Volume3 10/6/04 10:09 AM Page 1 U•X•L ENCYCLOPEDIA OF water science Volume3 10/6/04 10:09 AM Page 3 U•X•L ENCYCLOPEDIA OF water science Volume 3 Issues K. Lee Lerner and Brenda Wilmoth Lerner, Editors Lawrence W. Baker, Project Editor water_fm 10/20/04 10:54 AM Page iv U•X•L Encyclopedia of Water Science K. Lee Lerner and Brenda Wilmoth Lerner, Editors Project Editor Imaging and Multimedia Manufacturing Lawrence W. Baker Lezlie Light, Kelly A. Quin, Dan Rita Wimberley Newell Editorial Charles B. Montney Product Design Jennifer Wahi Permissions Denise Buckley, Shalice Shah- Composition Caldwell, Ann Taylor Evi Seoud ©2005 by U•X•L. U•X•L is an imprint or information storage retrieval sys- Cover photographs reproduced of Thomson Gale, a division of tems—without the written permis- courtesy of Photodisc by Getty Thomson Learning, Inc. sion of the publisher. Images (volume 1, sailboats), courtesy of Digital Vision Ltd. 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ISBN 0-7876-7617-9 (set : hardcover : alk. paper) — ISBN 0-7876-7673-X (v. 1 : hard- cover : alk. paper) — ISBN 0-7876-7674-8 (v. 2 : hardcover : alk. paper) — ISBN 0- 7876-7675-6 (v. 3 : hardcover : alk. paper) 1. Water—Encyclopedias, Juvenile. 2. Hydrology—Encyclopedias, Juvenile. I. Lerner, K. Lee. II. Lerner, Brenda Wilmoth. III. Baker, Lawrence W. GB662.3.U95 2005 553.7—dc22 2004021651 This title is also available as an e-book. ISBN 0-7876-9398-7 (set) Contact your Thomson Gale sales representative for ordering information. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 water_ch12 10/20/04 10:52 AM Page 377 S S Chapter 12 Environmental Issues SAcid Rain Acid rain is a general term describing the pollution that occurs when acids fall out of the atmosphere (mass of air sur- rounding Earth). The principal pollutants that produce acids in the atmosphere are sulfur dioxide (SO ) and nitrogen oxides, 2 like nitrogen oxide (NO) and nitrogen dioxide (NO ). These 2 compounds combine with water in the atmosphere to form sul- furic acid (H SO ), and nitric acid (HNO ). Acid rain has sig- 2 4 3 nificantly affected the waters that flow into lakes and rivers, as well as the lakes and rivers themselves. In turn, the plants and animals that depend on lakes, rivers and oceans are harmed by acid rain. When describing acid rain, scientists use the more precise term acid deposition. Scientists distinguish between two types of acid deposition: dry and wet. Dry deposition includes acidic gases and solid particles containing sulfuric and nitric acid that settle out of the air and land on the ground or other surfaces. Dry deposition usually occurs very close to the point where the pollutants are released. Wet deposition occurs when precipita- tion, such as rain, sleet, fog, and snow, becomes acidic and falls to the ground. Wet deposition can occur hundreds of miles (kilometers) from the place where the air pollution originates. Acid rain and the pH scale The scale that is used to measure the acidity of a substance is called the pH scale. The pH scale runs from 0 to 14. If a mate- rial has a pH of 7 it is neutral, meaning that it is neither acidic nor alkaline (basic). Substances with pH values less than 7 are acidic and substances with pH values greater than 7 are alka- 377 water_ch12 10/20/04 10:52 AM Page 378 SSS line. Distilled water is neutral, with a pH of 7. Lemon juice and vinegar are both acidic; they have pH values of 2.3 and 3.3, respec- Art and Acid Rain tively. Baking soda, with a pH of 8.2, and milk of magnesia, with a pH of 10.5, are both Acid deposition is extremely corrosive, alkaline. Combining an alkaline substance especially to soft stones. Many famous with an acidic substance results in a sub- buildings throughout the world show signs of acid damage. For example, the Parthenon in stance with a pH value that is closer to 7 than Athens, the Coliseum in Rome, and the Taj either of the original substances. This is Mahal in India have all been damaged by called neutralization. acid deposition. Monuments in Poland and A substance that has a pH of 3 is ten times stained glass windows in Sweden have also more acidic than a substance that has a pH of suffered from corrosion. Several famous 4; a substance that has a pH of 3 is one hun- cathedrals in England including St. Paul’s, dred times more acidic than a substance with York Minster and Westminster Abbey have shown the effects of acid deposition. Most of a pH of 5, and so on. Given their respective this damage is the result of dry deposition. pH values of 2.3 and 3.3, lemon juice is a ten times stronger acid than vinegar. All of the acid damage on famous struc- tures results in very high restoration costs. Natural rain water is slightly acidic. In 1984 the Statue of Liberty in New York Chemical reactions between pure water and harbor had to be dismantled at substantial carbon dioxide in the atmosphere result in a cost because of damage to its metal frame weak acid. The pH of natural rainwater is and copper covering by acid deposition. A between 5 and 6. This acidity is useful study in England showed that if sulfur emis- because when the rain falls to the ground, it sions were reduced by 