HUMAN ACTIVITIES THAT AFFECT EARTH’S ECOSYSTEMS

Unit Overview

In the previous unit, we studied about natural occurrences and how they affected the changes in ecosystems. In this unit we will study the effect that human activity has on an ecosystem. The comparison will yield some similarities and some differences. One major difference is that humans are capable of reason and have the ability to alter their actions that may be causing harm to the environment. This study will focus on environmental effects which result from unintended chemical pollution, those which result form deliberate human activities, and those which result from accidents.

Examples of Unintended Chemical Pollution

Because we do not fully understand the interconnections between all organisms in an ecosystem, humans often introduce chemicals into the environment purposefully or without knowledge of doing so that may produce undesirable results. Sometimes these chemicals are introduced to combat a problem, such as elimination of a pest. At other times, they are the result of human activity or human error, neither of which were intended. Sometimes the results are evident immediately, but often it is years before we are aware of the results. Even with our vast knowledge of chemistry and engineering, millions of pounds of chemicals are introduced into the environment from our factories and utility suppliers everyday. Utility supplies are those industries that provide us with our water, electricity, communications, and fuels, and allow us to have our modern standard of living. Most of us want to keep our laborsaving devices and our modern technological devices, such as cell phones, computers, and DVD players, and we should consider how we can maintain these without doing damage to our planet and also to ourselves. To do so is being a responsible citizen of planet Earth.

Let’s begin by discussing how the production of electricity can affect our environment. In order to create electricity, we must have motion between a

magnetic field and a coil of wire. In order to get that motion, some form of energy is needed. In the United States, coal is used more often than other energy source. The Ohio Valley has many power generating plants because the Ohio River provides a means of transporting coal, and the water from the river is used for cooling in the production process. Coal is a fossil fuel that comes from the earth and contains many minerals. It is mostly carbon which burns, releasing carbon dioxide. However, there are other contaminants in the coal, most frequently mercury and sulfur. The sulfur produces sulfur dioxide when burned in the power plant. When released into the air and exposed to the moisture from rain or fog, weak sulfuric acid is formed. Another source of contamination is the exhaust from automobiles which contains nitrogen oxides, sometimes abbreviated as NOx. This too produces an acid, called nitric acid, when mixed with moisture in the air. When this acid rain returns to Earth, the ecosystem can suffer. Acid rain is defined as any precipitation (snow, rain, fog) that has a pH equal to or less than 5.5. On the pH scale, any number below 7 indicates an acid, and the lower the number, the stronger the acid.

The pH in the Chemistry of Nature (03:19)

Although we see little of the acid rain effects here, states to our east have noticed their lakes, in particular, are becoming more acidic, and some have lost much of the aquatic life they once sustained. Because the prevailing winds blow from west to the east in the United States, the states to the east of the electricity production have been receiving more acid rain than those where most of the sulfur and nitrogen oxides are produced. Numerous studies have been done on lakes in the Adirondack Mountains of New York state. In the mid 1980’s, about one-fourth of over 1000 lakes studied were without fish. Most of these were small, shallow lakes in the southwest part of the state and were at high altitudes where winds from the west would affect them. Those that did have fish in them had fewer varieties than before. Birds and other form of aquatic life that feed on fish, such as ducks, loons, osprey, and kingfishers, were affected. Not only was their diet affected, but in some cases the number of offspring declined.

pH values increasing acidity 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0

This diagram shows the effect of acidic water on various species of aquatic life. Since the text that is left of the diagram is difficult to read, the order from top to bottom is: rainbow trout, brown trout, brook trout, smallmouth bass, fathead minnow, pumpkinseed sunfish, yellow perch, bullfrog, wood frog, American toad, spotted salamander, clam, crayfish, snail, and mayfly. The gray indicates the pH at which that species can no longer live so they either die or move to another area.

The soil in these areas is unable to neutralize the acid. The acid dissolves aluminum and other metals from the soil that can be toxic. Some trees, such as maples, have been harmed, and the bird species that inhabits the area have been harmed. Amphibians, who spend part of their time on land and part in the water, are also affected. (See chart above.) As a means of combating the problem, planes have released a chemical, calcium silicate, over the land to neutralize the acid. This has helped solve the problem. Some trees are responding well and lakes are returning to their original acidity.

