Why do we care about dissolved oxygen?
Fish and other aquatic animals can only use oxygen that has dissolved in the water - which is MUCH less abundant than it is in our atmosphere. Dissolved oxygen concentrations in water can only reach about 12 ppm (or 0.0012%), compared to our atmosphere, which is about 20% oxygen.
"Coldwater" fish such as trout need at least 6-7 ppm. If oxygen concentrations get too low, these fish, and many of the aquatic insects they feed on, will not be able to survive.
Oxygen in water also affects other chemicals in the water. At very low oxygen concentrations many metals dissolve into a more harmful form. At higher oxygen concentrations these same metals are not harmful.
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Oxygen can get so low in polluted waters that all the fish are killed. Luckily these fish kills are rare in East Canyon Creek watershed.
How do human activities affect dissolved oxygen in East Canyon Creek?
Fish and plants use oxygen to help them convert food or sugars to other body parts and energy. Microbes that decompose dead material use oxygen the same way. This is why streams with a lot of dead material (leaves, animal waste, etc) may have VERY low dissolved oxygen concentrations.
Humans also affect the temperature of streams which in turn can affect dissolved oxygen, because less oxygen can dissolve into warm water than in cold water.
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