Karst & Nonkarst Watershed Models
This activity aligns with the following National Science Education Standards: Content Standard D: Earth and Space Science– Structure of the Earth System; and Content Standard F: Science in Personal and Social Perspectives–Natural Hazards
As the article indicates, many caves are found in karst regions, landscapes that feature the slow dissolving of underground rock such as limestone, dolomite, and gypsum. In addition to caves, karst landscapes feature sinkholes and underground streams. Karst areas are characterized by broken, weathered bedrock near the soil surface.
A watershed is an area of land where all water collects and drains into a common body of water, such as a lake, river, or ocean. In a watershed, all precipitation that falls drains from upland areas to a low point or basin, and the collected water drains to this point. All uses of the land on the surface of a watershed can dramatically affect the groundwater of an area.
A major problem in karst areas is that sinkholes have long been used as dump sites for various waste materials. As surface waters funnel into the depressions in the ground, water leaches contaminants from the solid wastes and quickly carries them through the network of open spaces underground. Other pollutants such as pesticides, fertilizers, and animal wastes are also carried across the ground and into the sinkholes. There are many other sources of pollution as well. And the problem is that any pollutants entering the groundwater system in karst areas receive very little or no filtration and continue into an aquifer that may supply water to nearby wells.
By creating models of karst and nonkarst watersheds, students will come to understand how human activities can have serious implications for the quality of our groundwater resources. (Note: Teachers can also create the models themselves and perform this activity as a demonstration.)
- Four two-liter plastic soda bottles for each set of models
- Tape and scissors
- Plastic tube or long straw
- Stones, sandbox sand, aquarium gravel
- Powdered drink mix (red in color)
- Aluminum foil
- 1/4 cup measuring cups
1. Have each student or group of students make two models, one of a karst watershed and one of a nonkarst watershed, according to the directions and diagram below.
Constructing a Karst Watershed
- A. Cut off the bottom 6 cm of bottle #1.
- B. Cut off the top 6.5 cm of bottle #2. Save the top for later use. Pour 5 cm of water into the bottom.
- C. Place bottle #1 upside down into bottle #2 as shown.
- D. Insert the plastic tube through bottle #1. (To keep it steady within the cut-off top, you may need to pack the tube with aluminum foil.)
- E. Packstones into the inverted bottle around the tube with the stone level higher at the edges and lower in the center.
- F. Lay sand on top of the stones following the curve up the sides of the bottle.
- G. Lay the cut-off top portion of 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.
Constructing a Nonkarst Watershed
- A. Follow steps A–C for the model above.
- B. Pack stones into the inverted bottle higher at the edges and lower in the center.
- C. Add a layer of aquarium gravel (slightly packed) higher at the edges and lower in the center. (Soil layers tend to be thinner in karst watersheds than in nonkarst watersheds. The gravel layer gives this model thicker "soil.")
- D. Add a layer of sand on top of the gravel following the curve up the sides of the bottle.
2. On the model, have students identify the ground water, rock, soil, and sinkhole. Ask students to predict what will happen when it rains.
3. Next, have students simulate rain by pouring an equal amount of water (about 1/4 cup) on each of the model watersheds.
After the "rain," discuss what happened.
4. Discuss how easily the water flowed to the water table. Then ask students what other substances can get into the groundwater from the surface.
5. Sprinkle the powdered drink mix across the top (sand) layer of each model. Have students predict what will happen when it rains next. Ask questions such as, "In which model will the groundwater become polluted first?"
6. Have students simulate the rain again. Observe the results and discuss with the class.
Assessment and Follow-up
After the activity, ask students the following questions to gauge their understanding:
- Why does the karst watershed model allow the groundwater to become polluted first?
- What are possible sources of groundwater pollution? (Many answers are possible, including pesticides, fertilizers, animal wastes, oil spills, damaged sewer lines or septic systems, and contaminants from landfills and other dumpsites.)
- What are some differences between a karst watershed and a nonkarst watershed? (Among characteristics students might cite are surface features, such as sinkholes, that are typical of karst landscapes, and underground features, such as broken bedrock and open spaces, which allow water to penetrate the ground and reach the groundwater more quickly; other types of watersheds do not have these features.)
- What are some ways in which groundwater pollution can be prevented? (Again, many answers are possible, including better monitoring and regulation of dumpsites, sewer systems, and underground storage tanks, particularly in karst regions.)
Adapted with permission from Project Underground, a national educational program on cave awareness. The group offers workshops, facilitator training, and an activity guide, Project Underground: A Natural Resource Education Guide, containing background information and 20 activities for grades K–12. For more information, write to Project Underground, 7502 Lee Highway, Radford, VA 24141, or call 540-381-8234; e-mail: email@example.com