New York is not the only state to suffer from acid rain. Some New England states, parts of eastern Canada, Florida, Pennsylvania, West Virginia, and northern Virginia also have experienced some damage to the ecosystem. Not only are natural habitats harmed, but also buildings and statues made of marble or limestone can slowly be dissolved by the acid rain, destroying their beauty and weakening their structure. The Taj Mahal in India and the historic Roman artworks have suffered from acid rain. In addition to treating the areas suffering from acid rain deposits, the Environmental Protection Agency has required power plants to install equipment to remove these harmful emissions from the air and to use coal that contains a lower sulfur content.

Creature Features: Changes to Environment (05:00)

However, another contaminant of the coal used in power plants has recently been in the news. That contaminant is mercury. Since coal comes from the ground as does mercury, there are traces of mercury in coal. When it is burned, the mercury is released into the atmosphere. In can then be inhaled or end up in the ecosystem in the soil or water. There are other sources of mercury contamination: mining dust, disposal or burning of materials that contain mercury, or natural deposits in the earth. Common everyday products that contain mercury are thermometers, barometers, some electrical switches, fluorescent lights, batteries, and fungicides. Improper disposal of these can also lead to contamination. Even natural disasters, like volcanic eruptions and forest fires, can release mercury into the atmosphere. However, one-third of the releases of mercury in the United States is due to the emissions of coal-burning power plants. For this reason, fish in lakes, rivers, and streams of the Ohio Valley have rather high concentrations of mercury.

Once in the ecosystem, mercury often changes from its elemental form to methylmercury which is soluble in water and very toxic. It is in this form that it enters aquatic life. Note the diagram below, which illustrates that the mercury is first taken up by small plants and animals and then by small fish that feed on these. As larger fish feed on many smaller fish, the concentration of mercury in their bodies increases. When people eat the larger fish, they consume mercury. The more fish that are eaten, the greater the concentration of mercury in a person’s

body. Because mercury is not easily eliminated from the body, it tends to build up in the body with added consumption.

What are the Effects of High Concentrations of Mercury?

The greatest effect is on an unborn child if the mother is exposed to high levels of mercury or has accumulated a large amount of mercury in her body. Effects on the child after birth can range from delayed development (first steps, first word), lower intelligence, and altered muscle and tendon reflexes. More severe effects are deafness, blindness, cerebral palsy, mental retardation, and miscarriage prior to birth. Young children may have reduced mobility, peeling and pinkness on hands, feet, and nose, or they may be irritable and have a rapid heartbeat. For adults who inhale mercury vapor, they may have irritated lungs, cough, shortness of breath, chest pain, nausea or vomiting, diarrhea, or high blood pressure. If heavily concentrated in an adult, mercury causes tremors, impaired memory and concentration, mood changes, weight loss, problems with language, brain damage, and kidney damage. Clearly, mercury is a severe poison and should be controlled.

To decrease the amount of mercury in the environment, power producing companies are using newly developed methods to reduce emissions. In addition to the methods used to eliminate the sulfur compounds that cause acid rain, activated carbon filters are proving useful in removing the mercury. Also proper disposal of common articles around the home that contain mercury is essential. Remember, never play with mercury! To avoid contamination by ingestion (eating), limit the consumption of fish to 12 ounces a week. Pregnant women, nursing women, and young children should never eat shark, king mackerel, tile fish, or swordfish.

Another unintended effect of our mechanized, industrialized society is the emission of large amounts of carbon dioxide into the air. This gas is always given off whenever fossil fuels such as coal, natural gas, or any petroleum product is burned. Water vapor is another product of the burning of fossil fuels. These two gases along with several others (methane, nitrous oxide, and halogenated hydrocarbons) are known as greenhouse gases because they are responsible for trapping heat in the earth’s atmosphere just like the glass in a greenhouse traps heat. In part, this is a good thing because if heat were not trapped, then the earth would be too cold for us to survive.

Here’s how it works. The sun’s radiant energy enters and passes through the earth’s atmosphere, that thin layer of mixed gases around our planet. As it strikes the water and soil, some of it is reflected and radiated back to space, but some is

absorbed and changed into heat. The earth then radiates this heat as infrared radiation. We cannot see this type of radiation but it is given off by heat lamps at fast food stores and delis to keep food warm. But, instead of radiating into space, it is trapped here by the greenhouse gases. Thus, the more greenhouse gases in the atmosphere, the warmer our planet will be. As we increase the amount of carbon dioxide in our atmosphere, the warming continues. This is known as global warming, demonstrated and explained in the diagram below.

