Автор: Пользователь скрыл имя, 14 Июня 2012 в 00:07, курс лекций
курс лекций по экологии на английском языке
1. What is soil?
Soil is one of our most fundamental and precious resources. Like clean air and water, life cannot survive without healthy soil. Since over 95% of our food comes from the land one way or another, managing soils so they remain healthy and productive is a matter of survival.
Franklin Delano Roosevelt, 32nd President of the United States, understood this. During the 1930s, Roosevelt wrote to state governors, “The nation that destroys its soils, destroys itself”. In the 1930s, the Great Plains, stretching from Texas into Canada, experienced an extended drought with 65% less rainfall than normal. Years earlier farmers had cleared the Great Plains of native prairie grasses and replaced them with miles and miles of wheat. Native prairie grasses could have survived the drought and preserved the soil, but wheat could not and repeated crop failures left soils bare. The land was literally swept away (in 1938 an estimated 850 million tons of topsoil!) by windstorms, creating the Dust Bowl. The United States no longer has a dustbowl, but the issue of soil degradation has not gone away. And with an increasing world population to feed, no doubt conserving and restoring our soil will only become more important.
Soil is just dirt, right? Well, not quite. Pick up a handful and really study it. Now, a pop quiz: is that handful of soil you hold living or dead? Any answers? It is kind of a trick question – soil is both alive and dead, a miniature ecosystem thriving beneath our feet.
The nonliving part of soil is made of weathered rocks and minerals plus the decayed remains of plants and animals (known as organic matter or humus) and air and water. But a healthy soil is also teeming with life. It is loaded with small animals (insects, worms), plants, fungi, bacteria and other microbes. A typical soil is 50% mineral and organic matter and 50% air and water that fill the soil pores spaces and sustain all the living organisms in the soil.
There are literally thousands of different types of soils around the world, but all do four main things to help sustain all life:
· Regulate and help control where rainfall and snowmelt goes. Without healthy porous soils, rainfall and snowmelt quickly runs off instead of soaking into the land. Soils also store water.
· Filter, buffer, degrade, detoxify and/or immobilize chemicals moving through the soil. Minerals and microbes in the soil perform this function as water percolates through soil and can clean water of potential pollutants.
· Sustain plant and animal life. Without healthy soil, the land would be barren of plants and thus animals (including humans) because almost all living organisms depend on plant productivity.
· Store and cycle nutrients essential for life (carbon, nitrogen, phosphorous, oxygen, hydrogen and many other trace elements). As plants and animals die (or produce wastes), vital nutrients go back into the soil where they are recycled by soil organisms and taken up by plants for another go around the “circle of life”. The soil food web is extremely diverse and essential for this cycling of nutrients.
Few realize the importance of these soil functions to our continued survival, so we tend to take soil for granted. This lack of awareness has led to problems for the soils. Around the world, soil is being degraded by erosion, desertification, compaction, salinization, nutrient depletion, and chemical pollution. While some of these processes are natural, human activities can and do aggravate them.
2. Services Supplied by Soil
Soil represents an important component of a nation's assets, one that takes hundreds to hundreds of thousands of years to build up and yet very few years to be lost. Some civilizations have drawn great strength from fertile soil; conversely, the loss of productivity through mismanagement is thought to have ushered many once flourishing societies to their ruin. Today, soil degradation induced by human activities afflicts nearly 20 percent of the Earth's vegetated land surface.
In addition to moderating the water cycle, soil provides five other interrelated services. First, soil shelters seeds and provides physical support as they sprout and mature into adult plants. The cost of packaging and storing seeds and of anchoring plant roots would be enormous without soil. Human-engineered hydroponic systems can grow plants in the absence of soil, and their cost provides a lower bound to help assess the value of this service. The costs of physical support trays and stands used in such operations total about US$55,000 per hectar.
Second, soil retains and delivers nutrients to plants. Tiny soil particles (less than 2 microns in diameter), which are primarily bits of humus and clays, carry a surface electrical charge that is generally negative. This property holds positively charged nutrients—cations such as calcium and magnesium—near the surface, in proximity to plant roots, allowing them to be taken up gradually. Otherwise, these nutrients would quickly be leached away. Soil also acts as a buffer in the application of fertilizers, holding onto the fertilizer ions until they are required by plants. Hydroponic systems supply water and nutrients to plants without need of soil, but the margin for error is much smaller—even small excesses of nutrients applied hydroponically can be lethal to plants. Indeed, it is a complex undertaking to regulate the nutrient concentrations, pH, and salinity of the nutrient solution in hydroponic systems, as well as the air and solution temperature, humidity, light, pests, and plant diseases. Worldwide, the area under hydroponic culture is only a few thousand hectares and is unlikely to grow significantly in the foreseeable future; by contrast, global cropped area is about 1.4 billion hectares.
