Study of Sulfate Reduction
249
oceanographic tables or determined in samples of the same water as is used
to dilute the sediments in the experimental vessels.
5.6.2.2 The Slurry Method
Sediment samples are taken from the grab or from the core tube with the aid
of a spoon into plastic containers of 100-150 ml capacity and closed without
air bubbles under the cap. Depending on the goal of research, the upper 0-3cm layer only is sampled. If it is necessary to make estimations on the vertical profile, the samples may also be taken from along the core or from the
depth of the grab monolith. At the same time, a sample of water of 1-21 is also
taken from the near-bottom layer.
Back in the laboratory before starting the experiments, first the calculated
amount of natural water (-70 ml per incubating subsample) is prepared as
follows. It is boiled to decrease oxygen content in it and cooled, being capped
by a rubber stopper with a tube pushed into the flask with the same water to
avoid contact with air; 0.5mI5% solution of Na2S9H20 1-1 and several drops
of 10% solution of FeS04 are added to this cooled water until the water
acquires a murky color. Then the water is neutralized down to pH 8.5 with
HCl, if necessary, and its volume adjusted to a mark on the flask to know its
exact volume; 1-2 mIl-I or 100-300IlCil-1 for seawater and 5-101lCi for freshwaters of the working solution of labeled sulfate is added to this volume. This
water, thus charged with radioisotopic solution, is distributed into the experimental vessels up to two thirds of their volume just before the sediment
samples are added. Test tubes of 50-60cm 3 capacity or standard calibrated
cylinders can be used as experimental vessels, both with plastic or rubber stoppers. The subsamples of sediments (5 cm 3 ) are taken with a calibrated tube
rinsed just before subsampling. After the sediment is discharged into the
experimental vessels, its remains on the inner walls of the tube are washed
down with the liquid contained there. Then the vessel is filled completely with
the same water containing the label, closed with a stopper without air bubbles,
and overturned several times to mix the sediment with the water. The use of
a common water sample charged with isotope for all samples within one series
avoids the boring procedure of measuring the sulfate content and its radioactivity in every incubated subsample, because in this case the inverse specific
radioactivity of labeled sulfate (Sr) is equal within the whole series. The series
of charged subsamples is placed for incubation in vertical position into the
darkened aquarium at the in situ temperature. The duration of incubation
depends on the temperature. If the latter is over 20°C, incubation should
be for 15-25 h, between 10 and 20°C it should be 1-2 days, and less than
10 °C up to 4 days. For each series, also one killed control should be made
with the sediment prekilled with formalin. When the incubation time ends,
the experimental vessel is opened, and 4-5 ml of supernatant water is discharged. It is fixed with 1 ml of 10% solution of ZnCb or Zn-acetate and its
249
oceanographic tables or determined in samples of the same water as is used
to dilute the sediments in the experimental vessels.
5.6.2.2 The Slurry Method
Sediment samples are taken from the grab or from the core tube with the aid
of a spoon into plastic containers of 100-150 ml capacity and closed without
air bubbles under the cap. Depending on the goal of research, the upper 0-3cm layer only is sampled. If it is necessary to make estimations on the vertical profile, the samples may also be taken from along the core or from the
depth of the grab monolith. At the same time, a sample of water of 1-21 is also
taken from the near-bottom layer.
Back in the laboratory before starting the experiments, first the calculated
amount of natural water (-70 ml per incubating subsample) is prepared as
follows. It is boiled to decrease oxygen content in it and cooled, being capped
by a rubber stopper with a tube pushed into the flask with the same water to
avoid contact with air; 0.5mI5% solution of Na2S9H20 1-1 and several drops
of 10% solution of FeS04 are added to this cooled water until the water
acquires a murky color. Then the water is neutralized down to pH 8.5 with
HCl, if necessary, and its volume adjusted to a mark on the flask to know its
exact volume; 1-2 mIl-I or 100-300IlCil-1 for seawater and 5-101lCi for freshwaters of the working solution of labeled sulfate is added to this volume. This
water, thus charged with radioisotopic solution, is distributed into the experimental vessels up to two thirds of their volume just before the sediment
samples are added. Test tubes of 50-60cm 3 capacity or standard calibrated
cylinders can be used as experimental vessels, both with plastic or rubber stoppers. The subsamples of sediments (5 cm 3 ) are taken with a calibrated tube
rinsed just before subsampling. After the sediment is discharged into the
experimental vessels, its remains on the inner walls of the tube are washed
down with the liquid contained there. Then the vessel is filled completely with
the same water containing the label, closed with a stopper without air bubbles,
and overturned several times to mix the sediment with the water. The use of
a common water sample charged with isotope for all samples within one series
avoids the boring procedure of measuring the sulfate content and its radioactivity in every incubated subsample, because in this case the inverse specific
radioactivity of labeled sulfate (Sr) is equal within the whole series. The series
of charged subsamples is placed for incubation in vertical position into the
darkened aquarium at the in situ temperature. The duration of incubation
depends on the temperature. If the latter is over 20°C, incubation should
be for 15-25 h, between 10 and 20°C it should be 1-2 days, and less than
10 °C up to 4 days. For each series, also one killed control should be made
with the sediment prekilled with formalin. When the incubation time ends,
the experimental vessel is opened, and 4-5 ml of supernatant water is discharged. It is fixed with 1 ml of 10% solution of ZnCb or Zn-acetate and its