The Greenhouse Effect (Global Warming) (04:28)

Climate is the long-term average of an area’s weather. Weather includes the temperature, wind direction and speed, and amount of precipitation in the form of rain, fog, sleet, and snow. Scientists study climate to see how it affects the growth of plants and distribution of animals. They can study the past weather from records and by looking at clues in the earth such as the layers of ice in glaciers, layers of the soil, and the growth of trees by studying tree rings. They use instruments to record the present weather and keep accurate records. From all this data they have seen that in the last one hundred years, the average temperature has increased one Fahrenheit degree. That does not seem like a lot, but four of the warmest years occurred in the 1990’s. Also during the ice ages when North America was, for the most part, under glaciers, the average temperature then was only 7 degrees Fahrenheit colder than it is now! From this and other studies, scientists predict that

in the next one hundred years the average temperature will increase 2 to 6 degrees Fahrenheit. Why is this a cause for concern?

With the increase in temperatures, more of the ice in glaciers will melt. Water also expands when heated so the volume of water on Earth will increase. This will cause coastal areas to become flooded. The rivers near the ocean may become more brackish (salty) as a result, which would change the types of fish and other aquatic species in the water there. Although some places may desire to have a warmer climate, what about areas of the Earth that are already very warm? It may cause drought in those areas, producing food shortages, and heat stress for all plants and animals living there. Weather patterns may change, including rainfall, violent storms, such as hurricanes, may become more violent, and El Nino’s may become more frequent. El Nino is a change in weather patterns throughout the world due to unusually warm waters in the east Pacific Ocean. The effects of El Nino are far ranging and include flooding along the coasts of Peru, California, and Ecuador, lack of rainfall in the Amazonian rainforest, drought and wildfires in the countries of the eastern Pacific and Africa, and wetter winters in the eastern and southern part of the U.S. while the western part experiences warmer winters. When drought occurs, crop yields are low and prices go up. Many of the poor in the world suffer from severe hunger. Lack of rainfall can also lead to lack of good drinking water and, again, people’s health suffers.

El Nino and La Nina (01:41)

Wildlife also suffers from drought and weather pattern changes. The migration of birds, whales, and fish can be affected. Coral beds can become bleached due to low tides and warm water. For example, in 1998 off the coast of the state of Washington tropical fish were being caught. Droughts can increase the likelihood of fires that kill animals or cause them to move to other areas.

A study of the Amazon rainforest shows that within the last 20 years, larger trees have grown faster than the smaller trees. One explanation is that the faster growing trees in the canopy responded to the excess carbon dioxide in the air. Because plants use carbon dioxide to produce their food, they help to combat the increase in carbon dioxide in the atmosphere. The vast region of the rainforests then can perhaps help us slow our global warming.

What has caused this increase in temperatures? The answer is not easily determined because there are many factors that must be considered. The amount of radiation we receive from the sun can vary and other factors that affect climate change could also be at work. Although meteorologists have studied weather for decades, many questions remain unanswered. One thing is certain, since the Industrial Revolution around two hundred years ago, humans have created more carbon dioxide emissions. That is the time when we shifted from doing work by hand or using animals to using machines to do the work. Machines require an energy source and if that energy source is a fossil fuel, then carbon dioxide and water vapor will be given off as the fuel is burned.

What can we do to slow this process? Any time we use electricity – watch TV, listen to CD’s, use a hairdryer or microwave – we are causing more greenhouse gases to be produced. Remember that most power generating plants use coal and others use oil. When we ride in a gasoline or diesel-powered vehicle, greenhouse gases are produced. Industries use fossil fuels to run their plants so when we buy their products, we are involved in producing greenhouse gases. Methane is produced by farm animals, landfills, and in coal mines so when we eat meat or throw away objects, we are adding to the problem. Before you begin thinking there is no hope, there are ways to cut our use of energy. For example, do not leave appliances on if you are not using them and only use them when needed. When riding in a car, go with several people, or, take a bus. If possible, ride a bike or

walk. Only buy products you really need, and instead of disposing of them, try to recycle or reuse them. Buy products that are energy efficient, which are rated or designated with an “Energy Star”. Some automobiles get much better gas mileage than others, which will save on the use of gasoline. This is what you and your family can do, but still more is needed. Industries and power companies must try to further reduce their emissions. Recently, the United States has refused to sign the Kyoto Protocol which requires industrialized nations to set limits on their greenhouse gas emissions. Government officials fear that putting limits on the emissions would restrict industry and cause the economy to suffer. It is true that global warming is still being studied and all the facts are not yet known, but if newer sources of energy that did not emit carbon dioxide and water vapor could be developed, a major part of the problem would be solved. These energies include the renewable energy sources, such as wind, hydropower from falling water, solar, and geothermal from the energy in the earth.

