7 Aquatic Ecosystems Overview Tell students that this chapter discusses

Transcription

1 CHAPTER 7 Aquatic Ecosystems Overview Tell students that this chapter discusses freshwater and marine ecosystems. Freshwater ecosystems are made up of lakes, rivers, and wetlands. Marine ecosystems include estuaries, coral reefs, and oceans. Aquatic ecosystems perform many environmental functions and support many plant and animal species. Unfortunately, pollution, development, and overuse threaten many of these ecosystems. Using the Figure Manatees live in both fresh water and salt water. In North America, most manatees are found in the estuaries, bays, and coastal ecosystems of states such as Florida. Manatees are often called sea cows because they lazily graze on aquatic vegetation. They are 3 to 4 m in length and usually weigh 360 to 545 kg. Unfortunately, manatees are sometimes hit by boats because they live in shallow water and cannot swim fast enough to avoid boats. C H A P T E R 1 Freshwater Ecosystems 2 Marine Ecosystems PRE-READING ACTIVITY 7 Two-Panel Flip Chart Before you read this chapter, create the FoldNote entitled Two-Panel Flip Chart described in the Reading and Study Skills section of the Appendix. Label the flaps of the two-panel flip chart with Freshwater Ecosystems and Marine Ecosystems. As you read the chapter, write information you learn about each category under the appropriate flap. Manatees live in both freshwater and saltwater ecosystems. Manatees are herbivores and will eat at least 27 kg (60 lb) of aquatic plants per day. PRE-READING ACTIVITY You may want to use this FoldNote in a classroom discussion to review material from the chapter. On the board, write each category from the Two-Panel Flip Chart. Then, ask students to provide information for each category. Under the appropriate category on the board, write the information that students provide. For information about videos related to this chapter, go to go.hrw.com and type in the keyword HE8 AQUV. 184 LS 4e Human beings live within the world s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected. (Section 1 and Section 2) SPSP 3c Humans use many natural systems as resources. Natural systems have the capacity to reuse waste, but that capacity is limited. Natural systems can change to an extent that exceeds the limits of organisms to adapt naturally or humans to adapt technologically. (Section 1 and Section 2) SPSP 4a Natural ecosystems provide an array of basic processes that affect humans. Those processes include maintenance of the quality of the atmosphere, generation of soils, control of the hydrologic cycle, disposal of wastes, and recycling of nutrients. Humans are changing many of these basic processes, and the changes may be detrimental to humans. (Section 1 and Section 2) SPSP 5b Human activities can enhance potential for hazards. Acquisition of resources, urban growth, and waste disposal can accelerate rates of natural change. (Section 1 and Section 2) SPSP 6e Humans have a major effect on other species. For example, the influence of humans on other organisms occurs through land use which decreases space available to other species and pollution which changes the chemical composition of air, soil, and water. (Section 1 and Section 2) 184 Chapter 7 Aquatic Ecosystems

2 S E C T I O N 1 Freshwater Ecosystems The types of organisms in an aquatic ecosystem are mainly determined by the water s salinity the amount of dissolved salts the water contains. As a result, aquatic ecosystems are divided into freshwater ecosystems and marine ecosystems. Freshwater ecosystems include the sluggish waters of lakes and ponds, such as the lake shown in Figure 1, and the moving waters of rivers and streams. They also include areas where land, known as a wetland, is periodically underwater. Marine ecosystems include the diverse coastal areas of marshes, swamps, and coral reefs as well as the deep, vast oceans. Characteristics of Aquatic Ecosystems Factors such as temperature, sunlight, oxygen, and nutrients determine which organisms live in which areas of the water. For instance, sunlight reaches only a certain distance below the surface of the water, so most photosynthetic organisms live on or near the surface. Organisms that live in aquatic ecosystems are grouped by their location and by their adaptations. Three groups of aquatic organisms include plankton, nekton, and benthos. Plankton are organisms that cannot swim against currents, so they are drifters. Drifting plants, called phytoplankton, are the food base for most aquatic ecosystems. The majority of phytoplankton are microscopic. Drifting animals, which may be microscopic or as large as a jellyfish, are called zooplankton. Nekton are free-swimming organisms, such as fish, turtles, and whales. Benthos are bottom-dwelling organisms, such as mussels, worms, and barnacles. Many benthic organisms live attached to hard surfaces. Organisms called decomposers, which break down dead organisms, are also present in aquatic ecosystems. CHEMISTRY Objectives Describe the factors that determine where an organism lives in an aquatic ecosystem. Describe the littoral zone and the benthic zone that make up a lake or pond. Describe two environmental functions of wetlands. Describe one threat against river ecosystems. Key Terms CONNECTION wetland plankton nekton benthos littoral zone benthic zone eutrophication Figure 1 Lake Louise in Alberta, Canada, is an example of a freshwater ecosystem. 185 Water Molecules The molecular structure of water gives it some very unusual properties. When water freezes, its molecular structure expands. Thus, solid water (ice) is less dense than liquid water. (The opposite is true for almost every other substance.) If water did not have this unique property, little aquatic life would exist outside the Tropics because in the winter, ice would sink and lakes and ponds would freeze solid, killing aquatic organisms. S E C T I O N Focus Overview Before beginning this section, review with your students the Objectives listed in the Student Edition. This section discusses the characteristics of freshwater ecosystems. Students also learn about how wetlands are an important kind of freshwater ecosystem. Bellringer Ask students to describe in their EcoLog a river and a lake that they have seen or visited. Tell students that they should describe how the two are similar and how they are different. Ask students to reread their descriptions after completing this section. LS Logical Motivate 1 Demonstration Observing Aquariums If you have an aquarium in the classroom, ask students to observe it. If you do not have an aquarium, show the class a photograph of one. Ask students to describe the different plants and animals in the aquarium. (The animals and plants observed depend on the aquarium.) Ask, What requirements do the fish in the aquarium need to survive? (The fish in the aquarium need food, oxygen, and the correct temperature of water.) Ask students, What would happen if a fish from the ocean were added to the aquarium? (Assuming the aquarium is a freshwater aquarium, the fish would die.) Lesson Plan Active Reading Section Quiz TT Bellringer Chapter Resource File Transparencies Chapter 7 Aquatic Ecosystems 185

3 Teach Discussion Beavers With the exception of humans, beavers may do more to reshape their landscape than any other mammal. Beavers build dams that can create ponds and divert streams to create areas of wetland. Because the water in a pond is standing, it seeps into the ground and increases the soil moisture in the area. Higher soil moisture allows different communities of plants to thrive. The ponds and associated wetlands provide homes and food for dozens of different species that otherwise could not survive in the area. Also, the dams trap sediments that wash off the land during floods. As a beaver pond slowly fills with sediments, the pond is converted into a meadow. Scientists estimate that 200 million beavers once lived in the continental U.S. In the 18th century, the beaver population was nearly decimated by hunting and trapping. The beaver dams fell into disrepair, and the ponds and wetlands that the dams had created were replaced with flowing streams. The loss of beavers changed many areas and affected the plants and animals that lived there. LS Verbal Figure 2 Amphibians, such as this bullfrog, live in or near lakes and ponds. Topic: Lakes and Ponds Code: HE80846 Figure 3 In a pond or lake ecosystem, the most diverse and abundant life occurs near the shore, where sunlight and nutrients are plentiful. In the open water, sunlight at and near the surface supports drifting phytoplankton. Lakes and Ponds Lakes, ponds, wetlands, rivers, and streams make up the various types of freshwater ecosystems. Lakes, ponds, and wetlands can form naturally where groundwater reaches the Earth s surface. As well, beavers can create ponds by damming up streams. Humans intentionally create artificial lakes by damming flowing rivers and streams to use them for power, irrigation, water storage, and recreation. Life in a Lake Lakes and ponds can be structured into horizontal and vertical zones. In the nutrient-rich littoral zone near the shore, aquatic life is diverse and abundant. Plants, such as cattails and reeds, are rooted in the mud underwater, and their upper leaves and stems emerge above the water. Plants that have floating leaves, such as pond lilies, are rooted here also. Farther from the shore, in the open water, there are no rooted plants. Here, phytoplankton make their own food by photosynthesis. As shown in Figure 3, nutrients and sunlight influence the location and types of organisms in a pond or lake ecosystem. Some bodies of fresh water have areas so deep that there is too little light for photosynthesis. In these deep areas, bacteria and other decomposers live on dead plants and animals that drift down from above. Fish adapted to cooler water also live there. Eventually, dead and decaying organisms reach the benthic zone, the bottom of a pond or lake, which is inhabited by decomposers, insect larvae, and clams. Some animals that live in lakes and ponds have interesting adaptations that help them obtain what they need to survive. Water beetles use the hairs under their bodies to trap surface air so that they can breathe during their dives for food. Whiskers help catfish sense food as they swim over dark lake bottoms. In regions where lakes partially freeze in winter, amphibians burrow into the littoral mud to avoid freezing temperatures. Transparencies TT Life Zones in a Lake 186 MISCONCEPTION ALERT Freshwater Plankton Many people think that plankton live only in the ocean. Plankton is a broad term that describes drifting plants phytoplankton and drifting animals zooplankton. Most plankton are microscopic, but some zooplankton are large enough to be seen with the unaided eye. Many times, zooplankton are larvae of aquatic mollusks or crustaceans. INCLUSION Strategies Learning Disabled Attention Deficit Disorder Have students develop a poster that shows the characteristics of plankton, nekton, and benthos. The poster should include examples of each type of organism and information about where in the ocean each organism is found. Students can provide images of each aquatic organism from the Internet. 186 Chapter 7 Aquatic Ecosystems

