Biology 18.2 Effects on Ecosystems Effects on Ecosystems.

Biology 18.2 Effects on Ecosystems

Effects on Ecosystems


Effects of Chemical Pollution:

Examples of global change such as ozone depletion or global warming occur on a large scale. But what about serious environmental problems that occur in our own neighborhood?

One major environmental problem that impacts us on a local level is chemical pollution.

Until recently people assumed that the environment could absorb any amount of pollution.



Lake Erie and other large lakes became polluted because of the assumption that they could absorb unlimited amounts of pollution in the form of industrial chemicals.

Because of this misconception, pollution has risen to dangerous levels in some areas. In a highly publicized incident, the oil tanker the Valdez ran aground offshore of Alaska in 1989. Oil from the tanker polluted 1000 miles of coastline injuring and killing thousands of marine mammals.



Despite costly and heroic cleanup efforts, damage to local wildlife and the ecosystem of Prince William Sound was extensive.

This extreme example is not an isolated occurrence, smaller oil spills occur all the time with little or no publicity and are responsible for 90% of all pollution from oil seepage.



Many of the most disastrous incidents of pollution involving industrial chemicals that are toxic or carcinogenic (cancer causing).

Until recently, there has been very little regulation of the manufacture, storage, transportation, and destruction of such chemicals.

A clear example occurred in Basel, Switzerland in in 1986. Firefighters putting out a warehouse fire washed 30 tons of mercury and pesticides that were stored in the warehouse into the Rhine River. These poisons flowed down the Rhine into the north Sea, killing large quantities of aquatic animals and plants.

Today, the Rhine river is recovering but it’s diversity of species is reduced from this event.


Agricultural Chemicals: In many countries, modern agriculture

introduces large amounts of chemicals into the global ecosystem.

These chemicals include pesticides, herbicides, and fertilizers.

Industrialized countries, like the United States, now attempt to carefully monitor side effects of these chemicals.

Unfortunately, large quantities of toxic chemicals that are no longer manufactured still circulate in the ecosystem.


Agricultural Chemicals: Pesticides: For example,

molecules of chlorinated hydrocarbons; a class of compounds that includes DDT, chlordane, lindane, and dieldrin, break down slowly in the environment.

They also accumulate in the fatty tissue of animals. As these molecules pass up through the trophic levels of the food chain, they become increasingly concentrated.

This process is called biological magnification.


Agricultural Chemicals: The presence of DDT in birds can

cause thin, fragile eggshells. This thinness causes the shells to break during incubation.

Because of DDT use, many predatory birds in the US , such as the bald eagle, failed to reproduce and their numbers dwindled near extinction.

In 1972, the use of DDT was severely restricted in the United States and the threatened population of birds, including eagles and hawks, has ever since been on the rebound.


Agricultural Chemicals: Unfortunately, chlorinated

hydrocarbons are still produced within the United States and exported to other countries where their use is still legal.

In order to meet the food needs of an increasingly crowded world, the use of chemicals is deemed necessary. We must learn to use them as wisely as possible or find safer alternatives.

Doing so will enable us to protect the productive capacity of Earth’s farmlands and create a sustainable future with safe food for all.

Biology 18.2 Effects on Ecosystems: Loss of Resources

Loss of Resources:

Among all the ways that ecosystems are being damaged, the one problem that stands out above all others is the consumption or destruction of resources that are not replaceable.

A polluted stream or river can be cleaned up but a species that has gone extinct can never be brought back.

Three kinds of nonrenewable resources are being consumed or destroyed at alarming rates: species of animals, topsoil and groundwater.


Extinction of Species:

Over the past 50 years, about half the world’s tropical ran forests have been burned to make pasture and farmland or have been cut for timber.

Many thousands more will be destroyed this year. The people responsible, often poor farmers, view the forest lands as a resource to be developed, much as Americans viewed North America’s forests a century ago.

The major problem is that as the rain forests disappear, so do the many varied species that call them home.



Today, no one knows how many species are being lost with the destruction of the rain forests.

To find out, scientists carefully log all of the residents of one small segment of forest and than extrapolate the data.

Scientists use what they know to predict what they don’t know by making educated guesses based on the information they are able to collect.

