Premium
Stable isotope fractionation during the methanogenic degradation of organic matter in the sediment of an acidic bog lake, Lake Grosse Fuchskuhle
Author(s) -
Conrad Ralf,
Claus Peter,
Casperb Peter
Publication year - 2010
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2010.55.5.1932
Subject(s) - methanogenesis , organic matter , environmental chemistry , fractionation , chemistry , anoxic waters , sedimentary organic matter , sediment , total organic carbon , methane , geology , chromatography , organic chemistry , paleontology
Lake Grosse Fuchskuhle is an acidic bog lake, which develops an anoxic hypolimnion during the summer season, so that sediment organic matter is degraded anaerobically to CH 4 and CO 2 . The δ 13 C values of organic matter and its degradation products were used for determination of the mass balance, degradation path, and fractionation factors. Addition of methyl fluoride, an inhibitor of acetoclastic methanogenesis, increasingly inhibited CH 4 production and resulted in accumulation of acetate (and a little propionate), which then was an additional end product of organic matter degradation. The δ 13 C of acetate‐methyl group was slightly lower than that of organic matter, indicating a small fractionation (about 4%) during the fermentative production of acetate. Chemolithotrophic acetogenesis was low (< 9%). The fraction of CH 4 produced from hydrogenotrophic methanogenesis was about 55‐67%. After incubation for 20 h the average δ 13 C of the degradation products was similar to that of sediment organic matter, both in the absence and the presence of CH 3 F. The produced total inorganic carbon (TIC) was further converted to CH 4 with apparent enrichment factors of 56–67%. The fraction of TIC that was actually converted to CH 4 was calculated to be about 33% and 23% in the absence and presence of CH 3 F, respectively. These data are consistent with the assumption that about half of the organic matter was incompletely degraded, resulting in the production of only CO 2 and H 2 , afterward converted to CH 4 . The data further show that the reduction of CO 2 to CH 4 was partially inhibited in the presence of CH 3 F.