METHANE AND CO2 EXCHANGE OVER PEATLAND AND THE EFFECTS OF AFFORESTATION

The exchange of CH4 and CO2 over extensive tracts of peatland has recently been measured using micrometeorological methods. Fluxes of CH4 measured in Caithness (UK) during May and June 1994 using eddy covariance yielded fluxes in the range -70 to +170 mu mol CH4 m(-2) h(-1) with a mean flux of 39 mu mol CH4 m(-2) h(-1). Landscape emissions of CH4 from peatland are shown to vary with water table and temperature, increasing from 25 mu mol CH4 m(-2) h(-1) at 5 per cent area to 50 mu mol CH4 m(-2) h(-1) with 30 per cent within the footprint occupied by pool. A positive temperature response of 4.9 mu mol CH4 m(-2) h(-1) degrees C-1 in the temperature range 6-12 degrees C was also observed. The mean day time fluxes of CO2 during May and June 1994, of -3.6 mmol m(-2) h(-1) were two orders of magnitude larger than the emission of CH4 of 40 mu mol m(-2) h(-1), while at night (when net radiation is negative) the respiration flux of CO2 averaged +2.2 mmol m(-2) h(-1) approximately two orders of magnitude larger than night-rime CH4 emissions of 30 mu mol m(-2) h(-1).