Groundwater & Wetlands Reading

CHAPTER 17 LESSON 3

Freshwater Groundwater and Wetlands

Key Concepts What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.

Before

Statement

After

• What is groundwater?

• Why are wetlands important?

• How do human activities affect groundwater and wetlands?

5. People use groundwater as a source of water.

6. Wetlands can naturally filter pollutants from

groundwater.

3TUDY #OACH

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Groundwater Some water that falls to Earth as precipitation soaks into the ground. Generally, water that lies below ground is called groundwater. Water seeps through soil and into tiny spaces, called pores, between sediment and rock. If you have ever been inside a cave, you might have seen groundwater. The water seeping down the sides of the cave is groundwater seeping through rock.

In some areas, groundwater is very close to the surface.

It keeps the soil wet. In other areas, such as deserts and other dry climates, groundwater can be hundreds of meters below the surface.

Groundwater can stay underground for long periods of time. It can remain there for thousands or millions of years.

However, humans interfere with this process when they drill wells to remove the water for everyday use.

Importance of Groundwater The amount of water under Earth’s surface is greater than the amount of freshwater in lakes and streams. Recall that about one-third of Earth’s freshwater is in the form of groundwater.

Reading Essentials

K-W-L Chart Create a K-W-L chart by making three columns on a piece of paper.

Label the first column “Know,” the second “Want to Know,” and the third “Learned.” Fill in the chart with what you know about groundwater, what you want to learn about it, and what you did learn as you read this lesson.

Key Concept Check

1. Define What is groundwater?

Freshwater

295

Water Source Groundwater is an important source of water Use a two-tab book to organize your notes about groundwater and wetlands and how each relates to the other.

Groundwater Wetlands

for many streams, lakes, and wetlands. Some plant species absorb groundwater through long roots that grow deep underground.

Water Supply People in many areas of the world rely on groundwater for their water supply. In the United States, about 20 percent of the water that people use daily comes from groundwater.

The Water Table Groundwater moves through tiny cracks and pores in rocks and sediment. Near Earth’s surface, the pores contain a mixture of air and water. This region is called the unsaturated zone because the pores are not completely filled with water.

Farther beneath the surface, in the saturated zone, the pores are completely filled with water. The upper limit of the saturated zone is called the water table. The unsaturated zone and the saturated zone are shown below.

Porosity Different rocks can hold different amounts of Visual Check

2. Show the water table by highlighting it across the length of the figure.

water. Water moves through different rocks at different speeds. Porosity is a measure of rock’s ability to hold water. Porosity increases with the number of pores in the rock. The higher the porosity, the more water a rock can hold.

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Land surface

Unsaturated zone Water table

Saturated zone Surface water

296

Freshwater

Reading Essentials

Permeability The measure of water’s ability to flow through rock and sediment is called permeability. Permeability depends on pore size and on the number of connections between pores. Even if a rock has many pores, they must form connected pathways for water to flow easily through the rock.

3. Contrast porosity and permeability.

Groundwater Flow Groundwater flows downhill beneath Earth’s surface just as it flows downhill across Earth’s surface. Groundwater in low-lying areas might seep out of the ground and into a stream, lake, or wetland. In this way, groundwater can become surface water. When surface water seeps into the ground, it becomes groundwater.

Wells People bring groundwater to Earth’s surface by drilling wells similar to the one shown below. Wells are usually drilled into an aquifer. An aquifer is an area of permeable sediment or rock that holds significant amounts of water. Groundwater flows from the aquifer into the well and is pumped to the surface.

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Precipitation helps replace groundwater that has been taken from wells. During a drought, less groundwater is replaced. The water level in a well drops. If the water level drops too low, the well runs dry.

Reading Check

Springs A spring forms where the water table rises to Earth’s

4. Describe how a well can

surface. The figure below also shows a spring. Some springs bubble to Earth’s surface only after a heavy rain or snowmelt. Many springs that are fed by large aquifers flow all the time.

go dry.

Well Spring

Stream Aquifer

rock able e m r Impe

Visual Check

5. Draw a line in the aquifer that shows the point at which the well would run dry.

Reading Essentials

Freshwater

297

Human Impact on Groundwater Polluted surface water can seep into the ground. This will then pollute the groundwater. Pollutants include pesticides, fertilizers, sewage, industrial waste, and salt used to melt ice on highways. Pollutants can travel through the ground and into aquifers that supply wells. People’s health can be harmed if they drink contaminated water from a well.

Key Concept Check

6. Explain How do human activities affect groundwater?

Reading Check

7. Identify Where do wetlands occur?

The water in an aquifer helps support the rocks and soil above it. In some parts of the world, water is being removed from aquifers faster than it can be replaced. This creates empty spaces underground. The empty space cannot support the weight of the rock and soil above. The ground can suddenly collapse, and a sinkhole forms.