30%, the savings in can dissolve minerals in the soil that plants repair to these famous buildings could be as use to grow. Acid rain is anywhere from ten high as $20 billion. to ten thousand times more acid than natural rain, with a pH between 4.5 and 1.5. WORDS TO KNOW The major sources of acid deposition Acid deposition forms from the burning of fossil fuels, which SAcid deposition: The collec- are used in cars, factories, electricity generation, and other tive term for dry deposition and wet deposition of acids as a industries. Fossil fuels were formed over thousands of years by result of air pollution. dead plants and animals. After these plants and animals died they were buried under sediments (particles of sand, silt, and SDry deposition: Acidic gases clay). The intense pressure and increases in temperature under and solid particles containing these sediments chemically changed the dead plants and animals acids that settle out of the air and land on surfaces. into the fuels that are used to drive cars and generate electricity today. When fuel is burned it not only releases the energy that is SWet deposition: Precipita- used to power electrical devices, but it also releases chemicals, tion that has become acidic as such as sulfur dioxide and nitrogen oxides that form acid rain. a result of air pollution. Car exhaust is a major source of the nitrogen oxides in the air. A second major source of nitrogen oxides in the air come in smelt- ing plants (factories that process metal), electrical facilities, and factories. Factories and power plants are also the major source of 378 U•X•L Encyclopedia of Water Science water_ch12 10/20/04 10:52 AM Page 379 Acid rain and other pollution scar a village monument in Derby, England.© Chinch Gryniewicz/Corbis. Reproduced by permission. sulfur compounds that cause acid rain. The U.S. Environmental Protection Agency (EPA) reports that about two-thirds of all sul- fur dioxide and one-quarter of all nitrogen oxides in the atmos- phere originate from coal burning electric power plants. Acid deposition in lakes and rivers Under natural conditions, rainwater, which is slightly acidic, runs through the soils near a lake. These soils often contain Acid Rain 379 water_ch12 10/20/04 10:52 AM Page 380 limestone or calcium, which is alkaline and neutralizes the acid. The water in a healthy lake usually has a pH around 6.5, which allows for the growth of a variety of plants, invertebrates (animals without a backbone), and fish. When acid rain falls on the ground and runs into lakes, ini- tially it is neutralized by the alkaline substances in the soils. Eventually however, these substances are used up and the water that runs into lakes and rivers is extremely acidic. This causes lakes to become acidic as well. This acidity is highly damaging to the plants and animals that live in lakes. For example, at pH values lower than about 6, crustaceans, mollusks, snails, salmon, rainbow trout, many insects, and plankton cannot sur- vive. At pH values lower than about 5.5, small fish such as whitefish and grayling will die. At pH values lower than about 4.5, all but the hardiest life dies. In addition, as more acidic water passes through the soils, chemical reactions occur in the soils that cause harmful miner- als such as aluminum to be released. These minerals run into the lake where they are taken up by plants and invertebrates. The plants and invertebrates are then eaten by fish, which are consumed by birds that live nearby. Because the birds must eat so many fish in order to survive, the aluminum is concentrated in their bodies. High levels of aluminum cause the birds to lay eggs with very fragile shells. Often the eggs break or become dry inside. Other times, baby birds are born with physical deformities. The EPA completed a survey of one thousand lakes in the United States in areas where acid deposition is suspected to be a problem. They found that 75% of the lakes surveyed did suffer from acidity. In addition, nearly half the streams sampled showed evidence of acidity. The major places where acid depo- sition was found to be a problem in the United States were Adirondacks and Catskill Mountains in New York State, the Appalachian mountains along the east coast, the northern Midwest, and mountainous areas of the Western United States. The report also mentioned that air pollution in the United States contributed to acidification of lakes and streams in Canada. Acid deposition in oceans Because of its chemical composition, the nitrogen and sulfur- based acids that cause acid deposition in fresh water lakes and rivers do not have a strong effect on the acidity of the ocean. However, carbon compounds in the atmosphere are responsible for increased acidity. Burning of fossil fuels releases carbon diox- 380 U•X•L Encyclopedia of Water Science water_ch12 10/20/04 10:52 AM Page 381 ide (CO ) into the atmosphere. Carbon diox- 2 ide levels in the atmosphere are currently the highest they have been in 55 million years. When it combines with seawater, this carbon dioxide produces carbonic acid, which makes seawater more acidic. This acidity will have a very negative effect on all marine