Environmental Degradation

<h1>Text Preview</h1> <p>Increases in the human population have had a great impact on the ecosystems of the Earth. Humans have destroyed the natural habitats of countless organisms. We continuously produce pollution that is harmful to all organisms. Humans have developed many chemicals that have been released into the environment.</p> <p>A particular chemical might not be harmful to most organisms in small amounts. But a phenomenon called biological magnification concentrates the chemical as it moves through the food chain. The insecticide DDT is a good example. Let's take a look at how the use of DDT harms the environment.</p> <p>Primary producers pick up DDT from the water or soil. Since DDT isn't excreted, the DDT concentration increases as it is passed from producers to high level consumers. Each consumer accumulates the DDT from all of the organisms it eats during its lifetime. Since humans are generally the highest level consumers, the chemicals we release into the environment to get rid of pests, can come back to harm us.</p> <p>Usually we can't see the toxic chemicals that have been released into the environment. But sometimes we can. One of the most visible types of pollution is air pollution by photochemical smog. High levels of smog are a problem for many major cities. In Los Angeles, there are "smog days," when the levels of smog are so high that it isn't safe for children to play outside during recess.</p> <p>Photochemical smog comes from the burning of fossil fuels, which generates carbon monoxide, carbon dioxide, sulfur dioxide, nitric oxide, and hydrocarbons. Nitric oxide and hydrocarbons react with sunlight to produce ozone. In the news, we usually hear about ozone depletion in the stratosphere, a problem we'll discuss in a moment. But at ground level, the presence of ozone causes respiratory and nervous system problems, harms plants, and damages plastics and rubber.</p> <p>The weather can affect the level of photochemical smog in a region. Normally, the temperature of the air decreases as we move away from the Earth. During the day, the air near the Earth is heated. The warm air rises, carrying the pollutants away. A thermal inversion can trap the smog. In a thermal inversion, the air near the ground is colder than the layer of air above it. The layer of warm air keeps the colder air from rising, trapping the smog near the Earth. Smog is also trapped in valleys, where there is less airflow to blow the pollutants away.</p> <p>We’ve seen that close to Earth, an increased level of ozone is a problem. In the stratosphere, the depletion of ozone is a problem. 50 kilometers above the Earth, the ozone layer absorbs much of the UV radiation from the sun. The depletions, called ozone holes, were first noticed in 1980. Since 1990, a 40 to 50% depletion has been observed over Antarctica every spring. Ozone holes may also develop over populated areas. Without the protective ozone layer, the risk of human skin cancer and cataracts increases because more UV radiation reaches the earth.</p> <p>Depletion of the ozone layer is caused primarily by chloride ions in the stratosphere. A chloride ion reacts with an ozone molecule to produce chlorine monoxide and molecular oxygen. The chlorine monoxide reacts with an oxygen atom to form molecular oxygen and a chloride ion. Since the chloride ion is regenerated, this is a catalytic reaction. One chloride ion can destroy as many as 100,000 ozone molecules.</p> <p>The most damaging chloride ions come from chlorofluorocarbons, which are used in aerosol sprays and refrigerants including freon. Because they destroy the ozone layer and stay in the atmosphere for a long time, many chlorofluorocarbons have been banned. However, the chloride ions already in the atmosphere will continue depleting the ozone layer for the next 30 to 100 years.</p> <p>We saw earlier that the products of combustion of fossil fuels react to form ozone. They also react with water to become acidic. Sulfur dioxide, nitric oxide, and carbon dioxide combine with water and lower the water's pH. Pure water has a pH of 7, but near urban areas, rainwater can have a pH as low as 4. This type of rain is known as acid rain. Near some cities, fog has had a pH as low as 1.7, which is close to the pH of battery acid.</p> <p>While the oxides are mainly emitted in urban areas, they can be deposited in other areas by acid rain. Acid rain lowers the pH of lakes and rivers, killing the plants and animals living there. While some organisms can survive, if the acid rain kills the less obvious organisms like invertebrates and detritivores, the entire ecosystem is affected.</p> <p>Acid rain is not the only type of water pollution. The Earth's water is polluted by trash, sewage, agricultural residue, and mining and industrial wastes. Pollutants can cause either health hazards or eutrophication. Health hazards are caused by disease causing agents, toxic chemicals, and radioactive substances. Eutrophication occurs when excess nutrients are added to the water, generally by fertilizer runoff. </p> <p>The excess nutrients cause an overgrowth of algae and plants. When the plants and algae die, the detritivores use up all the oxygen in the water for cellular respiration. As a result, aerobic organisms in the water, including fish, don't have enough oxygen, and they die.</p> <p>We've looked at how burning fossil fuels causes smog and acid rain. One of the products of combustion is carbon dioxide, which is also responsible for global warming Global warming is the increase in the average temperature of the Earth's atmosphere. Because of the burning of fossil fuels, the amount of carbon dioxide in the atmosphere has increased 25% in the last 150 years. The carbon dioxide keeps heat from escaping into space, causing the global temperature to increase.</p> <p>Water vapor also traps heat. As the global temperature increases, more water vaporizes, which raises the temperature even more. More water vapor causes an increase in precipitation in coastal regions and droughts inland. Increasing temperatures in polar regions cause glaciers to melt and sea levels to rise. This puts all coastal cities in danger of flooding.</p> <p>All of the environmental problems we've discussed so far have been caused by humans releasing chemicals into the environment. We are also harming the environment by directly destroying ecosystems. Poor land use practices can turn land that was once able to sustain agriculture into a desert. Deforestation, for logging and to clear land for other uses, displaces animals as well as destroying the plant life. Destroying tropical rain forests kills huge numbers of organisms, including ones we haven't even discovered yet.</p> <p>Let's take a closer look at how human actions threaten many species of wildlife.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>