Another source of contamination unintentionally produced by humans came from the use of chemicals that helped to solve a problem, but also created one. In the l940’s a pesticide known as DDT was widely used to keep control of insects that damaged crops and to destroy mosquitoes that carried diseases, and was very effective. Although still used in the tropics to control malaria, a disease carried by mosquitoes, it was banned in 1972 in the United States. It was found that DDT stays in the environment for an extended period of time and causes undesirable effects. It can travel many miles in organisms that contain it, by water, and by wind. Aquatic organisms and their young are most severely affected. The growth of algae is slowed and it causes the death of lake trout. Eggs of the flounder are abnormal if the fish has been exposed to DDT. Birds, especially birds of prey like the peregrine falcon, lay eggs that have shells so thin that they often break before the time to hatch so the offspring are lost. Just like the larger fish have a higher concentration of mercury than smaller ones, the birds of prey eat other animals that have been exposed to DDT which increases the concentration of DDT within them to hazardous levels. This resulted in a serious decline in these bird populations. Other birds were affected because although DDT did not injure earthworms, it was harmful to the birds that ate the worms. Mammals were also affected. Bats often died during migration; mink and shrew were highly affected with mice, voles, and

hares showing less sensitivity. The chemical takes at least 15 years to diminish in the soil. In time, we have seen the return of a healthier habitat once this pesticide was eliminated.

Another group of chemicals that has caused problems are PCB’s or polychlorinated biphenyls. They were used in electrical transformers and other electrical devices as coolants and lubricants because they did not burn and were good insulators. They were also used in paints, plastics, rubber products, and dyes. Production was stopped in 1977 because it was found that when these chemicals leaked into the environment from waste sites or old electrical equipment, they remained in the soil or in sediments at the bottom of streams and lakes for many years. It was found that animals that ingested PCB’s could develop cancer and suffer ill effects to the body’s systems. In humans, the effects are harder to predict since we cannot do laboratory studies on humans. It is thought they might possibly cause low birth weight, lower IQ, and lower growth rate. The clearest threat of contamination is by eating contaminated fish. It is theorized that PCB’s may cause some skin conditions like acne and rashes.

Another chemical that is used much less than before and which we know is quite harmful to development is lead. Lead is known as a heavy metal, and it is one of the chemical elements. Previously, it was used as a pigment in paint, glazes for ceramics, caulking, pipe solder, and gasoline. It is still used in some solder, ammunition, batteries, and as a shield for x-rays or radioactive substances. Lead attacks the central nervous system, especially in young children producing anemia, stomach aches, muscle weakness, and brain damage. Even today 4.4% of young children have elevated lead levels. What is the source? Older homes may still have lead paint on their walls. If this paint flakes off, children may eat it because it tastes sweet. If the paint is sanded or is chalky, the dust can get in the air and be breathed in. Also, young children often crawl on the floor and then put whatever they find in their mouth. Some contamination can come from the water system if solder has been used in the joints of copper pipes in the house. To avoid lead contamination, run the water at least 30 seconds before using it to flush out the pipes or use a water filter that removes lead. Paint over old paint. Do not try to remove it because the dust created is a more serious hazard. Keep floors where young children play free of dust and tracked in dirt.

Another airborne hazard that is a result of our modern mechanized society is ozone. You have probably heard that we need the ozone layer above the earth to prevent the entry of ultraviolet rays from outer space, perhaps causing skin cancer. It is true that high in our atmosphere, ozone is desirable. However, it is not

desirable to breathe. Ozone is produced from oxygen and hydrocarbons or nitrogen oxides that use the energy of sunshine or lightning. It is a gas and when breathed in, can cause shortness of breath, wheezing, and coughing. It is particularly hazardous for people who have asthma, chronic bronchitis, or emphysema. Ozone tends to be concentrated in urban areas where there is a lot of traffic. Often weather reports will issue ozone alerts. It is best then to stay inside and avoid a lot of physical effort if the ozone reading is high.

Examples of Intentional Practices that Can Harm an Ecosystem

Much of the land in the United States is devoted to agriculture, the raising of crops and animals to feed us and much of the rest of the world. Some practices in farming have led to pollution of our rivers and streams. The leading cause of pollution in our rivers and lakes is runoff, which is rainwater that flows across the surface of the earth carrying with it dissolved materials and small particles. The Mississippi River receives runoff from 31 states that produces an area of low oxygen in the Gulf of Mexico known as the dead zone. The two biggest culprits are sedimentation and animal waste. Sedimentation results from soil particles being carried by wind or water into streams or lakes, making the water cloudy. This limits the amount of sunlight that can reach the bottom where aquatic plants grow. It can also smother fish by clogging their gills. Animal waste is another problem with over one billion tons a year being produced in the United States.

