EARTH SCIENCE geology, the environment, and the universe 2008 (27)

BIG Idea The use of natural resources can impact Earth’s land, air, and water 26.1 Populations and the Use of Natural Resources MAIN Idea More demands are placed on natural resources as the human population increases Trash from the mountain 26.2 Human Impact on Land Resources MAIN Idea Extraction of minerals, farming, and waste disposal can have negative environmental impacts 26.3 Human Impact on Air Resources MAIN Idea Manufacturing processes and the burning of fossil fuels can pollute Earth’s atmosphere 26.4 Human Impact on Water Resources MAIN Idea Pollution controls and conservation protect water resources GeoFacts • Climbers have left more than 50 tons of trash on the top of Mount Everest • In 1993, laws were passed requiring climbers to bring down the nonbiodegradable items they take up • Many groups remove trash, including used oxygen tanks, batteries, and other nonbiodegradable items 732 Empty oxygen canisters (t)Art Wolfe/Photo Researchers, (b)2003 National Geographic Society, (bkgd)Craig Lovell/CORBIS Human Impact on Resources Start-Up Activities Sources of Water Pollution Make this Foldable to compare the two main types of waterpollution sources LAUNCH Lab What resources are used in classroom items? As you learned in Chapter 24, natural resources include air, water, land, and living organisms Use of natural resources can have global impacts Procedure Read and complete the lab safety form Working in groups of two or three, make a pile of 15 items from your classroom Make a data table for your items Record as much of the following information as you can • What resources were used to make the item? • Are the resources renewable or nonrenewable? • Where was the item made? Analysis Observe How many different resources are represented by the items in your collection? Calculate What percent of your 15 items were renewable and what percent were nonrenewable resources? Fold a sheet of paper in half from top to bottom STEP Fold in half again, as shown STEP STEP Unfold once and cut along the fold line of the top flap to make two tabs Label the tabs Point Sources and Nonpoint Sources STEP Point Sources Nonpoint Sources FOLDABLES Use this Foldable with Section 26.4 As you read this section, explain the two main types of pollution and give some examples of each Visit glencoe.com to study entire chapters online; explore • Interactive Time Lines • Interactive Figures • Interactive Tables animations: access Web Links for more information, projects, and activities; review content with the Interactive Tutor and take Self-Check Quizzes Chapter Section 26 •1Human • XXXXXXXXXXXXXXXXXX Impact on Resources 733 Section 6.1 Objectives ◗ Summarize the typical pattern of population growth of organisms ◗ Describe what happens to populations when they reach carrying capacity ◗ Identify environmental factors that affect population growth Review Vocabulary population: individual organisms of a single species that share the same geographic location at the same time New Vocabulary exponential growth carrying capacity density-independent factor density-dependent factor Figure 26.1 Beavers can alter their environments to suit their needs Notice how, by damming the stream, the beavers have changed the water level Infer How might this affect the other organisms living in this environment? ■ 734 Chapter 26 • Human Impact on Resources Larry Lee Photography/CORBIS Populations and the Use of Natural Resources MAIN Idea More demands are placed on natural resources as the human population increases Real-World Reading Link How many pets you have? If you only have one pet, it might not take much time or money to care for it What if you had eight pets? The amount of time and money you would need to properly care for your pets might put a strain on your money and activities Similarly, as world population grows, it puts a strain on available natural resources Resources and Organisms Like all organisms, humans need natural resources to grow, reproduce, and maintain life Among the resources that organisms require are air, food, water, and shelter To meet their basic needs, most organisms are adapted to their immediate environment They live in balance with the natural resources provided within their environment For example, songbirds live in grassy meadows, forage for grass seeds to eat, weave nests out of dried grasses and twigs, and drink water from ponds or streams nearby Other organisms, however, alter their environment to better meet their needs For example, beavers build dams, like the one in Figure 26.1, across streams to create ponds where none previously existed Such alteration of the environment has both positive and negative impacts: it kills some trees and displaces both aquatic and terrestrial organisms, but at the same time, it creates a new wetland environment for other organisms Of all organisms, however, humans have an unequaled capacity to modify their environments This capacity allows humans to live in every terrestrial environment on Earth As a result, humans also have the greatest impact on Earth’s natural resources Population Growth Exponential Population Growth Mouse population (millions) Population growth is defined as an increase in the size of a population over time A graph of a growing population resembles a J-shaped curve at first Whether the population is one of dandelions in a lawn, squirrels