By Kimberly Mullen, CPG
Part 1: Review of types of wetland information: Bog vs. fen
- A bog is acidic and is not connected to the groundwater (refer to Lesson Plan #3 of the Wetland Curriculum for a complete delineation of these terms). A fen is connected to the groundwater, (either gaining or losing water to it), it is mineral-rich (Ca, K, Mg, Ma) and tends to have a high pH value (typically around 8 and above). The water level and temperature typically remain constant throughout the seasons.
- Fens can produce peat (like bogs do). Fens have hydric soils, these prevent the surface water from leaching back into the ground, creating standing water in the fen. Fens are formed in areas of glacial activity (layers of gravel from glacial outwashes and moraines allow the groundwater to flow freely into the fen).
- Because of the constant, cool water temperatures and unique geology of the area, fens attract a number of plants and animals that are not found in other areas of the state. Marl is produced in fens because of the high mineral content and the cool temperatures.
- A simplified fen stratigraphy (a profile of a fen) would consist of:
- Alluvium — may have a layer of alluvial material or a glacial deposit on surface (gravel/sand)
- O Horizon — peat (decomposing organic material)
- A Horizon — clayey soil with some organic material present
- B Horizon — clay soil, some weathered rock
- C Horizon — glacial gravel (granite, gneiss, weathered, rounded stones) and weathered bedrock
- Bedrock — limestone.
Activity
Using the simplified stratigraphy, students will construct their own version of a fen. Teachers may need to monitor use of scissors and screwdriver (or actually do the work yourself) to avoid injury of students (depending on age and maturity level of class). Students will work in teams of two or three. Go over the entire exercise prior to handing out the materials and instruction sheet. Give a specific amount of time to complete the fen construction. After each team finishes, have the team spokesperson explain the team fen to the class (why they did what they did). Then fill the pan with about two or three inches of water. Have each team bring their fen up to test it (simply place the fen bottle in the pan). Each team must write down what happens. Did it work? Why/why not? What happens when the fen is removed from the pan? Discuss all results as a class.
Hints: best working layers are gravel, clay, soil/peat, gravel/sand. Straw can be used to allow the groundwater to travel through the soil/peat faster (and cleaner), acting as a hydraulic conduit to the ground surface. Allow students to reason it out if possible, they will learn more.
Materials
- 2-liter empty plastic soda bottles
- Scissors
- Screwdriver (or something similar to punch holes in the bottles)
- Pea-gravel (can use aquarium stones)
- Sand
- Peat moss or topsoil
- Clay (cut in blocks about 2.5 inches square)
- Dishpan or casserole dish (must be able to hold water)
- Containers to hold gravel, sand, soil (paper cups, coffee cans, etc.)
- Plastic drinking straws.
Building a fen: student instructions
Each student team must collect:
- One 2-liter bottle
- Scissors
- Screwdriver
- 1 cup of sand
- 1 cup of gravel
- 1/2 cup of soil/peat moss
- One block of clay
- One plastic drinking straw.
Each student team must record their work and turn in the lab sheet with the names of the team members and the work completed.
- Using the scissors, cut the plastic bottle in half.
- Cut three holes (diameter of a pencil) in the bottom of the bottle using the screwdriver.
- Using the information from class (about fens), decide, as a team, what each material (sand, gravel, soil/peat, clay, straw) represents. Write this down on the team lab sheet.
- Now, as a team decide the order in which the material will be placed in the bottle to accurately represent a fen. The straw may be cut into small sections as needed, or not used at all, if the team decides. This must also be recorded on the team lab sheet.
- Construct the fen using the order in Step 4 above.
- Wait for the other teams to finish. Pick a spokesperson for the team to explain the fen to the class.
- The teacher will “test” each fen by placing the “fen” bottle in the pan filled with two or three inches of water. Water will seep into the holes and enter the fen. Record what is observed for the team fen.