Abstract

Objective

In this experiment you will test the effects of acidic water conditions on an aquatic environment containing algae, worms, snails, and plants.

Introduction

Acid rain occurs when pollution in the atmosphere (sulfur dioxide and nitrogen oxide) is chemically changed and absorbed by water droplets in clouds. When there is precipitation, the droplets fall to earth as rain, snow, or sleet. The polluting chemicals in the water droplets form an acid by combining with the hydrogen and oxygen in the water. These acidic droplets (pH < 5) can increase the acidity of the soil and affect the chemical balance of lakes and streams.

"Acid rain is a serious environmental problem that affects large parts of the US and Canada." (EPA, 2006) Acid rain accelerates weathering in carbonate rocks and accelerates building weathering. It also contributes to acidification of rivers, streams, and forest damage at high elevations (Wikipedia contributors, 2006).

What is an acid? An acidic solution will donate hydrogen ions and usually taste sour, like lemon juice. Acids are the opposite of bases, which accept hydrogen ions and usually feel slippery, like soapy water. How do you tell if something is an acid or a base? You use a chemical called an indicator, which changes in color when it goes from an acidic to basic solution. Indicators can be extracted from plant pigments, like red cabbage. If you want to learn how to make your own acid indicator, read the Science Buddies experiment Cabbage Chemistry.

In this experiment you will use an indicator that is concentrated on little strips of paper called "pH test strips". The color of the paper will indicate the pH of the solution you are measuring. Each one unit change in pH is a 10-fold change in the number of hydrogen ions in solution. Your pH test strips will come with a color chart that you can use to measure the pH of your vinegar solutions. This will give you a measurement of the acidity of your aquatic environments.

The goal of this experiment is to test the effects of acid rain on a simple aquatic ecosystem, consisting of small plants and animals. You will use household vinegar to create different solutions of various acidities. You will then observe the organisms in the experimental environment to determine the effects of acidic conditions on viability. To measure viability, you will count the number of living and non-living organisms in each experimental environment over time.

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• Acid rain
• pH
• Environmental toxicity
• Aquatic organisms
• Aquatic environments

• How will acidic conditions affect an aquatic ecosystem?
• Will all of the organisms be affected similarly or differently?
• Which pH ranges will cause an effect?

Bibliography

What can you do to reduce acid rain? The following website lists dozens of actions you and your family can take to reduce the use of fossil fuels, which emit sulphur dioxide and nitrogen oxides into the atmosphere, causing acid rain:

• The Green Lane. (2002, December 19). What's being done? What can you do? Retrieved July 3, 2006, from Environment Canada's website: http://www.ec.gc.ca/acidrain/done-you.html

This project was adapted from the Duckweed Bio-Assay protocol from Cornell University:

• EIP. (n.d.). Assessing Toxic Risk: Student Edition. Retrieved July 3, 2006, from the Cornell University Environmental Inquiry Program's website: http://ei.cornell.edu/teacher/pdf/ATR/Protocol2.pdf

This is a site just for kids that discusses acid rain:

• EPA. (2006). Acid Rain Students Site. Retrieved July 3, 2006, from http://www.epa.gov/acidrain/education/site_students/index.html

This site provides a thorough definition of acid rain:

• Wikipedia Contributors. (2006). Acid precipitation. Wikipedia: The Free Encyclopedia. Retrieved July 3, 2006, from http://en.wikipedia.org/w/index.php?title=Acid_precipitation