in a city park, or herring gulls on an island, the initial increase in population is small because the number of adults capable of reproducing is low As the number of reproducing adults increases, however, the rate of population growth increases rapidly As shown in Figure 26.2, the population then experiences exponential growth, which is a pattern of growth in which a population grows faster as it increases in size 3.5 3.0 2.5 2.0 1.5 1.0 0.5 11 13 15 17 19 21 23 25 Months Figure 26.2 If two mice were allowed to reproduce in perfect conditions and all their offspring survived, the population would grow slowly at first, but then would accelerate quickly ■ Reading Check Explain exponential growth Why is this an important concept to understand in relation to how organisms affect their environment? Limits to population growth If the population graphed in Figure 26.2 were studied for an extended period of time, what you think would happen to the size of the population? Would it continue to grow exponentially? Many of Earth’s natural resources are in limited supply, and therefore, most populations cannot continue to grow forever Eventually, one or more limiting factors, such as the availability of food, water, or shelter will cause a population to stop increasing This leveling-off of population size results in an S-shaped curve, similar to the one in Logistic Population Growth Figure 26.3 Population Carrying capacity The number of organisms that any given environment can support is its carrying capacity When population size has not yet reached the carrying capacity of a particular environment, the population will continue to grow for several reasons First, there will be more births than deaths because of adequate resources Second, because of the availability of resources, more individuals might move to the area than die or leave If the population size temporarily exceeds the carrying capacity, the number of deaths will increase, or the number of births will decrease until the population size returns to the carrying capacity A population at the carrying capacity for its environment is in equilibrium The population will continue to fluctuate around the carrying capacity as long as natural resources remain available Carrying capacity 10,000 8000 6000 S-curve 4000 2000 11 13 15 17 19 21 23 25 Time period ■ Figure 26.3 A population grows exponentially until it reaches its carrying capacity Carrying capacity is limited by the resources available to the population Predict what would happen if the population exceeded carrying capacity Interactive Figure To see an animation of carrying capacity, visit glencoe.com Section • Populations and the Use of Natural Resources 735 Environmental limits Environmental factors that not depend on population size, such as storms and fires, are density-independent factors Density-independent factors affect all populations that they come in contact with, regardless of population size, as Figure 26.4 shows Environmental factors that affect population growth, such as disease, predators, and competition for food, are called density-dependent factors Densitydependent factors are often biotic factors that increasingly affect a population as the population’s size increases One example of a density-dependent factor can be seen in populations of white-tailed deer in the United States White-tailed deer are found in most of the continental United States In some areas, deer populations have grown in recent years due largely to a decrease of natural predators Although the population is increasing, the amount of food available to the deer does not change For this reason, every year many deer starve to death The densitydependent factor in this example is the lack of food due to overpopulation ■ Figure 26.4 A forest fire is one example of a density-independent factor of population growth Fires can affect trees, birds, mammals, and other populations Fires, like the one that occurred here, can also encourage new growth Section Human Population Growth During your lifetime, you might have seen an increase in the number of cars, houses, and roads around you The human population on Earth is growing The growth curve is still in the J-shaped stage The human population is expected to continue to grow for at least another 50 years at its current rate The human population has not yet reached carrying capacity, but the current rate of growth cannot continue forever As the population increases, demand for natural resources will also continue to increase steadily Use of natural resources has already had global environmental implications Assessment Section Summary Understand Main Ideas ◗ All organisms use resources to maintain their existence The use of these resources has an impact on the environment ◗ As populations increase, the demand for resources increases Because resources are limited, populations will stop growing when they reach carrying capacity ◗ Populations grow exponentially at early stages Earth is currently experiencing a human population explosion 736 CORBIS Chapter 26 • Human Impact on Resources MAIN Idea Explain how an increasing human population places more demands on Earth’s natural resources Identify three limiting factors that keep populations from growing indefinitely Compare density-dependent and density-independent factors that limit population growth Think Critically Predict how a small population of bacteria placed in a petri dish