Methanogenesis in the sediment of the acidic Lake Caviahue in Argentina |
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| Authors: | Matthias Koschorreck Katrin Wendt-Potthoff Burkhard Scharf Hans H Richnow |
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| Institution: | 1. Helmholtz Centre for Environmental Research – UFZ, Department of Lake Research, Brückstr. 3a, D-39114 Magdeburg, Magdeburg, Germany;2. Helmholtz Centre for Environmental Research – UFZ, Department of Isotope Biogeochemistry, Permoserstr. 15, D-04318 Leipzig, Germany |
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| Abstract: | The biogeochemistry of methane in the sediments of Lake Caviahue was examined by geochemical analysis, microbial activity assays and isotopic analysis. The pH in the water column was 2.6 and increased up to a pH of 6 in the deeper sediment pore waters. The carbon isotope composition of CH4 was between − 65 and − 70‰ which is indicative for the biological origin of the methane. The enrichment factor ε increased from − 46‰ in the upper sediment column to more than − 80 in the deeper sediment section suggesting a transition from acetoclastic methanogenesis to CO2 reduction with depth. In the most acidic surface layer of the sediment (pH < 4) methanogenesis is inhibited as suggested by a linear CH4 concentration profile, activity assays and MPN analysis. The CH4 activity assays and the CH4 profile indicate that methanogenesis in the sediment of Lake Caviahue was active below 40 cm depth. At that depth the pH was above 4 and sulfate reduction was sulfate limited. Methane was diffusing with a flux of 0.9 mmol m− 2 d− 1 to the sediment surface where it was probably oxidized. Methanogenesis contributed little to the sediments carbon budget and had no significant impact on lake water quality. The high biomass content of the sediment, which was probably caused by the last eruption of Copahue Volcano, supported high rates of sulfate reduction which probably raised the pH and created favorable conditions for methanogens in deeper sediment layers. |
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| Keywords: | methanogenesis acidic lake biogeochemistry sediment carbon isotopes |
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