1. Read The Background Scoop on Sand.

Additional background information:
When sand is in a container such as a glass, or the basin of a pond with an impermeable clay layer, the sand grains are partially supported by water. If sand is not in a container, the water drains right through until all that remains is the hard-to-remove layer of water covering the damp sand grains. The water is pulled away by gravity and compared to soils with smaller particles, water moves through sand very quickly.

For plants and animals that live in the sand, this means that life can be greatly influenced by how well a site drains. Sandy sites that are poorly drained, such as a small depression with an impermeable layer, are actually aquatic environments during a wet season and support aquatic plants and animals. Well-drained, sandy sites, such as a small ridge or knoll of sand, are as dry as deserts during Florida’s dry season.

2. Keeping the soils separate, moisten each soil type with 1 cup of water.
   
   
3. Place 1 gauze pad (flat) over the holes in the bottom of each soda bottle.
   
   
4. Put 4 cups of each soil type in a different soda bottle and firmly compact the surface.
   
   
5. Copy the following table on the chalkboard or overhead projector and have each student make a copy on a piece of notebook paper.
   
   

6. Have each student predict which soil type will allow water to flow through most rapidly.
   
   
7. Assign two students to each soil type. One student will be the time-keeper and will observe at eye level with the bottom of the soda bottle. The other student will make "rain" over the soil.
   
   
8. The three teams should start at the same time so the class can make visual comparisons. The student who pours merely turns the quart of water over so the water "rains" from the holes on the lid.
   
   
9. Have all students write down how long it takes for the water to start dripping from the bottom of each soda bottle.
   
   
10. Measure the water that drained through the soils to determine which soil type holds the most water. Have students fill in their tables.
    
    
11. Ask your class to think about how plants might survive in soil where rain drains through rapidly.
    
    
12. Look at the color of the water that drained from each soil type. Which water is the clearest? (Water draining through sand should be much clearer than water draining through other soils.) Use this opportunity to begin a discussion of scrub habitat as a water purification and water recharge habitat. This role of sandy uplands, recognized by water management districts, is an important one. Sand acts as a filter, taking out small particles. Sand also provides a place for bacteria to grow. These bacteria help remove impurities, such as the high levels of nutrients that seep from septic tanks. However, some chemicals, such as pesticides, pass through easily and move into the ground water.
    
    

Scrub is not only a good habitat for filtering and cleaning water, but it also stores water. The water that sinks deep into the sand does not evaporate and, if the sand is deep, the water goes beyond the reach of roots. Even when the water is within a couple of feet of the surface, it may be low in oxygen and plant roots may not be able to grow in this oxygen-free zone.

Water that lies in the sand beneath the Florida scrub moves slowly and follows the contours of impermeable zones underground. Eventually this water flows out into lakes or in seeps and creeks along the edge of a ridge. Because this happens very slowly and the water does not evaporate, scrub is an ideal water storage and recharge area—even though water cannot be seen for most of the year!

The next time you and your students go out to a scrub site, remind them of these experiments on sand and water. In most parts of Florida, scrub areas are adjacent to wet areas, or have little wet areas within them. As shown in the activities, sand can make an aquatic habitat, or an extraordinarily dry habitat depending on the drainage of the site. Often, dramatic changes in the vegetation can be seen that seem to have no good explanation. Usually the reason is differences in drainage. With a little practice, you and your students can begin to pick out plants associated with a higher water table, such as shiny lyonia (fetterbush) and Highlands scrub St. John’s wort. Florida rosemary indicates a deep water table. Some drought-adapted plants, such as cactus, can live where the water table is shallow, as long as the site never floods.