with limited nutrients will change over time Draw a graph to represent the population growth MATH in Earth Science If a city has 300,000 residents and an average birth rate of 1.5 children per person, how many people will there be in the next generation? Self-Check Quiz glencoe.com Section 6.2 Objectives ◗ Describe the environmental impact of mineral extraction ◗ Discuss the environmental problems created by agriculture and forestry, and list possible solutions ◗ Explain how urban development affects soil and water Review Vocabulary erosion: movement of weathered materials from one location to another by agents such as water, wind, glaciers, and gravity New Vocabulary reclamation deforestation pesticide bioremediation Human Impact on Land Resources MAIN Idea Extraction of minerals, farming, and waste disposal can have negative environmental impacts Real-World Reading Link Do you spend much time talking on the telephone, listening to a digital music player, or using a computer? Perhaps you use a microwave oven to heat after-school snacks Many of the materials in these items are derived from land resources Mining for Resources How much land per year you think is necessary to provide the raw materials that you use? Each year, a typical person in the United States consumes resources equal to the renewable yield from approximately of forest and farmland Many of these raw materials come from under the surface of Earth To access these resources for human use, they must be extracted through one of many mining techniques Mining techniques can have a significant impact on Earth’s surface Modern societies require huge amounts of land resources, including iron, aluminum, copper, sand, gravel, and limestone Unfortunately, the extraction of these resources often disturbs large areas of Earth’s surface, as shown in Figure 26.5 Groundwater can become polluted, natural habitats can be disturbed or destroyed, and air quality can suffer Finding a balance between the need for mineral resources and controlling the environmental change caused by extraction can be difficult, but scientists, in conjunction with mining companies, have created ways to reduce the impact of mining on the environment Figure 26.5 Mines, such as the one shown here, can have negative environmental impacts such as topsoil erosion Determine Where would the eroded topsoil go? What other environmental impacts might a mine like this one have? ■ Section • Human Impact on Land Resources 737 Stephanie Maze/CORBIS Restoring the land In the United States, the Surface Mining Control and Reclamation Act of 1977 requires mining companies to restore the land to its original contours and to replant vegetation in a process called reclamation However, vegetation cannot grow without topsoil Mining companies can scrape the topsoil off of the land surface prior to mining and stockpile it for reclamation after materials have been removed Figure 26.6 shows a strip-mined area that has been reclaimed Although reclamation repairs much of the damage that surface mining causes, it can be extremely difficult to restore land to its original contours and vegetation Reading Check Explain why it is important to have legis■ Figure 26.7 Runoff from a nearby mine pollutes this river The presence of metals, including iron, causes the orange color in the runoff 738 Chapter 26 • Human Impact on Resources lation requiring mining companies to restore land to its original contours Underground mining Underground mining, also called subsurface mining, is used where mineral resources lie deep under the ground Underground mining is less disruptive to the land surface than surface mining, but it still has impacts on the environment For example, although the underground mines cannot be seen, the mountains of waste rock dug from under the ground are stockpiled on the surface The water in Figure 26.7 is orange because precipitation seeps through mine waste piles and causes a decrease in pH, dissolving many harmful metals in the waste When the runoff from the piles reaches the stream, which has a higher pH, the higher pH causes the metals to come out of solution and discolor the water Although many mining companies build large holding ponds to contain polluted water until it can be treated, these ponds sometimes leak (t)© 1995 Hallmark Cards, Inc Photography by John Perryman/courtesy of THE WILDS, (b)Charles E Rotkin/CORBIS ■ Figure 26.6 The Wilds, in Ohio, is one example of reclamation of land that was once strip-mined Here, exotic animal species such as these scimitar-horned oryxes are housed The Wilds uses reclaimed land to educate visitors about conservation Forestry VOCABULARY ACADEMIC VOCABULARY Clearing forested land is another way in which topsoil is lost Worldwide, thousands of hectares of forests are cut down annually for firewood, charcoal, paper, and lumber In parts of the world, the clearing of forested land results in deforestation, which is the removal of trees from a forested area without adequate replanting Deforestation often involves clear-cutting, the complete removal of all the trees in an area Clear-cutting can cause erosion of topsoil Fortunately, the negative environmental impacts of deforestation can be minimized through the practices of selective logging and the retention of buffer zones of trees along streambeds In selective logging, workers remove only designated trees This practice reduces the amount of ground left