The TerrAqua Column

Whether your students are in third grade or college, the TerrAqua Column (TAC) is a perfect vehicle to make science dynamic, relevant, and fun. Students learn the excitement of constructing their own environmental chambers from recycled materials, and they gain ownership and pride in the experiments they design. The TAC provides a compact, inexpensive, do-it-yourself model to explore the link between land and water and allows you to focus on specific aspects of a complex world.

Constructed from two 2-liter soda bottles, the TAC has three basic biotic components: soil, water, and plants (animals - such as snails, insects, or tadpoles - may be added to the system, also). By varying just one of the components you can explore how one variable affects the whole system. How does salt affect the growth of plants? How does adding fertilizer to the soil affect algal growth in the water chamber? What type of soil is best for purifying water?

Experimentation with the TAC is practically unlimited. Help your students define a question, then design an experiment to explore it. For example, students might observe that a lake near school is suddenly overtaken with algae. Given all the environmental factors influencing the lake, it would be difficult to determine exactly what encouraged the slimy green stuff to get out of control.

Students could build several TACs to explore what specific factors might encourage algal growth. Encourage them to take samples of lake water and local soil, for example, then to test the samples under different conditions to determine in which environments algae grow best.

The more clearly students learn to define their questions and plan their studies, the more successful the experiments will be. Variables to consider include the type and amounts of soil, water, and plants. Remember, depending on their source, the soil and water likely contain algae, fungi, mites, worms, etc. Substances that might affect terrestrial and aquatic systems include nutrients (fertilizers) or pollutants (salts, pesticides, acids).

With every experiment you run, set up one control TAC in which you do not vary any of the components. This acts as a standard against which you can compare the effects of the variables you change.

Remember, keep it simple. The TAC is a simple model, but all of its parts are dynamic. Keep your investigations very simple by changing only one variable of the system at a time. Keep the following questions in mind:

1. What question are you exploring?
2. What specific idea (hypothesis) are you testing?
3. What variable will you change in your experiment?
4. What items will you need?
5. What is your experimental procedure?
6. Do the results of your experiment support the hypothesis?

Adapted with permission from Paul H. Williams, Bottle Biology (1993), Kendall/Hunt Publishing Company.