groundwater & wetlands reading

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GroundwaterSome 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 GroundwaterThe 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.

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

5. People use groundwater as a source of water.

6. Wetlands can naturally filter pollutants from groundwater.

Key Concepts • What is groundwater?• Why are wetlands

important?• How do human activities

affect groundwater and wetlands?

Key Concept Check1. Define What is groundwater?

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.

Groundwater and Wetlands

FreshwaterLESSON 3

CHAPTER 17

Reading Essentials Freshwater 295

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Water Source Groundwater is an important source of water 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 TableGroundwater 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 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.

Visual Check2. Show the water table by highlighting it across the length of the figure.

Use a two-tab book to organize your notes about groundwater and wetlands and how each relates to the other.

Groundwater Wetlands

Unsaturated zone

Saturated zone

Land surface

Surface water

Water table

296 Freshwater Reading Essentials


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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.

Groundwater FlowGroundwater 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.

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.

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

Visual Check5. Draw a line in the aquifer that shows the point at which the well would run dry.

3. Contrast porosity and permeability.

Reading Check4. Describe how a well can go dry.

Well

Impermeable rock

Spring

Stream

Aquifer



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Reading Check8. Describe the soil conditions in a bog.

Human Impact on GroundwaterPolluted 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.

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.

WetlandsWater 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 WetlandsScientists 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.

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 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 Check7. Identify Where do wetlands occur?

Key Concept Check6. Explain How do human activities affect groundwater?



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Importance of WetlandsWetlands 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.

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 WetlandsMany 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.

Key Concept Check10. Summarize Why are wetlands important?

9. Explain how wildlife uses wetlands.

Key Concept Check11. Discuss How do human activities affect wetlands?



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Mini Glossary

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?

What do you think

END OF LESSON

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

ConnectED

aquifer: an area of permeable sediment or rock that holds

significant amounts of water

groundwater: water that lies below ground

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

rock and sediment

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

water table: the upper limit of the saturated zone

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

or all of the year

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 Swamps Marshes

Soil acidic, nutrient poor slightly acidic, nutrient rich

Climate warmer areas

Plant Growth trees and shrubs grass and shrubs

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



groundwater & wetlands reading

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water source groundwater

water tablegroundwater

water seeps

groundwatersome water

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important source of