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Production of methane from alasses in eastern Siberia: Implications from its 14 C and stable isotopic compositions
Author(s) -
Nakagawa Fumiko,
Yoshida Naohiro,
Nojiri Yukihiro,
Makarov VladimirN.
Publication year - 2002
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 - 10.1029/2000gb001384
Subject(s) - methane , environmental chemistry , organic matter , carbon dioxide , δ13c , methanogenesis , isotopes of carbon , carbon cycle , permafrost , carbon fibers , atmospheric methane , total organic carbon , stable isotope ratio , chemistry , environmental science , geology , ecosystem , ecology , oceanography , physics , biology , materials science , organic chemistry , quantum mechanics , composite number , composite material
The radiocarbon ( 14 C) and stable isotopic ( 13 C and D) compositions of methane and carbon dioxide from alasses (typical landforms in permafrost terrain, consisting of lakes and wetlands) were measured around Yakutsk, eastern Siberia, where few isotope studies have been done. The carbon isotopic compositions of methane and carbon dioxide were used to study the pathways of methane formation in alasses. The mean value of methane and of carbon dioxide in each alass ranged from −63.9 to −58.2‰ and from −16.7 to −0.6‰, respectively. In small alasses, where the supply of fresh organic matter from surrounding wetland ecosystems is large, methane was produced almost equally from acetate fermentation and CO 2 reduction pathways. In larger alasses the CO 2 reduction pathway slightly dominates over acetate fermentation, owing to a smaller supply of labile organic matter. The 13 C enrichment in CO 2 in large lakes indicates depletion of methane precursors. Gas‐bubble methane is depleted in deuterium (the mean δD value from lakes is −360 ± 14‰ and from shores is −380 ± 20‰), which reflects the deuterium‐depleted environmental water (from −136 to −117‰) of alasses. Lake methane relatively enriched in D is interpreted to be the result of depletion in the hydrogen pool in lake sediments. Methane in shallow lakes is somewhat enriched in 14 C relative to modern biogenic methane and is produced from fresh, recently fixed organic matter. The 14 C content of methane from deeper lakes is 10–20% less than that of shallow lake methane, indicating a greater contribution from older methane derived from deeper parts of the sediment. The mean 13 C, D, and 14 C of methane from the alasses in general are estimated to be −61.1 ± 4.4‰, −363 ± 20‰, and 104 ± 6 pMC, respectively. This corresponds to the reported mean isotopic composition of methane from wetlands for δ 13 C, but shows lower value for δD and 14 C content.