGS: Index of Abstracts
TEMPORAL AND SPATIAL TRENDS OF FLUXES AND CONCENTRATIONS
OF CO2 ABOVE AND WITHIN THE CANOPY AT HOWLAND, MAINE:
University of Maine, Orono, ME 04469.
In order to develop and evaluate models of net carbon exchange,
we have collected profiles of CO2 through and above the
canopy for extended periods over three years as well as collected
short-term trial data of diurnal CO2, water vapor, and
sensible heat fluxes above the canopy as measured by eddy correlation.
For fluxes, carbon dioxide concentrations were measured with a LI-COR
model LI-6251 fast response IRGA housed at the base of the tower.
The air sampled from 26 m (7 m above the canopy) was brought through
tubing to the IRGA. Both vertical air movement and water vapor density
were measured adjacent to the inlet of this tubing at the same elevation
using a Campbell Scientific model CA-27 1-D sonic anemometer and
a Campbell Scientific model KH-20 krypton hygrometer. For eddy flux
analysis, sampling of the three sensors occurred at a frequency
of 10 Hz during sampling periods of 30 min. The CO2 concentration
profile through the forest was determined from sequentially collected
samples at three levels within the canopy and at 7 meters above
canopy using a system consisting of a dedicated LI-6252 CO2
analyzer, switching valves, pumps, Teflon inlet tubes, calibration
gases, and dedicated datalogger (model 21X, Campbell Scientific).
These data are used to determine a storage flux of CO2
associated with the change in CO2 concentration within
the air column. The effects of atmospheric stability, stomatal conductance,
and soil moisture on concentrations and fluxes are described.