4 How Nutrients Affect Lakes Eutrophication is an increase in the amount of nutrients in an aquatic ecosystem. A lake that has a large amount of algae and plant growth due to nutrients, as shown in Figure 4, is known as a eutrophic lake. As the amount of plants and algae grows, the number of bacteria feeding on the decaying organisms also grows. These bacteria use the oxygen dissolved in the lake water. Eventually, the reduced amount of oxygen kills oxygen-loving organisms. Lakes naturally become eutrophic over a long period of time. However, eutrophication can be accelerated by runoff. Runoff is precipitation, such as rain, that can carry sewage, fertilizers, or animal wastes from land into bodies of water. Freshwater Wetlands Freshwater wetlands are areas of land that are covered with fresh water for at least part of the year. The two main types of freshwater wetlands are marshes and swamps. Marshes contain nonwoody plants, such as cattails, while swamps are dominated by woody plants, such as trees and shrubs. Wetlands perform several important environmental functions, as shown in Table 1. Wetlands act as filters or sponges because they absorb and remove pollutants from the water that flows through them. Therefore, wetlands improve the water quality of lakes, rivers, and reservoirs downstream. Wetlands also control flooding by absorbing extra water when rivers overflow, which protects farms and urban and residential areas from damage. Many of the freshwater game fish caught in the United States each year use the wetlands for feeding and spawning. In addition, these areas provide a home for native and migratory wildlife, including the blue herons shown in Figure 5. Wetland vegetation also traps carbon that would otherwise be released as carbon dioxide, which may be linked to rising atmospheric temperatures. Reading Check How can wetlands reduce damage that is caused by flooding? (See the Appendix for answers to Reading Checks.) Table 1 Environmental Functions of Wetlands trapping and filtering sediments, nutrients, and pollutants, which keep these materials from entering lakes, reservoirs, and oceans reducing the likelihood of a flood, protecting agriculture, roads, buildings, and human health and safety buffering shorelines against erosion providing spawning grounds and habitat for commercially important fish and shellfish providing habitat for rare, threatened, and endangered species providing recreational areas for activities such as fishing, birdwatching, hiking, canoeing, photography, and painting READING SKILL BUILDER Reading Organizer As they read this section, encourage students to make a chart in their EcoLog of the different types of freshwater ecosystems. The chart should have two columns. The first column should list the ecosystem (lakes, ponds, wetlands, rivers, and streams). The second column should have a description of the ecosystem. LS Logical Figure 4 A eutrophic lake, like the one above, contains large amounts of plants as a result of high levels of nutrients. Figure 5 Wetlands provide habitat for many plants and animals, including the great blue herons shown below. 187 MISCONCEPTION ALERT What Is a Wetland? Wetlands are not always easy to identify. For example, vernal pools may contain water only in the spring and may dry up the rest of the year, but they are still wetlands. Wetlands are identified based on their water, soil, and vegetation. In wetlands, water floods the area consecutively for at least 7.5% of the growing season. Wetland soil, called hydric soil, remains wet long enough to create oxygenpoor conditions. Plants in wetlands are hydrophylic, meaning that they are adapted to growing in wet soil with little oxygen. Debate Natural Vs. Constructed Wetlands Wetlands are sometimes destroyed during construction projects. When a project destroys wetland habitat, the builder often has to create and maintain constructed or human-made wetlands in another area. Divide students into two groups. Assign one group to be supporters of protecting natural wetlands and the other group to be supporters of constructed wetlands. Ask each group to research their subject and then debate the issues. LS Verbal Using the Figure Identifying Wetlands Ask students to look at Figure 3. Ask students, Where are the wetlands located in the figure? (The wetlands are around the edge of the pond.) Which of the two main types of wetlands are represented? (marsh) What do you think will happen to the wetland plants as the pond dries up? (The wetland plants will eventually die and will be replaced with nonwetland plants.) LS Visual SKILL BUILDER Writing Tell students that their city is planning to build a golf course. Golf courses normally use fertilizer and pesticides to keep the grass green and healthy. Tell students that the city s plan also calls for creating lakes around the golf course that will be available for fishing. Based on what students have learned about how nutrients affect lakes, discuss how creating lakes around the golf course will affect the organisms that live in the lake. Have students write a onepage letter to the city council in which they outline potential problems with making the lakes available for fishing. LS Interpersonal Answer to Reading Check Wetlands reduce the damage that is caused by flooding by absorbing extra water when rivers overflow. Chapter 7 Aquatic Ecosystems 187

5 Figure 6 This map shows the locations of large freshwater wetlands in the United States. Teach, continued The Everglades Nearly 90 years ago, an enthusiastic scientist with the United States Department of Forestry received a small packet of seeds in the mail from a colleague in Australia. The seeds were of the melaleuca tree. The scientist scattered the seeds across the Florida Everglades, hoping the water-loving trees would dry up the mucky wasteland to make way for agricultural and residential development. Since then, the melaleuca has spread across thousands of acres of South Florida wetlands. The tree has no natural consumers in South Florida and has driven out many native plants and animals. Scientists are currently trying to eradicate the tree by experimenting with another import from Australia a melaleuca-eating insect. Ask students to find out more about the problems with melaleuca trees and the eradication program. Students should prepare a brief report on their findings. LS Verbal Connection to History The Florida Everglades Because of the work of many writers, conservationists, and naturalists, former U.S. President Truman dedicated the Everglades National Park in The park was established to protect the wildlife and habitat of the Florida Everglades. The Florida Everglades is one of only three sites on Earth declared an International Biosphere Reserve, a World Heritage Site, and a Wetland of International Importance. The other two sites are located in Tunisia and Bulgaria. Figure 7 A marsh is a type of wetland that contains nonwoody plants. Marshes As shown in Figure 6, most freshwater wetlands in the United States are located in the Southeast. The Florida Everglades is the largest freshwater wetland in the United States. Freshwater marshes tend to occur on low, flat lands and have little water movement. In shallow waters, plants such as reeds, rushes, and cattails root themselves in the rich bottom sediments. As shown in Figure 7, the leaves of these and other plants stick out above the surface of the water year-round. The benthic zones of marshes are nutrient rich and contain plants, numerous types of decomposers, and scavengers. Waterfowl, such as grebes and ducks, have flat beaks adapted for sifting through the water for fish and insects. Water birds, such as herons, have spearlike beaks that they use to grasp small fish and to probe for frogs buried in the mud. Marshes also attract many migratory birds from temperate and tropical habitats. The salinity of marshes varies. Some marshes have slightly salty (brackish) water, while other marshes have water that is as salty as ocean water. The organisms that live in and around a marsh are generally adapted to the specific range of salinities of its water. Wetland Plants Have students search the Internet to find five common wetland plants that grow in or near their state. Then have students locate and print out a picture of each plant. Students can start their search at their state s natural resources or conservation department. Transparencies TT Freshwater Wetlands in the United States Chapter 7 Aquatic Ecosystems Wetland Nurseries Tampa BayWatch is a nonprofit organization that monitors, restores, and protects the marine and wetland environments in the Tampa area. Over 2,000 students at area high schools help the restoration efforts by constructing, maintaining, and transplanting wetland plants. These nurseries help raise plants that are used in restoration projects. Encourage interested students to find out about wetland restoration efforts in their area. Students could also find out if they can help by establishing wetland nurseries in other areas.

6 Figure 8 The American alligator is a common reptile that lives in marshes and swamps. Swamps Swamps occur on flat, poorly drained land, often near streams. The species of trees and shrubs in a swamp depend on the salinity of the water and the climate of the area. For example, mangroves are trees that grow in saltwater swamps in tropical climates. Freshwater swamps are the ideal habitat for many amphibians, such as frogs and salamanders, because of the continuously moist environment. Swamps also attract birds, such as wood ducks, that nest in hollow trees near or over the water. Reptiles, such as the American alligator in Figure 8, are the predators of swamps and will eat almost any organism that crosses their path. Human Impact on Wetlands Wetlands were previously considered to be wastelands that provide breeding grounds for disease-carrying insects. Therefore, many have been drained, filled, and cleared for farms or residential and commercial development, as shown in Figure 9. For example, the Florida Everglades once covered 8 million acres of south Florida, but now covers less than 2 million acres. The important role of wetlands as purifiers of wastewater and in flood prevention is now recognized. Wetlands are vital habitats for wildlife. Law and the federal government protect many wetlands, and most states now prohibit the destruction of certain wetlands. MATHPRACTICE Wetland Conversion From 1982 to 1992, approximately 1.6 million acres of wetlands on nonfederal lands in the United States were converted for other uses. Fifty-seven percent of the wetlands were converted into land for development. Twenty percent of the wetlands were converted into land for agriculture. How many acres of land were converted into land for development? How many acres of land were converted into land for agriculture? MATHPRACTICE Answers 1. 57% 1,600,000 acres 912,000 acres 2. 20% 1,600,000 acres 320,000 acres Debate The Florida Everglades The Florida Everglades is the largest wetlands area in North America. In the 1800s, the first canals were dug to begin draining the Everglades to make way for development. This trend has continued until recent years. Many plans have been devised to save and protect the Everglades. The Comprehensive Everglades Restoration Plan is a 20-year project that will cost an estimated $7.8 billion to complete. Divide the class into two groups. Ask one group to research the advantages of the project and the other group to research the disadvantages of the project. Organize a debate and have the two groups present their findings to a mock hearing of the Florida State Legislature. LS Verbal Figure 9 The wetland above has been drained for agricultural purposes. Wetlands such as the one above typically serve as breeding areas for ducks. The oil rig on the left is located in a marsh along the coast of Louisiana. 189 Gone Fishin Tell students to imagine that they are going fishing in a small freshwater pond located in their home state. Have them do research and then write a short paragraph about the types of fish they are likely to catch and the type of bait they will need. Students may begin their research with the department that oversees natural resources in their state. Suggest that interested students follow up their research with an actual fishing trip. They could then compare the results of the trip with their research findings. Suggest that students include a description of their findings in their Portfolio. Activity Wetlands in Your Neighborhood Ask students to find and observe at least one wetland near their school or home (if students cannot find a wetland to observe, have them perform this activity on an aquatic ecosystem of their choice). Have students write a brief physical description of the wetland and explain why it qualifies as a wetland. Have students answer questions about the wetland such as, What types of plants and animals live in the wetland? Is the wetland threatened or in danger of being drained or developed? Have students present their descriptions to the class. LS Interpersonal Chapter 7 Aquatic Ecosystems 189

