BIO 116 – Intro. To Env. Science
S. Dockstader, Instructor
Name______________________________________
Spring 2007
Dissolved Oxygen in Water
Answer Key
ANALYSIS QUESTIONS
1. At what temperature was the dissolved oxygen concentration the highest? Lowest?
The amount of dissolved oxygen will be the highest at the coldest temperature and lowest at
the warmest temperature
2. Draw a line on your graph that connects the data points. What does your data indicate how
the amount of dissolved oxygen in the water is affected by the temperature of water? (Be
sure to explain the shape of your curve)
As the temperature increases, the amount of dissolved oxygen decreases. The relationship
does not appear to be linear
Please refer to your data graph to answer analysis questions 3-5:
3. If you analyzed the invertebrates in a stream and found an abundant supply of caddisflies,
mayflies, dragonfly larvae, and trout, what minimum concentration of dissolved oxygen
would be present in the stream? What maximum temperature would you expect the stream to
sustain?
Since trout are present, the minimum amount of dissolved oxygen would be 6.5mg/L.
According to these data, fast-moving water could not be warmer than 30-32 ºC. However,
this temperature is much higher then trout actually live in.
4. Mosquito larvae can tolerate extremely low dissolved oxygen concentrations, yet cannot
survive at temperatures above approximately 25°C. How might you account for dissolved
oxygen concentrations of such a low value at a temperature of 25°C? Explain.
Other factors must have caused the low dissolved oxygen levels. Bacteria and other
organisms can lower the dissolved oxygen of water when they respire aerobically.
5. Why might trout be found in pools of water shaded by trees and shrubs more commonly than
in water where the trees have been cleared?
Trout require high dissolved oxygen levels. Since trees shade the water from the sun, they
help to keep the water cool. Cool water has a higher dissolved oxygen level than warm water
and is preferred by trout.
* Adapted from Experiment 15 from the third edition of Biology with Computers: Biology Experiments Using
Vernier Sensors. Vernier Software & Technology, Beaverton, OR 97005-2886
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Dissolved Oxygen in Water
Note the measured values will be different because the sensors were not calibrated. The
trend of the graph should look similar.
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