S. Lojen et al., Decomposition of sedimentary organic matter and methane formation in the recent sediment of Lake Bled (Slovenia), CHEM GEOL, 159(1-4), 1999, pp. 223-240
Decomposition of sedimentary organic matter and methane formation in a eutr
ophic dimictic subalpine lake (Lake Bled, NW Slovenia) were investigated by
measurement of in situ concentrations of dissolved inorganic carbon (DIC)
in the pore water and its stable carbon isotopic composition, as well as by
incubation experiments. The isotopic composition of carbon in the methane
produced during incubation experiments was also studied. The ratio between
methane produced by acetate fermentation and CO2/H-2 reduction was estimate
d from delta(13)C-DIC vs. DIC concentration profiles in sediment pore water
using a mathematical model developed by LaZerte [LaZerte, 1981. The relati
onship between dissolved carbon dioxide and its stable isotope ratio in aqu
atic sediments. Geochim. Cosmochim. Acta 45, 647-656]. It was found that in
the spring acetate fermentation is dominant when about 65% of methane is p
roduced by this reaction pathway, whereas in the autumn, over 90% of the me
thane results from CO2 reduction. delta(13)C of methane released during a 6
-week incubation experiment with sediment taken in the autumn varied betwee
n - 70 to - 85% V-PDB, i.e., values typical of methane produced by CO2/H-2
reduction, in spite of methane oxidation evident from the low delta(13)C-CO
2 values, thus confirming the results obtained by mathematical modelling. (
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