Environmental Engineering Reference
In-Depth Information
Sorokin has not detected SRR in the most part of the water column. In more
recent studies based on this method we [66-68] and Gulin [34] found that main
part of the Black Sea hydrogen sulfide is produced in the water column. Sorokin
subscribed to this view in his latest monograph [92]. According to our data,
the annual hydrogen sulfide production in the deep-sea sediments is 5.53·10 6
tons of sulfur, while in the water column the annual production is 20.2·10 6
tons of sulfur [67, 68]. Table 1 summarizes literature data on the annual sulfide
production in water column and sediments of the Black Sea.
Table 1. Annual H 2 S production in the water column and bottom sediments of the Black Sea
anoxic zone (depth below 200 m, total area - 306 × 10 3
km 2 ).
References
[66 - 68]
[34]
[1]
[92]
Water column
66
140
10
114
gm 2 y 1
Bottom sediments
18
16
17
12
gm 2 y 1
Annual production
26
48
8
27
10 6
t
All the data on the isotopic composition of hydrogen sulfide dissolved in the
water column measured at 17 stations (Fig. 1) are presented in Table 2. Figure 2
shows the typical water column distribution ofδ
34 SH 2 S with depth. It is evident
from these data that the isotopic composition of sulfur in the upper layers of
the hydrogen sulfide zone is less depleted in
34 S than in the deeper water
34 S values are the lowest (up to -42‰) and relatively uniform
independent of the location. The difference between the isotopic composition
of sulfide and sulfate (δ
column, where δ
34 S = 19.3‰) in the Black Sea water is more than 60‰.
So far no experiments with pure cultures of sulfate-reducing bacteria and
“natural populations” [14, 17, 37, 55] have resulted in such considerable differ-
ence between the δ
34 S values of sulfate and hydrogen sulfide. The maximum
fractionation factor in these experiments was 46‰. It is notable that in most
of the studies the lower fractionation factors have been observed at higher
cell-specific sulfate reduction rates and vice versa [14, 17, 55].
German scientists who have studied fractionation processes in 36 pure cul-
tures of sulfate reducers used a wide range of substrates. Their results casted
doubt that the inverse relationship between the sulfur isotopic fractionation and
the specific rate of sulfate reduction exists [23]. Despite the fact that the au-
thors have experimented with cells of different sizes, they expressed obtained
specific SRRs in moles/cell/day, which was an error. For example, one cell
of a rod-shaped sulfate-reducer (cell size 0.5
1.2 µm) contains 0.2 µm 3 of
biomass, the volume of a large spherical cell of Desulfosarcina variabilis (2 µm
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