Careers In Earth Science

Geochemist Technician Some geochemist technicians take core samples from lakes to analyze the pollutants in lake sediments. To learn more about Earth science careers, visit glencoe.com.

Freshwater wetlands A wetland is any land area that is covered with water for a part of the year. Wetlands include environments commonly known as bogs, marshes, and swamps. They have certain soil types and support specific plant species. Their soil types depend on the degree of water saturation.

Bogs Bogs are not stream-fed but instead receive their water from precipitation. The waterlogged soil tends to be rich in Sphagnum, also called peat moss. The breakdown of peat moss produces acids, thereby contributing to the soil's acidity. The waterlogged, acidic soil supports unusual plant species, including insect-eating pitcher plants such as sundew and Venus flytrap.

^P Reading Check Identify how a bog receives water.

Marshes Freshwater marshes frequently form along the mouths of streams and in areas with extensive deltas. The constant supply of water and nutrients allows for the lush growth of marsh grasses. The shallow roots of the grasses anchor deposits of silt and mud on the delta, thereby slowing the water and expanding the marsh area. Grasses, reeds, sedges, and rushes, along with abundant wildlife, are common in marsh areas.

Swamps Swamps are low-lying areas often located near streams. Swamps can develop from marshes that have filled in sufficiently to support the growth of shrubs and trees. As these larger plants grow and begin to shade the marsh plants, the marsh plants die. Swamps that existed about 200 mya developed into present-day coal reserves that are common in Pennsylvania and many other locations in the United States and around the world.

Model Lake Formation

How do surface materials determine where lakes form? Lakes form when depressions or low areas fill with water. Different Earth materials allow lakes to form in different places.

Procedure Bl t^

1. Read and complete the lab safety form.

2. Use three clear plastic shoe boxes. Half fill each one with Earth materials: clay, sand, and gravel.

3. Slightly compress the material in each shoe box. Make a shallow depression in each surface.

4. Slowly pour 500 mL of water into each of the depressions. Analysis

1. Describe what happened to the 500 mL of water that was added to each shoe box.

2. Compare this activity to what happens on Earth's surface when a lake forms.

3. Infer in which Earth materials lakes most commonly form.

Percentage of Wetland Area Lost, 1780s-1980s

Percentage of Wetland Area Lost, 1780s-1980s

Hawaii 12%

H Over 80%

Figure 9.21 The area of wetlands in the United States was drastically reduced until the 1980s. Since then, efforts have been made to preserve wetlands.

ME\

20%

28%

----

-NJ^

37%

39%

CT

Hawaii 12%

H Over 80%

SDE 54%

Wetlands and water quality Wetlands play a valuable role in improving water quality. They serve as a filtering system that traps pollutants, sediments, and pathogenic bacteria contained in water sources. Wetlands also provide vital habitats for migratory waterbirds and homes for an abundance of other wildlife. In the past, it was common for wetland areas to be filled in to create more land on which to build. Government data reveal that from the late 1700s to the mid-1980s, the continental United States lost 50 percent of its wetlands, as shown in Figure 9.21. By 1985, it was estimated that 50 percent of the wetlands in Europe were drained. Now, however, the preservation of wetland areas has become a global concern.

Figure 9.21 The area of wetlands in the United States was drastically reduced until the 1980s. Since then, efforts have been made to preserve wetlands.

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