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Science Experiment: Water Shed
This science project is good for all ages to understand what happens to rainwater.
Setting the Scene: Northeast Florida and the St. Johns River Watershed
A raindrop that falls to earth does one of three things:
- Evaporates back into the atmosphere;
- Soaks into the ground;
- Flows over the ground as run-off.
In Florida, much of the rainfall evaporates or sinks into the underground reservoirs known as aquifers.
The remaining water follows the third path: running across the ground to swamps, streams, ponds, rivers, and lakes. These bodies of surface water support fish, wildlife, and people. In northeast Florida, a raindrop that falls in Brevard County can wind up in the St. Johns River and flow through a series of lakes. The river becomes wider and spreads out into wetlands and inlets before flowing into the Atlantic Ocean near Jacksonville, 310 miles from the river’s starting point.
All the way, the water flows downhill, pulled by gravity. The entire region that drains water along this path is known the St. Johns River Watershed. A watershed is a drainage area, or basin, that collects water from the higher lands. The boundary of a watershed is defined by the high points or ridges that are known as the divide. When rain falls on the other side of the divide, it runs off in another direction and collects in another watershed.
The Basic Science: Non-Point Source Pollution
Pollution comes from two types of sources. The first, known as point source pollution, comes from a single, identifiable place, like a factory that allows contaminants to leak on the ground or down the drain. If these sources are identified, the pollution can usually be reduced or eliminated.
The other type of pollution is non-point source pollution. It is harder to identify and correct because it is everywhere around us, and we are partially to blame for it. It is a few drops of oil on the driveway, used paint thinner poured on the ground, a few specks of rubber and metal from a car tire, pesticides or fertilizers sprayed on the lawn, or waste from your pets or wild animals left on the ground. Left sitting on the ground, these contaminants eventually get washed through the watershed and into a body of water, either surface water or an aquifer.
In addition, changing the nature of the land surface in a watershed can disrupt the natural flow of water into underground aquifers and into streams and lakes. Roads and parking lots create :impervious” surfaces, meaning that water cannot pass through them. Since impervious surfaces prevent water from seeping down into aquifers, more water runs across the ground, which stresses storm water collection systems and contributes to the possibility of sudden flooding.
The proportion of land covered by impervious surfaces, especially in rapidly growing areas like northeast Florida, is getting bigger every year, so problems related to non-point source pollution are growing too.
Building a Model: Polluting and Cleaning a Watershed
Once contaminants enter the soil or water, they can follow the same path through the watershed as raindrops. By knowing how water travels through a watershed, we can predict what areas might be affected by a chemical spill, and we can take measures to protect the downstream areas. On the other hand, if we find pollution in a body of water, we might be able to trace it to its source and get rid of it. In this science project, you can explore the routes of water and contaminants, see the effects of impervious surfaces on water flow, and take steps to clean up pollutants that have already entered your model watershed. You can use this information to help prevent water contamination within your own watershed.
- Plastic basin
- Newspapers, wax paper, tin foil, bits of sponge, cotton balls, paper towels, plastic wrap, sticks
- Spray bottle with water or small watering can
- Blue and red food coloring for point-source pollutants
- Salad oil for non-point-source pollutants
- Model toys for houses
- Drain made of clear plastic tubing, silicone sealer, and a binding clip
- Crumple newspapers or other materials to fashion the contours of a watershed. The activity works best if there are several low places, not just one central depression where all the rain collects. Make sure a watershed divide stands out. Create ridges, valleys, and places for streams or lakes. You may even want to create a place for a residential neighborhood and a shopping mall.
- Cover the watershed with different surfaces: Several layers of paper towels can represent soil, and pieces of sponge or cotton can be vegetation. Use plastic or foil to create impervious roads and parking lots. Use model toys to build neighborhoods, businesses, and factories.
- Write your predictions about how water will flow through the watershed. Then add a “rainstorm” by spraying or sprinkling water. Observe how the water seeps into the ground and flows across the impervious surfaces.
- Now add pollutants. Place some non-point source pollutants on the roadways, parking lots, and lawns. Put tiny dots of food coloring near factories for point-source pollutants. Produce another rainfall, and observe the paths of pollutants.
- Based on your observations, where would be a good place to get your drinking water? To place a landfill?
Putting it all together
How do various pollutants flow within a watershed? Create hypotheses, and test them in your model using a range of different pollutants, such as food coloring, oil, tinted isopropyl alcohol, talcum powder, and Kool-Aid.
illustrate the movement of pollution in your watershed, and carefully describe the behavior of various types of pollutants.
Once a watershed is contaminated or polluted, what might you be able to do to remove the pollution? Develop a strategy for cleaning a polluted watershed, and test your strategy using your model. Continue to change and refine your strategy until you develop a technique that works.
Where might you find pollutants in your watershed that are similar to the ones you modeled?
How might you help prevent watersheds from being polluted in the future? Develop a public plan for preventing pollution in a watershed. Create posters and ads that inform the public of the dangers related to non-point source pollution.
You live in the St. Johns River Watershed. Research its boundaries, and learn about the various land uses within it.