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The Hydrologic Cycle (page 2)

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Author: Janice VanCleave

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Model the hydrologic cycle using moist soil as a source of water. Repeat the original experiment, but fill the bowl with about 1 inch (2.5 cm) of soil and add warm water to moisten the soil.

Design Your Own Experiment

The Movement of Water from Place to Place

  1. Transpiration adds water to the hydrologic cycle. Demonstrate transpiration by placing a clear plastic bag over a group of leaves at the end of a stem of a tree or bush. (Do not cut or break the stem off the plant.) Secure the bag to the stem by wrapping tape around the open end of the bag. Observe the contents of the bag as often as possible for two to three days. The water leaving the plant's leaves evaporates, thus it is in the gas phase. Explain the phase change in the bag. For more information about transpiration, see Janice VanCleave's Plants (New York: Wiley, 1997), pp. 12–15.
  2. Design a display to represent the hydrologic cycle. A sample diagram with labeled parts is shown in Figure 34.2. Colors and a legend can be used to show how pollutants (substances that destroy the purity of air, water, or land), such as chemical fertilizers added to the soil, can be added to waterways.
  3. Are pollutants transported by the hydrologic cycle? Design a way to analyze condensed water for dissolved materials. One way would be to repeat the original experiment, adding table salt to the water in the bowl. Collect the condensed water and taste it. Design a way to collect the water, such as placing a container inside the bowl beneath the plastic wrap. Remember that when tasting materials, all supplies used must be clean.

Get the Facts

  1. Deforestation is the clearing of trees from land. Find out how this and other human activities, such as the growth of cities and the building of dams and reservoirs, affect the hydrologic cycle. For information, see Weather, The Nature Company Guides (Time-Life Books, 1996), pp. 120–121.
  2. About 97% of all the Earth's water is contained in the oceans as salt water. Find out about the remaining 3%, which is fresh water. How much of fresh water is locked up as ice? How much is underground? What part of fresh water is on the surface in lakes and rivers? What part is in the soil and the air? For information, see Jack Williams's The Weather Book (New York: Vintage Books, 1992), pp. 86–87.
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