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ACID RAIN
1. Precipitation absorbs carbon dioxide from the atmosphere and falls to earth as an extremely weak solution of carbonic acid. This is a natural occurrence that poses no threat to the environment. However, when sulfur and nitrogen oxides from industrial pollution chemically combine with the precipitation it becomes dangerously acidic and is termed “acid precipitation” or as it is more commonly called, “acid rain”.
2. To understand acid rain, we first must understand what an acid is. Acidity or alkalinity is measured on a pH scale which ranges from 1 to 14. A substance with a pH of 7 is considered neutral. Low pH values indicate acidity while high values indicate alkaline conditions, the lower the number, the stronger the acid.
3. Unpolluted rain is slightly acidic with a pH of 5.0 to 5.2. In areas of central and northern Europe, the eastern United States, and Russia the annual average pH of precipitation is now between 4 and 4.5 which is 5 to 8 times more acidic than unpolluted rain.
4. The acid-forming compounds come from natural as well as manmade sources. A volcanic eruption can cause acidic conditions covering half the globe. Decay processes involving both plant and animal materials, which occur in marshes, swamps, and oceans, can also produce chemicals that can increase acidic deposits. Many researches, however, believe that a major source of increased acid in rainfall is such industrial activity as the burning of fossil fuels like coal, gasoline, fuel oil, and natural gas.
5. The effects of acid rain are difficult to pinpoint. We know that when a stream or lake becomes too acidic, fish and their food sources are effected. Acid stress can cause fish to die. Small amounts of acid can also affect the ability of fish to reproduce.
6. Acid rain is also believed to reduce crop yields and deteriorate buildings and roads. There are also indications that acid precipitation also may be causing a reduction in forest production.
7. Since air moves without restriction from region to region, from nation to nation, and from continent to continent, any solution to the problem will require international cooperation.
II Прочтите 1-ый абзац текста и письменно ответьте на следующий вопрос:
When does the precipitation become dangerously acidic?
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Контрольная работа № 5
(для специальностей ЭТФ)
Вариант 5
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PROBLEMS OF SOUTH FLORIDA ECOSYSTEMS
1. Each member of an ecosystem belongs to the environment of every other part of that system, so any change in one alters the environment for all the others. And as those components react to the alteration, they in turn continue to transform the environment for the others.
2. Since human beings first walked the earth, they have affected each ecosystem they have inhabited. For example, a century ago the interconnected Kissimmee River – Lake Okeechobee – Everglades ecosystem comprised one of the most productive and stable wetland regions on earth. But marsh and slow-moving water stood in the way of urban and agricultural development. Intricate systems of ditches and canals were built and, since 1900, half of the original 4 million acres of the Everglades has disappeared.
3. The Kissimmee River has been channelized into an arrow-straight ditch, and wetlands along the river have been drained. Levees have prevented water in Lake Okeechobee from contributing sheet flow to the Everglades, and highway construction has deviled the region, further disrupting natural drainage patterns. Fires have been more frequent and destructive, and entire biotic communities have been eliminated by lowered water levels. During excessively wet periods, portions of the Everglades are deliberately flooded to prevent drainage canals from overflowing. As a result, animals drown and birds cannot rest and reproduce. South Florida's wading bird population decreased by 95% within a hundred years.
4. Without the natural purifying effects of wetland systems, water quality in South Florida has deteriorated, and with lower water levels, salt water encroachment is a serious problem in coastal areas. Today, backed by regional, state, and 227 federal agencies, scientists are struggling to restore South Florida's ailing ecosystems. There are extensive plans to allow the Kissimmee River to meander again across its former floodplain, to return agricultural land to marsh, and to restore historic water flow patterns through the Everglades.
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5. The problems of South Florida should serve as a useful lesson. Alterations of the natural environment should not be undertaken without serious consideration of all the consequences. All citizens of the earth must understand the effects of their actions on the complex earth system.
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What plans do scientists have for restoring South Florida's ailing ecosystems?
Контрольная работа № 5
(для специальности ТД)
Вариант 1
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