7 Answer to Reading Check Runoff can maintain or improve the health of river organisms by washing nutrients from the surrounding land into the river. If runoff contains toxins from waste, it can damage the health of river organisms. Close Reteaching Concept Mapping Have students create a concept map using the following terms: freshwater wetlands, lakes, littoral zone, freshwater ecosystems, eutrophication, traps and filters pollutants, runoff, benthic zone, buffers shorelines, phytoplankton, zooplankton, and decomposers. Remind students that they must supply words that show clear connections between the terms used in their maps. Quiz 1. How does a lake become eutrophic? (A nutrient-rich lake supports a lot of plants and algae. The lake s bacterial population grows as bacteria break down dead plants and algae and use up oxygen that other organisms need to survive.) 2. What are phytoplankton and what role do they play in an aquatic ecosystem? (Phytoplankton are drifting plants that are usually microscopic in size. They produce most of the food for an aquatic ecosystem.) Alternative Assessment A Fish Tale Have students imagine that they are a fish journeying through three freshwater ecosystems: a pond, a lake, and a river. Ask students to describe what they see, including details about the characteristics of each body of water and the organisms encountered along the way. Encourage students to include their description in their Portfolio. Figure 10 A river changes dramatically as it flows from a mountaintop to flat land. S E C T I O N 1 Review 1. List two factors that determine where an organism lives in an aquatic ecosystem. 2. Compare the littoral zone of a lake with the benthic zone of a lake. 3. List two environmental functions that wetlands provide. How do these functions affect you? 4. Describe one threat against river ecosystems. 190 Answers to Section Review 1. Answers may vary. Sample answer: temperature and nutrients 2. The littoral zone exists in shallow, sunlit water, while the benthic zone occupies the dark bottom of a lake or pond. 3. Wetlands trap and filter pollutants, which improves water quality downstream. Wetlands also absorb excess water and reduce the likelihood of a flood. 4. Answers may vary. Sample answer: Sewage dumping threatens river ecosystems. Rivers Many rivers originate from snow melt in mountains. At its headwaters, a river is usually cold and full of oxygen and runs swiftly through a shallow riverbed. As a river flows down a mountain, it becomes warmer, wider, and slower, containing more vegetation and less oxygen. Figure 10 compares the water flow of two sections of two different rivers. A river changes with the land and the climate through which it flows. Runoff, for example, may wash nutrients and sediment from the surrounding land into a river. These materials affect the growth and health of the organisms in the river. Life in a River Near the churning headwaters, mosses anchor themselves to rocks by using rootlike structures called rhizoids. Trout and minnows are adapted to the cold, oxygen-rich headwaters. Trout are powerful swimmers and have streamlined bodies that present little resistance to the strong current. Downstream, plants such as the crowfoot set roots in the river s rich sediment. The leaves of some plants, such as the arrowhead, vary in shape according to the strength of the river s current. Fish such as catfish and carp also live in the calmer waters. Rivers in Danger Communities and industries affect the health of rivers. People draw water from rivers to use in homes and manufacturing. People may also use rivers to dispose of their sewage and garbage. These practices have polluted rivers with toxins. The toxins have killed river organisms and made river fish unsuitable for eating. Today, runoff from the land puts pesticides and other poisons into rivers and coats riverbeds with toxic sediments. As well, dams alter the ecosystems in and around a river. Reading Check What effect can runoff have on the health of organisms that live in and around a river? CRITICAL THINKING 5. Identifying Relationships A piece of garbage that is thrown into a stream may end up in a river or an ocean. What effects might one piece of garbage have on an aquatic ecosystem? What effects might 100 pieces of garbage have on an aquatic ecosystem? 6. Analyzing Processes Write a short paragraph that explains how fertilizing your yard and applying pesticides can affect the health of a river ecosystem. WRITING SKILLS 5. Answers may vary. In general, more garbage will have more of a harmful effect on the ecosystem. 6. Sample answer: Rain can wash fertilizers and pesticides off my yard and into a river. Fertilizers can cause an increase in plant growth, and pesticides can kill plants and animals in the river. 190 Chapter 7 Aquatic Ecosystems

8 S E C T I O N 2 Marine Ecosystems Marine ecosystems are ecosystems that contain salt water. Such ecosystems are found in and around the world s oceans. In the open water, the amount of sunlight and available nutrients vary from one part of an ocean to another. In coastal areas, the water level and salinity usually change during the day. Coastal Wetlands Coastal land areas that are covered by salt water for all or part of the time are known as coastal wetlands. Coastal wetlands provide habitat and nesting areas for many fish and wildlife. Coastal wetlands also absorb excess rain, which protects areas from flooding, they filter out pollutants and sediments, and they provide recreational areas for boating, fishing, and hunting. Estuaries Many coastal wetlands form in estuaries. An estuary is an area in which fresh water from a river mixes with salt water from the ocean. As the two bodies of water meet, currents form and cause mineral-rich mud and dissolved nutrients to fall to the bottom. Figure 11 illustrates how the waters mix in such a way that the estuary becomes a nutrient trap. These nutrients then become available to producers, and in some shallow areas, marsh grass will grow in the mud. Estuaries are very productive ecosystems because they constantly receive fresh nutrients from the river. The surrounding land, such as the mainland or a peninsula, protects estuaries from the harsh force of ocean waves. Objectives Explain why an estuary is a very productive ecosystem. Compare salt marshes and mangrove swamps. Describe two threats to coral reefs. Describe two threats to ocean organisms. Key Terms estuary salt marsh mangrove swamp barrier island coral reef Topic: Estuaries Code: HE80536 Figure 11 The mixing of fresh water and salt water at the mouth of a river creates a nutrient-rich estuary. Lesson Plan Active Reading Section Quiz Chapter Resource File Transparencies TT Bellringer TT The Formation of Estuaries 191 S E C T I O N Focus Overview Before beginning this section, review with your students the Objectives in the Student Edition. This section describes marine ecosystems, such as estuaries, coral reefs, and open oceans. Students also learn about threats to these ecosystems. Bellringer Provide specimens or photographs of common organisms that live in various marine ecosystems, such as coral, shells, sponges, and starfish. Show them to the class one at a time, and ask students which marine ecosystem each organism is from. Then ask students what part or zone of the marine ecosystem the organism is adapted to. (For example, a piece of coral would be found near the surface in shallow ocean waters.) LS Visual Motivate Identifying Preconceptions Singing Whales At the beginning of class, have students close their eyes and sit quietly. Play a brief audiotape of a dolphin or whale song. Afterward, ask students, What is the largest animal on Earth? (the blue whale) Inform students that blue whales can weigh over 110 metric tons (over 242,000 lb), which is about 15 times the weight of the largest African elephant, and are larger than any dinosaur. Ask students, Why can t animals of that size live on land? (They would not be able to support their weight.) Can you think of other organisms that might form part of the blue whale s marine community? (Answers may vary. Blue whales live at various depths in the open ocean. They may share their community with other whales, fish, dolphins, and seals.) LS Auditory 2 Chapter 7 Aquatic Ecosystems 191

9 Teach QuickLAB Skills Acquired: Experimenting Interpreting Answers 1. The salt water will sink below the fresh water and will not mix completely. QuickLAB Estuaries Procedure 1. Place a few drops of red food coloring in a test tube filled with water. 2. In a separate test tube, add salt water and a few drops of yellow food coloring. 3. Gently place some of the fresh water solution on top of the salt water solution. Analysis 1. How do fresh water and salt water interact in an estuary? Plants and Animals of Estuaries For a week each spring, horseshoe crabs, shown in Figure 12, crawl out of the ocean and onto the beaches of Delaware Bay. In the shallow areas along the shore, the crabs mate and lay billions of eggs. Many migrating shorebirds depend on these eggs for food. Estuaries support many marine organisms because estuaries receive plenty of light for photosynthesis and plenty of nutrients for plants and animals. Rivers supply nutrients that have been washed from the land, and because the water is shallow, sunlight can reach all the way to the bottom of the estuary. The light and nutrients support large populations of rooted plants as well as plankton. The plankton in turn provide food for larger animals, such as fish. Dolphins, manatees, otters, and other mammals often feed on fish and plants in estuaries. Oysters, barnacles, and clams live anchored to marsh grass or rocks and feed by filtering plankton out of the water. Organisms that live in estuaries are able to tolerate variations in salinity because the salt content of the water varies as fresh water and salt water mix when tides go in and out. Demonstration Salinity Change Students may be unfamiliar with salinity changes as the tides come in and out in estuaries. To show students how salinity changes, use a tall jar or large graduated cylinder and a hydrometer. Hydrometers may be found at aquarium stores, where they are used to measure salinity in a marine aquarium. Fill the jar or cylinder three-quarters full of tap water, and place the hydrometer in the jar. Record the reading. In a separate container, dissolve as much table salt as possible in hot tap water. Have students watch the hydrometer as you slowly add the salt-saturated water. Ask students to describe how the hydrometer changed as the salt solution was added. LS Kinesthetic The Chesapeake Bay is the largest estuary in the United States. The bay produces large amounts of seafood each year, supports many species of wildlife, and provides recreation for millions of people. However, the ecosystems of the bay are threatened by several environmental problems. For example, pollution builds up because the small tide flushes pollutants out of the bay very slowly. Pollution builds up because only a very narrow opening joins the bay and the ocean. By 1980, the Chesapeake Bay was severely polluted with toxic industrial chemicals. Pesticides as well as excess nutrients ran into the bay from housing developments, farms, and wastewater (including sewage). Marsh grasses and plankton were dying, and fish, oysters, and crabs were disappearing. Birds of prey, such as bald eagles, had 192 Restoration of the Chesapeake Bay almost vanished. Therefore, fishers, environmentalists, and residents became alarmed and launched campaigns to save the bay. Restoring Chesapeake Bay habitats and water quality is not easy. Maryland and Virginia, the main bordering states of the bay, have different environmental laws. Also, the bay s watershed covers parts of four other states. Interested groups would have to work together if they were to restore the bay. The Chesapeake Bay Program was set up as a partnership between the Environmental Protection Agency, the District of Columbia, Maryland, Pennsylvania, Virginia, and citizen advisory groups. Goals included reducing chemical pollution, removing dams that prevented fish from migrating, and reforesting river banks to reduce soil erosion. The Chesapeake Bay forms where the Potomac, Rappahannock, and other rivers meet the Atlantic Ocean. Remarkable progress has been made in the last 20 years. About half of the wastewater flowing into GEOGRAPHY CONNECTION Coastal Settlements Throughout history, a disproportionate amount of human settlement has occurred in coastal areas. There are several reasons. First, having access to a body of water facilitates travel and trade with other areas. In addition, the fish and other organisms in oceans represent a valuable and readily available resource. Also, the climate in coastal areas is usually moderated by the nearby water body. Historically, the ocean and its organisms have figured prominently in human culture. For instance, the ocean is a powerful symbol in many religions, and cowrie shells were perhaps the first form of established currency. 192 Chapter 7 Aquatic Ecosystems

