CARBON-DIOXIDE AND METHANE FLUXES FROM DRAINED PEAT SOILS, SOUTHERN QUEBEC

Fluxes of CO2 and CH4 were determined by a static chamber technique at eight drained swamp peatland sites, with crop and forest covers. Over a 6-month period (May - October, 1991), CH4 fluxes ranged from -5 to 7 mg CH4 m-2 d-1 and were not correlated with either soil temperature or water table position. Integrated seasonal emissions were -0.40 to 0.04 g CH4 m2 over 147 days; the sites with a forest or grass cover were a small sink of CH4 whereas the sites with horticultural crops showed no significant flux. Laboratory incubations showed that the highest CH4 consumption rates (3 to 9 mug CH4 g-1 d-1) occurred in the least disturbed soils. The results, when compared with CH4 fluxes from nearby swamps which have been unaffected by drainage, suggest that drainage of temperate peatlands has reduced emissions of CH4 to the atmosphere by 0. 6 - 1 x 10(12) g CH4 yr-1. CO2 fluxes ranged f rom 0 to 16 g CO2 m-2 d-1 and were correlated with the seasonal pattern of temperature in the upper part of the soil profile. Integrated seasonal fluxes for the sites in which root respiration was an unimportant contribution were 0.6 - 0.8 kg CO2 m-2 over 181 days. Aerobic laboratory incubations revealed CO2 production rates of 0.2 - 1.4 mg CO2 g-1 d-1, an average of 5 times the rate under anaerobic conditions. Using bulk density and loss-on-ignition data, we found that the seasonal CO2 fluxes translate into surface lowering of the peat of about 2 mm yr-1, whereas the commonly observed lowering in these cultivated peatlands is 20 mm yr-1. These data suggest that processes other than direct oxidation, such as shrinkage and aeolian erosion, are the major contributor to the surface lowering of the peat.