ABSTRACT: A methane budget at the ground and water surface level was estimated in various ecosystems in Shiga Prefecture, central Japan, and its seasonality was measured. Measuring sites were set up in 9 of 11 land use types in Shiga Prefecture, and methane fluxes were measured by the chamber method for 1 yr. Methane emission rates from sources were generally high in summer: the mean emission rate was 19.4 mg CH₄ m^-2 h^-1 from a paddy field and 9.6 mg CH₄ m^-2 h^-1 from a Phragmites swamp in July-August. In 4 main types of forest, atmospheric methane was absorbed 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 methane was emitted in summer, about 370 Mg CH₄ d^-1 in July-August. In winter, however, the methane emission from the area as a whole was much lower than that in summer, owing to a decrease of methane emission from the sources. In particular, forest ecosystems absorbed about 3.4 Mg CH₄ d^-1 in November-December, an amount exceeding that of the emission from the other land use types. Summing the annual methane emissions and absorption of every land use type and adding the estimates of methane emissions from domestic animals and landfills, the annual net release 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 paddy fields to the total emission was the highest, at 81.7%. The annual methane absorption by forests was estimated to be about 1.0 Gg CH₄, representing 2.7% of the total emission.

KEY WORDS: Methane budget . Wide area . Emission and absorption . Seasonal change

Published in CR Vol. 6, No. 1 (1996) on January 30
ISSN: 0936-577X. Copyright © Inter-Research, Oldendorf/Luhe, 1996