bare and thus helps prevent erosion Adequate sufficient to satisfy a requirement or meet a need She filled her gas tank to ensure she had an adequate supply of gas for the trip Urban Development As the human population continues to increase, more people live in cities and towns Agricultural land located near cities is being converted to suburban housing As people populate areas that were once agricultural or rural, stores and industry follow Seventy percent of the population in North America lives in urban and suburban areas, and an estimated billion people worldwide will be living in cities and towns by the year 2025 The development of urban areas has many environmental impacts When towns and cities expand into rural areas, natural habitats are lost to roads, houses, and other buildings Development leaves less land for agricultural use, which puts pressure on the remaining farmland for increased production Other problems are created when concrete and asphalt cover large areas Because there are fewer opportunities for rainwater to soak into the ground, groundwater supplies are not recharged, and flooding increases during heavy rains Solid waste Each person in the United States generates an average of 1.5 kg of solid waste per day Where does it all go? Much of it is buried in landfills Figure 26.8 shows the percentages and material types that were disposed in landfills in the United States in 2003 2003 Total Waste Generation–215 million metric tons (before recycling) Wood 5.8% Other 3.4% Glass 5.3% Rubber, leather, and textiles 7.4% Paper 35.2% Metals 8.0% ■ Figure 26.8 This circle graph shows the total solid waste generated in the United States in 2003 Determine What material composed the highest percentage of solid waste in the United States in 2003? Why you think this was the case? Could this material be recycled? Yard trimmings 12.1% Plastics 11.3% Food scraps 11.7% Section • Human Impact on Land Resources 739 Model Nutrient Loss How does soil lose nutrients when subjected to farming, strip-mining, or development? If an area of soil has no plant cover for an extended period of time, the nutrients in the soil can be washed away by rainfall Procedure Read and complete the lab safety form Place a coffee filter inside the funnel Place the funnel so that it is resting inside the 100-mL beaker Pour the sand mixture into the coffee filter Measure 50 mL of water and pour it into the sand mixture Record your observations Carefully remove the funnel with the sand mixture and discard the water as instructed by your teacher Replace the funnel with the sand mixture in the 100-mL beaker Repeat Steps through four times 10 Discard the sand mixture and funnel as instructed by your teacher Analysis Observe What did you notice about the water as you repeated the investigation? Analyze Why were you instructed to discard the water in between investigations? Predict If the material in the sand represents nutrients needed for plant growth, and the sand represents soil, what would happen if you tried to grow crops in the soil at the end of your investigation? Infer In what other ways might nutrient loss impact the environment? Apply How could you slow the process of nutrient loss? 740 Chapter 26 • Human Impact on Resources Additional contamination occurs as a result of industrial processes Heavy metals, such as lead and mercury, and poisonous chemicals, such as arsenic, are by-products of many industrial processes and can pollute the soil and groundwater Some of this type of contamination has been caused by industries that operated before the dangers of improper waste disposal were known Agriculture Vegetation, including agricultural crops, needs the nutrients from topsoil to grow It can take thousands of years for topsoil to form, and thus, once it is lost, it is hard to replace Whenever fields are plowed and the plants whose roots hold the soil in place are removed, topsoil can be eroded by wind and water and nutrients can be lost The addition of fertilizers can help replace some of the nutrients, but there are other substances in topsoil that fertilizers cannot provide Topsoil contains trace minerals as well as organisms such as earthworms and nitrogen-fixing bacteria Earthworms burrow into soil, providing oxygen and space for plant roots to grow, and nitrogen-fixing bacteria take nitrogen out of the air and make it available to plants Topsoil also has an abundance of organic matter, including fecal material from organisms that live in the soil as well as decaying organisms Organic matter helps hold moisture, reduces erosion, and releases nutrients back into the soil Soil erosion can be reduced and fertility can be increased by using a variety of farming practices as shown in Figure 26.9 Effects of pesticides Chemicals applied to farm fields to control weeds, insects, and fungi are called pesticides Pesticides have played an important role in boosting food production worldwide by eliminating or controlling organisms that destroy crops However, some pesticides remain in the environment for long periods of time Pesticides can slowly accumulate in organisms higher on the food chain, such as fishes and birds Some pesticides also kill beneficial insect predators along with destructive insects When pesticides kill decomposers, such as worms, the overall fertility of topsoil deteriorates Insects can develop resistance to an insecticide, causing some farmers to use