Acid Rain
Acid Rain, or acid precipitation, is a result of air pollution. When water vapour from the oceans and the land rises and enters the atmosphere it is neutral i.e. pH 7, and is almost pure. When any type of fuel is burnt, lots of chemicals are produced, which are given off as gases. Power stations, factories and cars all burn fuels and therefore emits polluting gases such as nitrogen oxides and sulphur dioxide. In the atmosphere, the tiny droplets of water react with variable amounts of carbon dioxide, sulphur dioxide and oxides of nitrogen to form various acidic compounds. These compounds then fall to the earth in either a dry form (as gases) or wet form (rain, snow and fog). The pH of rainfall can vary from as low as pH 4 to about pH 5.8. Acid Rain can cause harmful effects to the environment such as to:
1). FORESTS – Acid rain falls into a forest and runs down into the soil below. Normally most soils are already slightly acidic and are therefore particularly susceptible to the effects of acid rain. Acid rain can dissolve and wash away the nutrients and minerals in the soil preventing the trees from growing. It can also cause the release of harmful substances such as aluminium into the soil, and wear away the waxy protective coating of leaves therefore damaging them and preventing them from being able to photosynthesise. A combination of these effects weakens the trees and as a cause of this can be more easily attacked by insects and diseases or injured by the weather.
2). RIVERS AND LAKES – Acid rain runs off the land and ends up in streams and lakes. As the acidity of the water increases, the water becomes clearer but plants and animals are unable to survive. Aluminium is insoluble in water but as the acidity of the water increases, aluminium becomes more soluble and is released into the water from the soil, harming fish and other aquatic animals. Also all lakes and rivers have their own fragile ecosystem with many different species of plants and animals all depending on one another to survive. If a species of fish is killed, this can affect the whole food web e.g. the animals which feed on the extinct fish will gradually disappear.
3). BUILDINGS – Acid rain helps to erode objects quicker. Statues, buildings, pipes and cars can all suffer from this. The worst affected are things made from limestone and marble as these types of rock are particularly susceptible and can be affected by air pollution in gaseous form as well as by acid rain.
4). HUMAN HEALTH – Acid rain can also result in human health concerns. It can aggravate respiratory ailments such as bronchitis and asthma. Drinking water may also be affected due to it may containing higher levels of toxic metals which have been dissolved from soils and pipes, increasing the acidity of drinking water supplies.
Deforestation and global warming
Deforestation is the clearing of tropical forests across the Earth. This process involves the cutting down, burning and damaging of trees. If the current rate of deforestation continues, the world’s rainforests will vanish within 100 years causing many harmful effects on the environment. Deforestation occurs for mainly agricultural purposes i.e. grazing cattle and planting crops. Modern agriculture occurs on a much bigger scale, sometimes deforesting some square miles at a time. Large cattle pastures often replace rainforests to grow beef for the world market
Commercial logging is another common form of deforestation, cutting down trees for sale as timber or pulp. This type of logging uses large and heavy machinery e.g. bulldozers, to remove cut trees and build roads. However this will cause many harmful effects on the environment such as:
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Clearing and burning of rainforests release vast amounts of greenhouse gases, mainly carbon dioxide, into the atmosphere. The plants and soil of tropical forests hold 460-575 billion metric tons of carbon worldwide. When a forest is cut and burnt, the carbon that was stored in the tree trunks joins with oxygen and released as CO2. Each year deforestation contributes to 23-30% of all the carbon dioxide in the atmosphere, which is believed to be responsible for half of global warming.
- Deforestation also leads to global warming due to it destroying one of the only ways to absorb excess carbon dioxide. Through photosynthesis, forests absorb and store so much carbon dioxide. Thus while more and more carbon is released into the atmosphere, there are less and less forests to remove it and ‘lock it up’ for many years as wood.
This means that the levels of carbon dioxide are slowly increasing due to deforestation both release huge amounts of carbon into the atmosphere and destroys one of the only means to absorb and store this substance.
Methane concentrations in the atmosphere have also begun to increase by more than 140%. The primary sources for methane are an increase in rice cultivation and domestic grazing of animals e.g. cattle. Anaerobic conditions associated with rice paddy flooding results in the formation of methane while grazing animals release methane to the environment as a result of herbaceous digestion.
Due to both levels of carbon dioxide and methane increasing, these may be causing global warming by increasing ‘the greenhouse effect’. This may therefore cause an increase in the Earth’s temperature of only a few degrees Celsius. This:
- may cause quite big changes in the Earth’s climate e.g. Evaporation will increase as the climate warms, which will increase average global precipitation therefore rainstorms are likely to be more frequent
- may cause a rise in sea level. It is said the sea level may rise two feet along most the U.S coast.
Water Pollution- fertilisers and sewage
When toxic substances enter lakes, streams, rivers and other water bodies, they get dissolved or lie suspended in water or deposited on the bed. This results in the pollution of water whereby the quality of the water deteriorates, affecting aquatic animals. Water has many sources. One of the most polluting is fertilisers.
Farmers add fertilisers to soil to replace the nutrients which crops remove. However excess fertilisers may be washed into rivers and lakes. Fertilisers can increase the amounts of nitrates and phosphates in the water, which can lead to the process of eutrophication. The stages in this process are:
- the increase in the growth of water plants
- the water body becomes choked with organic substances and organisms and as a result some of these die due to competition e.g. penetration of light into the water is diminished and therefore decreases the productivity of plants and hence their production of oxygen.’
- rapid growth of microorganisms e.g. algae, which feed upon the dead organisms so that it is recycled.
- the water becomes depleted in oxygen due to the increased use of oxygen by the microorganisms for respiration. The oxygen cannot be replenished due to the lack of water plants in the darkened, deeper waters.
- lowered oxygen results in the death of fish and other aquatic animals, due to oxygen shortage.
- Further, some of the algal species that ‘bloom’ produce toxins that render the water useful. The result is a foul smelling, waste filled body of water, which has occurred in many places e.g. Baltic Sea.
Sewage is primarily organic in nature and therefore is prone to bacterial decay. As a result, untreated sewage is a source of food for microorganisms. This means that the oxygen concentration in the water will be reduced and therefore aquatic life is stared of the oxygen it needs and also leads to the breakdown of proteins and other nitrogenous compounds, releasing hydrogen sulphide and ammonia, both toxic to marine organisms. Solids suspended in sewage may also blanket river and sea beds preventing respiration and blocking light. The decaying organic matter and nutrients in sewage enhance plant growth and therefore starts the process of eutrophication.
