Suggestions for In-class Activities

Since the purpose of this project it to determine the quality of a source of water, it is important to understand the meaning of the various tests and to understand how just even one factor might influence the conditions of your aquatic ecosystem. It is also important to know how to conduct the tests with a fair degree of accuracy so that your results will be "believable."

To help students understand what the test results mean (with respect to a healthy ecosystem) and to give them practice conducting the water sampling tests, it is recommended that they do preliminary testing on water obtained from an established aquarium. Factors such as temperature, pH, dissolved oxygen, BOD, carbon dioxide, nitrates, phosphates, turbidity, and coliform bacteria are all very important influences in an aquarium and even slight variations in levels can affect the fish and other organisms which live there. Students can also practice microscope skills by looking for microorganisms in the aquarium water.

Aquarium Water Testing

Follow the directions for each of the tests you will be conducting on water obtained from an established aquarium (preferably one that has both live fish and plants). Students should record their results and then discuss what each of their results mean.

Temperature:

What is the temperature in the aquarium? What would happen to the fish if the temperature increased? Decreased? How is temperature regulated in the aquarium?

pH:

What is the pH in the aquarium? What pH should pure water have? How does the pH level in the aquarium compare to the pH of pure water? Is the water acidic or alkaline (basic)? What would happen if the pH increased or decreased in the aquarium? What factors might influence pH in a lake or pond outside?

Dissolved Oxygen:

What is the DO level in the aquarium? Where does the oxygen come from? Why is oxygen needed in the water? What would happen if the DO level increased or decreased in the aquarium?

Biological Oxygen Demand:

What is the BOD level in the aquarium? How is BOD related to organic waste in the water? What would a high BOD level mean? What would a low BOD level mean? How is BOD related to DO levels?

Carbon Dioxide:

What is the CO2 level in the aquarium? What type of aquatic life depends on CO2 for survival? What would happen if the CO2 level increased or decreased in the aquarium? How is CO2 level related to DO level?

Phosphates:

What is the level of phosphates in the aquarium? Where might the phosphates come from? What would happen if the phosphate level increased or decreased? What would you expect to see if the phosphate level was high? How does the phosphate level relate to DO and BOD levels?

Nitrates:

What is the level of nitrates in the aquarium? Where might the nitrates come from? What would happen if the nitrate level increased or decreased? What would you expect to see if the nitrate level was high? How does the nitrate level relate to DO and BOD levels?

Turbidity:

What is the level of turbidity in the aquarium? What is turbidity? Describe how the turbidity level relates to what you can see (or cannot see) in the aquarium? What would happen if the turbidity level increased?

Coliform Bacteria:

Were there any coliform bacteria present in the aquarium? How might the presence or absence of coliform bacteria affect the water and aquatic life in the aquarium? How might the presence of coliform bacteria affect DO and BOD levels?

Microorganisms:

Looking through a microscope, try to identify any of the organisms you found in the water. If you can't identify them, draw a picture of what you see. What kinds of organisms would you expect to see in a healthy aquarium? What kinds of organisms would you expect to see in an unhealthy aquarium?

Extensions to the aquarium tests:

• Fill a beaker or jar with some of the aquarium water and place a mixture of soil, leaves, and grass (organic waste) in the water. Keep the beaker at room temperature for about a week. After a week, repeat the tests and record the results. What do you observe from the appearance of the water? Is algae present? How did pH, DO, BOD and CO2 levels change? Why do you think they changed? Is coliform bacteria present? Why/why not? Looking under microscope, does it appear that the number or types of organisms changed? Why might some organisms not be present any longer?
  
• Fill a beaker or jar with some of the aquarium water and add a dropperful of concentrated fertilizer to it. Keep the beaker near a window or under a grow light at room temperature for about a week. After a week, repeat the tests and record the results. What do you observe from the appearance of the water? Is algae present? How did pH, DO, BOD, CO2, phosphate and nitrate levels change? Why do you think they changed? Is coliform bacteria present? Why/why not? How would organisms in the water be affected by the addition of the nutrient-rich fertilizer?