10 Estuaries provide protected harbors, access to the ocean, and connection to a river. As a result, many of the world s major ports are built on estuaries. Of the 10 largest urban areas in the world, 6 were built on estuaries. These 6 cities are Tokyo, New York, Shanghai, Buenos Aires, Rio de Janeiro, and Bombay. Threats to Estuaries Estuaries in populated areas were often used as solid waste landfills. The landfills were then developed and used as building sites. This practice occurred widely in California, which now has plans to restore some of its estuary wetlands. The pollutants that damage estuaries are the same pollutants that damage other aquatic ecosystems: sewage, industrial waste, and agricultural runoff. Most of these pollutants eventually break down over time, but estuaries cannot cope with the excessive amounts produced by dense human populations. Figure 12 Horseshoe crabs go to the Delaware Bay, an estuary between New Jersey and Delaware, to lay their eggs. Activity Save the Chesapeake Bay Ask students to make posters to increase public awareness about the problems in the Chesapeake Bay. Tell students to select one aspect of the problems in the bay and have them develop a poster that explains the issue and offers suggestions for solutions. Encourage students to illustrate their posters. Display the posters around the classroom or in the hallway. LS Interpersonal This great egret lives in one of the estuaries that borders the Chesapeake Bay. the bay is now biologically treated to remove pollutants and excess nutrients. Bald eagles are back, and industry has reduced the chemical pollutants released into the bay by nearly 70 percent. Planting trees has restored forested buffers to about 60 percent of the river banks, and populations of fish, such as striped bass, are increasing. However, the number of people in the bay area is increasing and the number of miles these people drive each year has increased even faster. In the last 30 years, miles traveled by vehicles increased four times as fast as the population. This has led to runoff from streets and lawns and pollution from vehicle exhaust, all of which harm the bay. The oyster harvest has decreased and the forested part of the bay s watershed is still decreasing. You can help save your local watershed in the following ways: by reducing the number of miles you Tides and Estuaries Have students select an estuary in the United States. Ask students to use the Internet to find the tide charts for a location on the estuary and a nearby spot on the coast. Tide charts may be found at the Web sites of newspapers for cities near the estuary. Ask students to write a brief description of how the tide in the estuary differs from the tide at a nearby point on the coast. Ask students to compare the tide levels on the coast and in the estuary. How do the tides affect the water in the estuary? LS Intrapersonal READING SKILL BUILDER drive, trying to conserve electricity and water, planting native vegetation, using only a small amount of fertilizer or water on your lawn or garden, and properly disposing of hazardous wastes such as motor oil, antifreeze, and cleaning fluids. You can help by picking up trash that others leave behind. You can also join a citizens group to help preserve estuaries. CRITICAL THINKING 1. Predicting Consequences If the Chesapeake Bay Program had never been founded, what might have happened to the Chesapeake Bay? Explain how one organism may have been affected. 2. Identifying Relationships How may the use of less fertilizer on plants and lawns help the Chesapeake Bay and other estuaries? 193 Brainstorming After reading the subsection on plants and animals of estuaries, have students brainstorm the adaptations that plants and animals would need to live in estuaries. You may need to prompt students into thinking about temperature changes, seasonal changes, and migratory predators. LS Verbal The Chesapeake Bay The Chesapeake Bay is the largest estuary in the United States. It is 320 km long and varies from 6.4 km wide at its narrowest point to 48 km wide at its widest point. The watershed for the bay covers parts of six states and more than 164,000 km 2. The watershed is five times larger than Maryland and one-fourth the size of Texas. In 2000, approximately 16 million people lived in the watershed. More than 2,700 species of plants and animals live in the Chesapeake Bay. Today, the biggest threat to the bay is nutrients in runoff from crops and lawns. Tell students that cleaning up the bay requires changes in the entire watershed and involves not only the federal government but also governments from six states. Answers to Critical Thinking 1. If the Chesapeake Bay Program was not founded, the Chesapeake Bay may not have been protected or restored. Without this protection, pollution could have increased and could have killed fish living in the bay. Fewer fish could have affected dolphins, which depend on the fish for food. 2. Using less fertilizer on plants and lawns could decrease the amount of fertilizer in runoff and could reduce nutrient pollution in the Chesapeake Bay. Chapter 7 Aquatic Ecosystems 193

11 Teach, continued Debate Disappearing Barrier Islands Divide the class into two groups. Assign one group to be for enhancement projects that rebuild and protect barrier islands and the other group to be against such programs. Have the groups research the issues and then debate the different viewpoints. LS Verbal Demonstration Barrier Islands Place a large, flat, clear glass pan on an overhead projector or on a tabletop. Pour about 2 cm of water into the pan. Tell students that the water represents the ocean and that one edge of the pan represents the coastline. To make waves, tap with a pen on the surface of the water opposite the coastline. Students should be able to see the waves. Ask students, What happens when waves reach the coastline? (The waves slap against the side of the pan.) Next, pour a line of sand about 5 cm from the edge called the shoreline. The sands should just barely reach the surface. Repeat the wave-making process. Ask students, What happens to the waves now that there is a barrier island? (The waves usually stop at the barrier island.) What effect would the barrier islands have on coastal erosion? (The barrier islands would reduce coastal erosion.) LS Kinesthetic Answer to Reading Check Both salt marshes and mangrove swamps are coastal wetlands. Both have been filled with waste and destroyed in many parts of the world. Figure 13 Mangrove swamps are found along warm, tropical coasts and are dominated by salt-tolerant mangrove trees. Ecofact Mangrove Swamps Mangroves cover 180 billion square meters of tropical coastlines around the world. The largest single mangrove swamp is 5.7 billion square meters, located in the Sundarbans of Bangladesh. This single mangrove swamp provides habitat for the Bengal tiger and helps supply approximately 300,000 people with food, fuel, building materials, and medicines. Figure 14 This barrier island is located off the coast of Long Island, New York. Barrier islands are separated from the mainland and help protect the shore of the mainland from erosion. 194 HISTORY CONNECTION North Carolina s Outer Banks Some of the best-known barrier islands in the United States are the Outer Banks of North Carolina. The islands were the site of England s lost colony and were used by the pirate Blackbeard. Nearby dunes hosted the Wright Brother s historic flight. Also, the scenic Outer Banks contains the country s first national seashore, Cape Hatteras. Salt Marshes In estuaries, where rivers deposit their load of mineral-rich mud, salt marshes form. Here, thousands of acres of salt marsh support a community of clams, fish, and aquatic birds. The marsh also acts as a nursery in which many species of shrimps, crabs, and fishes find protection when they are small. As they grow to maturity and migrate to the sea, they are eaten by larger fish or caught by commercial fisheries. Salt marshes, like other wetlands, absorb pollutants and protect inland areas. Mangrove Swamps Mangroves, such as those shown in Figure 13, are several species of small trees adapted for growing in shallow salt water. Most mangroves have wide, above-ground root systems for support. Dense growths of mangrove trees in swampy areas called mangrove swamps are found in tropical and subtropical zones. Mangrove swamps help to protect the coastline from erosion and reduce the damage from storms. They provide habitat for about 2,000 animal species. Like salt marshes, mangrove swamps have been filled with waste or used for development projects in many parts of the world. Rocky and Sandy Shores Rocky shores have many more plant and animal species than sandy shores do. The rocks anchor seaweed and the many animals that live on it, such as sea anemones, mussels, and sponges. Life on sandy shores, although less diverse, is abundant in the water and in the sand and sediments. In the water and on land, animals are adapted to the effects of drying and exposure at low tide. At low tide, birds poke and prod about for animals that have not attached themselves firmly enough or buried themselves deeply enough to escape the tidal pull. Barrier islands, such as the one in Figure 14, often run parallel to sandy shores. These islands help to protect the mainland and the coastal wetlands from storms and ocean waves. Reading Check Name two things that a salt marsh has in common with a mangrove swamp. READING SKILL BUILDER Comparing and Contrasting Divide the class into small groups. Have each group read about salt marshes and mangrove swamps. Then, ask each group to compare salt marshes with freshwater marshes and mangrove swamps with freshwater swamps. Ask each group to develop a chart describing the similarities and differences. 194 Chapter 7 Aquatic Ecosystems

