Environmental Engineering Reference
In-Depth Information
Diffusion
Bioturbation
Sinking
Photo-oxidation
Precipitation
S assimilation/metabolism
SO
4
2
−
COS
DMS
COS
SO
4
2
−
Particulate Sulfur (AA/DMSP)
DMS
H
2
S
SO
4
2
−
Oxic Sediment
Anoxic
Sediment
H
2
S
Particulate Sulfur (AA/DMSP)
SO
4
2
−
FeS
2
/CuFeS
2
/Fe
1
−
x
S
Fig. 12.4 The sulfur cycle involves transformation of sulfur in the water column through physical
mechanisms such as diffusion (
light blue line
), bioturbation (
purple line
), and sinking (
dark blue
line
); chemical mechanisms of photooxidation (
orange line
), and precipitation (
yellow line
); and
biological mechanisms of sulfur assimilation and metabolism by phytoplankton (
green dash-dot
line
) and reduction and oxidation by bacteria in the sediment (
orange dashed line
)
is highly toxic to most organisms. In the deeper layers of the sediment, sulfide reacts
with iron and precipitates as iron sulfides such as pyrite (FeS
2
)[
30
]. Some sulfide
remains in the sediment, and, when mixed back into the oxic zone through pro-
cesses such as bioturbation, is quickly oxidized by sulfur-oxidizing bacteria into
sulfate, which can then remain in the sediment or be released into the overlying
water [
31
]. Sulfur oxidation and reduction by bacteria in the sediment are also
important to the functioning of the nitrogen cycle in oxygen-minimum zones [
32
].
In these environments, sulfate reduction provides a significant amount of the ammo-
nium used in the anammox reaction in anaerobic environments, and nitrate reduction
may be coupled to sulfide oxidation, indicating that the anaerobic mechanisms in
the sulfur cycle may also be important in the nitrogen cycle [
32
].
The presence of hydrogen sulfide around hydrothermal vents has resulted in the
development of unique organisms with the ability to use the energy contained in
hydrothermal fluids to produce organic compounds through chemoautolithotrophy
[
33
]. At hydrothermal vents seawater comes into contact with magma from the
