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DISSOLVED OXYGEN
Dissolved oxygen is oxygen that is dissolved in water. It gets there by diffusion from the
surrounding air, by aeration of water which has tumbled over falls and rapids and as a
waste product of photosynthesis. Fish and aquatic animals cannot split oxygen from
water or other oxygen containing compounds. Only green plants and some bacteria can
do that through photosynthesis and similar processes. Virtually all the oxygen we
breathe is manufactured by green plants. A total of three-fourths of the Earth's oxygen
supply is produced by algae - Phytoplankton (tiny green plants) in the oceans.
photosynthesis
In the presence of
light and chlorophyll
Carbon dioxide + water
oxygen + Sugar
If there is not enough oxygen in the water supply, it may be because the water is too
warm, or because there are too many bacteria or aquatic animals in the area. If aquatic
animals don't have enough predators to keep their numbers down, they will over
populate and use great amounts of dissolved oxygen.
One of the ways oxygen levels are often reduced in agricultural areas is via the run-off
from farm fields containing fertilizers. This phosphate and nitrate rich water also
"fertilizes" the water way causing the number and size of plants to grow a great deal.
Then, if weather becomes cloudy for a few days, respiring plants will use much of the
available dissolved oxygen. When the increased number of water plants eventually die,
they become food for bacteria, which in turn multiply and use large amounts of oxygen.
This can have drastic effects on the types of plants and animals that are able to live in
this body of water and, over time can greatly change the plant and animal life in and
around it.
The amount of dissolved oxygen an aquatic organism needs depends upon its species,
the temperature of the water, pollutants present, the physical state of the organism and
more! Consequently, it's impossible to accurately predict minimum dissolved oxygen
levels for specific fish and aquatic animals.
Nevertheless, numerous scientific studies suggest the minimum amount of dissolved oxygen that
will support a large population of many kinds of fish is from 4-5 parts per million (ppm). Good
fishing water generally averages about 9 ppm dissolved oxygen.
When dissolved oxygen drops below 3 ppm, even the rough fish die.
Species of Fish
Northern Pike
Black Bass
Sunfish
Perch
Black Bullhead
Lowest Amount of DO to survive
(mg/L) Summer
6.0
5.5
4.2
4.2
3.3
Lowest Amount of DO to survive
(mg/L) Winter
3.1
4.7
1.4
4.7
1.1
Name ____________________________________________ Hour______________
Dissolved Oxygen Questions
1. Name 3 ways that Oxygen can get into water:
2. Write a formula for Photosynthesis:
3. What produces the majority of Oxygen that we have here on Earth?
4. How much of the Earth’s Oxygen comes from Algae?
5. What is “Phytoplankton”?
6. What can Lower the amount of Oxygen in water?
7. What will happen if Phosphates and Nitrates get into the water?
8. What will happen to oxygen levels in the water when Water Plants Die?
9. The “amount of dissolved oxygen that an aquatic organism needs depends upon”:
10. What is the Minimum amount of Dissolved Oxygen that most fish need to live?
11. Good fishing water has about how much Dissolved oxygen?
12. When dissolved oxygen drops below _______________________ all fish die.
13. From the chart – Which fish can tolerate the lowest amount of oxygen in the water?
14. From the chart – Which fish needs the most oxygen in the Summer months?