12 Coral Reefs Coral reefs are limestone ridges built by tiny coral animals called coral polyps and the algae that live inside them. Coral polyps secrete skeletons of limestone (calcium carbonate), which slowly accumulate and form coral reefs. Thousands of species of plants and animals live in the cracks of coral reefs, which makes coral reefs among the most diverse ecosystems on Earth. Because reef-building corals live only in warm salt water where there is enough light for photosynthesis, coral reefs are found in shallow, clear tropical seas. Figure 15 shows the locations of coral reefs. Only the outer layer of a reef contains living corals, which build their rock homes with the help of the photosynthetic algae that live within them. Corals, such as those shown in Figure 16, are predators that never chase their prey. Their stinging polyps capture small animals that float or swim close to the reef. Because of their convoluted shape, coral reefs provide a habitat for a magnificent variety of fish, snails, clams, sponges and many other types of organisms. Coral Reefs in Danger Coral reefs are fragile ecosystems. If the surrounding water is too hot or cold for too long, or if it is too muddy, polluted, or high in nutrients, the algae that live in the corals will leave or die. As a result, the corals turn white, a condition called coral bleaching. If coral bleaching occurs often or long enough, coral animals and the reefs they build will die. Since the twentieth century, bleaching events have been occurring more frequently, mainly due to human activities. About 50 percent of the world s coral reefs are now in danger of destruction. In addition, global warming, oil spills, and polluting runoff have been linked to the destruction of coral reefs. As well, overfishing upsets the balance of a reef ecosystem by devastating fish populations. Because coral reefs grow slowly, a reef may not be able to repair itself when parts of it are stressed or destroyed. Figure 15 Coral reefs are found in warm, shallow waters, where there is enough light for photosynthesis. Coral reefs support a great diversity of species. Cause-and- Effect Map Create the Graphic Organizer entitled Cause-and-Effect Map described in the Appendix. Label the effect with Disappearing Coral Reefs. Then, fill in the map with causes of disappearing coral reefs and details about the causes and effects. Figure 16 Coral reefs (bottom) are built by tiny coral animals called coral polyps. The stinging polyps of fire coral (top) capture animals by poisoning them. 195 Group Activity Coral Reefs In this activity students will illustrate a coral reef for the classroom. To begin, tape a large sheet of butcher paper to one wall of the classroom. Label it Coral Reef, and draw an outline of a coral reef formation on the paper. Provide students with construction paper, scissors, markers, tape, glue, and pictures or drawings of coral reef inhabitants. Instruct students to pair up and select a living organism that is associated with the coral reefs. Have them illustrate or construct their animal, and glue or tape it to the appropriate location on the Coral Reef. Examples may include sharks, fish, eels, shrimp, sponges, rays, sea anemones, and urchins. When the project is finished, have students comment on the diversity of living things found in and around a coral reef. Suggest that students document their comments and include them in their Portfolio. LS Intrapersonal English Language Learners INCLUSION Strategies Gifted and Talented Ask students to research three types of coral on the Internet. Students should be able to identify each coral type, describe the organisms living in and around the coral, discuss how the reefs form, and identify where each type of coral is found. Notable Quotes Roll on, thou deep and dark blue ocean roll! Ten thousand fleets sweep over thee in vain; Man marks the earth with ruin his control Stops with the shore Lord Byron The sea is tired. It s throwing back at us what we re throwing in there. Senator Frank Lautenberg Have students discuss the contrary opinions provided by these two quotes. Ask students, How might the attitude expressed by Lord Byron have led to the conditions described by Senator Lautenberg? (The belief that the ocean was immune to the impact of people may have sanctioned behaviors that threaten the marine environment.) LS Logical Cause and Effect Map You may want to use this Graphic Organizer to assess students' understanding of the topic. Collect the Graphic Organizers from the students, and correct any mistakes before returning the Graphic Organizers. Transparencies TT Coral Reefs of the World Chapter 7 Aquatic Ecosystems 195

13 Teach, continued Group Activity Marine Ecosystems Divide the class into three groups. Assign each group a portion of this section to teach to the class. Group one will teach about the estuary ecosystem. Group two will teach about coral reefs. Group three will teach about the ocean. Tell each group they must create a lesson plan for their topic that includes objectives, the actual lesson, a handout (daily assignment), and a visual aid. Give students two days to prepare. Then have them present their lesson to the class. Suggest that students include their lesson plan in their Portfolio. LS Interpersonal Transparencies TT Life Zones in the Ocean Figure 17 The amount of sunlight available determines which organisms can live in each layer of the ocean. FIELD ACTIVITY Make a Miniature Aquatic Ecosystem Make your own aquarium by collecting organisms from an aquatic ecosystem near your home or school. Be sure to collect some water from the aquatic ecosystem. Bring your collection back to school and set up an aquarium. If necessary, research the Internet to find out the special care that your ecosystem may require. Examine a few drops of your collected water under the microscope. Be sure to look for algae or other forms of life. Record and draw your observations in your EcoLog. Observe and record the changes you see in your aquarium over the next 3 weeks. What conditions are needed to keep your miniature ecosystem healthy? 196 Career Oceanographer Oceanographers study the chemical and physical properties of seawater and the way ocean water moves (e.g., currents, tides, and waves). Oceanographers also study the sea floor and how it is changing because of plate tectonic forces. Oceanographers use many tools to study the ocean, such as satellites, radio buoys, ships, and submersibles. Oceanographers take classes in marine biology, geology, ecology, chemistry, physics, and geography. Oceans Because water absorbs light, sunlight that plants can use for photosynthesis penetrates only about 100 m (330 ft) into the ocean. As a result, much of the ocean s life is concentrated in the shallow, coastal waters. Here, sunlight penetrates to the bottom and rivers wash nutrients from the land. Seaweed and algae grow anchored to rocks, and phytoplankton drift on the surface. Invertebrates and fish that feed on these plants are also concentrated near the shore. Plants and Animals of Oceans In the open ocean, phytoplankton grow only in areas where there is enough light and nutrients. As a result, the open ocean is one of the least productive of all ecosystems. Phytoplankton have buoyancy devices, such as oil bubbles, that prevent them from sinking into deep water, which is too dark for photosynthesis. The sea s smallest herbivores are the zooplankton, which live near the surface with the phytoplankton they eat. The zooplankton include jellyfish, tiny shrimp, and the larvae of fish and bottom-dwelling animals, such as oysters and lobsters. Fish feed on the plankton as do marine mammals such as whales. The depths of the ocean are perpetually dark, so most food at the ocean floor consists of dead organisms that fall from the surface. Decomposers, filter feeders, and the organisms that eat them live in the deep areas of the ocean. Figure 17 illustrates the types of organisms that may be found in the layers of the ocean at various depths, depending on available sunlight. Oceans of the World Have students research the major oceans of the world and create a magazine-style article that compares the oceans. Ask students to include descriptive examples of living organisms unique to each ocean. Students could include their article in their Portfolio. LS Verbal 196 Chapter 7 Aquatic Ecosystems

14 Threats to the Oceans Although oceans are huge, they are steadily becoming more polluted. Most ocean pollution arises from activities on land. For example, runoff from fertilized fields may cause algal blooms, some of which are poisonous. Waste from cities and industries, fertilizers, and sewage running off the land are the main sources of coastal pollution in the United States. Overfishing and certain fishing methods are also destroying some fish populations. Immense trawl nets can entangle organisms that are larger than the holes in the nets. Marine mammals such as dolphins, which must breathe air, can drown in the nets. Some ships illegally discard fishing lines into the ocean, where they can strangle and kill animals such as the sea lion in Figure 18. Arctic and Antarctic Ecosystems The arctic ecosystems at the North and South Poles are marine ecosystems because nearly all the food comes from the ocean and seas. The Arctic Ocean is rich in nutrients from the surrounding land masses. It supports large populations of plankton, which feed a rich diversity of fish in the open water and under the ice. The fish are food for ocean birds, whales, and seals. Beluga whales, shown in Figure 19, feed on nearly 100 different arctic organisms. Fish and seals also provide food for polar bears and people on land. The Antarctic is the only continent never colonized by humans. Even during the summer, only a few plants grow at the rocky edges of the continent. As in the Arctic, plankton form the basis of the Antarctic food web. They nourish large numbers of fish, whales, and birds such as penguins, which cannot fly because their wings have evolved for swimming. Reading Check the ocean? S E C T I O N 2 Review What are two threats to organisms that live in 1. Explain why estuaries are very productive ecosystems. Why are estuaries vulnerable to the effects of pollution? 2. Compare salt marshes with mangrove swamps. 3. Describe two factors that can damage coral reefs. 4. List two ways in which animals of the oceans are threatened. Answers to Section Review 1. Estuaries are very productive because they constantly receive nutrients from rivers and from the ocean. Estuaries are vulnerable to pollution because ocean, lake, and river pollutants enter estuaries and because dense human settlements surround most estuaries. 2. Salt marshes are dominated by marsh grasses and develop in estuaries, while mangrove swamps are dominated by mangrove trees and develop in tropical and subtropical areas. 3. Water that is too hot or cold can damage reefs by killing corals. Muddy water can kill the algae that live within corals. Figure 18 This sea lion was strangled by a fishing net off the coast of California. Figure 19 Beluga whales inhabit the Arctic Ocean. CRITICAL THINKING 5. Predicting Consequences Suppose that the sea level suddenly rose by 100 m. What would happen to the world s coral reefs? Explain. 6. Analyzing Processes Read the description of estuaries in this section, and explain why cities are often built on estuaries. How would building a city on an estuary affect the plants and animals living in the estuary? READING SKILLS Overfishing is destroying some fish populations, and trawl nets can entangle and drown marine mammals, such as sea lions. 5. A 100 m rise in sea level would kill off most of the world s coral reef ecosystems, because the algae in corals need water shallow enough to allow sufficient light through for photosynthesis. 6. Cities are often built on estuaries because estuaries provide protected harbors, access to the ocean, and connection to a river. Building a city on an estuary would reduce populations of many animals through fishing and pollution. Answer to Reading Check Coastal pollution and overfishing threaten organisms that live in the ocean. Close Reteaching Marine Ecosystem Types As a class, review the types of marine ecosystems covered in this section. Have students get into small groups to quiz each other on the main characteristics of each marine ecosystem. Then, have students draw diagrams of each marine ecosystem and label each component and/or layer. Quiz English Language Learners 1. Why are estuaries a mineral-rich environment? (Estuary waters mix to trap mineral-rich mud washed from rivers.) 2. How are salt marshes and mangrove swamps different? (Marsh grasses dominate salt marshes, while mangrove trees dominate mangrove swamps. Salt marshes are most commonly found on the Atlantic coast and along the Gulf of Mexico. Mangrove swamps are found in tropical and subtropical zones.) 3. What are the primary producers in the open ocean? (plankton) 4. Name two threats to the ocean. (pollution and overfishing) Alternative Assessment Underwater Tour Have students write and perform a skit in which 8 to 10 students operate a special submarine that takes a small group of guests (the rest of the class) on an underwater tour through the different depths of the ocean. Each student in the crew can describe characteristics of the ocean at each level. Have the guests devise questions for the crew members. Chapter 7 Aquatic Ecosystems 197