Third, soil plays a central role in the decomposition of dead organic matter and wastes, and this decomposition process also renders harmless many potential human pathogens. People generate a tremendous amount of waste, including household garbage, industrial waste, crop and forestry residues, and sewage from their own populations and their billions of domesticated animals. A rough approximation of the amount of dead organic matter and waste (mostly agricultural residues) processed each year is 130 billion metric tons, about 30 percent of which is associated with human activities (derived from Vitousek et al. 1986). Fortunately, there is a wide array of decomposing organisms—ranging from vultures to tiny bacteria—that extract energy from the large, complex organic molecules found in many types of waste. Like assembly-line workers, diverse microbial species process the particular compounds whose chemical bonds they can cleave and pass along to other species the end products of their specialized reactions. Many industrial wastes, including soaps, detergents, pesticides, oil, acids, and paper, are detoxified and decomposed by organisms in natural ecosystems if the concentration of waste does not exceed the system's capacity to transform it. Some modern wastes, however, are virtually indestructible, such as some plastics and the breakdown products of the pesticide DDT.
The simple inorganic chemicals that result from natural decomposition are eventually returned to plants as nutrients. Thus, the decomposition of wastes and the recycling of nutrients—the fourth service soils provide— are two aspects of the same process. The fertility of soils—that is, their ability to supply nutrients to plants—is largely the result of the activities of diverse species of bacteria, fungi, algae, crustacea, mites, termites, springtails, millipedes, and worms, all of which, as groups, play important roles. Some bacteria are responsible for "fixing" nitrogen, a key element in proteins, by drawing it out of the atmosphere and converting it to forms usable by plants and, ultimately, human beings and other animals. Certain types of fungi play extremely important roles in supplying nutrients to many kinds of trees. Earthworms and ants act as "mechanical blenders," breaking up and mixing plant and microbial material and other matter (Jenny 1980). For example, as much as 10 metric tonnes of material may pass through the bodies of earthworms on a hectare of land each year, resulting in nutrient rich "casts" that enhance soil stability, aeration, and drainage.
Finally, soils are a key factor in regulating the Earth's major element cycles—those of carbon, nitrogen, and sulfur. The amount of carbon and nitrogen stored in soils dwarfs that in vegetation, for example. Carbon in soils is nearly double (1.8 times) that in plant matter, and nitrogen in soils is about 18 times greater. Alterations in the carbon and nitrogen cycles may be costly over the long term, and in many cases, irreversible on a time scale of interest to society. Increased fluxes of carbon to the atmosphere, such as occur when land is converted to agriculture or when wetlands are drained, contribute to the buildup of key greenhouse gases, namely carbon dioxide and methane, in the atmosphere. Changes in nitrogen fluxes caused by production and use of fertilizer, burning of wood and other biomass fuels, and clearing of tropical land lead to increasing atmospheric concentrations of nitrous oxide, another potent greenhouse gas that is also involved in the destruction of the stratospheric ozone shield. These and other changes in the nitrogen cycle also result in acid rain and excess nutrient inputs to freshwater systems, estuaries, and coastal marine waters. This nutrient influx causes eutrophication of aquatic ecosystems and contamination of drinking water sources—both surface and ground water— by high levels of nitrate-nitrogen.
3. PROBLEMS WITH SOIL
Erosion by wind and water is a natural process, but humans do many things to make it worse with poor agricultural and land use practices. Soil that is not covered by plants is particularly susceptible to wind and water erosion. Overgrazing by livestock, excessive plowing, and removing all crops and crop residue at the end of the growing season leaves soils bare and vulnerable to wind and water. Deforestation, especially clear-cutting, can leave the land denuded and a prime target for erosion. Poor construction and building practices, such as completely removing all natural plant communities to build homes, malls and other projects, also contribute to erosion. Just visit a local construction site after a rainstorm to see erosion in process.
