Measurements of Forest-Atmosphere Isotopic CO2 Exchange by Eddy Covariance
Abstract
Isotopic CO2 flux measurements are a promising means for partitioning the net ecosystem exchange of CO2 into photosynthetic and respiratory components. This approach to partitioning is possible in principle because of the distinct isotopic signatures of respired and photosynthesized CO2, but has been infeasible in practice—especially in forests—because of the difficulty of measuring isotopic ratios with sufficient precision and time response for use in eddy covariance (EC) flux calculations. Recent advances in laser spectroscopic instrumentation have changed that. We report measurements of isotopic (13C and 18O) CO2 exchange made by eddy covariance at Harvard Forest between April and December, 2010. The measurements were made using a continuous-wave quantum cascade laser spectrometer (Aerodyne Research Inc.) sampling at 4 Hz and are, to our knowledge, the first EC isotopic flux measurements at a forest site. The spectrometer can measure δ13C and δ18O with internal precisions (standard deviation of 1-minute averages) of 0.03 ‰, and [CO2] with an internal precision of 15 ppb; the instrumental accuracy, calibration, and long-term stability are discussed in detail. The isotopic data are considered in relation to environmental variables (PAR, temperature, humidity, soil temperature and moisture), and a first attempt at flux partitioning using the isotopic fluxes is presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B23H0500W
- Keywords:
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- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry