SEWAGE DISPOSAL   Leave a comment

Perhaps no factor is more useful in the control of disease than the science of sewage disposal. It safeguards a community’s water supply by removing water-carried wastes including microscopic dissolved material, solid matter such as human waste, and harmful chemicals and bacteria.

Sewage is generally divided into two classes: domestic, or sanitary, sewage and industrial waste. Domestic waste water includes the used water of businesses and homes; industrial waste water is that discharged during industrial operations. Both the strength and volume of waste water may be markedly influenced by industrial wastes, which constitute about 80 percent of the sewage in the United States.

Sewage Treatment

Sewage systems collect waste water and treat it before discharging it back into the environment. These systems consist of intricate networks of underground conduits, or sewers, that convey the sewage through the treatment process to the point of disposal.

Sewage systems also handle the flow of rainwater, either separately or as part of a single system. Separate systems are generally preferable because, in single systems, heavy rainfall can overload treatment plants, with the result that untreated overflow can become a source of pollution. In separate systems, rainwater is often allowed to flow into streams untreated because it is assumed to be relatively clean.

Sewage is processed in three major steps, called primary, secondary, and tertiary treatments. Most areas do not use all three, and different areas use the treatments in different ways.

Primary treatment. The initial, and sometimes the only, method of cleaning waste water is primary treatment, which consists of removing floating chunks and fine particles of solid waste. The simplest form of primary treatment is a cesspool, now found primarily in rural areas. A cesspool is a big tank with a porous bottom and sides that lets the liquid waste water filter into the ground while holding the solid waste. Periodically the tank must be cleaned; the solid matter, called sludge, is sometimes used for fertilizer or landfill. Septic systems are somewhat similar, though the tank is connected to a drainage field so that more waste can be dispersed over a wider area.

In larger communities, sewer water passes first through a screen, which filters out the larger debris. It then runs through a grit chamber, a long, shallow trough with a dip in the bottom that acts like a trap. As water moves through the trough, small, hard materials in the water drift down to the bottom and fall into the trap. Grease floats to the surface and is skimmed off. The trap, like a cesspool, is periodically scraped clean.

After going through the screen and grit chamber, the sewage still contains small suspended solids about 1 ton per million gallons (3,790,000 litres) of waste water To remove some of these, the sewage is trickled into a sedimentation tank, or settling basin. The water enters through a pipe, then circulates slowly while the suspended particles settle to the floor. The top layer of water continually runs out through exit holes.

The sludge from sedimentation tanks may be sent through a tank called a digester, where bacteria digest it, producing carbon dioxide and methane gas and other by-products. Any combustible gases may then be collected and used to heat the digestion tanks and buildings and to fuel gas engines in the plant. The sludge may also be buried or dumped as landfill, burned, or dried in sludge drying beds for use as fertilizer.

Primary treatment removes about half of the suspended solids and bacteria in sewage, and about 30 percent of the organic wastes. Sometimes chlorine gas is added to the effluent (the liquid remaining after sedimentation) to kill most of the remaining bacteria. Some cities use chemicals that coagulate some of the solids into particles of a size and weight that will settle, so that they can be separated in a settling tank. The use of chemicals makes it possible to remove 80 to 90 percent of the suspended solids.

Secondary treatment. Today, large cities are usually required to put their wastes through both primary and secondary treatment because primary treatment alone removes so little organic material. Secondary treatment uses aerobic, or oxygen-breathing, bacteria to decompose organic wastes. The main object is to put the waste water in contact with as many bacteria as possible while keeping it aerated so that the bacteria have an adequate supply of dissolved oxygen.

One of the most common secondary treatments of this type is the activated-sludge method, so called because it uses sludge that is activated, or teeming with micro-organisms After going through primary treatment, the sewage is put into the activated-sludge tank, where it is aerated by pumps or blasts of compressed air. The compounds produced by the bacteria remain mostly suspended in the water and flow out with it into a secondary sedimentation tank.

The sludge from the bottom of the tank is handled in much the same way as the sludge from the primary sedimentation tank, except that about a quarter of it is recirculated back into the activated-sludge tank. This recirculation serves to seed the activated-sludge tank with fresh bacteria. The activated-sludge method permits almost any desired degree of treatment by varying the period of aeration. It removes about 95 percent of bacteria and more than 90 percent of suspended solids and organic matter.

Another method of secondary treatment is the trickling-filter method. Generally, rotating arms slowly spray the sewage over a shallow circular tank containing a layer of gravel or crushed rock. The rocks are covered with a slimy coating of micro-organisms that break down the organic wastes in the sewage. After this process, as in the activated-sludge method, the water that has been filtered is passed into a secondary sedimentation tank for removal of organic matter that has sloughed off from the stones of the filter. Trickling filters, together with primary treatment and final sedimentation, will remove most suspended solids.

Tertiary treatment. Waste water that has received primary and secondary treatment still contains dissolved materials that make it unsuitable for almost all uses except irrigation. Tertiary treatments, which depend largely on artificial chemical processes, are designed to remove these materials in order to make the effluent safer to discharge into waterways and safer for industry to use. A number of methods may be used, including radiation treatment, discharging the effluent into lagoons, and chlorination.

Sewage may also be passed through filters made of activated carbon, which consists of finely ground charcoal grains with rough, pitted surfaces that trap impurities. Alternatively, sewage may be strained through a screen made of tiny seashells called diatomaceous earth. The effluent may also be treated with chemicals that transform the dissolved organic material. Some chemical compounds, for example, combine with the nitrates in sewage to produce various salts. Such treatments are expensive, however, and are difficult to perform routinely.


The use of specially constructed sewers dates to the time of Babylon and ancient Greece, but only during the 19th and 20th centuries was the water-carriage sewage system adopted in the Western world. In these early systems, streams often served the dual purpose of sewage disposal and water supply, and hence there were frequent, disastrous epidemics of cholera, typhoid fever, and other water-borne diseases. The most effective methods of sewage treatment were not developed until the second quarter of the 20th century. Today, because of the greater amount of sewage from growing populations and industrial activity, there is an unprecedented quantity of legislation designed to control water pollution. As a result, scientists and engineers continually search for methods to further increase the levels of sewage treatment.

Posted 2012/04/21 by Stelios in Education

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PEST CONTROL   Leave a comment

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwin’s theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

Organisms considered harmful to humans or their interests are called pests. They include plants or animals that carry disease, cause disease, or destroy crops or structures. The definition of a pest is subjective. An ecologist would not necessarily consider a leaf-eating caterpillar on a corn plant a pest, but a farmer might. The term pest may refer to insects, viruses, and bacteria that carry or cause disease. It may also refer to organisms that destroy crops or man-made structures. Plants, such as weeds or fungi, and vertebrates, such as rats, mice, and birds, are sometimes called pests when they destroy crops or stored foods.

The elimination of pests or the inhibition of their reproduction, development, or migration is known as pest control. The control of pests has a great influence on the world economy. Even with current pest-control measures, agricultural pests are responsible for the annual destruction of millions of acres of crops worldwide. In South east Asia, rodents have been known to destroy as much as 50 percent of a rice crop before it is harvested. In the United States, over 500 million dollars are lost annually to insect and rodent infestation of stored foods and grains.

Some insects are considered pests because they are wood-eaters. They are a threat to wooden structures houses and other buildings, trees, and fences. Several species of ants, bees, and beetles can also damage wooden structures.

In the field of agriculture, pest control is used to protect farm crops and forests that are harvested for their wood. Pest control has also contributed to the management of many health-threatening diseases, including plague, encephalitis, yellow fever, malaria, and typhus.

Chemical Control

The most common method of pest control is the use of pesticides chemicals that either kill pests or inhibit their development. Pesticides are often classified according to the pest they are intended to control. For example, insecticides are used to control insects; herbicides to control plants; fungicides, fungi; rodenticides, rodents; avicides, birds; and bactericides to control bacteria. Pesticides also include chemosterilants and growth regulators, which are used to interfere with the normal reproduction or development of the pest.

Pyrethrum, old genus of composite family which botanists now place in genus Chrysanthemum; most garden varieties were derived from Chrysanthemum roseum, or Pyrethrum roseum, a handsome perennial with finely dissected leaves and white to crimson and lilac flowers; the flowers of Chrysanthemum cinerariaefolium, used in insecticides, had important part in U.S. troops’ fight against malaria-carrying mosquitoes in World War II.

Chemical control of pests probably began with poisonous plant compounds. In the 18th and 19th centuries, farmers ground up certain plants that were toxic to insects or rodents plants such as chrysanthemums or tobacco. The plant “soup” was then applied directly to either the crops or the pests. Chemists later discovered that they could extract the toxic compounds from these poisonous plants and apply the compounds as liquid sprays. Such chemicals as nicotine, petroleum, coal tar, creosote, turpentine, and pyrethrum (obtained from a type of chrysanthemum) were eventually extracted for use as sprays. Organic compounds such as these were eventually replaced by more effective inorganic chemicals, including arsenic, lime, sulphur, strychnine, and cyanide.

With the advent of synthetic organic compounds during World War II, a dramatic change occurred in pest control. The discovery of the insecticidal properties of the synthetic compounds DDT (dichlorodiphenyltrichloroethane) which was widely used against disease-spreading insects during the war and BHC (benzene hexachloride) made the notion of pest-free crops realistic. The development of another synthetic organic compound, the selective herbicide 2,4-D (2,4-dichlorophenoxyacetic acid), led to the development of other selective herbicides.

With the discovery of DDT, 2,4-D, and BHC, researchers began to develop other synthetic organic pesticides, especially growth regulators, chemosterilants, pyrethroids (compounds with insecticidal properties similar to those of pyrethrum), and organophosphate chemicals. This research expanded in order to develop other, non chemical, methods of pest control after the harmful persistence of pesticides in the environment was recognized. It was discovered in the 1950s that DDT and its related compounds are not easily broken down in the environment. DDT’s high stability leads to its accumulation in insects that constitute the diet of other animals. These high levels of DDT have toxic effects on animals, especially certain birds and fishes. Scientists also found that many species of insects rapidly develop populations that are resistant to the pesticide.

By the 1960s, the value of DDT as an insecticide had decreased, and in the 1970s severe restrictions were imposed on its use. In the United States, the Federal Environmental Pesticide Control Act of 1972 and the Federal Insecticide, Fungicide, and Rodenticide Act passed in 1972 required pesticide manufacturers to conduct scientific tests on the biological activity, defectiveness, persistence, and toxicity of any new pesticide before the chemical could be marketed. In the late 1980s, the average cost to develop and register a pesticide product was 10 million dollars. In the 1960s and 1970s, public objections were raised over the indiscriminate use of pesticides. The Environmental Protection Agency (EPA) was created in 1970 to ascertain past damage and possible future damage that could occur to the environment as the result of widespread pesticide use, and to set up programs to combat environmental problems.

An alternative concept of integrated pest management was adopted for many agricultural pests. This approach involves non-chemical pest-control methods, including crop exclusion, crop rotation, sanitation, and biological control. These methods augment other pest control programs designed to minimize pesticide usage.

Biological Control

The biological control of pests involves exposing them to predators or parasites. The use of predators and parasites is usually accompanied by a program in which pest-damaged fields are scouted and pest population estimates are made. Predators and parasites are then released by the millions to assure control of the target pest.

China (or People’s Republic of China), country in e. Asia; area 3,692,000 sq mi (9,561,000 sq km); cap. Beijing; pop. 1,165,888,000. Circa 1995.

Biological pest control was used by the ancient Chinese, who used predacious ants to control plant-eating insects. In 1776, predators were recommended for the control of bedbugs. The modern era of biological pest control began in 1888, when the vedalia beetle was imported from Australia to California to control the cottony-cushion scale insect. This biological control project saved the citrus-fruit industry.

Insect predators also have been used to control the bean beetle, tomato horn worms, and aphids. Another biological method is the use of bacteria against grubs, or insect larvae. For example, the bacterium Bacillus thuringiensis is used to control the caterpillar larvae of the gypsy moth, as well as the larvae of mosquitoes In the 1980s, mosquito-eating fish and nematodes that prey on such soil insects as corn root worms were introduced as biological-control agents.

Since the 18th century, the breeding of host plants for pest resistance also has been used to control pests. Wheat has been the object of the most extensive plant-resistance research. Effective wheat-breeding programs have led to the development of new wheat varieties that are resistant to rusts various parasitic fungi that infect the leaves and stems of the plant. Corn breeding has resulted in varieties resistant to other fungal diseases, including smut and leaf blight. The classic example of this plant-resistance approach to pest control was the control of phylloxera, insects that attacked the root stock of the European wine grape and almost completely ruined the European wine industry. The problem was solved by grafting the European plants onto the resistant American wine grape root stock.

The development of insect predators to control structural pests has met with little success. Nematodes have been used against termites in laboratories, but field tests have not been successful. Parasitic wasps used against various cockroach species have also been unsuccessful in the field.

Other Controls

Cultural control methods are used to alter the pest’s environment and thereby reduce access to breeding areas, food, and shelter. Cultural methods have been used to control the yellow-fever mosquito, which breeds in swamps and small pools of water. With the draining of swamps and the elimination of stagnant pools and other containers where water accumulates, the number of potential breeding places for the pest is reduced. Cultural control has also been used against structural pests, which depend on protected places such as cracks in side walks, roads, or buildings; garbage; and weeds for survival. Structural pests are often effectively deterred when openings to potential hiding places are sealed and debris and refuse are eliminated.

Crops are sometimes protected from harmful pests through diverse planting techniques. Crop rotation, for example, prevents the development of fungus and bacterium populations. Open-area planting relies on the wind to hinder flies and other insects that damage vegetable crops.

Physical or mechanical control methods are effective against some pests. Such controls include sticky barriers, heat killing (for storage pests), and flooding (for ground pests). Pressure-treated wood is protected against many wood-damaging fungi and insects. Traps are another mechanical method of pest control. Some traps are designed to either kill or capture rodents and other vertebrate pests. Netting and metal shields are used to keep birds from damaging fruit crops or from roosting on buildings. Electrical light traps attract insects and electrocute them. In some buildings, fans are installed above doors to prevent the entry of flying insects.

An area of pest-control research that has received much attention in recent years involves baiting traps with the pest’s own sex attractants, or pheromones. Pheromone traps have been used extensively against the fruit fly and gypsy moth. Pheromones are also being used to attract and trap pests that infest stored foods and grains.

Many countries use importation and quarantine regulations to control the importation of foreign plant or insect pests. Fruit is especially prone to insect infestation and disease. In the United States, the Animal and Plant Health Inspection Service monitors incoming products and materials and requires certain products to be treated prior to entry. Similar controls exist in other countries. Some regions have quarantine regulations to ensure that certain insect pests are not brought into the area. In the United States, individual states have their own inspection services. Some states even have border inspection stations to prevent unauthorized transport of plants across state lines.

Assisted by George W. Rambo.

ECOLOGY (Part 1 of 3)   Leave a comment

DEFINITION:1 a) the branch of biology that deals with the relations between living organisms and their environment b) the complex of relations between a specific organism and its environment 2 Sociology the study of the relationship and adjustment of human groups to their geographical and social environments.

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwins theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

The science that deals with the ways in which plants and animals depend upon one another and upon the physical settings in which they live is called ecology. Ecologists investigate the interactions of organisms in various kinds of environments. In this way they learn how nature establishes orderly patterns among a great variety of living things. The word ecology was coined in 1869. It comes from the Greek oikos, which means “household.” Economics is derived from the same word. However, economics deals with human “housekeeping,” while ecology concerns the “housekeeping” of nature.

Interdependence in Nature

Ecology emphasizes the dependence of every form of life on other living things and on the natural resources in its environment, such as air, soil, and water. Before there was a science of ecology, the great English biologist Charles Darwin noted this interdependence when he wrote: “It is interesting to contemplate a tangled bank, clothed with plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and so dependent upon each other in so complex a manner, have all been produced by laws acting around us.”

Ecology shows that people cannot regard nature as separate and detached something to look at on a visit to a forest preserve or a drive through the country. Any changes made in the environment affect all the organisms in it. When vehicles and factories hurl pollutants into the air, animals and plants as well as humans themselves are harmed. The water they foul with wastes and silt threatens remote streams and lakes. Even ocean fisheries may experience reduced catches because of pollution.

The Balance of Nature

Each kind of life is suited to the physical conditions of its habitat the type of soil, the amount of moisture and light, the quality of air, the annual variations in temperature. Each survives because it can hold its own with its neighbours However, the continued existence of the whole group, or life community, involves a shifting balance among its members, a “dynamic equilibrium.”

Natural balances are disrupted when crops are planted, since ordinarily the crops are not native to the areas in which they are grown. Such disturbances of natural balances make it necessary for man to impose artificial balances that will maintain or increase crop production. For the effective manipulation of these new equilibriums, information on nature’s checks and balances is absolutely essential, and often only a specialist is able to provide it. For example, if a farmer were told that he could increase the red clover in his pasture with the help of domestic cats, he might ridicule the suggestion. Yet the relationship between cats and red clover has been clearly established. Cats kill field mice, thus preventing them from destroying the nests and larvae of bumblebees. As a result, more bumblebees are available to pollinate clover blossoms. The more thoroughly the blossoms are pollinated, the more seed will be produced and the richer the clover crop will be. This cat-mouse-bee-clover relationship is typical of the cause-and-effect chains that ecologists study.

The Wide Scope of Ecology

Long before a separate science of ecology arose, men in all sorts of occupations were guided by what are now regarded as ecological considerations. The primitive hunter who knew that deer had to stop at a salt lick for salt was a practical ecologist. So too was the early fisherman who realized that gulls hovering over the water marked the position of a school of fish. In the absence of calendars, men used ecological facts to guide their seasonal endeavours They planted corn when oak leaves were the size of a squirrel’s ear. They regarded the noise of geese flying south as a warning to prepare for winter.

Natural history, the study of nature in general; forerunner of the sciences of biology and ecology.

Until about 1850, the scientific study of such phenomena was called natural history, and the student of the great outdoors was called a naturalist. Afterwards, natural history became subdivided into special fields, such as geology, zoology, and botany, and the naturalist moved indoors. There he performed laboratory work with the aid of scientific equipment.

While the scientists were at work in their laboratories, other men were continuing to cope with living things in their natural settings on timber lands, on range lands, on crop lands, in streams and seas. Although these men often needed help, many of their problems could not be solved in the laboratory.

The forester, for example, wanted to know why trees do not thrive on the prairie, the desert, and the mountaintop. The rancher wanted to know how to manage his pastures so that his cattle would flourish, and how such creatures as coyotes, hawks, rabbits, gophers, and grasshoppers would affect his efforts.

As for the farmer, almost every part of his work posed problems for which scientific answers were needed. The game manager came to realize that his duties entailed much more than the regulation of hunting. To preserve the animals for which he was responsible, he had to make sure they had the right kinds of food in all seasons, suitable places to live and raise their young, and appropriate cover.

The fisherman learned that most aquatic life fares poorly in muddy and polluted waters. He became interested in land management and waste disposal when he discovered that the silt he found so troublesome came from rural areas where timber, range land, and crop land were mishandled and that the waters he fished were polluted by urban wastes. The ocean fisherman wanted to know why fish were abundant in one place and scarce in another. He needed information on the breeding habits of his catches and of the tiny animals and plants upon which they fed.

These are all ecological problems. To solve them the ecologist must understand biology the science of living things including botany and zoology. He must also understand the sciences that deal with weather, climate, rocks, earth, soil, and water.

An ecologist is concerned with both the past and the future. The present and potential condition of a field, stream, or forest cannot be understood without knowing its earlier history. For example, great stretches of light-green aspen trees may grow in parts of the Rocky Mountains while nearby slopes are covered with dark-green fir and spruce trees. This indicates that a forest fire once destroyed stands of evergreens. Aspens are the first trees capable of growing on the fire-scarred land. After about 40 years spruce and fir seeds begin to germinate in the shade of the aspens. In the course of time the evergreens can be expected to regain their lost territory.


Ecology is a relatively young science. Its laws are still being developed. Nevertheless, some of its principles have already won wide acceptance.

The Special Environmental Needs of Living Things

One of these principles can be stated as follows: life patterns reflect the patterns of the physical environment. In land communities vegetation patterns are influenced by climate and soil. Climate has a marked effect on the height of dominant native plants. For instance, the humid climate of the Eastern United States supports tall forest trees. Westward from Minnesota and Texas the climate changes from sub humid to semiarid. At first the land has squatty, scattered trees and tall grasses or thickets. As the climate becomes drier, tall-grass prairies dominate. Finally, on the dry plains at the eastern base of the Rockies, short-grass steppe appears.

Rocky Mountains (or Rockies), chain of ranges, along e. side of North American Cordilleras from Mexico to Alaska.

Climates and plant varieties change quickly at the various elevations of mountain range. At very high altitudes in the Rockies, alpine range lands exist above the timberline. Here, the climatic factor of cold outweighs that of moisture, and tundra vegetation similar to that of the Arctic regions is nurtured. West of the Rockies, however, in basins between other mountains, the desert scrub vegetation of arid climates prevails. Near the northern Pacific coast may be found lush rain forests typical of extremely humid temperature climates.

Though moisture and temperature determine the overall pattern of a region’s vegetation, unusual soil conditions may promote the growth of un-typical plant species. Thus, even in arid climates cat tails grow near ponds and forests rise along streams or from rocky outcrops where run off water collects in cracks.

Plants and animals flourish only when certain physical conditions are present. In the absence of such conditions, plants and animals cannot survive without artificial help. Domestic plants and animals ordinarily die out within a few generations without the continued protection of man. Of all the forms of life, man seems least bound by environmental limitations. He can create liveable conditions nearly everywhere on the planet by means of fire, shelters, clothing, and tools. Without these aids, man would be as restricted in his choice of habitat as are, for example, such species as the polar bear, the camel, and the beech tree. However, given his capacity to develop artificial environments, man is able to range not only over the entire Earth but also in the heights of outer space and the depths of the ocean bottom.

Communities of Plants and Animals

Community, in biology, a group of organisms living together in a particular environment.

Closely related to the life patterns principle is the principle of biotic communities. According to this principle, the plants and animals of a given area its biota tend to group themselves into loosely organized units known as communities. The community is the natural home of each member-species.

This means that certain types of plants and animals live together in readily identified communities. Pronghorn antelope are associated with dry steppe grasslands; moose inhabit northern spruce forests; and such trees as oak and hickory or beech and maple are found together in forests. By contrast, certain living things cat tail and cactus, for example never share the same natural environment.

Large communities in turn contain smaller ones, each with its own characteristic biota. Bison, coyotes, and jack rabbits are part of the grasslands community. Fox squirrels, wood pigeons, and black bears are part of the forest community. By means of computers, ecologists have simulated communities containing various plants and animals. In this way they have been able to determine optimum populations for each of the species in a community.

ECOLOGY (Part 3 of 3)   Leave a comment

HOW DDT KILLED THE ROBINS. Dutch elm disease threatened to destroy most of the majestic elms that once flourished along residential streets. To eliminate the beetles that carry this fungus disease, many communities sprayed their elms with massive doses of DDT. The pesticide stuck to the leaves even after they fell in the autumn. Earthworms then fed on the leaves and accumulated DDT in their bodies. When spring came, robins returned to the communities to nest. They ate the earthworms and began to die in alarming numbers. Of the females that survived, some took in enough DDT to hamper the production or hatching of eggs. Robin populations were so seriously affected by DDT poisoning that the very survival of the songbird seemed in jeopardy. This experience was a vivid example of the far-ranging effects that flow from upsets in the delicate balances of nature.

Ironically, the DDT did little to prevent the spread of Dutch elm disease.

By the 1970s ecologists had accumulated considerable evidence demonstrating that the widely used pesticide DDT and its metabolites, principally DDE, altered the calcium metabolism of certain birds. The birds laid eggs with such thin shells that they were crushed during incubation. This discovery was one of many that led to the imposition of legal restraints on the use of some agricultural pesticides.

Ecologists know that the well-being of a biotic community may require the preservation of a key member-species. For example, the alligator performs a valuable service in the Florida Everglades by digging “‘gator holes.” These are ponds created by female alligators when they dig up grass and mud for their nests. During extremely dry spells, these holes often retain enough water to meet the needs of bobcats, raccoons and fish until the arrival of rainy weather.

Many birds use the holes for watering. Willow seeds take root along the edges, and fallen willow leaves later add substance to the soil. Thus, many forms of life are sustained by ‘gator holes. But poachers have been hunting the alligators almost to extinction for their valuable hides.

As a result, the number of ‘gator holes can be expected to dwindle, and various forms of Everglades wildlife may be deprived of these refuges. Such ecological findings strengthen the case for the protection of alligators.

Another ecological threat to the Everglades arose in the late 1960s, when plans were made to build a jet airport near the northern end of the national park. The airport would have wiped out part of a large swamp that furnishes the Everglades with much of its surface water. Ecologists and conservationists opposed the project, arguing that it would hamper the flow of surface water through the park and thus endanger the biota of the unique Everglades ecosystem.

Their arguments aroused public concern, and in 1970 plans for the airport were dropped.

An Ecological Mistake

Kaibab National Forest, forest in Arizona, adjoining Grand Canyon National Park; 1,780,475 acres (691,395 hectares); forest headquarters Williams, Ariz.

At times, seemingly practical conservation efforts turn out to be mistakes. Cougars, or mountain lions, and deer were once abundant in Grand Canyon National Park and Kaibab National Forest. Because the cougars preyed on the deer, hunters were allowed to shoot the cougars until only a few were left.

With their chief enemy gone, the deer of the area increased so rapidly that they consumed more forage than the Kaibab could produce. The deer stripped the forest of every leaf and twig they could reach and destroyed large areas of forage in the Grand Canyon National Park as well. The famished deer grew feeble, and many defective fawns were born. Finally, deer hunting in the Kaibab was permitted, in the hope that the size of the deer herd would drop until the range could accommodate it. In addition, the few surviving cougars were protected to allow them to multiply. They then resumed their ecological niche of keeping the herd size down and of killing those deer not vigorous enough to be good breeding stock.

The Ecological Control of Pests

Many of the insects and other pests that have plagued North America originated elsewhere. There these pests were held in check by natural enemies, and the plants and animals they infested had developed a measure of tolerance toward them. However, when they were placed in an environment free of these restraints, the pests often multiplied uncontrollably.

At first, farmers fought the pests with toxic sprays and other powerful chemicals. However, these methods were expensive, sometimes proved unsuccessful, and were often dangerous. After decades of use, some pesticides were banned. In certain instances, pesticide use gave way to an ecological approach.

Research showed that severe damage from certain pests the Mexican beetle and the European corn borer, for example is confined to crops grown on particular types of soil or under certain conditions of moisture. Changes in land use helped control some pests. Others were controlled biologically by importing parasites or predators from their native lands. This important form of pest control proved successful in limiting damage by scale insects.

By destroying birds and other animals, as well as their breeding places, people lose valuable allies in their constant war with insects. Once, when the sportsmen of Ohio supported a proposal to permit quail hunting, the farmers of the state objected. They knew that a single quail killed enough insects to make it worth at least as much to them as a dozen chickens.

In some 3,000 locally organized Resource Conservation Districts ecological principles are being used to guide land use and community maintenance practices. These districts encompass the federal lands of the United States and more than 95 percent of its privately owned farmlands.


Throughout the world man-made communities have been replacing the communities of nature. However, the principles that govern the life of natural communities must be observed if these man-made communities are to thrive. People must think less about conquering nature and more about learning to work with nature.

In addition, each person must realize his interdependence with the rest of nature, including his fellow human beings. To safeguard life on Earth, people must learn to control and adjust the balances in nature that are altered by their activities.

Maintenance of the Environment

Climate cannot be changed except sporadically by cloud seeding, inadvertently by pollution, and on a small scale by making windbreaks or greenhouses. However, human activities can be successfully adapted to the prevailing climatic patterns. Plants and animals, for example, should be raised in the climates best suited to them, and particular attention should be paid to the cold and dry years rather than to average years or exceptionally productive years. In the United States the serious dust storms of the 1930s occurred because land that was ploughed in wet years to grow wheat blew away in dry years. Much of that land should have been kept as range land

Soil is a measure of an environment’s capacity to support life. It forms very slowly but can be lost quickly as much as an inch in a rainstorm. Wise land use ensures its retention and improvement.

For agricultural purposes, land is used principally as timber land, range land, or crop land Timber land and range land are natural communities. Crop land is formed when what was originally timber land or range land is cultivated. To ensure the best possible use of land, it is classified according to its ability to sustain the production of timber, pasture, or crops.

Water, like soil, is a measure of the abundance of life. Usable water depends on the amount and retention of rainfall. An excessive run-off of rainwater, however, may result from human activities for example, the building of roads and drainage ditches; the construction of extensive parking areas and shopping centres; the unwise harvesting of timber; year-round grazing of ranges; and the cultivation of easily eroded lands. Excessive run-off may cause floods. It may also lead to drought, which can occur when too little water is stored underground. Moreover, run-off strips soil from the land. This is deposited in reservoirs, ship channels, and other bodies of water. These silt-laden bodies must then be either dredged or abandoned. Water movements in and out of the soil must be controlled in such a way as to minimize damage and maximize benefits.

The Conservation of Natural Communities

Community, in biology, a group of organisms living together in a particular environment.

The communities of plants and animals established by humans usually consist of only a few varieties, often managed in a way that harms the environment. By contrast, natural communities usually enhance the environment and still yield many products and sources of pleasure to people.

Land once cultivated but now lying idle should be restored to the natural communities that formerly occupied it. In addition, people should use the findings of ecology to improve their artificial communities such as fields, gardens, orchards, and pastures. For example, few man-made agents for the control of pests can outperform the wide variety of insect-eating birds.

The Curtailment of Waste

Modern machines and weapons and the harmful wastes of technology can be used to destroy the environment. At the same time, the wise use of machinery can also enable humans to conserve their surroundings. Just as negotiation rather than warfare can be employed to resolve international disputes, no doubt the means can be devised to curtail the destructive wastes of factories and vehicles. True, ever-growing demands for goods and services, nurtured by increasing human populations and rising expectations, are placing more and more pressure on the environment. An understanding of the causes and consequences of environmental deterioration, however, may bring about a change in the goals that people pursue and the means they use to achieve these goals.

Increases in human material possessions have been accompanied by a potentially dangerous worsening of the natural environment. A central function of ecology is to study human interactions with the natural environment in order to modify them favourably.

Assisted by E.J. Dyksterhuis, Professor of Range Ecology, Texas A & M University.


Books for Children

Jaspersohn, William. How the Forest Grew (Greenwillow, 1980).

Pringle, Laurence. City and Suburb: Exploring an Ecosystem (Macmillan, 1975).

Sabin, Francene. Ecosystems and Food Chains (Troll, 1985).

Selsam, M.E. How Animals Live Together, rev. ed. (Morrow, 1979).

Books for Young Adults

Billington, E.T. Understanding Ecology, rev. ed. (Warne, 1971).

Pringle, Laurence. Lives at Stake: The Science and Politics of Environmental Health (Macmillan, 1980).

Sharpe, G.W. Interpreting the Environment, 2nd ed. (Wiley, 1982).

Sharpe, G.W. and others. Introduction to Forestry, 4th ed. (McGraw, 1976).

CONSERVATION (Part 1 of 5)   Leave a comment

The reasonable use of the Earth’s natural resources water, soil, wildlife, forests, and minerals is a major goal of conservation. Conservation is the preservation and maintenance of the environment to meet human needs for production while insuring that proper consideration is also given to aesthetics and recreation. An effective conservation program results in a continuous production and supply of native plants and animals, and the continued availability of critical mineral resources. Timber, fuels, ores, and other resources are being depleted at such a rapid rate that the need to conserve them has become crucial. The prevention of environmental pollution from industrial, agricultural, urban, and domestic sources, including toxic chemicals, radioactive wastes, and elevated water temperatures, is another concern of conservation. People concerned with conservation seek to prevent the waste of natural resources, to maintain a high-quality environment, and to preserve the natural heritage for future generations.

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwin’s theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

2300 BC: Invention of paper In ancient Egypt paper was made from the papyrus plant. The stalk was split, sliced, pressed and dried into thin sheets. In China, a government servant named Ts’ai Lun is credited with inventing paper in AD 105. He made the paper from mulberry fibres, hemp waste, rags, fish nets, and other materials. It took many centuries for this invention to travel west: it reached Samarkand, in Central Asia, by 751 and Baghdad by 793. Finally, through Arab contacts, this technology arrived in Europe in about the 12th century. Three hundred years later the invention of printing with moveable type spurred the demand for paper in Europe. Even so, processes for making it were not technologically advanced, and shortages persisted for several hundred years. The use of wood pulp in the early 19th century greatly increased the paper supply. In the 20th century, concern over deforestation led to the growth of recycling processes for paper.

 Soot, car fumes, and acid rain pollute the air.

The world’s rain forests are being destroyed.

Toxic waste and garbage contaminate the water.

Pesticides and chemicals poison our food.

Strip mining ravages the land.

Gas and oil are wasted.

Humans have been slowly destroying the world’s resources for years.

The goal of conservation is to make the environment clean and healthy while continuing to use the Earth’s resources. This goal is gaining popularity throughout the world as all nations begin to see the results of abusing the environment.

Everyone must think seriously about the environment. Humans cannot live happy, healthy lives in an unhealthy world.

Renewable Resources can be maintained with careful planning. Examples include:

wild animals


soil and water


Non-renewable Resources will eventually be used. Examples are:

oil, coal, and gas

gold and silver



Natural resources are sometimes classified as renewable or non-renewable Forests, grasslands, wildlife, and soil are examples of renewable resources. They can be regenerated, and prudent management can maintain them at steady levels. Such resources as coal, petroleum, and iron ore are non-renewable Consumption, wasteful or not, of their limited supply speeds the rate at which they are depleted.

Every creature, large or small, plays a part in the balance of nature.

Balance of nature means the way in which everything in nature depends upon other things in nature in order to live. All of nature works well together, with one creature or plant or mineral supporting others. Sometimes it appears that the elements of nature are not working well together, for example when a volcano erupts or when lightning starts enormous forest fires. However, both of these events that may seem like total disasters are extremely helpful in that they make it possible for new habitats to be created.

In many cases, people have upset this balance of nature. The Earth’s environment can handle some of the bad things done to it, but with so many people living on the Earth, there’s no such thing as “a little bit” of damage. All people on Earth need a healthy, balanced environment.

Natural resources are a vital part of sustaining human life, and conservation measures are designed to control, manage, and preserve them so that they can be used and appreciated to the fullest. Freshwater habitats must be kept clean for drinking and for recreational activities. Soils must be kept fertile, without the accumulation of toxic chemicals from pesticides or herbicides, to provide fruits and vegetables. Forests must be managed in a manner that can provide not only lumber and pulpwood for paper products but also homes for native wildlife. The use of oil, coal, and minerals important for an industrial society must be carefully monitored to be certain that the supply does not dwindle too rapidly. The proper conservation of these natural resources is of key concern in maintaining the balance of nature in a world with a large human population.

The Abuse of Natural Resources

When the first European settlers arrived in North America, they found a continent rich in natural resources. Much of the land was covered with forests where wild animals abounded. Great herds of bison roamed the grasslands. The soil was deep and fertile. Clean lakes and streams, unpolluted with silt and chemical wastes, held a wealth of fish.

In the struggle to obtain food, clothing, and shelter the settlers cut down and burned most of the Eastern forests. As they moved westward, they ploughed up the grasslands to plant corn and wheat. Their growing cities dumped sewage and waste materials from factories into the lakes and streams.

The roots of hundreds of thousands of ground-covering plants and grasses form a sponge-like net that holds the topsoil in place and soaks up rainwater.

If this plant cover is removed:

There is no net to hold the soil down, and nothing for rain to soak into.

The good soil needed for farming and the water needed to fill underground reservoirs wash away into streams and rivers.

Flooding occurs because the rivers and streams can’t hold all of the water and soil that is washing away.

Flooding is a major problem in areas of North America where rain tends to fall quickly in heavy thunderstorms. In Europe rains usually fall slowly and gently enough not to wash away bare topsoil.

The settlers who first came to North America didn’t know that the heavy rains of America would cause so much damage to bare soil. They also had no idea that the methods they used to plough and plant crops were causing soil problems to worsen.

Much of the spring and summer rain in the United States falls in torrential thunderstorms, especially in the vast Missouri, Mississippi, and Ohio river basins. The farmers who settled the country were mainly Europeans who had been used to gentle rains. The methods of tilling and planting which they brought with them were not suited to the new climate. The land’s capacity for water storage was diminished by the loss of the grasses that hold soil in place and prevent the escape of rainwater. With the blotter like plant cover gone, many rivers flooded when the winter snows melted. During natural drought periods, wells ran dry and crops died in the fields. Dust storms blew the topsoil away. Birds and animals that once thrived in the forests and on the prairies became scarce. Some kinds vanished forever. Fish died in the unclean waters.

The Conservation of Natural Resources

The Earth’s environment will continue to become less healthy unless all nations work together to improve it. To protect our world, everyone must understand the need for conservation.

People who worry about the environment have grouped together into organizations that fight for conservation, such as:

the Sierra Club


the Nature Conservancy

the World Wildlife Fund

Many of these groups have succeeded in getting laws passed to protect land, wildlife, and other natural resources. Once laws have been passed, anyone who disobeys them can be punished.

The abuses of the past and even the present have emphasized the need for the wise use of natural resources. Conservation groups have promoted corrective legislation and instituted legal proceedings against violators. People have been made increasingly aware that their continued existence depends on these efforts to stop environmental deterioration.

Individuals have no right to destroy nature’s wealth for profit. The logging company that cuts down too many trees without replanting for the future; the industrial plant that fouls a river or pollutes the air with its wastes; the farmer who neglects his own farm and so damages his neighbour’s land are injuring their whole community. The camper whose carelessness starts a forest fire; the automobile driver who wastes gasoline; the picnickers who tear up armfuls of wild flowers or litter the landscape with their garbage; the hunter who kills more than the legal limit all are abusing natural resources. Conservation is everyone’s responsibility. It is a uniquely human problem. Stringent laws to stop the waste and destruction of natural resources must be supported and effectively enforced.


  1. Rampant streams destroy land and fail to recharge underground water sources.

  2. Bad forestry leaves timber fire-prone and causes soil erosion and flooding.

  3. Poor farming methods drain soil fertility and hasten erosion by wind and water.

  4. Sprawling, monotonous suburbs blight good land and foster obsolescence.

  5. Rural industrial parks create pollution that can affect downstream communities.

  6. Abandoned mining operations poison streams and permanently scar the landscape.

  7. Haphazard placement of industry leads to the pollution of water and air in cities.

  8. Failure to treat garbage and sewage adequately contaminates the surroundings.

  9. Bad industrial zoning downgrades nearby property and produces urban eyesores.

  10. Polluted rivers cannot sustain fish life and need costly purification for drinking.

  11. Poorly managed traffic facilities snarl urban travel and aggravate air pollution.

  12. Densely grouped high-rise apartment buildings wall out air and sunlight.

Conservation can help maintain the natural beauty of a community. When land is mistreated, the countryside can become unattractive. Vacant lots covered with trash, bare roadsides, and garbage-laden streams are ugly. Conservation also helps preserve areas suitable for recreation. As cities grow crowded, natural areas are needed for people enjoying leisure time. People need city parks, county forest preserves, and national parks; grass and trees bordering roads and highways; and sparkling streams.

Posted 2011/12/21 by Stelios in Education

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CONSERVATION (Part 2 of 5)   Leave a comment


Polluted water in one part of the world affects water sources everywhere. This happens because water moves through what is called the hydro logic cycle.

In the hydro logic cycle

1) water moves into the air and clouds as it evaporates from oceans, lakes, and rivers.

2) the winds that blow around the Earth blow the water vapour around until enough builds up inside a cloud to cause rain to fall.

3) wherever that rain falls, sooner or later it will flow into another body of water.

In this way, a water molecule that left the ocean near California may fall as rain in India. Unfortunately, products that pollute the water can also be carried to other parts of the world along with the water molecules.

Water is an essential natural resource. Everyone uses it. It is needed in homes for drinking, cooking, and washing. Communities must have it for fire protection and recreational activities such as swimming, boating, and fishing. Industries use it to produce electricity and to perform a large number of manufacturing processes.

Watersheds and Their Importance

Watershed (or drainage basin), area of land, of any size, from which all precipitation flows to a single stream or set of streams.

A watershed is the area drained by a river or a stream in a region. Such an area slopes toward a common land trough. Some rain runs off, or drains, over the ground surface. Run-off water forms small streams, which flow into larger ones. These eventually join to form rivers.

A natural watershed conserves water. It has clear streams and an ample cover of trees, grasses, and other plants. Plants help contribute to form a part of the topsoil called humus. Humus consists of decaying leaves and wood, bacteria, dead insects, and other plant and animal remains. It provides some of the nutrients for new plant life. Together with a network of roots, it acts as a blotter that soaks up rain. Plants break the force of falling rain and scatter the drops over leaves and branches. Some of the water returns to the air by evaporation. Part of the water used by plants is passed through their leaves into the air again by transpiration. The rest of the water sinks into the earth through countless tiny channels. Some of the spaces in the soil through which water percolates are caused by natural features of the geology or soil itself. Others are made by plant roots and burrowing animals like earthworms, insects, and moles.

The level at which the earth is permanently saturated is known as the water table. This vast underground water supply fluctuates with the seasons and the amount of rainfall. During long, heavy rains the soil may not be able to soak up all the water. Some of it runs off the surface, but in a forested watershed it moves slowly. Deep snow that melts slowly allows water to soak into the soil gradually.

When all the trees in an area have been cut down or burned off due to poor forestry practices, or grasses and other plants have been stripped off by fire, overgrazing, or poor farming practices, the watershed suffers. The water from rainfall flows over the ground’s surface instead of being absorbed by the vegetation and organic materials that would be present on a natural forest floor.

When there are no leaves and branches or grasses to break the force of falling rain and the blotter of roots and humus is gone, mud closes the channels through which water sinks into the soil. If the land is level, the water stands in stagnant pools; if it slopes, the water runs downhill into the rivers. Streams in a mismanaged watershed become brown with silt, or suspended soil, because the racing water carries soil along with it.

A mismanaged watershed can result in destructive floods in the spring because heavy rains and melting snows overflow the riverbanks. In the summer, streams, springs, and wells can dry up because little or no water has sunk into the underground reservoirs.

Water Pollution

Water can be polluted by many things. One of these is the topsoil or silt that washes into streams and rivers. This silt washes into streams and rivers from land that has been badly managed.

When silt washes into streams and rivers, two harmful things may happen.

1) Silt that floats in the water limits the amount of air in the water. Fish need air to breathe. When silt limits the air in the water, the fish die.

2) As the movement of water slows down, silt drops to the bottom of the stream beds

There are ways of controlling erosion of silt from land into streams and reservoirs. Conservationists try to make sure that the right steps are taken to prevent the silting of streams.

The silting of streams is one kind of water pollution. A heavy load of silt kills fish indirectly by reducing the amount of oxygen in the water. Then, as the flowing water slows, silt is deposited on stream beds Reservoirs behind dams also fill with silt unless erosion is stopped in watersheds above.

The main problem with our waterways is that they have been used as a garbage can for every kind of human waste that you might imagine.

Raw, untreated sewage contains:

  • garbage from individuals and businesses

  • waste products from industry

  • run-off from sewers

Raw sewage is unhealthy and can cause outbreaks of disease. It also severely pollutes the environment.

Raw sewage can be treated in special ways to make it less harmful to the environment. For example, poisonous metals and objects that take a long time to break down can be removed from the waste so it can break down faster.

Other kinds of water pollution have created other problems. Many waterways are used as dumps for household and industrial wastes. Some communities dump untreated sewage and garbage into the nearest streams. Industries contaminate the waterways when they discharge acids, chemicals, greases, oils, and organic matter into them. Such materials foul drinking water and endanger public health. They destroy commercial fisheries. They also make waterways unusable for recreational purposes. Leaks and spills from offshore oil wells and wrecked or damaged oil tankers have caused the widespread destruction of marine life.

A food chain is made up of plants and animals linked together like a chain. Each creature depends on the other creatures in the chain for food.