Desertification can occur in grassland regions that are subjected to continual overgrazing by livestock and even natural animal populations. Too many animals feeding on the grasses will actually kill usually hardy grasses. Bare soils will lose topsoil to wind and water erosion leaving only sand behind. Droughts, common in the semiarid climate of most grasslands, can intensify this process. Large sections of Africa and Asia are at great risk for desertification, but so is the western United States.
Compaction results when soils are compressed by heavy machinery (and sometimes large herds of grazing animals). Soils become less porous and lose their ability to retain water. Water will run off severely compacted soils and few plants can grow in them.
Stalinization can occur where soils are continually irrigated. Irrigation waters contain dissolved salts (as do all soils). When irrigation water evaporates, the salts are left behind. In poorly drained soils, the salts are not washed away and begin to accumulate in the topsoil. Plants cannot grow in soil that is too salty.
Nutrient depletion occurs because agriculture disrupts the normal cycling of nutrients through the soil food web when crops are harvested. This removes all the nutrients and minerals they absorbed from the soil while growing. In a natural system, as plants die, they remain in place and decay releasing nutrients back to the soil. Farmers know this and must use fertilizers (organic and synthetic) to maintain soil nutrients, or soils would lose their ability to grow crops. Certain soils, such as those in the tropical rainforest, are especially susceptible to nutrient depletion when cleared for agricultural use. Farmers must clear new lands in only a few years, as soils become depleted and unable to grow food.
Pollution occurs because of the literally billions of pounds of chemicals (pesticides and fertilizers) we douse our soil with every year (almost a billion pounds of pesticides each year in the United States alone). These chemicals can disrupt the soil food web, reduce the soil’s biodiversity and ultimately ruin the soil. The chemicals also runoff the soil into surface waters and move through the soil polluting groundwater. And do not just blame farmers for the problem. Anyone with a lawn may be a big contributor, too. According to the Department of Agriculture, in the United States, lawns take up more land than any other single crop and are treated with four to ten times more pesticides per acre than farms.
Write these in English:
Главными источниками загрязнения являются:
1) Жилые дома и бытовые предприятия. В числе загрязняющих веществ преобладает бытовой мусор, пищевые отходы, фекалии, строительный мусор, отходы отопительных систем, пришедшие в негодность предметы домашнего обихода; мусор общественный учреждений – больниц, столовых, гостиниц, магазинов и др.
2) Промышленные предприятия. В твердых и жидких промышленных отходах постоянно присутствуют те или иные вещества, способные оказывать токсическое воздействие на живые организмы и их сообщества. Например, в отходах металлургической промышленности обычно присутствуют соли цветных и тяжелых металлов. Машиностроительная промышленность выводит в окружающую среду цианиды, соединения мышьяка, бериллия. При производстве пластмасс и искусственных локон образуются отходы бензола и фенола. Отходами целлюлозно-бумажной промышленности, как правило, являются фенолы, метанол, скипидар, кубовые остатки.
3) Теплоэнергетика. Помимо образования массы шлаков при сжигании каменного угля с теплоэнергетикой связано выделение в атмосферу сажи, несгоревших частиц, оксидов серы, в конце концов оказывающихся в почве.
4) Сельское хозяйство. Удобрения, ядохимикаты, применяемые в сельском и лесном хозяйстве для защиты растений от вредителей, болезней и сорняков. Загрязнение почв и нарушение нормального круговорота веществ происходит в результате недозированного применения минеральных удобрений и пестицидов. Пестициды, с одной стороны, спасают урожай, защищают сады, поля, леса от вредителей и болезней, уничтожают сорную растительность, освобождают человека от кровососущих насекомых и переносчиков опаснейших болезней (малярия, клещевой энцефалит и др.), с другой стороны – разрушают естественные экосистемы, являются причиной гибели многих полезных организмов, отрицательно влияют на здоровье людей. Пестициды обладают рядом свойств, усиливающих их отрицательное влияние на окружающую среду. Технология применения определяет прямое попадание на объекты окружающей среды, где они передаются по цепям питания, долгое время циркулируют по внешней среде, попадай из почвы в воду, из воды в планктон, затем в организм рыбы и человека или из воздуха и почвы в растения, организм травоядных животных и человека.
Вместе с навозом в почву нередко попадают болезнетворные бактерии, яйца гельминтов и другие вредные организмы, которые через продукты питания попадают в организм человека.
