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Sulfate Reduction
Sulfate reduction assays were set up using a modification of the
vial of sediment received approxi-
technique of Ivanov^ (1964) . Each
mately 1 pCi of Na„ SO, in 1 ml of anoxic ASW. Samples were mixed and
incubated for 2.0 n. The reaction was stopped by the addition of 0.5
ml of 2% zinc acetate followed by 0.2 ml of formalin. Samples were
assayed and rates determined in the Montana State University lab as
described by J^rgensen (1978). H„ S was distilled to traps containing
2% zinc acetate. Radioactivity was determined by counting the zinc
acetate trap (5 ml) in 10 ml Aquasol (New England Nuclear) on a Beckman
LS-100C liquid scintillation counter. Correction for quenching was by
the channels ratio method.
Methane Production
Methane production was measured by quantifying the increase in
methane in the head-space of vials containing sediment. A 0.2 ml gaseous
subsample was removed at desired intervals and analyzed by flame
ionization gas chromatography (see below).
Acetate Metabolism
..Acetate metabolism was measured by adding approximately 0.5 (JCi of
[2- C]-acetate in 1.0 ml of sterile anoxic sulfate-free ASW. Samples
were mixed and incubated for 2.0 h unless otherwise stated... The reaction
was stopped by the addition of 0.2 ml formalin. C0„ and/or
CH, were measured in samples of the gas headspace (see below).
Hydrocarbon Metabolism
All radiolabelled hydrocarbons except benzene and toluene were diluted
in benzene to the desired activity. The radioisotopes were added
to vials and the benzene allowed to evaporate completely before addition
of sediment and anaerobic tubing as described above. Anoxic ASW
(1.0 ml) was added to each sample to mix sediment and Radiolabelled benzene and toluene were dissolved
radioisotopes.
in anoxic ASW and
added (1.0 ml) after anoxic tubing of sediment. When indicated, samples
were incubated in darkness by wrapping with aluminum foil or
electricians tape. In one experiment samples contained in anaerobi-
cally sealed tubes were incubated within an anaerobic chamber (Gaspak)
with a H„ "\/C0 atmosphere. During long term incubations gaseous metabolities
( C0„ and/or CH.) were quantified in samples of the gas
headspace as described below. After incubation was completed, samples
were poisoned by addition of 0.5 ml 10% formalin. Carbon dioxide was
reabsorbed by addition of 2 ml 2N NaOH. The sediment was extracted
four times by vortex mixing with 6 ml methylene chloride: methanol
(9:1) followed by centrifugation to break the emulsion. Solvent frac-
tions were removed from beneath the aqueous phase and pooled together
with three 6 ml rinses of the original sample vial. Anhydrous sodium
sulfate was added to dry the sample. The extract was concentrated to
0.1 ml by evaporation and the volume increased by addition of 0.7 ml of
hexane. This sample was separated into saturate (f,), aromatic (f ? )
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