An Example of Severe Erosion

Modern farming methods often have animals crowded together in pens or stock yards where their waste is also concentrated. If this enters rivers and lakes it can breed disease. In addition, as we have seen with DDT, pesticides and fertilizers can dissolve in rainwater and contaminate water, killing aquatic life.

Good farming practices can reduce these problems. There will be less runoff if plants cover soil since their roots tend to hold the soil in place. On hilly ground, farmers can plant grass crops like hay, wheat, or oats to hold the soil or utilize contour strip farming. This utilizes strips of land that are tilled and planted around the hill. In one strip a row crop like corn can be planted. Row crops leave part of the soil exposed and can contribute to erosion, but if the next strip is a grass crop, then that slows down the erosion process. No-till corn can also be planted which utilizes a technique, that does not require the ground to be plowed before planting. However, it does require the use of lots of herbicides to kill weeds and grasses. Good waste management includes having watertight areas where animal waste can be stored before it is placed on the fields for fertilizer. This reduces the need for some chemical fertilizers and can reduce runoff. Pest control that includes biological controls, such as lady bugs, as well as only using chemicals specifically when needed, can prevent further runoff problems and protect our water supply.

Mountaintop Removal as a form of strip mining, has generated a lot of controversy in the last few years, especially in states like West Virginia where coal is mined in mountainous territory. This practice started in the 1960’s and was being done on a large scale by the 1990’s. America’s demand for more electricity, the increased demand for low sulfur coal, and the development of massive drag line shovels to move the dirt have all been contributors to this increased activity. As the name implies, the top of a mountain is blasted to break up the rock which is then removed to get to the seam of coal. Because the rock is broken with space between the rock pieces, it takes up more space than it did previously. To get rid of the rock and soil, they are dumped into steep valleys. This often interferes with streambeds and contaminates streams with sediments from the mine. As a result, 7% of the Appalachian forests have been destroyed and 1,200 streams have been buried or polluted from 1985 to 2001. While the blasting is going on, wells can be disturbed and foundations of houses can be cracked. Seams of water under the ground can be disrupted creating water supply problems for some people. In addition, water is needed to wash the coal. This creates water laden with coal dust and other debris, and must be kept from entering the water supply.

The result is that many acres of the Appalachian forest are being turned into grasslands once the mining is finished and the land is leveled off (reclaimed). The wildlife that once existed in the forest has migrated elsewhere. In a state like West Virginia, where more dollars are generated from tourism than from the coal industry, some think that mountaintop removal should be banned. Some in the Mountain State want to keep the beauty of its mountains.

(above) This site is prepared by removing all the trees. Most of the lumber is chopped and used for paper products like napkins and paper towels.

(above) Huge draglines, 22 stories high, remove the blasted rock and soil from the site. Its bucket can hold 24 compact cars.

As the pictures above and below show, the land is drastically changed during the process of mountaintop removal. Because the forest has been replaced by a barren area, at least until grasses begin to grow, the threat of flooding is real. Floods have destroyed some houses and entire communities in the areas where this form of mining has been practiced. Even so the Environmental Protection Agency (EPA) does have rules regarding this practice to minimize the effects on water, fish, and wildlife. There is to be no mining within 100 feet of a stream so that no harm is done to the stream. Sediment control structures must be built to keep streams clear. Water used to wash the coal must be contained. Once mining is finished, the land must be returned to its approximate original contour, which means it should be returned to the way it once looked as much as possible. Those opposed to mountaintop removal say that these regulations are not always enforced.

(above) On the sides of the mountain, the rocks and soil (known as spoil) are placed. This creates a barren landscape instead of a forested hillside.

(above) Slurry ponds contain the water with which the coal was washed as well as coal dust, clay, and toxic chemicals. The mixture is known as sludge.

Another problem associated with coal mining is that of acid mine drainage. Acid mine drainage results when water seeps from abandoned mines, usually shaft mines that go deep into the earth, and carries with it dissolved iron, aluminum, toxic metals, and acid. The water often looks reddish-brown because of the high iron content. The source of the pollution is a result of the reaction of ground water

on iron sulfide, a compound often found in the earth. Since 1978 mine owners have been required to treat any water coming from the mine, so the problem exists today because older mines have been abandoned and are polluting the streams around them. Acid mine drainage stunts the growth of plants in the area of contamination, harms wetlands, contaminates ground water, and damages concrete and metal structures. Because the Appalachian Mountains have been heavily mined for coal, it is estimated that over 7,500 miles of streams have been affected in this area alone. Often these streams contain very little aquatic life. As the drainage water is diluted in the stream, some of the iron will fall out of solution and appear on the bottom of the stream as a rusty, orange sediment. This can be seen in parts of Wolf Run outside East Springfield, Ohio to this day.