5) Транспорт. Каждый автомобиль выбрасывает в атмосферу в среднем в год 1 кг свинца в виде аэрозоля. Свинец выбрасывается в выхлопными газами автомобилей, осаждается на растениях, проникает в почву, где он может оставаться довольно долго, поскольку слабо растворяется. Наблюдается ярко выраженная тенденция к росту количества свинца в тканях растений. Автотранспорт в Москве выбрасывает ежегодно 130 кг загрязняющих веществ на человека.
Почву загрязняют нефтепродуктами при заправке машин на полях и в лесах, на лесосеках и т.д. Самоочищение почв, как правило, - медленный процесс. Токсичные вещества накапливаются, что способствует постепенному изменению химического состава почв, нарушению единства геохимической среды и живых организмов. Из почвы токсические вещества могут попасть в организмы животных, людей и вызвать тяжелейшие болезни и смертельные исходы.
Good farmers and ranchers develop conservation plans to maintain the health of their land. You can, too, no matter how big or small your yard is (even if you do not have a yard at all!). Conserving the land is everyone’s responsibility and necessary for future generations.
Simple Things You Can Do Right Now
1) Think organically and buy locally. Shop at you local farmer’s market for produce and other products. Support small family farmers using sustainable practices. 2) Start a compost pile with yard and kitchen waste and use it as mulch around your landscaping. It enriches your soil, better than the bags of synthetic fertilizer you buy at the garden store and it’s free! It also protects soil from erosion, prevents weeds, and conserves moisture. 3) Stop trying to kill every weed in your lawn. While you neighbors may dislike your dandelions, think of how much the rest of your soil food web will benefit. 4) Have your soil tested for nutrient levels before fertilizing and apply only the nutrients needed. Try to use natural fertilizers rather than synthetic fertilizers. Most importantly, do not overfertilize your landscape. Excess nutrients just runoff, polluting the water and wasting your money. 5) Leave grass clippings on your lawn. If you have a mulching mower, you can even let leaf clippings remain. They will decompose adding organic matter back to your soil.
Somewhat More Involved But Easier Than You Might Think
1) Accept fruits and vegetables with a few blemishes. Picture perfect produce requires massive amounts of pesticides and fertilizer.
2) Reduce the amount of lawn you have. Plant native wildflowers and grasses and create your own little prairie. You can cut down on fertilizer and pesticide use (and the amount of time you waste mowing!). 3) Plant groundcovers around your home where erosion is likely to occur, such as steep hillsides. 4) If your community does not have a yard waste composting program, help organize one. 5) If you see major wind or water erosion at a construction site, report it to the company and your local soil conservation service.
For Those “Marching for the Cause”: Things that Will Earn You a “Green” Star
1) Use only organic pesticides or biological controls (think ladybugs – they eat 50 to 75 aphids per day!) around your home and in your yard.
2) Join a community supported agriculture farm. You supply money (and sometimes labor) to a family farm in return for a share of the crops. You take on part of the risk of farming during bad years, but share in the bounty during good years. Besides, it is good to know how your food is grown and kids love visiting “their farm” every week to pick up the goodies. 3) Plant rows of trees as windbreaks around your property. They reduce erosion by slowing down the wind and even capture dust that is in the air. 4) Install drip irrigation systems in your landscape. They conserve water and get water directly to the plants where they need it most, the roots.
5. What is Air Pollution?
Air is the ocean we breathe. Air supplies us with oxygen which is essential for our bodies to live. Air is 99.9% nitrogen, oxygen, water vapor and inert gases. Human activities can release substances into the air, some of which can cause problems for humans, plants, and animals.
There are several main types of pollution and well-known effects of pollution which are commonly discussed. These include smog, acid rain, the greenhouse effect, and "holes" in the ozone layer. Each of these problems has serious implications for our health and well-being as well as for the whole environment.
One type of air pollution is the release of particles into the air from burning fuel for energy. Diesel smoke is a good example of this particulate matter. The particles are very small pieces of matter measuring about 2.5 microns or about .0001 inches. This type of pollution is sometimes referred to as "black carbon" pollution. The exhaust from burning fuels in automobiles, homes, and industries is a major source of pollution in the air. Some authorities believe that even the burning of wood and charcoal in fireplaces and barbeques can release significant quantities of soot into the air.
