Measurements of CH 4 and N 2 O fluxes at the landscape scale using micrometeorological methods

Abstract

Flux gradient, eddy covariance and relaxed eddy accumulation methods were applied to measure CH 4 and N 2 O emissions from peatlands and arable land respectively. Measurements of N 2 O emission by eddy covariance using tunable diode laser spectroscopy provided fluxes ranging from 2 to 60 µ mol N 2 O m -2 h -1 with a mean value of 22 µ mol N 2 O m -2 h -1 from 320 h of continuous measurements. Fluxes of CH 4 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 µ mol CH 4 m -2 h -1 with means of 14.7 µ mol CH 4 m -2 h -1 and 22.7 µ mol CH 4 m -2 h -1 respectively. Emissions of CH 4 from peatland changed with water table depth and soil temperature; increasing from 25 |Amol CH 4 m -2 h -1 at 5% pool area to 50 p.mol CH 4 m -2 h -1 with 30% within the flux footprint occupied by pools. A temperature response of 4.9 (xmol CH 4 m -2 h -1 °C -1 in the range 6-12 °C was also observed. The close similarity in average CH 4 emission fluxes reported for wetlands in Caithness, Hudson Bay and Alaska in the range 11 to 40 jamol CH 4 m -2 h -1 suggests that earlier estimates of CH 4 emission from high latitude wetlands were too large or that the area of high latitudes contributing to CH 4 emission has been seriously underestimated.