Geoscience Reference
In-Depth Information
4.1.4.1
Processes Affecting the Dissolved Oxygen
Balance in Water
The processes affecting the DO balance in aquatic ecosystems include atmospheric
reaeration, photosynthesis and respiration, oxidation of organic matter, oxidation of
inorganic matter, sediment oxygen demand, and nitrification.
56,64,65
These processes
are shown in Figure 4.5.
4.1.4.1.1 Reaeration
Dissolved oxygen concentrations in unpolluted water are usually close to, but less
than, 10 mg l
−1
.
66
If oxygen concentrations decrease below the saturation level due
to various physical, chemical, and biological processes, replenishment is provided
via atmospheric reaeration.
67
The dissolved oxygen saturation concentration is affected by several environmental
factors including temperature, salinity, and partial pressure variations due to elevation.
It decreases with increasing temperature and salinity and decreasing partial pressure
of oxygen.
45
There are several empirical equations to express the effects of these factors
on the oxygen saturation concentration. The following equation can be used to establish
the dependence of oxygen saturation concentration on temperature.
68
5
7
1 575701
.
×
10
6 642308
.
×
10
ln(
o
)
=−
139 34411
.
+
−
sf
2
T
T
a
a
(4.6)
10
11
1 243800
.
×
10
8 621949
.
×
10
+
−
4
4
T
T
a
a
Surface
Exchange
Photosynthesis
• Algae
• Macrophyte
•Fe
2+
•Mn
2+
•S
2
−
•
Respiration
Dissolved
Oxygen
Oxidation
•
Fish
NH
+
•
Zooplankton
Respiration
Decomposition
• Organic Matter
• SOD
FIGURE 4.5
Processes effecting dissolved oxygen concentration.
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