Bringing in the Pond with iMovie

Unit of Practice #2: Permeability of soil and the water table

Title: Permeability of soil and the water table
This unit teaches younger elementary children about where pond water comes from and why it doesn't always dry up like a mud puddle might. Children will learn which soils allow water to flow through it and how to guess what keeps the water in the pond.

Unit details
Subject: Earth Science
Learning Levels: Primary
Author: Randy Yerrick

Detailed standards

Students will describe soil types found near ponds and in their communities based upon their consistency, appearance and permeability.
Students will compare the permeability of soil types based upon the speed at which water drains through them.
Students will hypothesize what kinds of soils are found around and in ponds based upon their pond observations and experimental findings.

Invitation
Have you ever tried to make your own pond? If you have, you know that digging a hole and filling it with water is not always successful. Most people don't consider the source of water in a pond or marsh when they try to replicate a similar habitat. If you want to raise frogs with lilypads and a natural environment, you are confronted with the issue of where does pond water come from? Most successful backyard ponds are constructed with water tight substances (e.g.: concrete, plastic) that keep water from leaking into the ground. But what is at the bottom of a pond or marsh that keeps the water in? Believe it or not, ponds may be filled by water running downhill or falling from the sky, or they may even be recharged by an underwater "river" called the water table. The water table is that ground water that seeps deep into the ground and follows the typical ground terrain all the way to a larger water body (e.g.: lake or ocean). Ponds are sometimes exposures of the top of the water table on its way to the sea and this accounts for their ever present water. Ponds which dry up periodically are usually low lying areas with impermeable bottoms to hold water in until it evaporates but which have no regular recharge of fresh water.

Situations
Data gathering and observations are best when viewed directly at the pond site. However, due to school constraints a trip to the pond may be prohibitive. This iMovie has at least two demonstrated soil types which can be tested along withother samples in classrooms for their permeability.

Tasks
Part 1
Students will collect several kinds of soil from a pond site. Many collection sites should be encouraged including the sediment found at the bottom of the pond. Students should be careful and assisted by an adult during this process as ponds can be dangerous places to get stuck in mucky bottom sediments. Maps should be kept of each soil type at the site and samples brought back to the class. Samples may vary based upon their depth as well.

Part 2
Students should fill styrofoam cups halfway with soil sediments and puncture 4 pencil holes in the bottom to allow water to pass through the cup. These soil samples should be dried for at least 48 hours prior to the experiment. Each cup should have an equal height of soil in it as it will be compared to other soils for how much water it holds and how quickly it allows water to pass through it. Each cup should be suspended above a second transparent cup which collects the water which passes through. One way to do this is to poke toothpicks through the sides of the styrofoam cups and place them on top of the second transparent cup. Sample soils should include clay, sand, gravel, and topsoil along with any other pond samples collected.

Once each sample is prepared and suspended above the clear cup, equal amounts of water should be poured on top of the sample at the same time. This will take some coordination, timing, and team work as someone will need to introduce the water to the samples while another is responsible for time keeping. The amount of water introduced to each sample should be uniform and should not exceed the volume of the collection cup in case the sample does not retain any water.

Once the water is poured onto the samples students should make observations of:

Which soil sample holds onto the most water? Which one retains the least?
Which soil sample let water pass through the quickest? Rank order the soils and discuss with your partners why different soils pass water differently. (Hint: pay close attention to the "spaces" between small pieces of dirt in your samples)
How long did it take the slowest soil to pass all the water? Was there a sample which did not seem to allow any water to pass through?
Which soil do you think is on the bottom of the pond? How do you think it got there?

Part 3
Students share their findings with other groups and retest any experimental findings which differ from other groups. Once there is consensus on the rank order of permeable soils, students return to the mapped samples from their site and discuss what kind of soil keeps the water in the pond.

Part 4 (optional) Extension
Students use their observations and experimental findings to design their own pond habitat in their backyard which requires the least amount of daily water replenishing. Students can draw diagrams and share their designs for adding plants and animals to simulate a pond ecosystem in a large pond or even a small fishbowl. Students can even collect plant and animal samples from an actual pond and sustain the ecosystem for a few days before returning each collected sample to its original site.

Interactions
It is important that the teacher assist in the collection of samples and mapping of the site. These can be dangerous and difficult tasks for some ponds. Teachers should also be prepared to facilitate the discussion of results from the water permeability tests as results can vary with the detailed care of the experimentor. Students are encouraged to share their results with one another as well as to compare their soil sediments with the ones demonstrated in the iMovie example. Students must cooperate to successfully complete the soil tests. Students may also use paint or draw programs like Appleworks 5 or 6 to share their designs for their own pond ecosystem.

Assessement
The accuracy of individual soil tests should be compared with the classroom results posted and given an opportunity to discuss their findings and repeat any questionable findings. Students use of data to corroborate or refute other groups' results in the discussion should serve as the primary source of individual students' understanding. Student designs which include impermeable soil bottoms like clay or fine sediment in the bottom of ponds should be given the highest rating. Students in small groups can be responsible for different tasks (e.g.: time keeping, observations, reporting) and receive group grades for their contributions.

Tools
iMovie, digital camera, computer, age appropriate reference books, Appleworks (optional)
Other materials include: styrofoam and transparent cups, soil samples, toothpicks, water, stopwatch.

For more information, please contact Randy Yerrick at ryerrick@mail.sdsu.edu