Eddy Covariance Measurements of Methane Fluxes Over Arable Land in Southern Ontario.

Agricultural soils provide a sink for atmospheric methane. Although the sinks are relatively small (~ -1 to -5 ng/m2s), this can translate to a significant quantity of methane consumption over large areas. The degree of sink strength can vary over time and space with changing soil moisture and texture, as well as variations in agricultural practices. Chamber measurements currently provide the majority of information on methane flux values for Ontario soils. Improvements in high-frequency trace gas instrumentation allows for easier eddy covariance flux measurements for methane, thus providing the opportunity for flux measurements over a larger integrated area than chambers. A Picarro G2311-f gas analyzer was recently acquired to measure CH4 and CO2 fluxes for a corn field in Southern Ontario treated with manure. The analyzer employs cavity ring-down spectroscopy to measure gas concentrations and integrates sonic anemometry for eddy covariance measurements. Since methane flux values are small for agricultural soils, noise tests assessed the detection limits of the Picarro system in order to differentiate between instrument noise and fluxes close to zero. A spectral response test characterized the analyzer's capacity to resolve flux values by using a random noise generator to simulate different sized eddies passing by an eddy covariance system. Results from these tests and the first field measurements obtained with this analyzer during the Spring of 2013 will be presented.