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Micro Water Cycle

Create a complete ecosystem within a terrarium and explore the water cycle as it occurs at your desk!

Heat from outside the jar will warm up the water in the "mini-lake", causing it to evaporate. As the water vapour cools on the lid, it will condense and precipitate (rain) down on the soil and the lake, and the water cycle will start all over again.

Moisture in an established terrarium is taken up by roots, and evaporates from the soil and plant leaves. It condenses on the terrarium roof and walls. Then, the condensed water falls down (like rain) and re-moistens the soil in a continual closed loop process. As long as the top is sealed, this process can continue cycling for months. This cycle mimics the water cycle found on a global scale. 

Objectives

  • Describe phases of the water cycle.

  • Model the water cycle.

Materials

  • Per Terrarium:
    commercial-size mayonnaise jar with screw-on lid
    small stones
    sand
    potting soil
    small plants such as mosses, ivy, baby ferns or small tropical plants
    shell or large bottle cap
    water

Key Questions

  • What causes the water to turn into water vapour?

What To Do

  1. Layer the following in the bottom of the jar: stones, 1 cm deep; sand, to cover stones; soil, about 10 cm deep.
  2. Create a nice arrangement for the plants and bury the roots in the soil. Don’t crowd the plants!
  3. Sprinkle a small amount of water over the plants and soil.
  4. Fill the shell or cap with water to create a “mini-lake” in the terrarium.
  5. Keep the terrarium in a shady place and watch what happens over the next few days.

Extensions

  • Experiment with a warmer or cooler "climate". How does that affect the speed of the water cycle?
  • What do the plants need to grow?
  • Experiment with changing the soil type – mix the sand with the soil or change the amount of water added.