The resulting estimates vary widely but it is clear Earth is losing many species.



Perhaps some 10 percent of all species teeter on the brink of extinction.

Worst-case estimates hold that perhaps we may loose up to one-fifth the world’s species of plants and animals; about 1 million species, during the next 50 years.

An extinction of this size has not occurred in at least 65 million years, since the end of the age of dinosaurs.

The tragedy is that as these species go extinct, so vanishes our chances to learn about them and any possible benefits these species may hold for us.



This situation is comparable to burning a library before reading the books, we loose forever the knowledge we might have otherwise gained.

For example, two potent anticancer drugs have been isolated from the plant species rosy periwinkle, a flower that occurs naturally in Madagascar.

Rosy periwinkle


Loss of Topsoil:

The United States is one of the most productive agricultural countries on the Earth, largely because of it’s fertile soil.

These soils have accumulated over tens of thousands of years. The Midwestern farm belt sits astride what was once a great prairie.

The topsoil of that ecosystem accumulated slowly as the remains of countless animals and plants decayed to form it.

By the time humans came to plough the prairie, the topsoil was more than a meter thick.


Loss of Topsoil:

This rich topsoil can not be replaced, and it is being lost at a rate of several centimeters each decade.

Turning over the soil to eliminate weeds, allowing animals to overgraze ranges and pastures, and practicing poor land management all permit wind and rain to remove more and more of the topsoil.

Since 1950, the world has lost one-third of it’s topsoil, primarily because of human activity.


Groundwater Pollution and Depletion:

A third resource we can not replace is ground water.

Much ground water is stored within porous rock reservoirs underground called aquifers.

Water seeps into aquifers too slowly to replace the large amount of water now being withdrawn by human population use.

http://geoscape.nrcan.gc.ca/h2o/bowen/images/groundwater_e.jpg


Groundwater Pollution and Depletion:

In most areas of the United States there is very little effort being made to conserve ground water.

Consequently, a large portion of it is wasted on watering lawns, washing cars, through leaky and inefficient faucets and toilets.

A great deal more ground water is being polluted by irresponsible disposal of chemical wastes. Once pollution enters the groundwater, there is no effective way to remove it.

http://geoscape.nrcan.gc.ca/h2o/bowen/images/groundwater_e.jpg

Biology 18.2 Effects on Ecosystems: Overpopulation

Growth of Human Population:

If all the problems associated with pollution mentioned earlier were solved, would all the world’s problems vanish overnight? Not likely!

Scientists all agree that a growing fundamental problem is the ever increasing population worldwide.

Overpopulation is an issue that is already creating problems in many areas of the world as too many people share too few resources.



Humans first reached North America at least 12,000 years ago by crossing the land bridge between Siberia and Alaska. Humans than spread throughout North and South America.

Ten thousand years ago the continental ice sheets that covered northern Europe and North America receded and agriculture soon developed. At this point there were only about 5 million people on Earth.



As agriculture produced more reliable food sources than hunting-gathering, the human population began to grow.

By about 2000 years ago, there were an estimated 130 million people on Earth.

By 1650, the world’s population had reached 500 million.



The world’s population exceeded 6 billion in October 1999 and the annual increase is now about 94 million people.

About 260,000 people are added to the world population each day, or about 180 every minute.

Population growth is fastest in developing countries of Asia, Africa, and Latin America.

It is slowest in the industrialized countries of North America, Europe, Japan, and in New Zealand.



In industrialized countries like the United States, about one- fifth of the population is under 15 years of age.

In developing countries like Nigeria, the percentage is typically twice as high, which may lead to explosive population growth in coming decades.



In recent years, the rate of population growth has actually been declining, specifically in industrialized countries.

The United Nations projects that the world’s population will stabilize at 9.7 billion by the year 2050.

As we are at present, population growth is uneven across the world. Population growth tends to be highest in the poorest countries that can least afford it.



At present, no one knows if the Earth will be able to support 6 billion people let alone the 9 billion projected by 2050.

Building a sustainable future is the most important task we as a world face in our present day.

The quality of our children’s lives in the future depends on the choices we make today to create a sustainable and balanced healthy environment for all.

Biology 18.2 Effects on Ecosystems Effects on Ecosystems.

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