Wetlands Water often collects in flat areas or depressions that are too shallow to form lakes. Instead, a wetland can be created.

A wetland is an area of land that is saturated with water for part or all of the year. Wetlands also form in areas that are kept moist by springs and along the shores of streams, lakes, and oceans.

The water in a wetland might be still or flow slowly.

Types of Wetlands

Marshes The water in marshes is supplied by runoff and precipitation. Marshes form in climates that are warmer and drier than where bogs form. The soil in a marsh is slightly acidic and rich in nutrients. Grasses and shrubs grow in marshes. A marsh can temporarily dry out in hot, dry weather.

Swamps The water in swamps is supplied by runoff and

Reading Check

8. Describe the soil conditions in a bog.

298

Freshwater

precipitation. Swamps form in climates that are warmer and drier than where bogs form. The soil in a swamp is slightly acidic and rich in nutrients. Trees and shrubs grow in swamps. Like marshes, swamps can temporarily dry out in hot, dry weather.

Bogs The water in bogs is supplied by runoff that is low in oxygen content. Bogs form in wet, cool climates. The soil in a bog is acidic and lacks nutrients. Sphagnum moss, wildflowers, and cranberries grow in bogs. Bogs also produce a thick layer of peat. Peat is the partially decayed remains of sphagnum moss. Peat holds water, so bogs rarely dry out.

Reading Essentials

Copyright Š Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Scientists identify wetlands by the characteristics of the water and soil and by the kinds of plants that live there. The three major types of wetlands are marshes, swamps, and bogs.

Importance of Wetlands Wetlands provide an important habitat for plants and wildlife. They help control flooding and erosion. Wetlands also help filter sediments and pollutants from water.

Habitat Many plants and animals live in wetlands. Wetlands provide food and shelter for young and newly hatched animals. Wetlands are home to some species of fish, amphibians, and birds. Wetlands are important rest stops and food sources for animals that migrate, especially birds.

Flood Control Wetlands help reduce flooding because they can store a large amount of water. Wetlands fill with water during the wet season and then slowly release water during times of drought.

9. Explain how wildlife uses wetlands.

Copyright Š Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Erosion Control Wetlands along the coast help reduce erosion of the shoreline and beaches. Wetlands can reduce the energy of wave action and storm surges. A storm surge is water that is pushed onto the shore by strong winds from a severe storm.

Filtration Wetlands are natural filters. They help prevent sediments and pollutants from reaching streams, lakes, groundwater, or oceans. Runoff that enters a wetland might have excess nitrogen from fertilizers or animal wastes. The bacteria and plants living in wetland soils absorb excess nitrogen. Wetland plants and soils also trap sediments and help remove toxic metals and other pollutants from the water.

Human Impact on Wetlands Many wetlands throughout the world have been drained of water and filled with soil. This newly formed dry land is used for roads, building sites, airports, and other purposes.

The disappearance of wetlands may be a cause of rising sea levels, coastal erosion, and the introduction of species that do not normally live in wetland areas. Scientists estimate that more than half of the wetlands in the United States have been destroyed over the past 300 years.

The Louisiana coastline has lost about 310 km2 of wetlands since 1950. Large parts of the coastal wetlands have been filled in to build roads and buildings. A lack of coastal wetlands might have contributed to the flooding that took place when Hurricane Katrina struck the area in 2005. Scientists and engineers have suggested that restoring some of the wetland areas could help avoid flooding in the future.

Reading Essentials

Key Concept Check

10. Summarize Why are wetlands important?

Key Concept Check

11. Discuss How do human activities affect wetlands?

Freshwater

299

Mini Glossary aquifer: an area of permeable sediment or rock that holds

porosity: the measure of rock’s ability to hold water

significant amounts of water

water table: the upper limit of the saturated zone

groundwater: water that lies below ground

wetland: an area of land that is saturated with water for part

permeability: the measure of water’s ability to flow through

or all of the year

rock and sediment

1. Review the terms and their definitions in the Mini Glossary. Write a sentence that describes why a rock can be porous but not permeable.

2. Complete the table below to identify the characteristics of the different types of wetlands.

Bogs Soil

Swamps

acidic, nutrient poor

Marshes slightly acidic, nutrient rich

warmer areas

Plant Growth

trees and shrubs

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Climate

grass and shrubs

3. How did the K-W-L chart help you organize the information about groundwater?

What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree.

Did you change your mind?

300

Freshwater

Connect ED

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

END OF LESSON

Reading Essentials