15 CHAPTER Highlights C H A P T E R 7 7 Highlights Alternative Assessment Nutrient Flow Have students make a poster that describes the flow of nutrients from the top of a mountain to the open ocean. The poster should illustrate how nutrients pass through all the different ecosystems on their way from the mountaintop to the open ocean. Encourage students to find photographs or make drawings of each of the ecosystems that the nutrients pass through. LS Visual Researching Estuaries Have students research a major estuary (besides the Chesapeake Bay) and create a report highlighting its historical significance, the seafood harvested from it, its current environmental health, and efforts to preserve or restore the ecosystem. Chapter Resource File Chapter Test Chapter Test Concept Review Critical Thinking Test Item Listing Field Activity Observation Lab CBL Probeware Lab Consumer Lab Long-Term Project 1 Freshwater Ecosystems 2 Marine Ecosystems Key Terms wetland, 185 plankton, 185 nekton, 185 benthos, 185 littoral zone, 186 benthic zone, 186 eutrophication, 187 estuary, 191 salt marsh, 194 mangrove swamp, 194 barrier island, 194 coral reef, 195 Main Ideas Aquatic ecosystems can be classified as freshwater ecosystems or marine ecosystems. The plants and animals in aquatic ecosystems are adapted to specific environmental conditions. Freshwater ecosystems include lakes, ponds, freshwater wetlands, rivers, and streams. The types of freshwater ecosystems are classified by the depth of the water, the speed of the water flow, and the availability of minerals, sunlight, and oxygen. Freshwater wetlands serve many functions within ecosystems. They trap and filter sediments and pollutants; reduce the likelihood of a flood; and buffer shorelines against erosion. Marine ecosystems are identified by the presence of salt water and include coastal wetlands, coral reefs, oceans, and polar ecosystems. Estuaries are among the most productive of ecosystems because they constantly receive fresh nutrients from a river and from an ocean. Estuaries provide habitat for a multitude of plants and animals. Coral reefs are susceptible to destruction because they must remain at tropical temperatures and they must receive a large amount of sunlight. Coral reefs provide habitat for approximately one-fourth of all marine species. Almost every person has an impact on aquatic ecosystems. Through understanding how we affect aquatic ecosystems, we can reduce the negative effects we have on them Chapter 7 Aquatic Ecosystems

16 C H A P T E R Using Key Terms Review Use each of the following terms in a separate sentence. 1. wetland 2. mangrove swamp 3. estuary 4. eutrophication 5. benthos For each pair of terms, explain how the meanings of the terms differ. 6. littoral zone and benthic zone 7. plankton and nekton 8. salt marsh and barrier island 9. wetland and coral reef STUDY TIP 7 Graph Skills Taking the following steps when reading a graph will help you correctly interpret the information. Be sure to read the title so that you understand what the graph represents. If the graph has axes, read the titles of both the x- and the y-axis. Examine the range of values on both the x- and the y-axis. Finally, examine the data on the graph, reading them from left to right, and put into words what you think the graph represents. Understanding Key Ideas 10. Wetlands are important to fisheries in the United States because a. wetlands are the easiest place to catch fish. b. wetlands are the breeding grounds for insects that are eaten by fish. c. wetlands provide the most desirable species of fish. d. many of the fish caught each year use wetlands for feeding and spawning. 11. Animals that live in estuaries a. tend to produce few offspring. b. are usually found in unpolluted environments. c. must be adapted to varying levels of salinity. d. are adapted to cold-water conditions. 12. Bacteria can kill organisms in eutrophic lakes by a. feeding on decaying plants and animals. b. reducing oxygen dissolved in the water. c. Both (a) and (b) d. Neither (a) nor (b) 13. Arctic ecosystems are considered marine ecosystems because a. arctic ecosystems contain an enormous amount of frozen sea water. b. arctic ecosystems are inhabited by few organisms. c. sunlight is limited. d. phytoplankton form the basis of arctic food webs. 14. Which of the following statements does not describe a function of wetlands? a. Wetlands buffer shorelines against erosion. b. Wetlands provide spawning grounds for commercially important fish and shellfish. c. Wetlands filter pollutants. d. Wetlands make good hazardous waste dumpsites. 15. Tiny animals, called coral polyps, that secrete limestone create a. barrier islands. b. coral reefs. c. swamps. d. salt marshes. 16. Mangrove trees grow a. along riverbanks. b. in freshwater wetlands. c. in tropical areas and in subtropical areas. d. in the benthic zones of lakes. 17. The Florida Everglades a. is the largest freshwater marsh in the United States. b. protects threatened and endangered wildlife. c. provides habitat for migratory birds. d. All of the above 18. Which of the following actions is an example of how humans affect wetlands? a. draining a wetland to create farmland b. clearing a wetland to build a housing development c. using a wetland as a landfill d. all of the above Assignment Guide 199 Section Questions 1 1, 4 7, 9, 10, 12, 14, 17, 18, 20 22, 27, 28, 31, , 3, 8, 9, 11, 13, 15, 16, 18, 19, 21, 23 27, 29, 30, 32, 33, 36, 37 CHAPTER 7 ANSWERS Review Using Key Terms 1. Sample answer: A wetland is an area where land is periodically underwater. 2. Sample answer: Mangrove trees grow in mangrove swamps. 3. Sample answer: An estuary is the area where a river meets the ocean. 4. Sample answer: Excess nutrients in a lake can cause an explosion of plant algae and bacteria called eutrophication. 5. Sample answer: Mussels, clams, and barnacles are bottomdwelling animals called benthos. 6. In a pond, the littoral zone is the shallow margin, while the benthic zone is the deep, openwater region. 7. Plankton are organisms that drift. Nekton are free-swimming organisms, such as fish and turtles. 8. A salt marsh is an ecosystem that develops in an estuary and is dominated by marsh grasses. A barrier island is a long, thin island that protects the shore from erosion. 9. A wetland is an area of land covered by water for at least part of the year, while coral reefs are limestone ridges built by corals. Understanding Key Ideas 10. d 11. c 12. c 13. d 14. d 15. b 16. c 17. d 18. d Chapter 7 Aquatic Ecosystems 199

17 CHAPTER Review 7 Review Short Answer 19. Answers may vary. Estuaries can be described as the best of both worlds because they lie at the interface of rivers and oceans and thus receive nutrients from both. 20. Answers may vary. Plankton are very small plants or animals that live suspended in the water. Nekton are free-swimming organisms, such as fish. Benthos are bottom-dwelling organisms. 21. Answers may vary. Wetlands trap and filter sediments and pollutants, absorb potential floodwater, and buffer the shorelines against erosion. 22. In a eutrophic lake, high nutrient levels foster plant and algae growth, which supports bacteria that feed on decaying plants and algae. Rising bacterial populations use up the oxygen in the water, which kills oxygen-loving organisms. 23. Mangrove swamps are dominated by mangrove trees. Interpreting Graphics 24. Of all the coral reefs in the world, 80% are still living ,300 km ,272 km ,300 km ,378 km 2 Short Answer 19. How does the phrase the best of both worlds relate to an estuary? 20. Explain the difference between the types of organisms that make up these classes: plankton, nekton, and benthos. 21. List three functions of wetlands. 22. Describe what happens when a lake is considered to be eutrophic. 23. What type of vegetation dominates mangrove swamps? Interpreting Graphics The pie graph below shows the percentage of coral reefs at risk in the world. Use the pie graph to answer questions What percentage of coral reefs are still living? 25. If there is a total of 255,300 km 2 of coral reefs in the world, how many square kilometers of coral reefs are at a high risk of being destroyed? 26. How many square kilometers of coral reefs are at a medium risk of being destroyed? Assume there is a total of 255,300 km 2 coral reefs in the world. 200 C H A P T E R 7 Status of the World s Coral Reefs high risk 24% medium risk 26% destroyed 20% low risk 30% Source: Global Coral Reef Monitoring Network? Concept Mapping?? 27. Use the following terms to create a concept map: lakes, estuaries, aquatic ecosystems, coral reefs, freshwater wetlands, freshwater ecosystems, rivers, oceans, marshes, marine ecosystems, swamps, coastal ecosystems, and mangrove swamps. Critical Thinking 28. Analyzing Relationships Write a short paragraph that explains the relationship between the speed of a river and the oxygen content of a river. WRITING SKILLS 29. Determining Cause and Effect Explain what may happen if the use of fertilizer on farms and lawns around an estuary is not controlled. 30. Making Comparisons Read the paragraph under the heading Threats to Estuaries in this chapter. How do these threats compare with those described under the heading Threats to the Oceans? READING SKILLS 31. Analyzing Relationships Explain why planting trees along a riverbank might benefit a river ecosystem. Cross-Disciplinary Connection 32. Demography Six out of 10 of the largest urban areas were built on estuaries. Three of these cities are Tokyo, New York, and Rio de Janeiro. Research the population of each of these cities, and predict what may happen if population numbers continue to increase. Portfolio Project 33. Research a Local Aquatic Ecosystem Observe an aquatic ecosystem near your school or home. This ecosystem can be as simple as a pond or stream or as complex as a lake or estuary. Observe the color of the water and the types of plants and animals. Record any interactions among the organisms that you observe. When you have recorded all of your data and observations, write a one-page report on the aquatic ecosystem. Concept Mapping 27. Answers to the concept mapping questions are on pp Critical Thinking 28. Answers may vary. In general, fast flowing rivers will have a high oxygen content and slow flowing rivers will have a low oxygen content. 29. Runoff from the fertilized areas will increase the amount of nutrients in the estuary, which will create eutrophic conditions that can choke the estuary. 30. Answers may vary. Estuaries located in populated areas are threatened by development. Many cities are built on estuaries because estuaries provide access to a river and to an ocean. Estuaries are also threatened by pollution. Oceans are threatened by pollution and overfishing. Certain fishing methods such as discarded fishing lines can threaten ocean organisms. 31. Planting trees along a riverbank will decrease erosion and flooding, and the trees will absorb some of the nutrients from the water. 200 Chapter 7 Aquatic Ecosystems

