Measurements of CH4and N2O fluxes at the landscape scale using micrometeorological methods

Abstract

Flux gradient, eddy covariance and relaxed eddy accumulation methods were applied to measure CH₄and 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 µ mol N₂O m^-2h^-1with a mean value of 22 µ mol N₂O m^-2h^-1from 320 h of continuous measurements. Fluxes of CH₄measured 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 CH₄m^-2h^-1with means of 14.7 µ mol CH₄m^-2h^-1and 22.7 µ mol CH₄m^-2h^-1respectively. Emissions of CH₄from peatland changed with water table depth and soil temperature; increasing from 25 |Amol CH₄m^-2h^-1at 5% pool area to 50 p.mol CH₄m^-2h^-1with 30% within the flux footprint occupied by pools. A temperature response of 4.9 (xmol CH₄m^-2h^-1°C^-1in the range 6-12 °C was also observed. The close similarity in average CH₄emission fluxes reported for wetlands in Caithness, Hudson Bay and Alaska in the range 11 to 40 jamol CH₄m^-2h^-1suggests that earlier estimates of CH₄emission from high latitude wetlands were too large or that the area of high latitudes contributing to CH₄emission has been seriously underestimated.