My Science Box

Lesson Plan
Subsidence Demonstration

1. Quickly review wetlands with the students. What are wetlands? Why are they important?
2. Next, tell students that you are going to show them a model of what happens to soil in wetlands over time. Bring out the tray with soil, the watering can and the pitcher of muddy water. Show the students what is in the tray. In particular, point out the level of the soil and the masking tape that marks the surface.
3. Explain to students that the soil in wetlands is a mixture of different sized sediments (clay, silt, sand), organic material, and water. In the soil there are air pockets. As soil gets exposed to rain, wind, and animals walking over it, it compacts. At this point, alternately use the hand trowel to pat down the soil in the tray and use the watering can of water to simulate rain. The level of the soil should subside up to an inch.
4. Ask the students what they notice. What happened to the level of the soil? Why? Ask students to help define compaction and subsidence given what they observed.
5. This process is always happening. Over time, the wetlands would sink completely underwater and disappear. Therefore, subsidence must be balanced by some other constructive force or the wetlands wouldn’t exist. Describe how rivers pick up sediments on their way down from the mountains in the watershed. Stir up the mud in the pitcher. These sediments are carried downstream by the water until they slow down as they pass through the wetlands. Pour some of the muddy water on the soil. Every so often, the river will flood, causing even more sediment to flow out onto the land. Mix up the pitcher thoroughly and pour a large quanity of the muddy water onto the wetlands, allowing a small layer of water to cover the surface and slowly drain out from the drain holes below.
6. Again, ask the students what they notice. What happened to the level of the soil? Why? Ensure that students see the balance between subsidence and sedimentation as natural events that contribute to a healthy wetland. Encourage students to predict what would happen if there was more sedimentation than subsidence or what would happen if flooding was prevented altogether.

Video

1. Tell students they will watch a video about Hurricane Katrina. If you have time, students may share some of the things they know about the disaster from the media.
2. Show the PBS Katrina video.

Discussion

1. Begin a discussion of the video focusing on why there are fewer wetlands and how that increased the severity of the damage caused by Katrina. Some questions you may want to consider include:
   • Before the Europeans came to Louisiana, was there more subsidence or more sedimentation? How do you know?
   • When New Orleans was first settled, was it above or below sea level?
   • Why did settlers build the levees? What effect did this have on the wetlands?
   • What else has been built by humans? What impact do these other structures have on the wetlands?
   • How much of the original wetlands remain? How quickly are wetlands being lost?
   • How do wetlands reduce the impact of hurricanes?
2. Allow the discussion of wetlands gradually transform into why wetlands are important and what we can do to save them. Some questions you may want to consider include:
   • Did people from the past not care about wetlands? (No, protecting their homes from flooding was more important to them and they didn’t know that wetlands were valuable.)
   • Should we care about wetlands loss? Why?
   • Do you think our politicians care about wetlands loss? Should they?
   • Do you think your parents know about wetlands loss? How can we teach them?
   • Should we protect the wetlands that are left? How should we do that?
   • Should we try to build new wetlands? Where?
   • What does it mean to be a steward of your environment?
3. End class on a positive note by brainstorming ways students can help protect, save or restore wetlands.