244
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
line or Zn-acetate (see below, Sect. 6.4). The trapped H 2S is then analyzed colorimetrically, iodometrically, or gravimetrically as the BaS04 precipitates after
the oxidation of sulfide to sulfate. The contents of H 2S in water samples is estimated colorimetric ally or iodometrically. The contents of AVS within 50 to 150
mgSdm- 3 of wet sediment in the upper layers of marine or freshwater sediments is its normal level. If it rises to 500--1000 mg dm- 3 , thc ecosystcm is
endangered and should be treated correspondingly to decrease the impact
caused by its destabilization. The appearance of even traces of free H 2S in
water columns is a sign of disastrous developments which need immediate
counteraction.
The level of the accumulation of AVS in the upper 0-5-cm layer of the
bottom sediment, like the possible appearance of free H 2S in the bottom water
layer, are controlled by the rates of reciprocal processes of H 2S production by
sulfate reduction bacteria and its chemical and biological oxidation. Therefore
to predict ecological developments connected with sulfur cycling it is also necessary to measure the in situ rate of sulfide formation during sulfate reduction. Whether this rate appears to be high (>10mgSdm- 3 day-l) even at a low
ambiental AVS content in the upper sediment layer, the basin may be endangered by a rapid subsequent rise of the boundary between gray oxidated and
black reduced sediments, and by the appearance of a black color on the bottom
surface. Then any stagnation and decrease of oxygen concentration in the
water columns can be accompanied by the appearance free H 2S in the water
columns and by mortality of zoobenthos. An example of the dependence of
the zoo benthos biomass on the sulfide content in the upper layer of bottom
sediments is given in Fig. 5.4.
The radioisotopic method for estimation of in situ rate of H 2S AVS formation during bacterial sulfate reduction was developed by Ivanov (1956), and
was based on the use of sulfate labeled with the sulfur 35S radioisotope. The
labeled 35S-SO/- sulfate is added to the samples of bottom sediments or water.
After some 20 to 30 h of incubation at the in situ temperature, the sulfide sulfur
formed during the incubation during the reduction of sulfate by bacteria is
extracted and its radioactivity is measured (R;). Having determined the
inverse specific radioactivity of ionic sulfate sulfur in the sample (Sr) , the
absolute amount of sulfide sulfur S2- produced during incubation in a given
sample is calculated as R;Sr.
This method was practically used for measuring the rate of sulfate reduction in sulfur lakes (Ivanov and Terebkova 1959), and modified version was
applied by Sokolova and Sorokin (1957); Kravtzov and Sorokin (1959) and
Sorokin (1960d) for measuring it in the sediments of water reservoirs,
meromictic lakes (Sorokin 1960d; 1970b, 1975), and the Black Sea (Sorokin
1962, 1964a, 1972b, 1983b). A thorough methodological studies made later by
Ivanov (1968), Jorgensen and Fenchel (1974), and Jorgensen (1977, 1978)
resulted in its further modification and modernization.
Some confusion in efforts to further improve it arose owing to the discovery of a significant labeling of pyrite (FeS2) and the element sulfur together
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
line or Zn-acetate (see below, Sect. 6.4). The trapped H 2S is then analyzed colorimetrically, iodometrically, or gravimetrically as the BaS04 precipitates after
the oxidation of sulfide to sulfate. The contents of H 2S in water samples is estimated colorimetric ally or iodometrically. The contents of AVS within 50 to 150
mgSdm- 3 of wet sediment in the upper layers of marine or freshwater sediments is its normal level. If it rises to 500--1000 mg dm- 3 , thc ecosystcm is
endangered and should be treated correspondingly to decrease the impact
caused by its destabilization. The appearance of even traces of free H 2S in
water columns is a sign of disastrous developments which need immediate
counteraction.
The level of the accumulation of AVS in the upper 0-5-cm layer of the
bottom sediment, like the possible appearance of free H 2S in the bottom water
layer, are controlled by the rates of reciprocal processes of H 2S production by
sulfate reduction bacteria and its chemical and biological oxidation. Therefore
to predict ecological developments connected with sulfur cycling it is also necessary to measure the in situ rate of sulfide formation during sulfate reduction. Whether this rate appears to be high (>10mgSdm- 3 day-l) even at a low
ambiental AVS content in the upper sediment layer, the basin may be endangered by a rapid subsequent rise of the boundary between gray oxidated and
black reduced sediments, and by the appearance of a black color on the bottom
surface. Then any stagnation and decrease of oxygen concentration in the
water columns can be accompanied by the appearance free H 2S in the water
columns and by mortality of zoobenthos. An example of the dependence of
the zoo benthos biomass on the sulfide content in the upper layer of bottom
sediments is given in Fig. 5.4.
The radioisotopic method for estimation of in situ rate of H 2S AVS formation during bacterial sulfate reduction was developed by Ivanov (1956), and
was based on the use of sulfate labeled with the sulfur 35S radioisotope. The
labeled 35S-SO/- sulfate is added to the samples of bottom sediments or water.
After some 20 to 30 h of incubation at the in situ temperature, the sulfide sulfur
formed during the incubation during the reduction of sulfate by bacteria is
extracted and its radioactivity is measured (R;). Having determined the
inverse specific radioactivity of ionic sulfate sulfur in the sample (Sr) , the
absolute amount of sulfide sulfur S2- produced during incubation in a given
sample is calculated as R;Sr.
This method was practically used for measuring the rate of sulfate reduction in sulfur lakes (Ivanov and Terebkova 1959), and modified version was
applied by Sokolova and Sorokin (1957); Kravtzov and Sorokin (1959) and
Sorokin (1960d) for measuring it in the sediments of water reservoirs,
meromictic lakes (Sorokin 1960d; 1970b, 1975), and the Black Sea (Sorokin
1962, 1964a, 1972b, 1983b). A thorough methodological studies made later by
Ivanov (1968), Jorgensen and Fenchel (1974), and Jorgensen (1977, 1978)
resulted in its further modification and modernization.
Some confusion in efforts to further improve it arose owing to the discovery of a significant labeling of pyrite (FeS2) and the element sulfur together