It takes many creatures at the bottom of a food chain to feed just one animal at the top of the chain.

If one link becomes weak, it affects all others in the chain. Here’s an example:

For a period of time humans sprayed a chemical pesticide called DDT on plants to kill bugs.

The DDT washed off the plants and into rivers, lakes, and streams. Fish ate the poison. Many fish died, but many others survived with traces of the poison in their bodies.

Some animals ate the poisoned fish. Still others ate poisoned insects. Finally, other creatures ate the animals that had eaten the poisoned fish and insects.

Since higher animals in the chain eat a large amount of the lower animals, each link was getting more and more DDT.

While large doses of DDT can kill, smaller doses do damage as well. For example, DDT causes the shells of bird eggs to be too thin. Many kinds of birds, such as the American bald eagle, poisoned by DDT, were unable to hatch young, and their numbers became smaller and smaller.

When conservationists and others saw the harm caused by DDT to various creatures such as the bald eagle, they reasoned that other creatures, including humans, were being harmed by the pesticide. Although the spraying of DDT was stopped by passing a law in the United States, it continues in other parts of the world.

The large-scale use of organic insecticides, herbicides, toxic metals, and pesticides, particularly DDT, has polluted streams and destroyed wildlife. Some pesticides tend to concentrate in the tissues of plants and animals in nature’s food chains. Thus organisms at the ends of these chains, including humans, may take in harmful amounts of pesticides deposited in their food supply.


Whenever land is stripped of its plant cover, soil is inevitably lost by erosion, the so-called silent thief. A single rainstorm can wash away centuries-old accumulations of soil from neglected or badly managed fields. Topsoil is an extremely valuable natural resource. Under this thin blanket of rich dirt and humus, in which plants grow best, is a less fertile material called subsoil. If the surface layer of topsoil is blown or washed away, the remaining subsoil cannot support plant life. The submarginal farms must eventually be abandoned.

Types of Soil Erosion

More than 700 million acres (283 million hectares) of agricultural land in the United States are subject to erosion. Some 230 million acres (93 million hectares) of crop land require constant supervision to control erosion caused by wind and water.

Dust storms are the evidence of wind erosion. Soil unprotected by plant cover simply blows away. During the 1930s millions of acres of farmlands were badly damaged by wind. Many fields lost from 2 to 12 inches (5 to 30 centimetres) of vital topsoil during this period. As a result, the entire southern Great Plains area was called the Dust Bowl.

One of the several kinds of water erosion is sheet erosion the wasting away of level land in thin layers. The deterioration may go on for years without being noticed, though the land yields successively smaller crops. A patch of subsoil showing through on some slight rise of ground may be the first sign that the land is nearly finished as a food producer.

Splash erosion is the washing away of soil by the direct battering of rain. Small channels dug in the soil by run-off are called rill erosion. The little rills run together, form a network of larger rills, and then develop into gullies. When gully erosion occurs, the land can become a desert.

Conservationists also recognize that livestock can overgraze a plot of land until severe soil erosion occurs. About 4 million acres (1.6 million hectares) of topsoil are lost every year through erosion, and about 85 percent of this is the result of overgrazing by livestock.

Although major losses of productive agricultural lands occurred in the first half of the 20th century due to erosion, a major concern today is the loss of natural habitats as a result of commercial development. Large tracts of productive land an estimated 1 million acres (400,000 hectares) each year are lost through road building, suburban housing and industrial site developments, and airport expansion. New dams often flood some of the most productive agricultural land and natural forest habitats.

Posted 2011/12/21 by Stelios in Education

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ENVIRONMENTAL POLLUTION (Part 2 of 2).   1 comment

Water Pollution

Since the beginning of civilization, water has been used to carry away unwanted refuse. Rivers, streams, canals, lakes, and oceans are currently used as receptacles for every imaginable kind of pollution. Water has the capacity to break down or dissolve many materials, especially organic compounds, which decompose during prolonged contact with bacteria and enzymes. Waste materials that can eventually decompose in this way are called biodegradable. They are less of a long-term threat to the environment than are more persistent pollutants such as metals, plastics, and some chlorinated hydrocarbons. These substances remain in the water and can make it poisonous for most forms of life. Even biodegradable pollutants can damage a water supply for long periods of time. As any form of contamination accumulates, life within the water starts to suffer. Lakes are especially vulnerable to pollution because they cannot cleanse themselves as rapidly as rivers or oceans.

A common kind of water pollution is the effect caused by heavy concentrations of nitrogen and phosphorus, which are used by plants for growth. The widespread use of agricultural fertilizers and household detergents containing these elements has added large amounts of plant nutrients to many bodies of water. In large quantities, nitrogen and phosphorus cause tiny water algae to bloom, or grow rapidly. When the algae die, oxygen is needed to decompose them. This creates an oxygen deficiency in the water, which causes the death of many aquatic animals. Plant life soon reduces the amount of open water. These events speed up the process of eutrophication, the ageing and eventual drying up of a lake.

Sedimentation also pollutes water. It is the result of poor soil conservation practices. Sediment fills water-supply reservoirs and fouls power turbines and irrigation pumps. It also diminishes the amount of sunlight that can penetrate the water. In the absence of sufficient sunlight, the aquatic plants that normally furnish the water with oxygen fail to grow.

Factories sometimes turn waterways into open sewers by dumping oils, toxic chemicals, and other harmful industrial wastes into them. In mining and oil-drilling operations, corrosive acid wastes are poured into the water. In recent years, municipal waste treatment plants have been built to contend with water contamination. Some towns, however, still foul streams by pouring raw sewage into them. Septic tanks and cesspools, used where sewers are not available, may also pollute the groundwater and adjacent streams, sometimes with disease-causing organisms. Even the purified effluent from sewage plants can cause water pollution if it contains high concentrations of nitrogen and phosphorus. Farm fertilizers in some regions fill groundwater with nitrates, making the water unfit to drink. Agricultural run-off containing dangerous pesticides and the oil, grime, and chemicals used to melt ice from city streets also pollute waterways.

Land and Soil Pollution

In order to sustain the continually growing human population, current agricultural methods are designed to maximize yields from crop lands In many areas, the overuse of land results in the erosion of topsoil. This soil erosion, in turn, causes the over-silting or sedimentation of rivers and streams.

One of the most hazardous forms of pollution comes from agricultural pesticides. These chemicals are designed to deter or kill insects, weeds, fungi, or rodents that pose a threat to crops. When airborne pesticides drift with the wind or become absorbed into the fruits and vegetables they are meant to protect, they can become a source of many illnesses, including cancer and birth defects.

Pesticides are often designed to withstand rain, which means they are not always water-soluble, and therefore they may persist in the environment for long periods of time. Some pests have developed a genetic resistance to these chemicals, forcing farmers to increase the amounts or types of pesticide.

The pesticide DDT provides the best-known example of the dangers of introducing synthetic chemical compounds into the environment. Chemically a chlorinated hydrocarbon, DDT was widely used for many years after World War II. At first it was highly regarded because it reduced the incidence of malaria throughout the world. Then, evidence began to show that DDT might be doing more harm than good. DDT, like other chemically stable pesticides, is not readily biodegradable. It has been found in the tissues of every organism tested for its presence. DDT is now known to affect biological activities. It reduces the rate of photosynthesis in marine phytoplankton, organisms that form the basis of most ocean food chains.

Although DDT has been banned in the United States and most other countries, it is still manufactured and used in some parts of the world. Many other pesticides also have been banned. Thousands of pesticides remain in use and, in some cases, their agricultural value may balance out their risks.

