Dynamics of greenhouse gas formation in relation to freeze/thaw soil depth in a flooded peat marsh of Northeast China

Flooded peat wetlands are an important global carbon pool and are relatively sensitive to frost degeneration due to global climate change. To study the dynamics of greenhouse gas (GHG) formations in the soil of a flooded peat marsh in response to freeze-thaw processes, CO2, CH4 and N2O fluxes and gas concentrations at different soil depths were measured in a flooded peat marsh in Northeast China during a freeze-thaw period (from November 2004 to July 2005). During the freeze period, the gas concentrations underneath the frozen soil increased as the freeze developed until the soil completely froze in the root (15−35 cm) and peat (35−80 cm) layers. The highest gas concentrations accumulated in the gley layer (80−120 cm) when the greatest freeze depth formed. During the thaw period, the gas concentrations increased above the frozen layer (15−60 cm); in contrast, the gas concentrations underneath the frozen layer (60-120 cm) rapidly decreased when the bottom of the frozen layer began to thaw. GHG emissions from the marsh were not correlated with gas concentrations underneath the frozen layer during the freeze period but were significantly correlated with gas concentrations above the frozen layer (15−60 cm) during the thaw period. The study suggested that large changes in GHG formation dynamics occurred underneath the frost in the flooded peat marsh when the frost began to thaw due to gas physical diffusion within the peat layer.