organisms that make shells out of calcium carbonate, such as corals and mollusks, because it reduces the availability of calcium ions (the building blocks of shells) in seawater. Acid deposition in forests The ways that acid rain harms forests are complicated and interconnected. Acid rain harms both the soils that trees use to grow and the trees themselves. As acid rain falls on the soil in a forest, it washes away nutrients such as calcium and magnesium that are needed by trees to grow. In addition, acid rain releases from the soil toxic (poisonous) min- erals such as aluminum that are then absorbed by the plants’ roots. This causes severe damage to the trees’ roots and weakens the trees. As acid rain falls on the trees them- selves, it burns the needles at the top and at the tips of branch- Acid rain damage in a es, which are then shed. This reduces the ability of the trees to German forest. © Boussu Regis/Corbis Sygma. make food from photosynthesis (process of converting the ener- Reproduced by permission. gy of sunlight into food) and to grow. Trees are then more vul- nerable to environmental stresses like disease, drought (prolonged periods of dry weather), and insects. A tree that is exposed to acid rain will absorb extra alkaline substances from the soil, making the soil acidic. This means that the acid rain falling on the soil makes the soil even more acidic, compound- ing the problems of acid rain. Decline in forests due to acid rain has been a serious prob- lem throughout the Northern Hemisphere. In the 1990s sur- veys of the Black Forest in Germany showed that half of the trees were dead or dying as a result of acid deposition. Between 1970 and 1998 nearly half the red spruce trees in the north- eastern United States died. Many sugar maples in Canada and the United States are also dying. Throughout Scandinavia, forests are dying because of acid rain. Most of the acid rain that affects these countries travels hundreds of miles (kilometers) from its sources in other parts of Europe. Acid Rain 381 water_ch12 10/20/04 10:52 AM Page 382 SSS Corrosion due to acid deposition Acid deposition damages most surfaces on which it falls. In particular, dry deposition Black Forest etches the paint on cars, corrodes metals, and Beginning in the 1960s scientists noticed deteriorates stone. In particular, buildings that many of the trees of Central Europe made of limestone and marble contain a lot of were dying. In particular, in the Black Forest, calcium carbonate. The acid in dry deposi- which is located in Southwestern Germany, a tion, reacts with the calcium carbonate to large number of trees showed signs of weak- form a powder. This powder is easily washed ening and dying. The term daldsterben, or away when it rains. A variety of famous build- tree death, was coined to describe the prob- ings and sculptures, especially in Europe, lem. The first trees to be struck with the have been damaged by acid deposition. affliction were the pines, followed by decidu- ous trees (trees that lose their leaves each The acid rain program year). By 1990 at least half the trees in the In 1990 the EPA established the Acid Rain Black Forest were harmed. Many trees dried out and died, while others dropped leaves or Program as part of the Clean Air Act. The goal became discolored. The problem was even- of the program is to reduce the emissions of tually attributed to acid deposition in the for- sulfur dioxide and nitrogen oxides. Much of est. Although several types of remediation the work in this program involves creating the techniques, such as replanting trees, were correct economic incentives for factories and tried, none have yet been successful. electrical plants to improve the quality of the Scientists assume that the damage to the materials they release into the air. Companies soil has made it so acidic that new trees can decide how they want to achieve emissions no longer grow in these ancient forests under reductions. Some may choose to install spe- current conditions. cial devices on their smokestacks that cleanse the pollutants out of the emissions. Others may use fuel that is less polluting or may use renewable energy sources. Finally, companies can trade for emissions allowances (the amount of pollutants that can be legally released) from companies that have already reduced their emissions below the standard levels. The Acid Rain Program has been more successful at control- ling sulfur pollutants than nitrogen pollutants. Since 1980 sul- fur emissions from large factories have fallen by nearly one-half, from 9.4 to 4.7 million tons of sulfur dioxide a year. Much of these improvements in emissions have occurred in the parts of the country where pollution is the biggest problem, such as in Ohio and Indiana. As a result the concentration of sulfuric acid in the Northeast and the Mid-Atlantic states has fallen by about 25% and lakes in these regions are showing signs of recovery. The emissions of nitrogen oxides have remained fairly constant over the last decade. As a result, the deposition of nitric acid into the environment has remained essentially unchanged. Juli Berwald, Ph.D. 382 U•X•L Encyclopedia of Water Science