18 MATH SKILLS Use the graph below to answer questions Percentage threatened Threatened Freshwater Fish Species A B C Country 34. Analyzing Data The graph below illustrates the percentage of freshwater fish species that are threatened in specific countries. What percentage of freshwater fish species are threatened in country B? in country D? 35. Evaluating Data If the number of freshwater fish species in country C totals 599 different species, how many of these species are threatened? WRITING SKILLS 36. Communicating Main Ideas What effect does overfishing have on estuaries? What effect does overfishing have on oceans? 37. Writing from Research Research endangered marine mammals of ocean and polar ecosystems. Write a one-page report on the factors that have caused these mammals to become endangered. D E READING SKILLS Read the passage below, and then answer the questions that follow. In the United States during the last 200 years, over 99 percent of native prairies have been replaced with farmland or urban development and most of the old-growth forests have been cut. Loss of so many of these habitats has resulted in losses of biodiversity. A new discipline, called conservation biology, seeks to identify and maintain natural areas. In areas where human influence is greater, such as agricultural areas, former strip mines, and drained wetlands, biologists may have to reverse major changes and replace missing ecosystem components. For example, returning a strip-mined area to grassland may require contouring the land surface, introducing bacteria to the soil, planting grass and shrub seedlings, and even using periodic fires to manage the growth of vegetation. Restoring an area to its natural state is called restoration ecology. 1. Which of the following phrases describes a likely task of a restoration ecologist? a. raising funds needed to create a national park b. returning missing ecosystem components to a drained wetland c. educating citizens about the need to protect a local habitat d. both (a) and (b) 2. Based on the passage, which of the following statements is true? a. Former strip mines tend to have a high level of biodiversity. b. A conservation biologist would most likely oppose the development of areas around the Grand Canyon. c. Periodic fires in some ecosystems do not help manage excess growth of vegetation. d. Most prairie ecosystems located in the United States have been preserved. Cross-Disciplinary Connection 32. Answers may vary. As population increases, pollution increases, which can have a negative effect on the estuaries. Portfolio Project 33. Answers may vary depending on the type of aquatic ecosystem that is studied and the time of year. Math Skills 34. about 12%; 5% about 234 species Writing Skills 36. Answers may vary. Overfishing removes fish populations from some estuaries. Marine mammals such as dolphins and seals feed on fish, so overfishing of estuaries drives these animals to look elsewhere for food and probably reduces their populations, too. Overfishing is destroying some fish populations in oceans as well. Destroying fish populations affects entire ecosystems because different fish eat and are eaten by various other organisms at different stages in their lives. 37. Answers may vary. Reading Skills 1. b 2. b 201 Chapter 7 Aquatic Ecosystems 201

19 Standardized Test Prep Estimated Time To give students practice under more realistic testing conditions, allow them 30 minutes to answer all of the questions in this practice test. Question 6 Full-credit answers should include the following points: agricultural pollution, such as pesticides, runs off fields into rivers sewage and industrial wastes are often dumped into rivers where rivers drain into oceans, this pollution enters the oceans Question 7 Full-credit answers should include the following points: marine ecosystems contain salt water, freshwater ecosystems contain freshwater marine ecosystems are located mainly in coastal areas and in the ocean freshwater ecosystems include lakes, ponds, rivers, and wetlands Question 10 Full-credit answers should include the following points: Scientists probably became aware of the importance of wetlands as wetlands began to disappear the concentration of pollution in other places increased CHAPTER 7 Understanding Concepts Directions (1 5): For each question, write on a separate sheet of paper the letter of the correct answer. 1 Organisms living in coastal areas must adapt to what changes? A. water level and degree of salinity B. water level and amount of sunlight C. temperature and availability of oxygen D. temperature and availability of nutrients Bleaching events lead to the destruction of what kind of marine ecosystem? F. coastal wetlands G. coral reefs H. mangrove swamps I. salt marshes Which of the following correctly lists types of organisms in aquatic ecosystems from shallowest to deepest? A. plankton, nekton, benthos B. plankton, benthos, nekton C. benthos, plankton, nekton D. benthos, nekton, plankton What is the difference between swamps and marshes? F. Marshes attract birds, swamps attract amphibians. G. Marshes are freshwater, swamps are saltwater. H. Marshes contain non-woody plants, swamps contain woody plants. I. Marshes are mostly in the southeast U.S., swamps in the northeast U.S. 5 Which of the following would be considered among the most productive ecosystems? A. barrier island B. estuary C. river D. salt marsh Directions (6 7): For each question, write a short response. 6 Most ocean pollution arises from activity on land. How does land pollution end up in the oceans? Standardized Test Prep 7 Aquatic ecosystems are divided into two types marine and freshwater. Compare and contrast marine and freshwater ecosystems. Reading Skills Directions (8 10): Read the passage below. Then answer the questions. Wetlands perform several important environmental functions. Some wetlands are used to produce commercially important products, such as cranberries. But wetlands were once considered to be wastelands that provide breeding grounds for insects. Therefore, many have been drained, filled, and cleared for farms or residential and commercial development. For example, the Florida Everglades once covered 8 million acres of south Florida, but now it covers less than 2 million acres. From 1982 to 1992 alone, 57 percent of wetlands were converted into land for development. Wetlands are vitally important as habitats for wildlife, and their important role in the environment is now recognized. 8 Which of the following is not an environmental function of wetlands? F. Wetlands are important as habitats for wildlife. G. Wetlands may be converted into land for development. H. Wetlands may be used to grow commercial products, such as cranberries. I. Wetlands trap and filter sediments and pollutants. 9 By approximately how much has the area of the Florida Everglades in south Florida decreased? A. 40 percent B. 75 percent C. 5 percent D. 60 percent 0 What could be inferred as the cause of scientific awareness of the importance of wetlands? Chapter 7 Standardized Test Prep Answers 1. A 2. G 3. A 4. H 5. B 6. Answers will vary. See Test Doctor for detailed scoring rubric. 7. Answers will vary. See Test Doctor for detailed scoring rubric. 8. G 9. B 10. Answers will vary. See Test Doctor for detailed scoring rubric. 11. G 12. A 13. H

20 Standardized Test Prep Interpreting Graphics Directions (11 13): For each question below, record the correct answer on a separate sheet of paper. The table below shows organisms whose presence or absence can be indicators of water quality. Use this table to answer questions 11 through 13. q w e Most sensitive species Caddisfly larvae, hellgrammites, stonefly larvae, mayfly nymphs, gilled snails, and water penny larvae Moderately sensitive species Clams, cranefly larvae, crayfish, damselfly nymphs, dragonfly nymphs, scuds, predacious diving beetle larvae, sowbugs, fishfly larvae, and alderfly larvae Tolerant species Aquatic worms, blackfly larvae, leeches, midge larvae, and pouch snails Living Water Quality Indicators mayfly nymph dragonfly nymph midge larva caddisfly larvae predacious diving beetle larva leeches If a water sample contains mayfly nymphs, what can you conclude about the water quality of the area where the sample was taken? F. The area has generally poor water quality. G. The area has generally good water quality. H. The water quality cannot be determined from such a sample. I. The water in the area has been chemically treated for pollutants. What group of organisms could be seen only in a sample taken from unpolluted water? A. leeches and caddisfly larvae B. leeches and dragonfly nymphs C. leeches and midge larvae D. leeches and predacious diving beetle larvae Water sample A contains only leeches. Water sample B contains leeches and predacious diving beetle larvae. What comparison can be made between samples A and B? F. Both samples A and B have the same water quality. G. Both samples came from the same water source. H. Sample A has relatively poorer water quality than sample B. I. Sample B has relatively poorer water quality than sample A. Test Imagine the increasing levels of pollution that would affect water quality and cause particular species to disappear. Question 12 Answer A is the correct choice because caddisfly larvae would not be seen in a sample of polluted waters. Answers B, C, and D could possibly come from an unpolluted area but do not necessarily come from an unpolluted area because similar samples could be draw from relatively polluted water sources. Question 13 Answer H is correct. Answers F and G are incorrect because the presence of predacious diving beetle larvae implies differing water quality between the two samples. It is very unlikely that one water source could produce samples with different water qualities. Answer I is incorrect because the presence of predacious diving beetle larvae indicates higher water quality. 203 Chapter 7 Standardized Test Prep 203

21 CHAPTER 7 EUTROPHICATION: TOO MUCH OF A GOOD THING? Teacher s Notes Time Required one 45-minute class period to perform procedure; 3 weeks to complete observations Lab Ratings EASY TEACHER PREPARATION STUDENT SETUP CONCEPT LEVEL CLEANUP Skills Practice Lab Observation HARD Skills Acquired Predicting Designing Experiments Experimenting Collecting Data Interpreting Organizing and Analyzing Data The Scientific Method In this lab, students will: Make Observations Ask Questions Test the Hypothesis Analyze the Results Draw Conclusions Materials The materials listed are enough for a group of two students. Objectives USING SCIENTIFIC METHODS Observe the effects of nitrates and phosphates on an aquatic ecosystem. Compare the growth of organisms in different levels of nutrients. Predict possible effects nitrates and phosphates would have on an aquatic ecosystem in your area. Materials C H A P T E R 7 distilled water eyedropper fertilizer, household use fluorescent lamp graduated cylinder guide to pond life identification jars, 1 qt (3) microscope microscope slides with coverslips plastic wrap pond water that contains viable organisms stirring rod wax pencil Step 5 Observe a drop of pond water under the microscope. 204 Skills Practice Lab: OBSERVATION Eutrophication: Too Much of a Good Thing? Plants depend on nutrients such as phosphates and nitrates to survive. However, when people release large amounts of these nutrients into rivers and lakes, artificial eutrophication can occur. In artificial eutrophication, nutrients cause algae and plant life to grow rapidly and then die off and decay. When microorganisms decompose the algae and plant matter, they use up oxygen in the water, which causes the death of fish and other animals that depend on oxygen for survival. Eutrophication is commonly caused by phosphates, which are often found in detergents, and by nitrates, which are found in animal wastes and fertilizers. In this lab, you will observe artificial eutrophication in an aquatic ecosystem. Procedure 1. Working with your team, use a wax pencil to label one jar Control, a second jar Fertilizer, and a third jar Excess fertilizer. 2. Put 750 ml of distilled water in each of the three jars. Read the label on the fertilizer container to determine the recommended dilution of fertilizer for watering plants. To the Fertilizer jar, add the amount of fertilizer recommended for a quart of water. To the Excess fertilizer jar, add 10 times this amount of fertilizer. Stir the contents of each jar thoroughly to dissolve the fertilizer. 3. Obtain a sample of pond water. Stir it gently but thoroughly to ensure that the organisms in it are evenly distributed. Measure 100 ml of pond water into each of the three jars. 4. Cover each jar loosely with plastic wrap. Place all three jars about 20 cm from a fluorescent lamp. (Do not place the jars in direct sunlight, as this may cause them to heat up too much.) 5. Observe a drop of pond water from your sample, under the microscope. On a sheet of paper, draw at least four different organisms that you see. Determine whether the organisms are algae (usually green) or consumers (usually able to move). Describe the total number and type of organisms that you see. Safety Cautions You can substitute plastic materials for glass materials in this activity. Broken glassware should be disposed of properly. As a class, review the safety cautions on the container of household fertilizer. Make sure that students follow all cautions when using and disposing of the fertilizer. Students should wash their hands immediately after handling the pond water. 204 Chapter 7 Aquatic Ecosystems