Fortunately, this situation can be corrected. Crushed limestone can be used to neutralize the acid, but this does not remove the iron and other metals. Other chemicals like ammonia or baking soda can be used also but this is often quite expensive. Alconox, an inexpensive commercial detergent and other detergents have been used to reduce the acid. A newer, less expensive approach is the use of wetlands. Bacteria that naturally occur in the wetlands can effectively remove the metals. The plant material in the wetlands serves as a filter to remove suspended solids. These wetlands must be specifically constructed for each site, and about 15 square meters of wetland for every liter per minute of flow from the mine is needed.

(above) Acid mine drainage deposits orange sediment in stream.

(above) Wetlands are developed to clean up the water. Bacteria and plants remove acid, iron, and other toxins.

Another practice, that affects an ecosystem is clear-cutting, which is the removal of all the trees in an area that are being logged. Like mountaintop removal for mining, clear-cutting as a method of logging is also controversial. Opponents say that this practice causes erosion. Trees with their extensive root systems hold the

soil. Although some roots may remain in the soil for some time after logging, they are probably nonfunctional and do not absorb water as before. Soil that washes away, depletes the land of nutrients for growing other plants and adds sedimentation to rivers. This makes the river shallower and more likely to cause flood conditions during heavy rains. Sedimentation also causes problems for irrigation systems and hydroelectric power plants. Because the rain washes away quickly without being absorbed, it can erode roads as well.

Trees add to the humidity of an area by transpiring, a process of giving off moisture through their leaves. This adds moisture to the air which increases the amount of rainfall. Trees also create shade which cools the environment. After clear-cutting is completed, the land is more of a grassland with higher temperatures and less rainfall, and, therefore, does not have the same kinds and numbers of animals as it did before.

Extreme examples of deforestation exist. One is Madagascar, the large island off the eastern coast of Africa. This island has lost so many trees due to deforestation that when it rains, the red soil turns the rivers red. Astronauts have seen the soil being carried into the Indian Ocean from their spaceships, and have said that it looks like Madagascar is bleeding. The hurricane season of 2004 left Haiti devastated. Much of the island’s forests have been cut down and made into charcoal for cooking. When hit by the high winds and excessive rain during the hurricanes, Haiti experienced massive flooding, which destroyed houses, water supplies, and human life. When the floods recede, the mud left behind can cause disease. Precious soil is also washed into the ocean leaving the island with even fewer resources.

(above) Stream Sedimentation in the rainforest after clear-cutting.

Rainforests are being clear-cut. Since 1978 over 500,000 square kilometers of forest have been lost in the Amazon rainforest because of clearing for cattle pastures, agriculture, logging, and road construction. This area is probably lost forever as a rainforest because the land now has other uses. The logged areas are often taken over by settlers since the roads the loggers built allow them access to this part of the jungle. Closer to home, clear-cutting is happening in forests owned by the U.S. government as well as individuals. Opponents say it is lessening the biodiversity of the forest even though tree seedlings are being planted. Some loggers use pesticides to control weed growth which may be harmful to the environment. The temperature increase due to the loss of shade can change the temperature and water flow in streams. Trout require cool water temperatures that may not exist if the steam is in direct sunlight most of the day. Increased sedimentation can also occur due to erosion.

Those in favor of clear-cutting insist that this really helps the forest by removing trash trees and underbrush which lessens the chance of forest fires. They say the huge forest fires in the West every year are evidence that when forests are left to mature on their own without proper management, destruction by fire is the result. They believe the clear-cutting has the same result as fire, mainly creating areas of rebirth in the forest which maintains the health of the forest. In addition, wood products and lumber are harvested. Some loggers reseed the area in “desirable” species, such as Ponderosa pine, and claim that these trees will be ready for harvest in 80 years as opposed to 120 years if they seeded naturally. The mature forest, they argue is not very biodiverse because huge trees create so much shade that

seedlings and other vegetation cannot survive. The older trees eventually die and as they fall, destroy other trees. They then rot on the ground.

