242
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
The incubation procedure remains the same as described above for
sulfide: O.lml of the thiosulfate working solution, or 1-5/-tl of the SO working
solution are added to 200-300-ml bottles. The portion of the elemental sulfur
solution first is injected into 2-3ml of water taken from the same bottle into
a small test tube with a plastic cork. The contents of the test tube is then vigorously shaken and this water is thcn transferred with the aid of a pipet
attached to the syringe back into the bottle and rapidly mixed. After the incubation ends, the same 0.5 ml of carrier solution is added to the samples with
thiosulfate to stop oxidation. First 1 ml of 2 % solution of sulfur (SO) in benzole
is added to the samples with element sulfur as a carrier. The sample is thoroughly mixed. Then 0.5 ml of 10% thiosulfate + 10% of sulfate-mixed carrier
solution is added to the freshwater samples, or only thiosulfate if they are
marine samples.
The processing of thiosulfate samples proceeds as described above with
sedimentation of thiosulfate sulfane sulfur as Ag2S and its subsequent oxidation and radioassay as BaS04. During sample processing with elemental sulfur,
the first operation is the separation of SO by filtration of water through the
membrane filters covered with MgC03. In the filtrate the sulfate is precipitated as BaS04, which is then separated by filtration. The thiosulfate passes
into the filtrate, where it is oxidized and sedimented as sulfate with BaCI2• The
amount of SO oxidized in this case is equal to the sum of radioactivity of sulfate
+ 112 of the radioactivity of thiosulfate. The calculation of the rate of SO and
s2ol- oxidation is made as described for sulfide.
The localization of active thiobacilli populations in water columns may be
characterized by the curves of their relative vertical profiles. To derive such
curves, the experiments are carried out in accordance with the scheme
described above for methane-oxidizing bacteria (see Sect. 5.2.2), but, instead
of methane, 0.3 ml of 1 % thiosulfate solution is added to each experimental
bottle. The remaining procedure is the same.
5.6 Study of Sulfate Reduction
5.6.1 General Remarks
The microbial reduction of sulfates to sulfides is among the key factors determining the "appearance" of aquatic ecosystems. It significantly influences their
structure and functional parameters as well as the very quality of aquatic environments (Ohle 1954; Sorokin 1960d; Kuznetsov 1963; Kellog et aI., 1972;
Goldhaber and Kaplan 1974; Jorgensen 1977, 1988; Ivanov 1979). Sulfates are
used by specialized obligate anaerobic sulfate-reducing bacteria as electron
acceptors during the respiratory decomposition of organic matter in anaerobic habitats of water bodies. The share of these bacteria in total anaerobic
decomposition of organic matter approaches 50%. The end product of their
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
The incubation procedure remains the same as described above for
sulfide: O.lml of the thiosulfate working solution, or 1-5/-tl of the SO working
solution are added to 200-300-ml bottles. The portion of the elemental sulfur
solution first is injected into 2-3ml of water taken from the same bottle into
a small test tube with a plastic cork. The contents of the test tube is then vigorously shaken and this water is thcn transferred with the aid of a pipet
attached to the syringe back into the bottle and rapidly mixed. After the incubation ends, the same 0.5 ml of carrier solution is added to the samples with
thiosulfate to stop oxidation. First 1 ml of 2 % solution of sulfur (SO) in benzole
is added to the samples with element sulfur as a carrier. The sample is thoroughly mixed. Then 0.5 ml of 10% thiosulfate + 10% of sulfate-mixed carrier
solution is added to the freshwater samples, or only thiosulfate if they are
marine samples.
The processing of thiosulfate samples proceeds as described above with
sedimentation of thiosulfate sulfane sulfur as Ag2S and its subsequent oxidation and radioassay as BaS04. During sample processing with elemental sulfur,
the first operation is the separation of SO by filtration of water through the
membrane filters covered with MgC03. In the filtrate the sulfate is precipitated as BaS04, which is then separated by filtration. The thiosulfate passes
into the filtrate, where it is oxidized and sedimented as sulfate with BaCI2• The
amount of SO oxidized in this case is equal to the sum of radioactivity of sulfate
+ 112 of the radioactivity of thiosulfate. The calculation of the rate of SO and
s2ol- oxidation is made as described for sulfide.
The localization of active thiobacilli populations in water columns may be
characterized by the curves of their relative vertical profiles. To derive such
curves, the experiments are carried out in accordance with the scheme
described above for methane-oxidizing bacteria (see Sect. 5.2.2), but, instead
of methane, 0.3 ml of 1 % thiosulfate solution is added to each experimental
bottle. The remaining procedure is the same.
5.6 Study of Sulfate Reduction
5.6.1 General Remarks
The microbial reduction of sulfates to sulfides is among the key factors determining the "appearance" of aquatic ecosystems. It significantly influences their
structure and functional parameters as well as the very quality of aquatic environments (Ohle 1954; Sorokin 1960d; Kuznetsov 1963; Kellog et aI., 1972;
Goldhaber and Kaplan 1974; Jorgensen 1977, 1988; Ivanov 1979). Sulfates are
used by specialized obligate anaerobic sulfate-reducing bacteria as electron
acceptors during the respiratory decomposition of organic matter in anaerobic habitats of water bodies. The share of these bacteria in total anaerobic
decomposition of organic matter approaches 50%. The end product of their