Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

摘要

Stable isotopes (δ13C, δD) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in13C (mean δ13C; −51.5 ±7.1‰ and−56.5 ± 4.6‰ for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(− 63 ± 5‰). Large seasonal variation was observed inδ13C(∼32‰) in the rice paddies, whereas variationinδD was much more smaller (∼20‰), indicating that variation inδ13C is due mainly to changes in methane production pathways.Values of δ13C were lower in swamps (−66.1 ±5.1‰)than in rice paddies. The calculated contribution of acetate fermentation fromδ13C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). δDin methane from Thai rice paddies (−324± 7‰ (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from−362 ± 5‰ (Mito: n=2) to −322 ± 8‰(Okinawa: n=3), due tohigher δD in floodwaters. 14C content in methane produced fromThai rice paddies (127±1 pMC) show higher 14Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).