Dissolved Oxygen Levels
Investigating the Solubility
of Gases
Solubility of Oxygen Gas in Water
• Check out this solubility
curve for oxygen gas in
water.
• What is the solubility at
20°C?
• At 40°C?
• What can you conclude
about the solubility of
oxygen as temperature
goes up?
Is this true for other gases?
Carbon dioxide
CH4 = methane, CO = carbon monoxide, He = helium
What can we conclude about the
solubility of gases in water with
respect to temperature?
Let’s do a demonstration!
I need two assistants.
How does the solubility of gases
compare with solids?
Compare at 30 °C
Another solubility factor is pressure
• So how does
pressure affect
solubility?
• When you open a can
of soda, what
happens to the
pressure of the soda?
• What happens to the
gas that was
dissolved in the
soda?
Could temperature have an affect
on the fish kill?
We just learned that temperature affects
how much oxygen gas can dissolve in
water, here the Snake River. Different
aquatic life forms have different
requirements for the concentration of
dissolved oxygen for survival.
The dissolved oxygen requirements are
different in summer and winter.
Dissolved oxygen requirements for
fish by season
Fish species
Summer (mg/L) Winter (mg/L)
Pike
6.0
3.1
Black crappie
5.5
4.7
Yellow perch
4.2
1.5
Green sunfish
3.3
3.5
Black bullhead
3.3
1.2
Trout
4.1
?
Salmon
3.9
?
Dissolved oxygen (mg liter-1) concentrations required by different Chesapeake
Bay species and communities (Source: EPA)
How does temperature
affect fish internally?
• As temperature increases, there is _____
dissolved oxygen in water for fish to
breathe!
• BUT, as temperature goes up, so does the
fish’s body temperature (it is a coldblooded creature) and its metabolism
increases. This means it eats more,
swims more and requires _____ dissolved
oxygen to breathe.
• Water temperatures can get too high for
fish, as in summer when long stretches
of hot weather lead to too little dissolved
oxygen in the water and large fish kills.
Maximum water temperature (24 hour exposure)
Trout
Catfish
Lake herring
Largemouth
bass
Northern pike
°C
°F
24
35
75
95
25
77
34
93
30
86
What human practices can lead to
higher temperatures in rivers?
• Industries that use natural bodies of
water to cool their heat-producing
processes, such as electrical power
generation.
Can there be too much
oxygen for fish?
Yes! When the total amount of
dissolved gases—oxygen
and nitrogen—reaches 110%
to 124% of saturation
(supersaturation), fish can
develop GAS BUBBLE
TRAUMA.
This situation can occur at the
base of a dam or hydroelectric project where
released water forms “froth.”
Gas Bubble Trauma
• The supersaturated gases cause bubbles
of oxygen and nitrogen to form in the fish’s
blood and tissues.
• The fish may be able to use some of the
oxygen, but the nitrogen bubbles block
blood flow within the fish, leading to death.
• This is related to the human condition
which affects scuba divers if they ascend
too rapidly called “the bends.”