Environmental Engineering Reference
In-Depth Information
Table 3.
The mean and range of concentrations of sulphur intermediates in the Black Sea
anoxic zone (from [97]).
Depth,
Number
H
2
S,
µ
M
S
0
,
µ
M
S
2
O
3
2
−
,
µ
M
m
of samples
Range
Average
Range
Average
Range
Average
115-150
16
0.5-22.1
8.1
0.06-5.4
0.66
0-1.7
0.45
150
7
13.5-28.8
15.3
0-1.2
0.38
0.05-1.5
0.54
160
8
16.5-34.6
20.1
0-2.2
0.53
0-3.4
1.1
170
5
3.7-36.9
23.5
0-1.0
0.41
0-1.6
0.60
180
4
11.4-42.1
24.5
0.13-0.63
0.44
0.04-3.7
1.3
200
5
n.d.
0.38-3.1
1.1
0.5-3.1
1.3
250
7
n.d.
0.34-5.1
1.3
0.26-5.9
1.6
300
5
n.d.
0.75-1.6
1.2
0.42-4.5
1.7
400
1
n.d.
n.d.
1.4
n.d.
1.6
500
4
n.d.
1.0-5.0
2.4
0.11-1.7
1.0
750
3
n.d.
0.59-1.4
0.91
1.3-2.7
2.1
1000
4
n.d.
1.5-2.5
2.1
1.0-4.2
2.1
1500
2
n.d.
2.3-2.9
2.6
1.7-2.7
2.2
2000
3
n.d.
2.1-4.6
3.4
1.5-3.5
2.8
elemental sulphur was collected on 0.2µm filters. The maximum concentration
measured at two central Black Sea stations in the anoxic zone was 61 nM (with
a minimum detection limit between 5 and 10 nM). In contrast with Volkov
[97], the concentration of S
0
did not change with depth. Luther [50] suspected
that very low concentrations of elemental sulphur and probably even lower of
polysulphides indicate that these species once formed can undergo rapid up-
take or disproportionation by microorganisms. Luther [50] data for elemental
sulphur are in the same order of magnitude as the data presented by Jørgensen
et al. [32]. Vairavamurthy and Mopper [92] have detected maximum concentra-
tions of sulphite and thiosulphate of 2.1 and 2.9 µM, respectively, in the Black
Sea bottom waters using a derivatization method with a high-pressure liquid
chromatography (HPLC) separation and quantification.
This brief overview of the existing data on the distribution of inorganic
sulphur intermediates in the Black Sea anoxic zone shows a confused picture
that may reflect both the non-equilibrium kinetics of chemical transformations
within the sulphur cycle, and differences in methods employed. The origin of
zero-valent elemental sulphur in the anoxic zone needs further investigation.
This is particularly relevant to studies addressing ventilation of the anoxic
zone by entrained modified Bosporus waters carrying dissolved oxygen and
the existence of sulphur disproportionation reactions in the anoxic interior.
Future progress in the field will depend on the advance in analytical techniques
