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Seasonal variations in methane flux andδ l3 CH 4 values for rice paddies in Japan and their implications
Author(s) -
Tyler Stanley C.,
Brailsford Gordon W.,
Yagi Kazuyuki,
Minami Katsuyuki,
Cicerone Ralph J.
Publication year - 1994
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/93gb03123
Subject(s) - flux (metallurgy) , nutrient , paddy field , straw , growing season , fertilizer , methane , nitrogen , zoology , poaceae , agronomy , field experiment , environmental science , chemistry , biology , organic chemistry
We have made measurements of the methane (CH 4 ) flux and δ 13 C value in CH 4 from rice paddies in Ryugasaki, Japan. This study is the first we are aware of in which a significant change in the δ 13 C signature of emitted CH 4 has been documented over the rice growing season. Nutrient treatments studied were of two kinds: compound mineral fertilizer either with or without rice straw from the previous growing season incorporated into the inorganic fertilizer. The calculated annual emission rates during the 1990 growing season were 43.1 g/m 2 (straw) and 40.6 g/m 2 (no straw) for the two treatments. In both treatments, CH 4 started out relatively enriched in 13 C, became lighter in 13 C, and then became more enriched again during the latter part of rice growth. The 1991 growing season showed a lower integrated flux in both nutrient treatments than for 1990 but plots of the fluxes versus time had the same general shape as the flux curves in 1990 and a similar although less pronounced trend in δ 13 CH 4 signal. Seasonal changes in δ 13 C are probably related to changes in CH 4 production and oxidation and plant‐mediated transport. The likelihood of each process occurring and its effect on δ 13 C values is discussed. The range of δ 13 CH 4 values from seasonal effects was ∼12‰ in 1991 for both nutrient treatments. The δ 13 CH 4 range for 1991 was ∼10‰ (straw) and ∼5‰ (no straw). Our data indicate that when using flux‐weighted isotopic signatures to put constraints on the tropospheric CH 4 budget, attention should be paid to seasonal changes in isotopic signatures from rice paddy CH 4 in a manner similar to that previously suggested from measurements in natural wetlands.