Evaluation of Greenhouse Gas Fluxes over Agricultural and Natural Ecosystems by means of Micrometeorological Methods

A new method for calculating diffusion velocities within the canopy boundary layer was established, and applied to the CO2 flux measurements resulting in grater accuracy than the normal aerodynamic method.A movable NDIR-CH4 analyzer for field measurements was developed. The vertical CH4 concentration gradient showing CH4 uptake by the ecosystem was obtained continuously over a grassland, which gave a downward CH4 flux of 30-60mg m-2h-1. CH4 flux over a flooded rice field ranged between 5-10mgCH4 m-2h-1 in the daytime and 3-5mg m-2h-1 at night. The daily amount of CH4 emission from the flooded rice field ranged between 80-210mgCH4 m-2d-1. At night the upward CO2 flux of the rice field was higher under high temperature conditions, which brought about a higher CO2 sink strength in cool summer weather than in hot summers.