ACTIVITY#3: Soda Bottle Watersheds

Make a watershed and see the effects of pollution on the water cycle.

A watershed is an area of land where all water collects and drains into a common body of water (ocean, river or lake).

In this activity you'll make two models of watersheds - one in a karst area and one in a non-karst area. What is karst, you ask? Karst is a terrain where the topography (landscape) is formed by dissolving rock, usually limestone, and is generally characterized by sinkholes, underground streams and caves.

When the underlying limestone rock collapses or caves in, sinkholes form. They provide direct access for surface water and pollution to enter and contaminate underground water supplies.

Sometimes, our activities on land can unknowingly contaminate the water underground. Ground water reservoirs support human and wildlife populations. A major problem in karst areas is that sinkholes have long been used as dump sites for various waste materials including household garbage, used equipment, agrochemical containers, and dead animals. As surface waters funnel into the depressions in the ground, water carries contaminants from the solid wastes through the network of open spaces (caves) underground. Other pollutants such as pesticides, fertilizers, and animal manure are also carried across the ground and down into the sinkholes and can end up in drinking water wells.

Construction of Model A - Karst Watershed

1. Cut off the bottom 2 1/2 inches of bottle #1 and tape it to make a hinge.

2. Cut off the top three inches of bottle #2. Save the top for later use. Pour two inches of water into the bottom.

3. Place bottle #1 upside down into bottle #2.

4. Insert the plastic tube through bottle #1.

5. Pack stones into the inverted bottle around the tube wit hteh stone level higher at the edges and lower in the center.

6. Lay sand on top of the stones following the curve up the sides of the bottle.

7. Lay the cut off top portion from bottle #2 upside down on the sand with the plastic tube extending through the cap screw portion. Arrange the tube until it extends no higher than the cap screw portion of the cut bottle and tape it into position. You may need to pack the tube with aluminum foil to keep it steady within the cut off top.

Model A:

Construction of Model B- Non-Karst Watershed

1. Follow steps one through three for Model A.

2. Pack stones into the inverted bottle higher at the edges and lower in the center.

3. Add a layer of aquarium gravel (slightly packed) higher at the edges and lower in the center.

4. Add a layer of sand on top of the gravel following the curve up the sides of the
bottle.

Model B:

NEXT...

1. On the models, identify the groundwater, rock, soil, and sinkhole. Make predictions about what you think will happen when it rains.

2. MAKE IT RAIN!!!...Pour an equal amount of water (about 1/4 cup) on both watersheds. What's happening?

3. ADD A POLLUTANT!!!...Place the beets or food coloring on the ground of the models. Which model will become polluted first?

THINK ABOUT...

• What are the differences between a karst watershed and other types of watersheds?
• Name at lease four sources of groundwater pollution.
• What are some ways to prevent groundwater from becoming polluted?
• Draw and label a picture of each of the watershed models.

This activity is adapted from: Project Underground, A Natural Resource Education Guide, 2000.