Environmental Engineering Reference
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between rDNA and chlorobactene of Chlorobiaceae measured in the photic
chemocline, the dark stagnant bottom waters (monimolimnion), and the dark
Holocene sediments, was therefore used to study the fate of ancient DNA in
the sulfidic aquatic and sedimentary environment.
The cycling of methane during the Holocene in Ace Lake as well as the
prokaryotes involved in methanogenesis and methanotrophy was reconstructed
based on the combined stratigraphic analysis of lipids and 16S rDNA [11]. In
this study we combined the latter lipid data with the data for carotenoids and
16S rDNA of GSB in order to get a more complete picture of the development
of Holocene anaerobic processes as well as physical characteristics of the water
column of Ace Lake.
2. EXPERIMENTAL
2.1 Setting
Ace Lake in the Vestfold Hills of eastern Antarctica (68 24'S, 78 11'E) is
a shallow saline meromictic lake with a maximum depth of 25 m, and usually
covered by ice for about 11 months of the year (Fig. 1). Salinity ranges from
6 at the surface to 43 in its bottom waters [8]. The water below 11.7 m
of present-day Ace Lake is anoxic, and contains high sulfide concentrations
(up to 8 mM towards the sediment; [18]), as a result of slow bacterial sulfate
reduction. At present, the water below 20 m of Ace Lake is depleted in sulfate
[9] (Fig. 2) and sulfate reduction rates are below the detection limit [19].
Methane occurs in the monimolimnion at depths greater than 11m, reaching
its highest concentration (up to 5mM) at the bottom of the lake [18] (Fig. 2).
Rates of methanogenesis in the water column of Ace Lake are slow reaching a
maximum of 2.5 µmol kg 1 day 1 at 20 m where sulfate is depleted [18].
During its post-glacial development, Ace Lake went through several climate-
induced stages as deduced from stratigraphic analysis of diatom assemblages
[15, 42], faunal microfossils [14, 51], as well as lipids and DNA of marine
haptophytes [12]. The oldest sediment layers recovered were deposited when
Ace Lake was a freshwater lacustrine basin filled with melt water (Unit III; 150-
135 cm, 10450-9400 calendar years before the present). Deglaciation caused
a world wide sea-level rise [53] and the introduction of surrounding seawater
into the freshwater basin. Subsequently, the isostatic rebound of the Antarctic
continent re-isolated Ace Lake from the ocean [2, 37, 53].
2.2 Sampling
Water samples were obtained in November 2000 using a Niskin bottle with
a length of 50 cm and a volume of 5 L from various positions in the water
column of Ace Lake. The sampling positions (measured from the ice sur-
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