ever-increasing amounts to control pests Further problems can be created when wind and rain carry pesticides away from farm fields and cause pollution in nearby waterways Visualizing Agricultural Practices Figure 26.9 Using agricultural conservation practices can help protect precious nutrients in the soil as well as help reduce topsoil loss Contour farming, crop rotation, and no-till farming are shown below Contour farming is often done on hillsides or other areas prone to erosion Farmers plant crops with the contour of the earth, slowing the flow of runoff and helping to prevent erosion No-till farming Farmers leave the unused portion of the crops on the field instead of plowing them under each year In this image, the crop in the previous year was wheat After the seeds were harvested, the stalks were left on the field to prevent erosion and maintain topsoil Contour farming No-till farming Crop rotation Crop rotation involves planting different crops in succession For instance, a farmer might plant alfalfa in a field one year, followed by corn the next year, and winter wheat the following year Crop rotation helps to maintain the soil’s nutrient balance and also helps to reduce the number of crop-specific pests To explore more about agricultural practices, visit glencoe.com Section • Human Impact on Land Resources 741 (tl)Envision/CORBIS, (tr)CORBIS, (br)Matt Meadows/Peter Arnold, Inc Figure 26.13 One chlorine atom from one CFC molecule can destroy many ozone molecules ■ Ultraviolet light breaks bond between carbon and chlorine atoms in a CFC molecule A released chlorine atom breaks up ozone (O³) molecule Interactive Figure To see an animation of ozone depletion, visit glencoe.com Chlorine atom breaks up another ozone (O³) molecule The chlorine atom bonds with an oxygen atom, leaving a molecule of oxygen gas (O²) Two oxygen atoms bond to form an oxygen (O²) molecule, releasing a chlorine atom A free oxygen atom breaks the oxygen-chlorine bond Ozone depletion Recall from Chapter 11 that the ozone layer in the stratosphere serves as a protective shield as it absorbs and filters out harmful UV radiation UV radiation has been linked to eye damage, skin cancer, and reduced crop yields In the early 1970s, scientists suggested that chlorofluorocarbons (CFCs) could destroy ozone in the upper atmosphere All of the CFCs present in the atmosphere are a result of human activity CFCs are released from cleaning agents, old refrigerators that are not disposed of properly, and propellants in aerosol cans Although CFCs are stable and harmless near Earth’s surface, they destroy ozone molecules, as shown in Figure 26.13, when they migrate into the upper atmosphere Since the mid-1980s, atmospheric studies have detected a thinning of the ozone layer, including an extremely thin area over Antarctica This hole was publicized in the news media as an ozone hole, which is a seasonal decrease in ozone over Earth’s polar regions Acid precipitation Another major air pollution problem is acid precipitation, which is defined as precipitation with a pH of less than 5.0 Recall from Chapter that pH is a measure of the acidity of a substance on a scale of to 14, with being neutral Natural precipitation has a pH of about 5.0 to 5.6, which is slightly acidic Acid precipitation forms when sulfur dioxide and nitrogen oxides combine with atmospheric moisture to create sulfuric acid and nitric acid Acid precipitation includes acidic rain, snow, fog, mist, and gas Although volcanoes and marshes add sulfur gases to the atmosphere, 90 percent of the sulfur emissions in eastern North America are of human origin Section • Human Impact on Air Resources 745 Figure 26.14 This map shows the pH levels of precipitation across the continental United States Explain why the pH is generally lower in the eastern half of the country Precipitation pH in the Continental U.S ■ Lab pH ≥ 5.3 5.2-5.3 5.1-5.2 5.0-5.1 4.9-5.0 4.8-4.9 4.7-4.8 4.6-4.7 4.5-4.6 4.4-4.5 4.3-4.4 < 4.3 Burning coal One cause of acid precipitation is coal-burning power plants Coal contains significant amounts of the mineral pyrite (FeS2) and other sulfur-bearing compounds When sulfurrich coal is burned, large amounts of sulfur dioxide are released The sulfur dioxide generated by midwestern power plants rises high into the air and is carried by winds toward the East Coast, where they mix with precipitation and fall to the ground The distribution of acid precipitation is shown in Figure 26.14 Effects of acid precipitation When acid rain enters surface waters, it damages aquatic ecosystems and vegetation and affects plants and soil Trees affected by acid precipitation might not be killed outright, but might become more susceptible to damage and disease Acid precipitation also depletes the soil of nutrients and damages buildings and statues by accelerating weathering Data Analysis lab Based on Real Data* Interpret the Data Are you breathing cleaner air? This table lists changes in emissions in the United State since the Clean Air Act of 1972 Think Critically Graph the data from the table Put years on the x-axis and the pollutant emissions per year on the y-axis Use different colors for each pollutant Infer why emissions of lead have declined so drastically since 1970 Evaluate Could you estimate the reductions for 2005 by looking at the graph? Explain why or why not 746 Chapter 26 • Human Impact on Resources Pollutant 1970 1980 Particulate matter