Share

Identifying Wetlands

Keywords: water plants, wetlands, hydrology; Grade Level: ninth through twelfth grade; Time Required: 85-minute period (not including follow-up activities)

Materials Needed

  • field guides of grasses, sedges, rushes, and other plants; Pond Life (A Golden Guide) is a useful guide for both ponds and emergent wetlands
  • shovel and/or auger
  • containers for samples (optional)

Goals of the Lesson

  • The students will be able to list and describe the three major categories of indicators used to delineate wetlands (hydrology, vegetation, soils)
  • The students will be able to identify hydrologic features that can be used to identify wetlands during a field inspection
  • The students will be able to list and identify several plants associated with wetlands
  • The students will be able to describe and identify a wetland soil.

Background Information

Since Pennsylvania was settled by Europeans, the state has lost over 50 percent of its wetlands. Wetlands serve several vital functions, including providing wildlife habitat, providing flood control, reducing pollution by sedimentation and by plants removing excess nutrients and toxic chemicals, and reducing erosion. Although there are many different types of wetlands, the Pennsylvania Department of Environmental Protection lumps wetlands into three major categories: forested wetlands, scrub-shrub wetland, and emergent wetlands (vegetated by herbaceous plants). ("An Introduction to Wetlands," DEP Fact Sheet; "Wetlands Values and Trends," NRCS/RCA Issue Brief 4)

There are three major categories used to identify and delineate wetlands: vegetation, soils, and hydrology. ("Recognizing Wetlands," U.S. Army Corps of Engineers) The following lesson is designed to help students understand these categories.

Procedure

  1. Take your students to a nearby wetland. The ideal situation would be to go to an old beaver pond or other pond that is slowly filling in. However, it is possible to make due with an undredged, unmowed ditch that often has standing water or another wet area.
  2. Have the students look at the area in general. Ask them if they have an idea where the wetland is and how they know. They may see standing water, sediments on leaves and other objects, water marks on trees, or drift lines. Pull out a plant and have the students observe the roots. They may see rust marks because oxygen has leaked out of the roots and caused iron in the soil to rust. This type of evidence is known as hydrologic evidence, signs that the soil is frequently saturated with water or flooded.

    Note: Often drainage is affected by a fragipan (hard-pan), which is a layer of soil compacted so tightly that it won't even let most roots penetrate.

  3. Some of the students may have also noticed the differences in plants. field guides or some other reference. Some plants common to wetlands in this area include sedges, rushes, horsetail, skunk cabbage, marsh marigold, cattails, sensitive fern (Onoclea), willows, elderberry, red osier dogwood, red and silver maples, American hornbeam (musclewood), and sweet birch. Sedges have triangular stems and three-ranked leaves. Rushes have hollow or pith-fitted round stems with usually hollow leaves. Some plants called rushes, such as beaked rushes, are actually sedges. Some of the plants observed can only be found in wetlands; others can be found both in wet and dry areas.
  4. Dig up some of the soil in the wetland and have the students describe it. They may observe a top layer of black "muck," which is organic matter that decays slowly due to the lack of oxygen. They may also notice a foul odor caused by sulfur compounds formed by anaerobic bacteria. Below the muck, they should notice that the soil is mostly gray. Most students mistakenly believe that gray means that it is clay. Although the soil may be higher in clay content, often it is not considered a clay soil. Texture the soil by the "feel method" (handout by S. J. Thien). The gray soil is called "gley" and it occurs when anaerobic bacteria reduce iron in the soil. Since many of the students don't know about oxidation and reduction, I usually tell them that the bacteria take the oxygen out of the rust to get iron. I then reinforce this concept by asking them the color of an iron object (gray). I then ask them what happens when the iron is exposed to water and air. (It rusts; oxygen from the air reacts with iron.) I then explain that the bacteria do the opposite by taking the oxygen out of the rust.
  5. Dig some soil at the edge of the wetland. Patches of gray and rust should be observed. These patches are called mottles. This is where the soil is saturated for part of the year and exposed to air for part of the year. This part of the soil is known as the "seasonal water table". Where the soil is a solid gray color, it is known as the "permanent water table."
  6. Give the students a brief quiz at the end of the lesson or the next day.
    • Ask them to give a few hydrologic features of a wetland.
    • Have them identify some of the most common wetland plants observed. Ask them how to distinguish a sedge and a rush from a grass.
    • Ask them what is the color of the mineral portion of the soil in the permanent water table and why it is that color.
    • Ask them why the seasonal water table soil has mottles of gray and rust.

Possible Follow-Up Activities

  1. If your wetland did not have a variety of plants, bring in specimens of common wetland plants.
  2. Take two dry samples of soil. Mix one with a little soil from a wetland. Saturate both samples with water, cover the sample, and observe what happens over the next few weeks. The soil mixed with the wetland soil should turn gray; whereas the regular soil should not. This is due to the presence of certain anaerobic bacteria in the wetland soil. This should demonstrate that gleying is a biological process.
  3. Use a soil survey book of your county to locate possible wetlands in your area. Wetland soils are called hydric soils and are usually poorly drained. Drainage classes are defined based on the depth to mottles (of gray and rust) from the surface of the mineral soil (not including organic matter on the top).
Drainage classes Depth to mottling
Poorly drained 0-8 inches (sometimes completely gleyed)
Somewhat poorly drained 8-18 inches
Moderately well drained 18-36 inches
Well drained > 36 inches

Note: Often drainage is affected by a fragipan (hard-pan), which is a layer of soil so tight that it won't even let most roots penetrate.

References

"An Introduction to Wetlands," DEP Fact Sheet.

"Recognizing Wetlands," U. S. Army Corps of Engineers, 1998.

Reid, George K. Pond Life . Golden Guide Publishing Company, Inc., 1995.

Thien, Steve J. "A Flow Diagram for Teaching Texture-by-Feel Analysis, " Journal of Agronomic Education . Vol. 8, 1979, pp. 54 - 55.

"Wetlands Values and Trends," NRCS/RCA Issue Brief 4, United States Department of Agriculture and Natural Resources Conservation Service, November 1995.

Author

Jeff Kerr, Tidioute Area School District