Given enough time, an area that has been clear-cut will return to forest through succession if left undisturbed. Studies have been done in Maine and it was found that within 7 to 10 years pictures taken by the Landsat satellite could not tell the difference between clear-cut land and forested land. Of course this was from a satellite miles in the sky. Perhaps the best answer as to whether a forest should be clear-cut or not lies in regulating and monitoring the results. By restricting the amount of area that can be clear-cut in any given area, by requiring good logging practices which safeguards soil and streams, and by reseeding if necessary, we may be able to keep our forests and have products, like beautiful hardwood lumber, for years to come.

Left: Signs of succession after clear-cutting in a Maine forest. Right: Blueberries are growing in the clear-cut area.

(above) Ferns and flowers are growing in the clear-cut.

(above) Young conifers are regrowing and wetlands were created by ruts caused by logging equipment.

Examples of Accidents that Affect an Ecosystem

In order to decrease our dependency upon fossil fuels and, thus, limit the amount of carbon dioxide we release into the atmosphere, other forms of energy have been developed. One of those is nuclear energy. When that phrase is uttered, we often think of the atomic bomb, which was indeed the first use made of nuclear energy. Nuclear energy requires the change of matter or substance into energy, a lot of

energy! Most of this energy is in the form of heat, but it is not without its hazards. Radioactive materials, which are required to produce this energy, are very hazardous to life because they give off invisible high energy rays and particles known as nuclear radiation. In large enough amounts, nuclear radiation can kill outright and in smaller amounts, it produces serious illnesses, such as cancer and birth defects. Realizing these dangers, governments must develop careful controls and safeguards to prevent harm to its citizens.

The United States has never had a serious accident, but it came close to it at Three Mile Island in Pennsylvania on March 28, 1979. The accident occurred due to a plumbing failure. Reactors can get very hot, so hot that the core can melt and release radioactive material into the environment. This condition is called a melt down. When the plumbing failure occurred, a valve opened to release excess pressure but failed to close, and operators were unaware of this. Water that should have been used for cooling escaped and the reactor began to heat up. Had the operators done nothing, the system would have fixed itself, but unfortunately, they shut off the emergency water supply needed to cool down the reactor. What followed was mass confusion, as sirens went off and lights blinked in the control room. Computers were overloaded with information and took over an hour to generate needed information. Phone lines were not able to handle the necessary information between operators and nuclear regulatory agencies, and the company that built the reactor. As a result government officials were not given enough information to know if they should order a mass evacuation. The end result was a terrified public that did not know whether to flee or not. Then a steam control valve leaked gases into the area around the reactor, making that part of the plant radioactive. Water was finally sent to the core to cool it down, but later a valve released a burst of radioactive gas that went into the atmosphere. It was discovered that a hydrogen bubble existed in the core. Hydrogen when mixed with oxygen is extremely explosive so there were fears that an explosion might occur. Fortunately conditions were not right for an explosion and did not happen. The bubble was gradually bled off and about a month later the plant was finally shut down. Investigation later showed that about half of the core had melted. A complete meltdown would have been disastrous. Human error seems to be at fault here, noting that if the operators had not shut down the emergency water supply, all would have been well. Also, the valve that had malfunctioned in the first place had done so eleven other times in other plants. No corrective measures or warnings had been issued. This accident was so severe that, to this date, no more nuclear power plants have been built in the U.S. Fortunately, the escaped radioactivity was of such low level that no effect has been detected in human, plant, or animal life in the region.

Basic structure of a nuclear power plant: The superheated water in the reaction vessel never mixes with the water that creates steam to run the turbine. This keeps the radiation confined to the containment structure unless accidents occur.

Unfortunately, things were much worse on April 25, 1986 at Chernobyl nuclear power plant in the USSR, which is now part of the Ukraine. This was the world’s worst nuclear accident. Thirty people were killed immediately and over 2,500 later died. During a safety test an explosion and fire blew the heavy steel and concrete lid off the reactor. The Russian government did not let the world know of the explosion initially. Instead, the country of Finland detected unusually high radiation in its atmosphere.

Investigations after the accident showed that many errors had been made – all of them avoidable and due to human action. First, the design and construction details had been altered during the construction of the reactor, making the design itself flawed, and causing steam instead of water in part of the cooling area. Water is a much better coolant than steam. During the test, safety procedures were violated so

that the cooling system could not do its job. Finally, there was poor communication between those conducting the test and the operators of the plant.

The environment suffered terribly. The cloud of radiation was blown high into the atmosphere and carried throughout the entire northern hemisphere. Immediate effects included large incidences of thyroid cancer and stress related illnesses. Pine trees died as well as other vegetation, and the number of wild animals declined. Cattails grew with three heads instead of one. Long term effects, especially in the children who were exposed, are still being studied. Genetic defects seem possible. Now animals have returned to the area even though mutations (genetic alterations) have occurred due to the large amount of radiation in the area.

