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ozone had stabilized. Even if the most stringent prohibitions against CFCs are implemented, however, scientists
expect that it will take at least 50 more years for the hole over Antarctica to close completely.
Plant and animal species are dying out at an unprecedented rate. Estimates range that from 4,000 to as
many as 50,000 species per year become extinct. The leading cause of extinction is habitat destruction, particu-
larly of the world’s richest ecosystems-tropical rain forests and coral reefs. If the world’s rain forests continue
to be cut down at the current rate, they may completely disappear by the year 2030. In addition, if the world’s
population continues to grow at its present rate and puts even more pressure on these habitats, they might well
be destroyed sooner.
A significant portion of industry and transportation burns fossil fuels, such as gasoline. When these fuels
burn, chemicals and particulate matter are released into the atmosphere. Although a vast number of substances
contribute to air pollution, the most common air pollutants contain carbon, sulfur, and nitrogen. These chemi-
cals interact with one another and with ultraviolet radiation in sunlight in dangerous ways. Smog, usually found
in urban areas with large numbers of automobiles, forms when nitrogen oxides react with hydrocarbons in the
air to produce aldehydes and ketones. Smog can cause serious health problems.
Acid rain forms when sulfur dioxide and nitrous oxide transform into sulfuric acid and nitric acid in the
atmosphere and come back to Earth in precipitation. Acid rain has made numerous lakes so acidic that they no
longer support fish populations. Acid rain is also responsible for the decline of many forest ecosystems world-
wide, including Germany’s Black Forest and forests throughout the eastern United States.
Estimates suggest that nearly 1,5 billion people worldwide lack safe drinking water and that at least 5 mil-
lion deaths per year can be attributed to waterborne diseases. Water pollution may come from point sources or
nonpoint sources. Point sources discharge pollutants from specific locations, such as factories, sewage treat-
ment plants, and oil tankers. The technology exists to monitor and regulate point sources of pollution, although
in some areas this occurs only sporadically. Pollution from nonpoint sources occurs when rainfall or snowmelt
moves over and through the ground. As the runoff moves, it picks up and carries away pollutants, such as pesti-
cides and fertilizers, depositing the pollutants into lakes, rivers, wetlands, coastal waters, and even underground
sources of drinking water. Pollution arising from nonpoint sources accounts for a majority of the contaminants
in streams and lakes.
With almost 80 percent of the planet covered by oceans, people have long acted as if those bodies of water
could serve as a limitless dumping ground for wastes. However, raw sewage, garbage, and oil spills have begun
to overwhelm the diluting capabilities of the oceans, and most coastal waters are now polluted, threatening ma-
rine wildlife. Beaches around the world close regularly, often because the surrounding waters contain high lev-
els of bacteria from sewage disposal.
3. HOW ECOSYSTEMS WORK. ECOSYSTEM MANAGEMENT
Ecosystem comprises organisms living in a particular environment, such as a forest or a coral reef, and the
physical parts of the environment that affect them. The term ecosystem was coined in 1935 by the British
ecologist Sir Arthur George Tansley, who described natural systems in "constant interchange" among their liv-
ing and nonliving parts.
The ecosystem concept fits into an ordered view of nature that was developed by scientists to simplify the
study of the relationships between organisms and their physical environment, a field known as ecology. At the
top of the hierarchy is the planet’s entire living environment, known as the biosphere. Within this biosphere are
several large categories of living communities known as biomes that are usually characterized by their domi-
nant vegetation, such as grasslands, tropical forests, or deserts. The biomes are in turn made up of ecosystems.
The living, or biotic, parts of an ecosystem, such as the plants, animals, and bacteria found in soil, are known as
a community. The physical surroundings, or abiotic components, such as the minerals found in the soil, are
known as the environment or habitat.
Any given place may have several different ecosystems that vary in size and complexity. A tropical island,
for example, may have a rain forest ecosystem that covers hundreds of square miles, a mangrove swamp eco-
system along the coast, and an underwater coral reef ecosystem. No matter how the size or complexity of an
ecosystem is characterized, all ecosystems exhibit a constant exchange of matter and energy between the biotic
and abiotic community. Ecosystem components are so interconnected that a change in any one component of an
ecosystem will cause subsequent changes throughout the system.
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