22 6. Based on what you have learned about eutrophication, make a prediction about how the pond organisms will grow in each of the three jars. 7. Observe the jars when you first set them up and at least once every three days for the next 3 weeks. Make a data table to record the date, color, odor, and any other observations you make for each jar. 8. When life-forms begin to be visible in the jars (probably after a week), use an eyedropper to remove a sample of organisms from each jar and observe the sample under the microscope. Record your observations. 9. At the end of your 3-week observation period, again remove a sample from each jar and observe it under the microscope. Draw at least four of the most abundant organisms that you see, and describe how the number and type of organisms have changed. Analysis 1. Describing Events After three weeks, which jar shows the most abundant growth of algae? What may have caused this growth? 2. Analyzing Data Did you observe any effects on organisms other than algae in the jar that had the most abundant algae growth? Explain. Step 7 Record your observations of the jars every 3 days for 3 weeks. Tips and Tricks If quart jars are not available, pint jars could be easily substituted by using one-half of the amount of distilled water, pond water, and fertilizer. If students obtain their own pond water, be sure that they obtain the water from a healthy pond. The location and appearance of the pond should be considered. For example, if the plants around the pond seem wilted or damaged, herbicides may have been sprayed recently and could in turn affect the outcome of the lab. Count estimation and extrapolation are additional skills that could be acquired during this lab. For example, have students take a percentage (25%) of the field of view under the microscope, count the numbers of organisms found within that percentage, and multiply the count by four. This calculation will give an estimate of the count of each sample and a better assessment of the effects of the regular samples and the fertilized samples. These calculations can be displayed on graphs. Conclusions 3. Applying Conclusions Did your observations match your predictions? Explain. 4. Drawing Conclusions How can artificial eutrophication be prevented in natural water bodies? Extension 1. Designing Experiments Modify the experiment by using household dishwashing detergent instead of household fertilizer. Are the results different? 2. Research and Communications Research the watersheds that are located close to your area. How might activities such as farming and building affect watersheds? Chapter Resource File Datasheets for In-Text Labs Lab Notes and Answers TESTED TEACHER APPROVED & 205 Answers to Analysis 1. Answers may vary. The jar with excess fertilizer should show the most growth. The extra fertilizer should stimulate additional plant and algae growth. 2. Answers may vary. Other organisms may increase in abundance as their food supply (algae) increases. However, if algae have begun to die and decay, the decay process may deplete oxygen in the jar, causing oxygen-dependent lifeforms to die as well. Answers to Conclusions 3. Answers may vary. 4. Artificial eutrophication can be prevented by controlling the application of fertilizers in areas where runoff is common. Holt Lab Generator CD-ROM Search for any lab by topic, standard, difficulty level, or time. Edit any lab to fit your needs, or create your own labs. Use the Lab Materials Quicklist software to customize your lab materials list. Denise Sandefur Nucla High School Nucla, Colorado Answers to Extension 1. Answers may vary. The samples with dishwashing detergent and excess dishwashing detergent should show the same amount of growth as the samples with fertilizer and excess fertilizer did. 2. Answers may vary. Chapter 7 Aquatic Ecosystems 205

23 Maps in Action WETLANDS IN THE UNITED STATES, 1780S VS. 1980S WETLANDS IN THE UNITED STATES, 1780s Vs. 1980s EARTH SCIENCE CONNECTION Background Many factors have contributed to the loss of wetlands between 1780 and The population of the United States has increased dramatically, and people have moved throughout the country. The pressures from increased population and development have affected wetlands. People tend to settle near wetlands because wetlands are a water and food source. Other factors have also increased the destruction of wetlands. For example, technological improvements have increased the use of land for agriculture, which has increased erosion. And the building of dams to impound water and control floods has reduced wetlands as well. In general, the greatest loss of wetlands has occurred in the eastern United States. This region has the highest population and has had a large population for the longest time. M A P S K I L L S Transparencies TT Wetlands in the United States, 1780s Vs. 1980s Use the maps of wetland loss in the United States to answer the questions below. 1. Using a Key Use the key to determine how many states had a decrease in wetland distribution from 5 to 12 percent to 1 to 5 percent. 2. Analyzing Data Is there any state on the map of wetland distribution in the 1980s that has the same percentage of wetland distribution as it did in the 1780s? If so, how many? 3. Analyzing Data Which states have had the greatest decrease in wetland distribution since the 1780s? 206 Answers to Map Skills states 2. yes; 18 states have the same percentage. 3. Arkansas, Illinois, Indiana, and Ohio 4. Development may have taken place and destroyed wetlands in Florida and Louisiana states 6. Answers may vary. Students should suggest that many more states will have lower percentages of wetlands. 4. Making Inferences What might have caused Florida s and Louisiana s wetlands to decrease in distribution? 5. Using a Key Use the key to determine how many states had a decrease in wetland distribution from 25 to 50 percent to 12 to 25 percent. 6. Identifying Trends If these trends of wetland loss continue, what might a map of wetland distribution of the United States look like circa 2040? 206 Chapter 7 Aquatic Ecosystems

24 EARTH SCIENCE CONNECTION Society & the Environment HURRICANE KATRINA AND NEW ORLEANS The city of New Orleans was built in the Mississippi River Delta, about 100 miles upriver from the Gulf of Mexico. This city is vulnerable to flooding from the Mississipppi River, Lake Pontchartrain to the north, and heavy rainfall from tropical storms. In addition, hurricanes that pass over the coast can create storm surges, waves up to 30 feet high. To help protect New Orleans from flooding, engineers and city planners built levees and flood walls along the river banks and lakeshore. They constructed pumps to move floodwater from lowerlying areas through canals into Lake Pontchartrain. Despite these measures, Hurricane Katrina overwhelmed the city in late August, Hundreds of people were killed, and hundreds of thousands were left homeless. Analyses of the catastrophe concluded that humanmade changes in the natural environment were partly responsible for the damage. Protection from the Sea The low-lying land of the Mississippi River Delta is a transitional area between the land and the ocean. It consists of saltwater and freshwater marshes, mud flats, and creeks, collectively known as coastal wetlands. Winds and currents move loose sediment to build up barrier islands. These islands shelter the coastal wetlands and mainland from the ocean. Plants growing in the wetlands trap sediment and help to stabilize the land. The Louisiana coast has about 40 percent of all the coastal marshes in the continental United States. These coastal wetlands are an important habitat for crustaceans, mollusks, fish, and birds. As well, they filter out pollutants from the river, absorb floodwater, and help to supply fresh water to aquifers. Eroding the Barrier Islands As levees confined the flow of the Mississippi River, sediment carried by the river was flushed farther out Over 80 percent of New Orleans was submerged by floodwater when Hurricane Katrina struck in August, into the Gulf of Mexico. The sediment was no longer deposited to build up more land. Canals that were built through the barrier islands to handle river traffic increased the erosion of the coastal wetlands. Soil dug from the canals was piled on the banks, smothering vegetation that had helped to hold the banks in place. The increased speed and volume of the water in the canals washed away more soil from the barrier islands. As the barrier islands eroded, the marshes and land behind them were left exposed and were washed away. The Impact of Katrina Most of the damage from Hurricane Katrina was caused by rising water that overflowed or broke through the levees. A wide shipping canal funneled a storm surge from the ocean into the city. The storm surge broke through the banks of the canal. Other canals, built to drain water into Lake Pontchartrain, had their flow reversed as the water level in the lake rose. Eventually, the city s drainage system failed when most of the pumping stations were submerged. What Do You Think? Many engineers and environmental scientists had predicted that the risk of flooding in New Orleans had been increased by poorly designed levees and canals, and by massive erosion. Should a large city have been built in such an unstable environment? 207 Answers to What Do You Think? Answers may vary. Student answers should take into account the short-term and long-term benefits and costs of building a city in the Mississippi River Delta. Choices that harm the environment often are cheap in the short term but very expensive in the long term. HURRICANE KATRINA AND NEW ORLEANS Background The Mississippi watershed covers more than one third of the continental United States. Over the centuries, massive quantities of soil carried by the river system from across the continent have been deposited at the river mouth. The land of the Mississippi Delta south of Baton Rouge has been built up from these deposits of soil. New Orleans was founded in 1718 on relatively high land along the banks of the Mississippi River. Between 1805 and 1836 the city expanded along a bend in the river, giving it the shape from which the nickname Crescent City is derived. An effective drainage system, using pumps and levees, allowed the city to expand away from the riverbanks during the 1900s into what used to be swampland. But the structures built to protect the city from floods created a trap. The higher the levees and floodwalls rose above the city, the harder it became to pump floodwater out. REAL-LIFE CONNECTION Wetland Restoration Techniques such as dredging, depositing sediment, and planting can help stabilize and expand wetland areas. Ask students to research the topic of wetland restoration using the Internet. The USGS National Wetlands Research Center is a good place to start. Have students use the information they find to create posters. The posters should explain the techniques of wetland restoration and give examples of places where the techniques are being used. Chapter 7 Aquatic Ecosystems 207