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 <>
"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).
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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
- This project was adapted from the Duckweed Bio-Assay protocol from Cornell University:
EIP, Date unknown. "Assessing Toxic Risk: Student Edition," Environmental Inquiry Program (EIP), Cornell University [accessed July 3, 2006]
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," U.S. Environmental Protection Agency (EPA) [accessed July 3, 2006]
http://www.epa.gov/acidrain/education/site_students/index.html - Wikipedia contributors, 2006. "Acid precipitation," Wikipedia, The Free Encyclopedia [accessed July 3, 2006]
http://en.wikipedia.org/w/index.php?title=Acid_precipitation
Materials and Equipment
- large bottle of white vinegar
- 3 gallons of distilled (bottled) water
- pH test strips (Alkalive pH Stix can be found at natural food pharmacies, or you can order pH test strips from a scientific supply company like Carolina Biological)
- measuring cups
- 6 large, reusable plastic containers with lids (6 cups / 48 oz, e.g. Glad or Zip-lock)
- permanent marker for labeling
- aquatic organisms: (should pick at least 2 plants and 2 animals)
- small, cheap fish (minnows, feeder fish, or goldfish from pet shop or bait shop)
- small pond snails (pond or aquarium supply store)
- water fleas (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 (spirulina, available at aquarium supply stores)
Experimental Procedure
- 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 permanent marker.
- Prepare the solutions for each container according to the data table below, one container for each experimental group. Use bottled water, not tap water, because it may contain harmful chemicals like chlorine or chloramine:
Bowl Water Vinegar Total Volume pH Observations 1 1000 mL 0 mL 1000 mL 2 900 mL 100 mL 1000 mL 3 800 mL 200 mL 1000 mL 4 700 mL 300 mL 1000 mL 5 600 mL 400 mL 1000 mL 6 500 mL 500 mL 1000 mL - Check the pH of each container with your pH test strips and record the data in your data table.
- 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. For example, "I added 10 snails,10 worms, and 20 duckweed plants to each container."
- Observe the animals and write down observations in the data table. Continue your observations for a few hours, or overnight if necessary.
- 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."
- 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 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:
Credits
Sara Agee, Ph.D., Science Buddies
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