marine polution

Ocean Problems

Greenhouse effect

is a warming of the lower atmosphere and surface of a planet by a complex process involving sunlight, gases, and particles in the atmosphere. On the earth, the greenhouse effect began long before human beings existed. However, recent human activity may have added to the effect. The amounts of heat-trapping atmospheric gases, called greenhouse gases, have greatly increased since the mid-1800's, when modern industry became widespread. Since the late 1800's, the temperature of the earth's surface has also risen. The greenhouse effect is so named because the atmosphere acts much like the glass roof and walls of a greenhouse, trapping heat from the sun.

Causes of climate change
Impact Global Warming
Limited Global Warming
Agreement on global warming
Analyzing global warming
Kyoto Protocol
Greenhouse effect
Scientific research
Why climates vary
Ocean problems
Southern Ocean
Pacific Ocean
Ozone hole
Environmental problems by petroleum
Changes in the atmosphere
Increasing Temperatures
Can Earth Explode ?
NASA Study
El Nino
The Procedure Of Implementation Afforestation And Reforestation Project Under The Clean Development Mechanism (CDM) In Indonesia
Reducing emissions from deforestation and forest degradation (REDD) in developing countries


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For thousands of years, people used the ocean and its vast resources with little concern for their conservation. But during the last two centuries, increases in human population, industrial development, and use of coastal regions has put the health of the sea at risk, forcing people to address ocean conservation problems. Many of the most important problems involve marine pollution, depletion of fisheries, habitat modification, and climate change.

Marine pollution. Pollutants (substances that cause pollution) enter the ocean through accidents, carelessness, and the deliberate disposal of wastes. The ocean can absorb some types of pollutants in certain quantities because of its great size and the natural chemical processes that occur within it. But the ocean's capacity to absorb and recycle pollutants can become overwhelmed.

People pollute the oceans in several ways. Major ocean pollutants include waste products, which people often dump deliberately into the ocean, and oil, which usually enters the sea by accident.

Waste products that enter the ocean include sewage, plastic litter, and industrial wastes. Sewage, such as human waste and ground-up garbage, often fouls coastal regions. This kind of waste contains organic matter that decomposes and reduces the levels of oxygen in the water. Low oxygen levels make the water unfit for animals. Sewage also contains nitrates, phosphates, and other nutrients that stimulate the growth of phytoplankton. An overabundance of certain phytoplankton produces a condition called eutrophication, which also reduces the water's oxygen levels. Rapid growth of some phytoplankton can create red tides. Red tide phytoplankton produce toxins that poison marine life.

Plastic litter can severely damage the ocean because it does not break down easily. Sea birds, turtles, seals, whales, and other marine animals can get tangled in plastic nets, bags, and packing material. These animals may also mistake plastic items for food and die of starvation if the plastic blocks their digestive system. In addition, plastics and other litter make the marine environment less attractive. Many countries ban the disposal of plastics into the ocean, but such litter remains a common problem on shorelines.

The deliberate dumping of industrial waste into the sea from ships and barges has also polluted oceans. Such wastes have included ash from power plants, contaminated sediments dredged from harbors, and even radioactive wastes. Since the 1970's, many countries have begun banning ocean dumping of most wastes. But the disposal of some types of wastes, such as dredged sediments, may likely continue.

Oil pollution enters the ocean from oil spills on land or in rivers. Oil also seeps into the ocean naturally from cracks in the sea floor. Oil tanker and oil well accidents at sea account for only a small portion of ocean oil pollution, but their effects may be disastrous. The world's largest accidental oil spill occurred in June 1979, when an oil well blew out off the east coast of Mexico and spilled about 140 million gallons (530 million liters) of oil. The world's largest oil spill occurred when Iraq deliberately released between 240 and 465 million gallons (910 and 1,760 million liters) of oil into the Persian Gulf during the Persian Gulf War of 1991. In water, much of the oil forms tarlike lumps, which foul beaches and other coastal areas. Oil also coats fish, birds, and mammals and kills many of them.

Fisheries. Since the latter part of the 1900's, the world's fishing industry has harvested fish from many ocean fisheries faster than the fish stocks can renew themselves. Some fishing techniques have proved especially destructive. These techniques include the use of dynamite and cyanide to stun or kill fish on coral reefs. They also include the use of nets that capture, injure, or kill species other than the ones being sought. In some cases, the depletion of commercially valuable fish species can alter marine ecosystems by making less valuable species more abundant. Such problems have led many countries to enforce limits on catch and even temporarily close a number of valuable fisheries.

Habitat modification. People have harmed marine ecosystems in many coastal regions by destroying such vital habitats as marshes; mangrove swamps, where the spreading roots of mangrove trees catch and hold silt from the water; and tidal flats, which are covered and uncovered twice daily by the tides. These environments often play an essential role in maintaining a healthy marine ecosystem. As a result, conservationists are attempting to stop further damage to such habitats and, in some cases, to restore the habitats to their natural state.

Climate change. Natural processes cause most kinds of climate change. But increasing evidence indicates that human activities can also produce changes in climate. Over the past 150 years, the combustion of such fossil fuels as petroleum, coal, and natural gas has increased the amount of carbon dioxide gas in the atmosphere by about 30 percent. Carbon dioxide traps heat from the sun in a process called the greenhouse effect. Increases in atmospheric carbon dioxide may enhance the greenhouse effect and significantly raise temperatures on Earth. Such changes in climate could greatly affect all marine ecosystems..

Scientists are working to determine the role of the ocean in climate, as well as the effects of human activities on climate change. Scientists have studied the possibility of disposing carbon dioxide into the depths of the ocean as a way to keep Earth from overheating.

Who owns the ocean? This question has become more important as countries have learned that fish and other ocean resources can be used up and that valuable minerals and sources of energy lie on and under the sea floor. The United Nations has worked to develop an agreement on ownership of the sea. Its efforts resulted in the Law of the Sea Convention, drafted in 1982. This treaty went into effect in 1994, after more than 60 nations ratified it. The treaty provides for a system to protect the economic and environmental interests of coastal nations, while allowing the free passage of other countries' ships.

Under the Law of the Sea Convention, the laws of a coastal nation apply throughout its territorial sea, which extends 12 nautical miles (22 kilometers) from the nation's shoreline. An exclusive economic zone (EEZ) extends, in most cases, 200 nautical miles (370 kilometers) beyond the nation's territorial sea. Each coastal nation, even if it is an island, has total control over resources and research within its EEZ. The remaining ocean area is defined as the high seas, where no nation may make a territorial claim. However, even on the high seas, various international agreements govern fishing methods and fishing catches, as well as disposal of wastes.

The United States has not signed the Law of the Sea Convention. At the time this treaty was drafted, the U.S. government believed the treaty did not adequately protect private industries involved in deep-sea mining operations. However, the United States is working to resolve this difference, and it supports exclusive economic zones and many other provisions of the treaty.

Contributor: Dana R. Kester, Ph.D., Professor of Oceanography, University of Rhode Island.

Source : World Book 2005.