Duration: 30 to 40 minutes
Vocabulary: gleyed soil, anoxic, sand, silt, clay, ground water, water table
Summary: Students learn about the qualities specific to wetland soil and try to identify it in the field.
Objectives: Students will gain a deeper understanding of how what makes wetlands special and how the soil there is different from the kind they might find in their backyard.
Materials: trays, soil charts, hand trowels, 5 gallon bucket of water, pencils, clip boards, sponge, small water canister
What is a wetland? If you left a hose running on your front lawn, would that then be a wetland? It turns out that wetlands are defined very specifically. One reason for this is because developers or land owners often want to build on wetlands, but because they are so important to water quality and wildlife, it is now illegal to build on them. Therefore, the first thing we need to know is to find out if indeed there is a wetland to present.
Wetlands are typically defined by three characteristics: the plants, the water, and the soil. When water sits on top of land for a long time, plants must adapt to live in those types of conditions and it changes the soil in very specific ways. Wetland scientists go to an area and look for these characteristics to find out if it is a wetland.
How can water be stuck on top of the ground without sinking in? There can be a few different reasons, but the main one has to do with ground water and the water table. When the water from rain hits the ground, at first it sinks in. Pretty soon, though, it hits the ground water–all the water that collects under ground. This ground water usually fuels small creeks in the area, and when any more water is added is fills the ground up until it just sits on top. Think of a sponge–once it is soaked with water, it can’t pick up any more! You have to ring it out (remove the water) for it to become absorbent again.
When water covers the soil for a long period of time, the first thing that happens is that all of the air is removed from the ground–just like you see air bubbles come out of a sponge as it fills with water. This has a dramatic effect because many different types of organisms that live in the soil and change the soil need oxygen to survive. For example, have you ever seen worms come out of the ground after a rain storm? This is because the rain water is pushing the oxygen out of the soil, and they don’t have enough to survive. When the oxygen in soil is gone, these types of organisms can’t live, and they don’t change the soil the way you would see in a forest or grassland. An area without oxygen is called an anoxic environment, and the only things that can survive there are special bacteria that can live without air. These bacteria change the color of the soil from a dark brown to different shades of gray and even bluish green–this is called gleyed soil. If you see these colors you know you have a wetland!
Use a sponge to demonstrate the way the air is squeezed out when water comes in (there should be air bubbles). Also show the way the water fills it up and then it is no longer absorbent and the water just sits on top/around the sponge. Note: It is usually helpful to wet a sponge a small amount before the demonstration–it helps it draw in the water more easily.
Divide students into pairs and give each pair a hand trowel. Along the edge where the water meets the soil, have students dig up a ‘wedge’ of soil. They should try not to just dig up random clumps, but rather to push the trowel down to form a triangular shape, and then try to lift the triangle out of the surrounding soil. Have students look for the grayish or greenish-blue color of gleyed soil. After looking at it as a whole, students can take apart the soil and examine what is inside. Students can also squeeze a small amount of soil in their hand–if it forms a ball easily, it has a lot of clay in it, which is another good sign of a wetland.
Have students compare their findings and contrast the differences between what they know of upland soils and wetland soil.
Ask students to name some ways wetland soils are different from other types of soil. What are some characteristics to look for to help identify wetland soil? Which would they rather live in if they were a worm?
Have students compare wetland soil to soil from the school yard or from their homes.
Have students pretend to scientists who need to determine whether a company is allowed to build a mall in a certain location. Is this location a wetland? How do they know? Have them write a letter to the company explaining why they cannot build on the location–include why wetlands are important to conserve!