METHANE BUDGET DETERMINED AT THE GROUND AND WATER-SURFACE LEVEL IN VARIOUS ECOSYSTEMS IN SHIGA PREFECTURE, CENTRAL JAPAN

A methane budget at the ground and water surface level was estimated i n various ecosystems in Shiga Prefecture, central Japan, and its seaso nality was measured. Measuring sites were set up in 9 of 11 land use t ypes in Shiga Prefecture, and methane fluxes were measured by the cham ber method for 1 yr. Methane emission rates from sources were generall y high in summer: the mean emission rate was 19.4 mg CH4 m(-2) h(-1) f rom a paddy field and 9.6 mg CH4 m(-2) h(-1) from a Phragmites swamp i n July-August. In 4 main types of forest, atmospheric methane was abso rbed by forest soils, at mean rates ranging from 0.01 to 0.12 mg CH4 m (-2) h(-1). The methane budget of Shiga Prefecture in each season was evaluated on the basis of the following data: A large amount of methan e was emitted in summer, about 370 Mg CH4 d(-1) in July-August. In win ter, however, the methane emission from the area as a whole was much l ower than that in summer, owing to a decrease of methane emission from the sources. In particular, forest ecosystems absorbed about 3.4 Mg C H4 d(-1) in November-December, an amount exceeding that of the emissio n from the other land use types. Summing the annual methane emissions and absorption of every land use type and adding the estimates of meth ane emissions from domestic animals and landfills, the annual net rele ase of methane to the atmosphere in Shiga Prefecture was estimated to be about 34.1 Gg CH4, Among all land use types, the contribution of pa ddy fields to the total emission was the highest, al 81.7%. The annual methane absorption by forests was estimated to be about 1.0 Gg CH4, r epresenting 2.7% of the total emission.