MEASUREMENTS OF CH4 AND N2O FLUXES AT THE LANDSCAPE SCALE USING MICROMETEOROLOGICAL METHODS

Flux gradient, eddy covariance and relaxed eddy accumulation methods were applied to measure CH4 and N2O emissions from peatlands and arable land respectively. Measurements of N2O emission by eddy covariance using tunable diode laser spectroscopy provided fluxes ranging from 2 to 60 mu mol N2O m(-2) h(-1) with a mean value of 22 mu mol N2O m(-2) h(-1) from 320 h of continuous measurements. Fluxes of CH4 measured above peatland in Caithness (U.K.) during May and June 1993 by eddy covariance and relaxed eddy accumulation methods were in the range 70 to 120 mu mol CH4 m(-2) h(-1) with means of 14.7 mu.mol CH4 m(-2) h(-1) and 22.7 mu mol CH4 m(-2) h(-1) respectively. Emissions of CH4 from peatland changed with mater table depth and soil temperature; increasing from 25 mu mol CH4 m(-2) h(-1) at 5% pool area to 50 mu mol CH4 m(-2) h(-1) with 30% within the flux footprint occupied by pools. A temperature response of 4.9 mu mol CH4 m(-2) h(-1) degrees C-1 in the range 6-12 degrees C was also observed. The close similarity in average CH4 emission fluxes reported for wetlands in Caithness, Hudson Bay and Alaska in the range 11 to 40 mu mol CH4 m(-2) h(-1) suggests that earlier estimates of CH4 emission from high latitude wetlands were too large or that the area of high latitudes contributing to CH4 emission has been seriously underestimated.