Greenhouse gas fluxes in a drained peatland forest during spring frost-thaw event

摘要

Fluxes of greenhouse gases (GHG) carbon dioxide (CO₂), methane(CH₄) and nitrous oxide (N₂O) were measured during a two monthcampaign at a drained peatland forest in Finland by the eddy covariance (EC)technique (CO₂ and N₂O), and automatic and manual chambers(CO₂, CH₄ and N₂O). In addition, GHG concentrations and soilparameters (mineral nitrogen, temperature, moisture content) in the peatprofile were measured. The aim of the measurement campaign was to quantifythe GHG fluxes during freezing and thawing of the top-soil, a time periodwith potentially high GHG fluxes, and to compare different flux measurementmethods. The forest was a net CO₂ sink during the two months and thefluxes of CO₂ dominated the GHG exchange. The peat soil was a smallsink of atmospheric CH₄ and a small source of N₂O. Both CH₄oxidation and N₂O production took place in the top-soil whereasCH₄ was produced in the deeper layers of the peat, which were unfrozenthroughout the measurement period. During the frost-thaw events of thelitter layer distinct peaks in CO₂ and N₂O emissions wereobserved. The CO₂ peak followed tightly the increase in soiltemperature, whereas the N₂O peak occurred with a delay after thethawing of the litter layer. CH₄ fluxes did not respond to the thawingof the peat soil. The CO₂ and N₂O emission peaks were not capturedby the manual chambers and hence we conclude that high time-resolutionmeasurements with automatic chambers or EC are necessary to quantify fluxesduring peak emission periods. Sub-canopy EC measurements and chamber-basedfluxes of CO₂ and N₂O were comparable, although the fluxes ofN₂O measured by EC were close to the detection limit of the system. Weconclude that if fluxes are high enough, i.e. greater than 5–10 μg N m?2 h?1,the EC method is a good alternative to measure N₂Oand CO₂ fluxes at ecosystem scale, thereby minimizing problems withchamber enclosures and spatial representativeness of the measurements.