THE EFFECT OF FORESTRY DRAINAGE PRACTICES ON THE EMISSION OF METHANE FROM NORTHERN PEATLANDS

Methane (CH4) flux was measured from undrained, drained, and ditched portions of treed fen, forested bog, and treed bog sites in the Wally Creek experimental drainage site (near Cochrane, Ontario), from May to October 1991. Drainage for 7 years lowered the water table from between -21 and -49 cm to -41 and -93 cm at the three respective sites. Drainage resulted in a conversion of the peatlands from a CH4 source (0 to 15 mg CH4 . m(-2). d(-1)) to a small CH4 sink (0 to -0.4 mg CH4 . m(-2). d(-1)). In contrast, CH4 efflux from the ditches ranged from <5 to >400 mg CH4 . m(-2). d(-1). The flux data were used to estimate the impact of forest drainage practices on net CH4 emissions from a forest drainage complex. For the treed and forested bogs, there was a net increase in CH4 emissions where ditch spacing was closer than 38 m. Even with very close ditch spacing (>12 m), there was a net decrease in CH4 flux from the treed fen. The results of this study indicate that the combination of low antecedent CH4 fluxes from an undrained peatland, and moderate fluxes from the drainage ditches, will produce a net increase in CH4 emissions from forest drainage.