Methane fluxes measured by eddy covariance and static chamber techniques at a temperate forest in central Ontario, Canada

• Main Authors: J. M. Wang, J. G. Murphy, J. A. Geddes, C. L. Winsborough, N. Basiliko, S. C. Thomas
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-06-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/10/4371/2013/bg-10-4371-2013.pdf

Methane flux measurements were carried out at a temperate forest (Haliburton Forest and Wildlife Reserve) in central Ontario (45°17´11´´ N, 78°32´19´´ W) from June to October 2011. Continuous measurements were made by an off-axis integrated cavity output spectrometer that measures methane (CH₄) at 10 Hz sampling rates. Fluxes were calculated from the gas measurements in conjunction with wind data collected by a 3-D sonic anemometer using the eddy covariance (EC) method. Observed methane fluxes showed net uptake of CH₄ over the measurement period with an average uptake flux (±standard deviation of the mean) of −2.7 ± 0.13 nmol m⁻² s⁻¹. Methane fluxes showed a seasonal progression with average rates of uptake increasing from June through September and remaining high in October. This pattern was consistent with a decreasing trend in soil moisture content at the monthly timescale. On the diurnal timescale, there was evidence of increased uptake during the day, when the mid-canopy wind speed was at a maximum. These patterns suggest that substrate supply of CH₄ to methanotrophs, and in certain cases hypoxic soil conditions supporting methanogenesis in low-slope areas, drives the observed variability in fluxes. A network of soil static chambers used at the tower site showed reasonable agreement with the seasonal trend and overall magnitude of the eddy covariance flux measurements. This suggests that soil-level microbial processes, and not abiological leaf-level CH₄ production, drive overall CH₄ dynamics in temperate forest ecosystems such as Haliburton Forest.