Micrometeorological measurements of trace gas fluxes from agricultural and natural ecosystems

The use of micrometeorological techniques in determining the fluxes of trace gases from surfaces has long been hampered by the availability of reliable and sensitive sensors for field measurements. Recently, new laser-based technology has been developed at the University of Guelph for the accurate, high-speed measurement of the concentration and fluxes of trace gases. This tunable diode laser trace gas analyzer system (TDLTGAS) has been used to continuously monitor nitrous oxide fluxes from several agricultural surfaces, in a research program initiated in 1991. The natural event that caused the largest fluxes was soil thawing during the spring on non-cropped plots (bare soil, bare soil plus manure, and ploughed-down alfalfa). Monthly average fluxes of between 70 and 110 ng m(-2) s(-1) were observed during March and April of 1993 and 1994. Emissions from alfalfa and bluegrass plots were between 2 and 6 ng m(-2) s(-1) during spring thaw. During the winter of 1993/94 emissions ranged from 2 to 6 ng m(-2) s(-1) for snow covered plots, except for the ploughed-down alfalfa which averaged 30 +/- 3.5 ng m(-2) s(-1). A summary of methane fluxes measured by our research group using the TDLTGAS over agriculture surfaces including rice paddies, and natural surfaces such as northern wetlands, lakes, and the boreal forest are also discussed.