Some urban areas are beginning to experience a serious problem regarding the disposal of garbage and hazardous wastes, such as solvents and industrial dyes and inks. In many areas landfill sites are approaching their full capacity and many municipalities are turning to incineration as a solution. Giant high-temperature incinerators have become another source of air pollution, however, because incineration ashes sometimes contain very high concentrations of metals as well as dioxins, a dangerous family of chemical poisons.

One answer to the garbage problem is recycling. Some towns have passed ordinances that encourage or require residents to separate glass and aluminium cans and bottles from other refuse so that these substances can be melted down and reused. Although lightweight steel, cardboard, and paper are also economically recyclable, most industries and cities still burn or bury large amounts of scrap metal and paper products every day.

Radioactive Pollutants

Cosmic rays, highly penetrating radiations reaching the Earth from outer space.

Radioactivity has always been part of the natural environment. An example of natural radioactivity is the cosmic radiation that constantly strikes the Earth. This so-called background radiation has little effect on most people. Some scientists are concerned, however, that humans have introduced a considerable amount of additional radiation into the environment.

Since the first atomic bomb was dropped on Hiroshima, Japan, on Aug. 6, 1945, there has been an increased awareness of the environmental threat posed by nuclear weapons and radioactive fallout. Many scientists are concerned about the long-term environmental impacts of full-scale nuclear war. Some suggest that the large amounts of smoke and dust thrown into the atmosphere during a nuclear explosion would block out the sun’s light and heat, causing global temperatures to drop.

Even the testing of nuclear weapons directly affects the environment. Such tests are rarely conducted above ground or in the ocean. International concern over the effects of these tests led the United States, Great Britain, and the Soviet Union to sign the Nuclear Test-Ban Treaty in 1963.

On April 26, 1986, the Chernobyl nuclear power plant in the Soviet Union malfunctioned creating the worst peacetime nuclear disaster. Many details of the Chernobyl accident remain undisclosed, but it is known that the radioactive core of the power plant became exposed, and there was a partial meltdown, releasing large amounts of radioactive materials. Because the medical effects of exposure to nuclear radiation can take years to become apparent, it is not yet known how many additional cases of cancer, birth defects, and skin disease will have been caused by the Chernobyl accident.

Another immediate environmental problem is the disposal of nuclear wastes. Some radioactive substances have a half-life of more than 10,000 years, which means they remain radioactive and highly dangerous for many thousands of years. In nuclear physics, a half-life is the period of time required for the disintegration of half of the atoms in a sample of a radioactive substance. Science has not yet found a safe method of permanent disposal of high level radioactive wastes. Even temporary storage of these wastes is a dangerous and expensive problem. Experiments are under way to investigate the possible use of salt mines several thousand feet below the surface of the Earth as repositories for spent nuclear fuel rods and similar highly radioactive substances.

Thermal, or Heat, Pollution

While the concept of heat as a pollutant may seem improbable on a cold winter day, at any time of year an increase in water temperature has an effect on water life. Heat can be unnaturally added to streams and lakes in a number of ways. One is to cut down a forest completely. The brooks and streams that flowed through it are then exposed to the sun. Their temperatures begin to rise. As they flow into larger bodies of water, these in turn are warmed. This can kill fish and other water animals incapable of tolerating the higher temperatures.

Heat pollution is a consequence of the rising energy needs of man. As electric power plants burn fossil fuels or nuclear fuel to provide this energy, they release considerable amounts of heat. Power plants are usually located near bodies of water, which the plants use for heat-dissipation purposes. Some stretches of the Hudson River in New York no longer freeze in winter because of the flow of hot water into the river from adjacent power plants. Living things especially such cold-blooded animals as fish are very sensitive to even small changes in the average temperature. Because of the added heat in waters affected by power plants, many aquatic habitats may be undergoing drastic change. In some instances, the warmer water may cause fish eggs to hatch before their natural food supply is available. In other instances, it may prevent fish eggs from hatching at all.

In addition, a very small rise in the average temperature of the Earth’s surface could produce profound climatic changes. Some experts believe that it would cause the Greenland and Antarctic ice caps to melt, raising ocean levels and inundating large areas of land.

Average worldwide temperatures can be affected when the products of combustion carbon monoxide, water vapour, and carbon dioxide are emitted into the air, especially at high altitudes. Since the normal level of carbon dioxide in the air is quite small, any significant addition is a potential threat. Although solar energy on its way to the Earth’s surface easily passes through layers of carbon dioxide, some of the heat escaping from the Earth would be absorbed by increased amounts of atmospheric carbon dioxide, much as heat is trapped in a greenhouse. A worldwide greenhouse effect of this type might produce a dangerously warmer world. Since the late 19th century, the average global temperature has increased between 0.54°F and 1.08°F (0.3°C and 0.6°C). Internationally, 1990 was the hottest year on record since official weather records first started being kept by the British in about 1860.

Noise Pollution

The hearing apparatus of living things is sensitive to certain frequency ranges and sound intensities. Sound intensities are measured in decibels. For example, a clap of thunder has an intensity of about 100 decibels. A sound at or above the 120-decibel level is painful and can injure the ear. Noise pollution is becoming an unpleasant fact of life in cities, where the combination of sounds from traffic and building construction reverberates among high-rise buildings, creating a constant din.

In addition, the intense volume at which some popular music, especially heavy metal rock music, is played has resulted in the loss of some or all of the hearing of a few musicians and members of their audiences. There is some evidence that extreme levels of noise can produce other deleterious effects on human health and on work performance.

Efforts to Halt Pollution

The solution of some pollution problems requires cooperation at regional, national, and international levels. For example, some of the acid rain that falls in Canada is caused by smokestacks of coal-burning power plants in the United States. Thus, rejuvenating the lakes of eastern Canada requires the cooperation of electric utilities in Indiana and Ohio.

Greenpeace Foundation, international organization for the protection of the environment.

In the United States laws have been passed to regulate the discharge of pollutants into the environment. The Environmental Protection Agency (EPA), which was formed through the National Environmental Policy Act (NEPA) of 1969, oversees most federal anti pollution activity. The National Environmental Policy Act also mandated the use of environmental impact statements, which require that businesses or governments examine alternatives and acknowledge the possible harmful effects of such activities as opening new factories, building dams, and developing new oil wells. With the advent of massive oil spills from supertankers, the washing up of medical wastes on shores in New York and New Jersey, and an increased build-up of toxic wastes, such international organizations as Greenpeace have become ever more dedicated to preventing environmental abuses and heightening public awareness of environmental issues.

The Clean Air Act, the Safe Drinking Water Act, and the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (known as Super fund) are among the laws that set standards for healthy air and water and the safe disposal of toxic chemicals. In 1990 President George Bush signed the Clean Air Act of 1990, the second amending legislation since the original Clean Air Act of 1970. The new law called for reductions in emissions of sulphur dioxide and nitrogen oxide by half, carbon monoxide from vehicles by 70 percent, and other emissions by 20 percent. The number of toxic chemicals monitored by the EPA would increase from 7 to about 250, and industry would be required to control their waste release by means of the best technology available. In the same year, the California Air Resources Board introduced the strictest vehicle-emission controls in the world. By 2003 the hydrocarbon emission of all new cars sold in California would have to be at least 70 percent less than that of 1993 models, and by 1998, 2 percent of all cars (rising to 10 percent by 2003) would have to release no harmful emissions at all. Several North-eastern states followed suit by introducing similar, though slightly less severe, controls.

Assisted by John H. Thomas, professor of biology at Stanford University, and Paul J. Allen, Director of Communications at the Natural Resources Defense Council, Washington, D.C.


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