Introducing the Concept of Life Sciences

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Part 2

What level of population can the world sustain? At what level of technology? At what impact to the environment?

Erosion Commotion - Lesson 2

Objectives

By the end of this lesson, students will be able to:

• Work in small groups, and collaborate results as a class
• Compare the erosion of a soil sample under different conditions
• Calculate results based on data
• Apply the information gained from the lab to a hypothetical situation
• Think globally

Background Notes

Topsoil is an essential component in the food chain and is inherently responsible for sustaining creatures like microorganisms, cattle and humans. One inch of topsoil is the result of plant decay over a period of hundreds of years, and yet it can be depleted in a matter of minutes by erosion.

Preservation of top soil is critical because there is a growing concern whether farmers can produce enough food to support the Earth's inhabitants. The second half of the twentieth century has witnessed a doubling of the world's population; and at a rate of 80 million new people each year, global population is projected to nearly double by the year 2050. The answer to exactly how many people the Earth can sustain is linked to issues affecting agriculture, of which soil erosion is a significant concern.

Materials

Each lab group should have:

• A different soil sample
• One piece of thick cardboard (30 x 30 cm)
• One basin-like container
• One jar
• Paper towels or filter paper
• Two or three blocks of wood
• 100 ml of water

Strategy

1. Depending upon the dynamics of your class, arrange students into small groups or partners. Explain the activity, then ask the students to predict the results based on their previous experience with water and soil.

2. Give each lab group a different sample of soil. (Suggestion: Find or create a mixture of soil samples with different compositions of sand, clay and silt.) Measure the mass of soil required to spread a 3 cm thick layer of soil on the piece of cardboard. Spread the soil out. If possible, let the soil settle for one to two days.

3. Slant the board by leaning it on the wood blocks. The cardboard should be slanted into a basin-like container.

4. Sprinkle 100 ml of water from 60 cm above the soil. Collect the run-off in the basin.

5. The basin now contains a mixture of water and soil.
Determine the exact amount of eroded soil by creating a filter for the run-off water
Measure the mass of the filter paper or paper towel
Take filter paper or fold a paper towel into a cone and place it over a jar
Pour run-off water from the basin into the jar
Measure the mass of the filter paper or paper towel again
6. Students can calculate the percentage of run-off water or soil by measuring the final mass and comparing that data to the original mass.

7. To give students a sense of the spectrum of variables that can affect soil erosion, present these questions:

Which produces more erosion - soil that is completely dry or partially dry? Let the soil sit for a few days without water. Then repeat the procedures, and measure the run-off. Repeat the experiment shortly after the soil has absorbed some water, and compare the measurements of run-off water and soil.
How does the angle of the soil affect erosion? Run the experiment with the cardboard at a different angle, and measure the run-off.

Optional: How does root growth affect erosion? Give students seeds that can sprout relatively quickly. Maintain the seeds by watering the soil sample as needed. After a few weeks, run the experiment again, and compare the results to the first trial.

8. After the series of trials, the class reconvenes, and shares data. Students collaborate their results by creating a class data table or chart. Table or chart comparisons could include the mass of dry soil and wet, the volume of run-off water, or the mass of run-off soil. As a class, students arrange the soils from best to worst according to their performance in the various experiments.

Follow-Up Questions
If you were responsible for planting a field of just one crop, which one would you choose and why? What steps would you take to avoid soil erosion? Draw a diagram of your field and the arrangement your crops.

How is the issue of global population related to worldwide soil problems?
As a farmer, what could you do to control run-off in your field to retain your valuable topsoil?

Additional Resources

Brown, Lester R., Christopher Flavin, Hilary French, State of the World 1998, W.W. Norton & Company, New York. 1998

Gonick, Larry and Alice Outwater. The Cartoon Guide to the Environment, Harper Perennial: New York. 1996.

Hart, Stuart. "Beyond Greening: Strategies for a Sustainable World," Harvard Business Review, Jan.-Feb. 1997.

Hawken, Paul. "Natural Capitalism," Mother Jones, Mar.-April 1997.

Hawken, Paul. The Ecology of Commerce, Harper Business, New York. 1993.

Meadows, Donella H., Dennis L. Meadows, Jorgen Randers. Beyond the Limits, Chelsea Green Publishing Company: White River Junction, Vermont. 1992.

Raven, Peter H., Linda R. Berg, George B. Johnson. Environment, Second Edition. Saunders College Publishing, Fort Worth. 1998. (textbook)

Starfish; Educational Resources for Sustainability

www.starfish.org/index.html

World Resources 1996-97, World Resources Institute, UNEP, UNDP, and the World Bank, Oxford University Press: New York. 1996.
www.wri.org

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