Winter methane dynamics in a temperate peatland

Methane (CH4) dynamics in pore water, snow pore air, and surface emissions were investigated in a temperate poor fen in New Hampshire over several winters. Total snowfall and average air temperatures during winter months (defined as December, January, and February) were climatologic indicators of significant flux rates from this midlatitude poor fen. Average winter emissions, for the five winters ending in 1994-1995, were 20, 39, 53, 56, and 26 mg m(-2) d(-1) amounting to 2.0, 5.2, 6.6, 9.2, and 2.0% of the total annual fluxes, respectively. Totaling emissions over 5 years that represent low to average snowfall, winter accounted for 4.3% of emissions to the atmosphere. Winter flux rates were near 55 mg m(-2) d(-1) for years with average snowfall, and 25 mg m(-2) d(-1) for years with low snowfall. Concentrations of CH4 sampled in pore water immediately beneath the ice were highly variable (0 to 1.1 mM). The concentration magnitude and standard deviation increased toward the fen center and correlated with spatial variation in hydrology, peat texture, and peat depth. CH4 stores increased in the near-surface pore water as the ice cover formed. Seasonal CH4 buildup in deeper peat began near the end of the growing season, probably due to changing transport mechanisms and temperature effects on solubility. Stored CH4 in the 25- to 75-cm peat layer decreased by 2.7 g m(-2) between January and June 1995.