25th International Meeting on Organic Geochemistry IMOG 2011

P-436
Methane oxidation in the water column of Lago di Cadagno
(Switzerland)
Carsten J. Schubert 1 , Andreas Krupke 2 , Mathias Kirf 1 , Daniela Franzke 2 , Marcel M.M.
Kuypers 2
1 Eawag, Swiss Federal Institute of Aquatic Science and Technology, Kastanienbaum, Switzerland, 2 MPI for
Marine Microbiology, Bremen, Germany (corresponding author:carsten.schubert@eawag.ch)
The methane cycle in the water column of Lago di
Cadagno was investigated. Lake Cadagno is a
meromictic lake located in the catchment area of a
dolomite vein rich in gypsum in the Piora valley in the
Southern Alps of Switzerland (46°33‘N, 8°43‘E). The
lake lies at 1923 m above sea level and has a
maximum water depth of 21 m in summer. It covers
an area of 26 ha with a volume of 2.4*10 6 m 3 and a
water temperature of 4-6°C below 13 m (Del Don et
al. 2001). The water column is characterized by a
high salinity monimolimnion and a permanent
chemocline moving during the year between a depth
of 9 and 14 m, separating the oxic epilimnion from the
anoxic, sulfidogenic hypolimnion. The lake bottom
below the redox transition zone is anoxic all the time
(Wagener et al., 1990). Due to the infiltration of
subaquatic spring water flowing through gypsum rich
dolomites, Lake Cadagno water contains relatively
high concentrations of sulfate (1.5 mmol l -1 ),
hydrogen-carbonate, calcium, magnesium, and
sulfide (1 mmol l -1 ) resulting from sulfate reduction in
the hypolimnion and sediments (Hanselmann &
Hutter, 1998; Del Don et al., 2001; Dahl et al., 2010).
We detected no oxygen below 10.8 m but high sulfide
(up to 280 �M) in the hypolimnion. Nitrate was not
available below 12.5 m, ammonium concentrations
increased to 40 �mol l -1 at 17.5 m depth (Halm et al.,
2009) and iron (II) was below 5 �mol l -1 in the bottom
water and not available in the uppermost sediments
(Hanselmann & Hutter, 1998).
High methane concentrations occur in the
hypolimnion (up to 48 �mol l -1 ) until methane
oxidation in the chemocline reduces methane
concentrations (300 nmol l -1 ). Methane oxidation is
indicated by an increase in carbon isotopic
composition from the hypolimnion (-76 ‰ VPDB) to
very heavy values (11 ‰ VPDB) in the chemocline.
Incubations at in-situ temperatures revealed methane
oxidation rates to be lowest in 9 m water depth (50
nmol l -1 h -1 ) under oxic conditions and highest in 13m
water depth (3300 nmol l -1 h -1 ) under anoxic
conditions. No common anaerobic methane oxidizers
(ANME group) were detected using FISH and also
AAA cells recently shown to occur in Lake Cadagno
sediments (Schubert et al. 2011) were missing.
Investigations using nano-SIMS measurements on
microbial cells from water samples incubated with 13 C
13
labeled methane showed highly C enriched
methanotroph type I cells at 10 m. Furthermore, we
will present the results from a combination of single
cell and lipid analysis.
References
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Frei, R., and Canfield, D.E. (2010) The behavior of
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Del Don, C., Hanselmann, K. W., Peduzzi, R., and
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