CO2 fluxes from peat in boreal mires under varying temperature and moisture conditions

1 CO2 emissions in boreal peatlands were measured during two seasons on various mire site types representing different nutrient statuses and water tables. In order to examine the long term effects of water table draw-down on the CO2 fluxes, the sites also included 25-50-year-old drainages. 2 On virgin sites the lowest CO2 fluxes were measured at ombrotrophic sites dominated by Sphagnum fuscum (78-127 mg CO2 m(-2) h(-1) at 12 degrees C, 60-200 g CO2-C m(-2) year(-1)) and the highest CO2 fluxes were at ombrotrophic sites with abundant understorey vegetation (183-259 mg CO2 m(-2) h(-1) at 12 degrees C, 290-340 g CO2-C m(-2) year(-1)). 3 Lowering of the water table by 1 cm increased CO2 fluxes by an average of 7.1 mg CO2 m(-2) h(-1) at 12 degrees C and 9.5g CO2-C m(-2) year(-1). In some cases the effect of ditches on the water table, and correspondingly on CO2 fluxes, was small. However, effective draining caused approximate to 100% increase in CO2 fluxes. Drainages had higher CO2 fluxes compared with virgin subsites at the same temperature and water table. 4 The effect of temperature on CO2 fluxes depended on the water table, the average Q(10) value being 2.9 with water tables of 0-20 cm and 2.0 with water tables below 20 cm. 5 CO2 fluxes are compared with primary production figures, and peat carbon stores and the carbon balance in changing climate are discussed.