Background Information
Most living things
including aquatic organisms use oxygen in respiration. Oxygen
comprises approximately 21% of the total gases in our atmosphere, some
of which naturally dissolves in water. The amount of oxygen dissolving
in water is influenced by many factors including water temperature , photosynthesis,
respiration, and turbulence. Only a small portion of atmospheric
oxygen can remain in water even under the most optimum conditions.
Dissolved oxygen (D.O.) is the amount of
oxygen present in water. All aquatic environments depend on D.O.,
because a vast majority of living organisms need oxygen in order to survive.
The level of dissolved
oxygen in a stream is closely linked to temperature. Cooler water
results in higher levels of dissolved oxygen. Warmer water results
in lower levels of dissolved oxygen. According to Henry's Law,
the amount of dissolved oxygen is inversely proportional to the temperature.
(This is illustrated in the chart below.) This variation of temperature
has a direct influence upon the variety of fish species found. Trout
and salmon are species which prefer the cooler temperatures.
Solubility of Oxygen in Water
|
Temperature C
|
Solubility mg/L
|
|
0
|
14.6
|
|
5
|
12.8
|
|
10
|
11.3
|
|
15
|
10.1
|
|
20
|
9.2
|
|
25
|
8.4
|
|
30
|
7.6
|
Note. Values are for water
exposed to normal air containing 21% oxygen at 760 mm pressure.
Photosynthesis
is the process by which plants and organisms capture the sun's light
energy and changes it to chemical energy. One of the waste products
produced from photosynthesis is oxygen (02). This is one factor that
helps determine the amount of D.O. within a stream. Organisms
that contain chlorophyll go through the process of photosynthesis; however,
all living things respire. Respiration
occurs when oxygen reacts with carbon containing molecules releasing carbon
dioxide (CO2), water (H2O) and energy. This use of oxygen is one
factor that lowers dissolved oxygen in streams. All living organisms
rely on respiration to help carry out the life processes such as movement,
reproduction and growth.
Another factor which
influences incorporation of oxygen into water is turbulence which occurs
when water travels around and over obstructions like boulders. These
obstructions force the water to split its path. As the water meets again,
it creates a rough interface called turbulence. This agitation incorporates
oxygen into the water.
Tendency for Oxygen to Dissolve Due to Turbulence
Turbulence Class
|
Turbulence Class
|
Dissolving Factor
|
|
0.00
|
0.00
|
|
1.00
|
0.6
|
|
2.00
|
2.00
|
|
3.00
|
3.00
|
|
4.00
|
7.77
|
|
5.00
|
23.0
|
|
6.00
|
37.0
|
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