Premium
Measurements of stable isotope ratios( 13 CH 4 / 12 CH 4 ; 12 CH 3 D/ 12 CH 4 ) in landfill methane using a Tunable Diode Laser Absorption Spectrometer
Author(s) -
Bergmaschi Peter,
Harris Geoffrey W.
Publication year - 1995
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 - 10.1029/95gb02582
Subject(s) - analytical chemistry (journal) , oxygen 18 , methane , chemistry , stable isotope ratio , oxygen , isotope , isotopes of oxygen , nuclear chemistry , environmental chemistry , physics , organic chemistry , quantum mechanics
Variations in the isotopic composition (δ 13 C, δD) of methane produced within a landfill site near Mainz, Germany, were studied using a newly developed tunable diode laser absorption spectrometer (TDLAS) method. Additional data on the mixing ratios of CO 2 , O 2 , N 2 , CH 4 itself and δ 13 C of the CO 2 in the landfill gas were also acquired. Samples taken from several branches of the landfill biogas collection system had methane isotopic compositions in the range δ 13 C = −62.3 to −55.3‰ VPDB ( n = 23) and δD = −327 to −287‰ VSMOW ( n = 23). Although the variability of the stable isotope ratios is small, several significant correlations were found between these and the other measured parameters, which provide insight into the microbiological processes occurring within the landfill. Several samples showed evidence of admixture of atmospheric air which occurs when the pumping rate in the collection branch exceeds the local methane production rate. A fraction of the atmospheric oxygen is consumed during the passage through the landfill and CO 2 is produced in addition to the CO 2 associated with methanogenesis. The consumption of oxygen is correlated with the δ 13 C and δD of CH 4 and the δ 13 C of CO 2 . The correlation is consistent with partial bacterial oxidation of CH 4 resulting in the progressive enrichment of the remaining CH 4 (α(δ 13 C) = 1.008 ± 0.003 and α(δD) = 1.044 ± 0.020) and in the formation of very depleted CO 2 . For samples showing no evidence of oxidation, there was a negative correlation between δD and δ 13 C(CH 4 )( r = −0.86, n = 14) and between δ 13 C(CO 2 ) and δ 13 C(CH 4 ) ( r = −0.95, n = 14), which we interpret as originating from slightly varying contributions from the two methanogenic pathways CO 2 reduction and acetate fermentation.