Flooding is also another effect of deforestation. Eroded soil may be deposited in rivers and streams (silting) blocking the flow of water. Rainwater is not retained and released slowly as trees have been removed. The water levels in rivers rise rapidly. Water flows inland causing floods to occur.
Desertification is another effect of deforestation. Sunlight falls directly onto the soil. Water evaporates rapidly from the soil which then hardens. With the topsoil eroded, plant life cannot be supported. Other organisms, which depend directly or independently upon plants for food, also disappear. The land becomes barren. The destruction of land leading to desert – like conditions is called desertification. Overgrazing also leads to desertification because the vegetation cannot be replenished fast enough. Desertification results in a loss of habitats, an extinction of many species of organisms, loss of robust wild species of plants that may be useful in treating disease e.g. Madagascar periwinkle used in cancer treatment, the delicate balance between oxygen and carbon dioxide becoming upset and climatic changes.
A climatic change is one of the effects of deforestation. In the forest, rainwater is retained and absorbed by the roots of trees. The water is lost during transpiration. The relative humidity of the air around the forest is high. The water vapour eventually condenses and precipitates as rain. When the trees are cleared the area becomes dry and warm and annual rainfall decreases.
One aspect of conservation is the prevention of indiscriminate cutting down of forests. Forests, a major source of oxygen, help to moderate the weather, and provide shade and protection for the soil. In many countries governments have set aside forests reserves. Laws that prohibit tree falling, hunting and other human activities that might harm the forest ecosystem protect these forest reserves. Laws that ensure that trees for timber are cut down selectively and at a regulated rate protect the remaining forests worldwide. Young trees and seed trees are not felled. New seedlings are planted to replace those trees that were cut down for timber. The forestry departments look after forest reserves and ensure that forest conservation laws are obeyed. They check the trees regularly and help control insects and diseases that harm them. Scientist in forestry departments carry out research to improve the quality of forest trees and make the forest more productive. These measures that are implemented help to reduce rapid deforestation. These methods also make sure that trees that are cut down, the land is used for good purposes.
Air pollution is another example of global impact. Pollution has been a problem to man for many years. It is the process by which harmful substances are added to the environment. As human population increases and as society becomes more industrialized and urbanized, the problem of pollution has become more serious. Many of the products of modern technology are toxic. These toxic wastes find their way into the air and water, threatening lives of organisms in the ecosystem. Therefore, the sources of pollution must be identified and techniques devised to prevent and reduce pollution. Air pollution results mainly from the incomplete burning of fuels such as coal, oil, petrol and wood. The gaseous pollutants introduced into the air may be due to human activities or natural occurrences such biological decay, forest fires or volcanic eruptions. Air pollution due to human activities include exhaust fumes from motor vehicles, chimney fumes from factories where fossil fuel is burnt, burning of garbage and the use of chlorofluorocarbons in foam packing.
Harmful pollutants released include sulphur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide and lead. These have many effects on the environment and on humans.
Burning of fossil fuel e.g. coal, oil and natural gas, releases sulphur dioxide and oxides of nitrogen into air. Sulphur dioxide at high concentrations has damaging effects on both plants and animals. Sulphur dioxide penetrates the leaves through the stomata. This damages the leaves and kills the plants. In certain parts of North America, smelting works have produced sulphur dioxide at such high concentrations that the entire vegetation has been completely destroyed. In humans, sulphur dioxide irritates and damages the sensitive lining of the eye, air passages and lungs. Prolonged exposure to the gas is linked to respiratory diseases. Sulphur dioxide and oxides of nitrogen react with oxygen and rainwater readily to form sulphuric acid and nitric acid. Rain containing these acids is known as acid rain. The death of fish in lakes and rivers of some countries has been attributed to large amounts of acid rain in such countries. Acid rain dissolves aluminium salts in the soil and washes them into rivers and lakes. These salts may reach a concentration that is poisonous to fishes.
The main source carbon monoxide is from exhaust of motor vehicles. Carbon monoxide combines with haemoglobin in the red blood cells to form carboxyhaemoglobin. This reduces the capacity of the blood to transport oxygen round the body. This is harmful and may be fatal in high concentrations.
Lead may be present in the air, water and the food we eat. Lead poisoning occurs when lead accumulates in the body over long periods. High concentrations of lead in the body may cause cramps, loss of control of the hands and feet, and even coma and death. Urban air contains a much higher concentration of lead than rural air.
The burning of organic compounds releases carbon dioxide into the air. Industrialization and increasing car pollution result in carbon dioxide being released in increasing concentrations into the atmosphere. The gas forms a layer over the earth’s surface retaining the heat radiated from the earth’s surface. This is called greenhouse effect. The result may be global warming. The possible effect is that world temperature may rise. Iceberg may melt, releasing a lot of water into the oceans. The sea level may rise and many low-lying countries may be flooded or submerged.
Chlorofluorocarbons are non-toxic, unreactive chemicals. They are used as aerosol propellants, as cooling agents in refrigerators and air – conditioners and in foam packing. Ozone is a gas that forms a layer over the earth. It absorbs much of the ultraviolet rays from the sunlight. When CFC’s are released into the atmosphere from aerosols, etc, they break down the ozone layer, allowing more ultraviolet light to penetrate into the earth. This increases the risk of skin cancer.
There are many ways of reducing air pollution. While pollutants from natural causes e.g. from volcanic eruptions cannot be avoided, those from human activities can be prevented or reduced. The following are some ways by which air pollution can be reduced: Use of catalytic converter in cars, less use of cars e.g. having car pools, use filters or scrubbers on chimney to remove sulphur dioxide, use of non- fossil fuels in factories or less use of fossil fuels especially near more densely populated areas, use of alkalis to neutralize acidic waste products from factories before they are released to the environment and use ozone- friendly products to prevent ozone depletion.
