ACID RAINS

First of all I should say that the only place on earth where pure water is found is in a laboratory. Rainwater always contains small amounts of impurities. These impurities come from dust particles or are absorbed from the gases in the air. If pure water is exposed to the air it absorbs carbon dioxide to form carbonic acid and becomes slightly acidic, dropping from pH 7 i.e. neutral, to pH 5,6. Even in remote, unpopulated areas rain can reach a pH of 4,5. However, a pH of less than 4,5 in rain is almost certainly caused by air pollution.

Acid rain is caused by the release of the sulphur dioxide and nitrous oxides. The main sources of sulphur dioxide are coal-fired power stations and metal working industries. The main sources of nitrous oxides emissions are vehicles and fuel combustion.

Sulphur dioxide reacts with water vapor and sunlight to form sulphuric acid. Likewise nitrous oxides form nitric acid in the air. These reactions take hours, or even days, during which polluted air may move hundreds of kilometers. Thus acid rain can fall far from the source of pollution.

When mist or fog droplets condense they will remove pollutants from the air and can become more strongly acid than acid rain. Even snow can be acid. Gases and particles, not dissolved in water, with a low pH can also be deposited directly onto soil, grass and leaves. It is possible that even more acidity is deposited in this way than by rain! Not much is known about this process, and it is particularly difficult to study.

There are some undoubted effects of acid rains:

•Acid rains can increase the acidity of lakes, dams and streams and cause the death of aquatic life.

•Acid rain can increase the acidity of soil, water and shallow groundwater.

•Acid rain has been linked with the death of trees in Europe and North America. In spite of a great deal of research, no one yet knows exactly how acid rain harms forests. Most of the forests of Europe consist of huge areas of one tree species. This encourages the spread of plant pests and diseases. It seems likely that acid rain weakens the trees, perhaps helped by other pollutants such as ozone, and then leaves the trees open to attack by disease. Acid rain also disrupts the availability of soil nutrients. The final death of a tree may result from a combination of stresses such as heat, cold, drought, nutrient disruption and disease.

•Acid rains erode buildings and monuments.

•Acid particles in the air are suspected of contributing to respiratory problems of people.

Scientists have many ways to solve this environmental problem. We need to use energy more efficiently at home, in our vehicles and in industry. We will have to think hard about alternative energy sources. It is possible to remove acidic emissions from coal burning, but this is very

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expensive. It may be possible to breed crops and trees that resist pollution, but this would only be a partial solution. In practice we will probably need a combination of all these ideas and innovations.

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WHAT IS THE GREENHOUSE EFFECT?

The greenhouse effect is unquestionably real; it is the essential for life on the Earth. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they trap heat) and reradiation downward of a part of that heat. Greenhouse gases are:

•Carbon dioxide. Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned.

•Methane. Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.

•Nitrous oxide. Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.

Naturally occuring greenhouse gases also include water vapour, ozone and few other gases.

Without a natural greenhouse effect, the temperature of the Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C).

Human activity has been increasing the concentration of greenhouse gases in the atmosphere. There is no scientific debate on this point. Preindustrial levels of carbon dioxide (prior to the start of the Industrial Revolution) were about 280 parts per million by volume (ppmv), current levels are about 370 ppmv and the expected level for the year 2065 is 560 ppmv. Since the beginning of the Industrial Revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%.

Scientists apologize that the increasing of the concentration of greenhouse gases and chemicals in the atmosphere lead to the global warming.

Global warming is a changing of the climate on the Earth that made life on the Earth possible.

What are the potential effects of rising temperatures? Why do we call global warming an environmental problem? In general scientists believe that rising temperature will lead to increase evaporation and therefore to more precipitation. But while some regions will experience increased

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rainfall, others will become dryer. Another effect is the rise of the sea levels, which will result in flooding low-lying coastal areas. This may also lead to increasing the salinity of the rivers and to decrease of water supplies. And finally climate changes may cause extinction of many species of birds, animals and plants. Even now a lot of species of animals, birds, fish and plants have either disappeared completely or on the verge of extinction.

Solutions to global warming - clean energy, energy efficiency and new environmentally sound technologies - already exist. The latest report from the International Panel on Climate Change (IPCC) says that hundreds of technologies are already available, at very low cost, to reduce climate damaging emissions and that government policies need to remove the barriers to these technologies.

Implementing these solutions will not require humans to make sacrifices or otherwise impede their quality of life. Instead, they will enable people to usher in a new era of energy, one that will bring economic growth, new jobs, technological innovation and, most importantly environmental protection.

Wind power is already a significant source of energy in many parts of the world. It can supply 10 percent of the world's electricity within two decades.

Solar power has been growing in a global capacity by 33 percent annually. Greenpeace and industry research shows that with some government support, the solar industry could supply electricity to over 2 billion people globally in the next 20 years.

By 2040 solar photovoltaics could supply nearly 25 percent of global electricity demand.

A report conducted by global financial analysts KPMG shows that solar power would become cost competitive with traditional fossil fuels if the production of photovoltaic panels was increased to 500 megawatts a year.

A renewable power plant in Asia could have the same costs and provide the same jobs as a coal-fired plant, but with significant environmental advantages.

Greenfreeze refrigeration technology, which is safe for the climate and the ozone layer, has spread around the world. It is an ideal solution for developing countries where cost and efficiency are particularly important.

Oil companies must stop exploring for more fossil fuels that the world cannot afford to burn. Governments need to subsidize renewable energy and force polluters to pay.

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AGRICULTURAL ECOSYSTEMS AND AGRICULTURAL

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ECOLOGY

Ecosystem as Landscape Building Block

The term "ecosystem" was first proposed by Tansley (1935) as a name for the interaction system comprising living things together with their nonliving habitat. He regarded the ecosystem as not only the organism complex, but also the whole complex of physical factors forming what we call the environment. It was first applied to levels of biological organization represented by unites such as community and the biome. Odom (1952) and Evans (1956) expanded the extent of the concept to include other levels of organization.

An Agroecosystem Model

What are the basic components of agroecosystems? Just as natural ecosystems they can be thought of as including the processes of primary production, consumption, and decomposition interacting with abiotic environmental components and resulting in energy flow and nutrient cycling. Economic, social, and environmental factors must be added to this primary concept because of the human element that is so closely involved with agroecosystem creation and maintenance.

Agroecosystem Characteristics

Agricultural ecosystems (referred to as agroecosystems) have been described by Odum (1984) as domesticated ecosystems. He states that they are in many ways intermediate between natural ecosystems (such as grasslands and forests) and fabricated ecosystems (cities).

Agroecosystems are solar powered (as are natural systems) but differ from natural systems in that:

1. there are auxiliary energy sources that are used to enhance productivity; these sources are processed fuels along with animal and human labor;

2. species diversity is reduced by human management in order to maximize yield of specific foodstuffs (plant or animal);

3. dominant plant and animal species are under artificial rather than natural selection; and,

4. control is external and goal-oriented rather than internal via subsystem feedback as in natural ecosystems.

Agroecosystems do not happen without human intervention in the landscape. Therefore, creation of these ecosystems (and maintenance of them as well) is necessarily concerned with the (human) economic goals of production, productivity, and conservation. Agroecosystems are controlled, by definition, by management of ecological processes.

Crossley, et al, (1984) addressed the possible use of agroecosystem as a unifying and in many ways clarifying concept for proper management of managed landscape units. All ecosystems are open, that is, they exchange biotic and abiotic elements with other ecosystems. Agroecosystems are extremely open — with major exports of primary and secondary production (plant and animal production) as well as increased opportunity for loss of

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