(above): The concrete structure built to contain the damaged reactor at Chernobyl.

(above) The abandoned city of Pripyat with the Chernobyl power plant in the background.

(above) This is an operating nuclear power plant in Leibstadt, Switzerland. The plume of white is condensing water vapor coming from the cooling tower. Once cooled, the water is probably re-circulated to cool the

reactor.

The river on the right is probably the source of that water. The round white structure is the containment building where the reactor is located. This building is heavily reinforced with concrete, lead, and steel to contain the radioactivity. When

properly operated, nuclear power plants are less hazardous to the environment than some coal-fired power plants.

Another type of major accident is an oil spill. Huge tankers carrying thousands of tons of oil transport this fossil fuel from one continent to another. Should the ship hit rocks or an iceberg due to storms or pilot error, spills can occur. The first spill occurred in 1967 off the coast of southwest England. The ship was the Torry Canyon.

There are various ways to clean up a spill. Non-aggressive methods involve little change to the shore organisms and no removal of objects on the shore. Machines may be used to physically remove the oil floating on the water. Tools like shovels are used on shore to remove oil, asphalt patches and tar balls. An absorbent material may be used to soak up the oil and low pressure sea water is used to wash the shore. Fertilizer may be applied to stimulate bacteria that will change the oil into less harmful substances. This method is very labor-intensive and tramples the shore. Aggressive cleaning requires removal of the shore material, which may be washed and returned, washing the shore with high temperature or high pressure water, and sand blasting. Natural cleaning is accomplished by nature itself and is due to the biodegrading and dispersal of the oil. Biodegrading refers to using natural organisms such as bacteria to change the oil into simpler substances. The bacteria require oxygen, proper temperature, and adequate nutrition in order to do this. Chemicals can be used to change the oil, with this process requiring light and oxygen. Dispersal refers to the breaking up and scattering of the oil. This can take from days to 20 years depending upon how many waves hit the shore, the strength of the waves, how many cracks and crevices exist along the shoreline, how steep the shore is, what the shore is made of (clay particles would not absorb as much oil as sand), and the thickness and volume of oil spilled.

Oil Spill from the Exxon Valdez (01:29)

On March 24, 1989, the Exxon Valdez hit Bligh Reef in Prince Edward Sound off the coast of Alaska. Though not a large spill, it happened in a very remote area where wildlife was abundant. The spill was reported in the media to a great extent, and a massive cleanup began which took three years. After ten years scientists went back to study the area and record the results.

Very little oil was found on the shore except at the highest areas where waves seldom reached or in protected pockets. After even two years the mussels, barnacles, snails, and algae were back to normal. Little sediment existed on the bottom. This is partly due to the fact that the weather is harsh here with strong waves, which can quickly disperse the oil. One area, known as the Bay of Isles, was a pocket-shaped depression that originally contained a lot of oil as the picture shows. The number and kinds of species of animals declined, but after ten years as seen in the bottom photo, life is slowly returning.

(above) The Bay of Isles two and seven years after the oil spill of the Exxon Valdez.

The effect on fish and animals varied with the species. Sea lions, pink salmon, whales, porpoises, dolphins, and one-half of the 23 species of sea birds were not affected by the spill. Now over half of the ducks, gulls, raptors, and other seabirds that had been harmed are doing well. The sea otter was not so fortunate. The sea otter relies on its thick fur to keep it warm and when soaked with oil, it lost its insulating ability. Many died, but after ten years they were doing as well as before the spill because of their high rate of reproduction. Some harbor seals died and others may have relocated. Their numbers were decreasing even before the spill.

Other factors that determine how well animals are affected by an oil spill are the time of year, the weather, the location, characteristics of the animals themselves, and human activities. No doubt recovery was more successful because of the cleanup efforts.

Unit Conclusion

Humans, as part of the ecosystem, have definite affects upon that ecosystem. Sometimes these are unintentional as in the case of chemicals thought to be safe or beneficial having toxic effects on part of the ecosystem. At other times, our practices end up causing problems, and there are also accidents, often the result of human error. If we are to be good caretakers of this planet, then we must use wisdom in our use of chemicals and methods. Scientific studies should be done to determine safety considerations and the expected effect upon the environment before chemicals are used or practices are begun. We should not be wasteful of our resources, but recycle and reuse where possible. Not only do plants and animals suffer, but we often bring disaster upon our own species as well if we do not act with caution and intelligence.

Now answer questions 1 through 22.