|Griffis, Timothy - UNIV. OF MINNESOTA|
Submitted to: European Geophysical Society; American Geophysical Union; European Union of Geosciences
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2003
Publication Date: April 3, 2003
Citation: Griffis, T.J., Baker, J.M. 2003. Measuring field-scale isotopic co2 fluxes with tunable diode laser absorption spectroscopy and eddy covariance. European Geophysical Society; American Geophysical Union; European Union of Geosciences. EAE03-A-11221. Technical Abstract: The combination of micrometeorological and stable isotope techniques offers a relatively new approach for improving the description of ecosystem scale processes. Here we combine eddy covariance and tunable diode laser absorption spectroscopy (EC-TDLAS) using the Trace Gas Analyzer (TGA 100, Campbell Scientific Inc., Utah, USA) to measure field scale isotopic CO2 ratios and fluxes of 12CO2 and 13CO2. The experiment was conducted in a recently harvested soybean field that had been in corn production the previous four years. Measurements were made over a period of 26 days from October 25 to November 19, 2002. The TGA 100 proved to be robust. Approximately 86% of the total half-hour isotope measurements were retained for analysis. There was considerable variability in the daily isotopic ratio of respiration (delta13Cr) ranging from -28.37 to -25.19 per mil. The delta13Cr values were consistent with C3 agricultural systems indicating that soybean decomposition and, perhaps, residual root respiration dominated the respiration efflux. The standard error of the half-hour isotopic ratio was typically 0.045 per mil. Gradients in 12CO 13CO2 were relatively small given the cold climatic conditions. Average gradients were 0.153 µmol mol-1 m-1 (standard error = 0.039) and 0.0018 µmol mol-1 m-1 (standard error = 0.0004) for 12CO2 and 13CO2, respectively. The average 12CO2 and 13CO2 flux was 63 and 0.72 µg m-2 s-1 and the isotopic flux ratio (13CO2/12CO2) for respiration was 0.012 (standard error = 0.0002) for the study period. Small half-hour variations in the respiration flux ratio were observed, which may have significant implications for net ecosystem flux partitioning theory. If the flux ratio of respiration is conservative on diurnal time-scales then the direct partitioning of daytime net ecosystem CO2 exchange into photosynthesis and respiration should be possible from daytime flux measurements of 12CO2 and 13CO2. Additional experiments are planned to study the effects of respiration and photosynthesis on the nighttime and daytime flux ratios during the growing season in order to partition net ecosystem CO2 exchange into its components.