Another type of pollution is the release of noxious gases, such as sulfur dioxide, carbon monoxide, nitrogen oxides, and chemical vapors. These can take part in further chemical reactions once they are in the atmosphere, forming smog and acid rain.
Pollution also needs to be considered inside our homes, offices, and schools. Some of these pollutants can be created by indoor activities such as smoking and cooking. In the United States, for example, people spend about 80-90% of their time inside buildings, and so their exposure to harmful indoor pollutants can be serious. It is therefore important to consider both indoor and outdoor air pollution.
6. Outdoor Air Pollution
For each city, the exact causes of pollution may be different. Depending on the geographical location, temperature, wind and weather factors, pollution is dispersed differently. However, sometimes this does not happen and the pollution can build up to dangerous levels. A temperature inversion occurs when air close to the earth is cooler than the air above it. Under these conditions the pollution cannot rise and be dispersed. Cities surrounded by mountains also experience trapping of pollution. Inversion can happen in any season. Winter inversions are likely to cause particulate and carbon monoxide pollution. Summer inversions are more likely to create smog.
Smog is a type of large-scale outdoor pollution. It is caused by chemical reactions between pollutants derived from different sources, primarily automobile exhaust and industrial emissions. Cities are often centers of these types of activities, and many suffer from the effects of smog, especially during the warm months of the year. (Additional information about smog and its effects are available from Environment Canada and the Air Quality Management District (AQMD) in southern California).
Another consequence of outdoor air pollution is acid rain. When a pollutant, such as sulfuric acid combines with droplets of water in the air, the water (or snow) can become acidified . The effects of acid rain on the environment can be very serious. It damages plants by destroying their leaves, it poisons the soil, and it changes the chemistry of lakes and streams. Damage due to acid rain kills trees and harms animals, fish, and other wildlife. (The U.S. Geological Survey (USGS), the Environmental Protection Agency (EPA), and Environment Canada are among the organizations that are actively studying the acid rain problem).
The Greenhouse Effect, also referred to as global warming, is generally believed to come from the build up of carbon dioxide gas in the atmosphere. Carbon dioxide is produced when fuels are burned. Plants convert carbon dioxide back to oxygen, but the release of carbon dioxide from human activities is higher than the world's plants can process. The situation is made worse since many of the earth's forests are being removed, and plant life is being damaged by acid rain. Thus, the amount of carbon dioxide in the air is continuing to increase. This buildup acts like a blanket and traps heat close to the surface of our earth. Changes of even a few degrees will affect us all through changes in the climate and even the possibility that the polar ice caps may melt. (One of the consequences of polar ice cap melting would be a rise in global sea level, resulting in widespread coastal flooding.) (Additional resources and information about the Greenhouse Effect and global warming are available from the Environmental Defense Fund (EDF), the Science Education Academy of the Bay Area (SEABA) and the Society of Environmental Journalists (SEJ).
Ozone depletion is another result of pollution. Chemicals released by our activities affect the stratosphere , one of the atmospheric layers surrounding earth. The ozone layer in the stratosphere protects the earth from harmful ultraviolet radiation from the Sun. Release of chlorofluorocarbons (CFC's) from aerosol cans, cooling systems and refrigerator equipment removes some of the ozone, causing "holes"; to open up in this layer and allowing the radiation to reach the earth. Ultraviolet radiation is known to cause skin cancer and has damaging effects on plants and wildlife. (Additional resources and information about the ozone depletion problem are available from the National Oceanic and Atmospheric Administration (NOAA) and Ozone ACTION)
7. Indoor Air Pollution
Many people spend large portion of time indoors - as much as 80-90% of their lives. We work, study, eat, drink and sleep in enclosed environments where air circulation may be restricted. For these reasons, some experts feel that more people suffer from the effects of indoor air pollution than outdoor pollution.
There are many sources of indoor air pollution. Tobacco smoke, cooking and heating appliances, and vapors from building materials, paints, furniture, etc. cause pollution inside buildings. Radon is a natural radioactive gas released from the earth, and it can be found concentrated in basements in some parts of the United States.
Pollution exposure at home and work is often greater than outdoors. The California Air Resources Board estimates that indoor air pollutant levels are 25-62% greater than outside levels and can pose serious health problems.
Both indoor and outdoor pollution need to be controlled and/or prevented.