Materials and Equipment

• Distilled water, bottled (3 gallons)
• Measuring cups
• Large, reusable plastic containers with lids, 6-cup/48-oz. (5)
• Permanent marker
• Small bottle of white vinegar
• Medicine dropper; available at most drug stores
• Clean spoon
• pH test strips with small increments of change between 3.0 and 6.0; these can be found from online science vendors like Ward's Natural Science at www.wardsci.com, catalog # 15V3152. Note: A pH meter can be used instead, if one is available.
• Aquatic organisms: (should pick at least 3 different types of plants and animals; buy a minimum of 15 of each species)
  • Small, inexpensive fish (minnows, feeder fish, or goldfish from a pet shop or bait shop)
  • Small pond snails; available from a pond or aquarium supply store
  • Water fleas, such as Daphnia; available at aquarium supply stores
  • Live tubifex; available at aquarium supply stores, bait shops, or found in pond bottoms
  • Aquatic plants like duckweed or elodea; available at aquarium supply stores, ponds, or nurseries
  • Algae, such as spirulina; available at aquarium supply stores
• Lab notebook
• Graph paper

Experimental Procedure

1. Rinse each container thoroughly with water. Do not use soap because it can coat the plastic container and may be harmful to the organisms in your experiment. Label each container with a number, using the permanent marker.
2. Using the measuring cup, add 1,000 mL (4 cups) of water to each container. Use distilled bottled water. Tap water may contain chemicals, like chorine or chloramine, which could harm the aquatic life and ruin your experiment.
3. Using the pH strips, test the pH of the water in container #1. Record the pH in your lab notebook in a data table like the one below. Do not add any vinegar to this container.

   Bowl	Water	Drops of Vinegar	pH	Observations
   1	1,000 mL	0 drops
   2	1,000 mL
   3	1,000 mL
   4	1,000 mL
   5	1,000 mL

4. For bowls 2–5, use the medicine dropper to add vinegar to the water, one container and one drop at a time. After adding each drop, mix the water with a clean spoon and measure the pH with the test strips. The goal is to create four different solutions with increasing amounts of acidity, ranging from just below the pH of distilled water (use your measurements for container #1 as a guide) to a pH of approximately 4.3 (the pH of the most acidic rainwater falling in the United States in 2000, according to the Environmental Protection Agency).
   • Bowl #2 should have the fewest drops of acid and thus be the least acidic (closest in pH to the distilled water).
   • Bowl #5 should have the most drops of acid and thus be the most acidic (close to a pH of 4.3).
   • In your data table record the number of drops of acid and the final pH for each bowl.
5. Evenly distribute the organisms into each container, being sure to add a mixture of plants (algae, duckweed, elodea) and animals (aquatic worms, snails, and small crustaceans). Write down the number of each type of organism you are adding to the containers in your lab notebook. For example, "I added 10 snails,10 worms, and 20 duckweed plants to each container."
6. Observe the animals and write down observations in the data table. Continue your observations for a few hours, overnight, or for a few days, if necessary.
7. For each observation, count the number of organisms that are still alive for each different plant or animal. This is called a viability assay, because you are counting the number of things that are viable, or still living. For example, "At 3 PM there were 5 living snails, 2 living worms, and 7 living duckweed plants."
8. Make a graph of your results. On the left side (y-axis) of the graph, make a viability scale by graphing the number of living organisms of each type. On the bottom (x-axis) of the graph make a scale of the pH of the water. Then make a line graph for each type of organism in your study. Did they respond similarly or differently to the changes in pH of your environment? What is the viable pH range for each organism? Which organisms are the most sensitive or the most resilient (strong) when it came to changes in acidity?

Variations

• Another way to test the effect of acid rain on plants is to germinate seeds in acidic conditions. Try using your solutions to wet a paper towel in a baggie, sprinkle in some seeds, and place in a sunny window to see how many will sprout.
• You can also try watering a series of plants with neutral and acidic water. How well will plants grow when watered with "acid rain" compared to neutral water?
• Try these other Science Buddies experiments to test the effects of toxins on aquatic environments:
  • Heavy Metal
  • Something's Fishy About That Fertilizer

• For more science project ideas in this area of science, see Environmental Science Project Ideas.

Credits

Sara Agee, PhD, Science Buddies

Last edit date: 2009-04-22 21:00:00