Inter-comparison of chamber and eddy-correlation flux measurements

At various sites in the Netherlands closed gas chamber measurements and eddy correlation measurements are carried out in order to determine greenhouse gas fluxes (CH4, N2O and CO2). For this purpose various measurement set-ups and devices are used. The results of all these measurements are used to understand small scale processes that generate the fluxes as well as to upscale the greenhouse gas balance. However, using varying measurement techniques for these analyses the question of comparability rises. In this research exercise, an attempt is being made to develop a measurement protocol that covers all measurement devices and methods available in our group(*), in order to guaranty the comparability of further analyses. All measurements are done during two measurement campaigns of three days each at two well know research locations in the Dutch peat meadow area (Horstermeer site and Reeuwijk site). Additionally, we work on the construction of a calibration tank for experimenting with the various flux chamber techniques. Six different types of chamber set-ups are compared in this study; including various box-designs, filtering of air, and closed or open boxes. Measurement devices consisted of two Photo Acoustic Field Gas-Monitors, two Licor 7500 open path infrared gas analysers, a QCL, a TDL and a DLT-100 Fast Methane Analyzer. In order to compare the measurement devices and set-ups and detect differences in the functioning, all data are processed with identical flux calculation programs. The build-up of gas concentrations in the chambers is studied in detail, before final flux-calculations are done. Additional to the comparability-analysis, a precise analysis of the variability of the fluxes in time and space can be done, using the multitude of measurements collected in the experiment. Final results are still in progress, but will be available at the time of the Carbo Europe Meeting in November 2006.