Acid Rain and Animals: How does acid rain affect brine shrimp?
In this experiment, you will use vinegar, which is an acid, to gradually lower the pH level of water containing brine shrimp. (As the pH level drops, acidity increases.) You will measure the changing pH level and observe how the shrimp react.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of acid rain. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
- the topic of the experiment
- the variable you will change
- the variable you will measure
- what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "All the brine shrimp will be dead by the time the pH level of the water reaches 4.5."
In this case, the variable you will change is the pH level of the water, and the variable you will measure is the number of brine shrimp that remain alive. You expect them all to die by the time the pH level reaches 4.5.
You will also set up a control experiment. It will be identical to the "real" experiment, except that the pH level will remain the same in the control water and decrease in the experimental water.
After each pH decrease in the experimental water, you will estimate the number of brine shrimp that remain alive in the experimental and the control water. If the shrimp in the experimental water are all dead by the time the pH reaches 4.5, while most remain alive in the control water, you will know your hypothesis is correct.
Level of Difficulty
Moderate, because of the time involved.
- 1 tablespoon of live brine shrimp (Brine shrimp are sold as fish food at tropical and saltwater fish shops. The clerk will measure 1 tablespoon of shrimp, which contains several hundred shrimp, and pour it into a container of water.)
- 2 wide-mouth jars
- distilled water at room temperature (or tap water that has been in an open container overnight to allow the chlorine in it to evaporate)
- 2 small, clear containers
- 2 labels and a marker
- litmus paper and a color scale
- white vinegar
- measuring spoons
- a stirrer
- 2 medicine droppers
- 1 package dry yeast
- Optional: small aquarium pump with two outlets and plastic tubing
$5 for the brine shrimp, litmus paper, and yeast. (The other materials should be available in most households.)
How to Experiment Safely
Be careful in handling the glass jars. If possible, wear goggles so the vinegar will not splash in your eyes.
- Fill both glass jars half-full of water.
- Use the two small, clear containers to divide the brine shrimp into two equal portions.
- Pour one portion of shrimp into each of the jars. Rinse the small containers. Label one jar Control and one Experiment.
- Dip a different strip of litmus paper into each jar, check the color scale, and record the beginning pH level of each jar on a chart like the one illustrated.
- Use the following steps to take a sample of water from each jar and estimate the number of live shrimp in it:
- Gently stir the water in the experimental jar until the shrimp are distributed evenly.
- Quickly use a medicine dropper to take out a sample of water and shrimp.
- Deposit the sample in one of the clear containers.
- Count or estimate the number of live brine shrimp in it.
- Record the number on your chart.
- Pour the sample back into the same jar.
- Rinse the dropper and container.
- Complete the same process with the control jar.
- Use the other medicine dropper to slowly add 2 tablespoons (30 ml) of vinegar to the experimental jar. Again measure and record the pH level in that jar. Do not add vinegar to the control jar.
- Place both jars in a warm, lighted place where they will not receive direct sun. Add a pinch of dry yeast to both jars as food for the brine shrimp.
- Optional: Attach a length of plastic tubing to each outlet on the aquarium pump. Insert one of the tubes into each jar so it rests on the bottom of the jar. Start the pump, which will keep the water gently moving and increase its oxygen content.
- Each day for a week:
- Add another pinch of dry yeast to both jars.
- Add 2 more tablespoons of vinegar to the experimental jar.
- Measure and record the pH levels of both jars.
- Repeat Step 5 to monitor how many live brine shrimp remain in both jars. If no live brine shrimp remain in the experimental jar before the end of the week, end the experiment.
Summary of Results
Use the data on your chart to create a line or bar graph of your findings. Then study your chart and graph and decide whether your hypothesis was correct. At what pH level did the brine shrimp in the experimental jar start to die in greater numbers? At what level were they all dead? Did most of the shrimp in your control jar survive until the end of the week? Write a paragraph summarizing your findings and explaining whether they supported your hypothesis.
Source: Experiment Central. U·X·L, 2000.