What are the causes of soil erosion?
The causes of soil erosion are :
(i) Deforestation - The roots of the plants hold the soil particles tightly and the plants slow down the speed of flowing water thus preventing the soil from erosion.
(ii) Leaving land uncultivated for long time will cause the soil to erode.
(iii) Excessive grazing will remove the vegetation cover of the land and cause soil erosion.
(iv) Flood or heavy rains can wash away the soil and cause soil erosion.
(v) High speed winds can also carry away the top layer of the soil and cause its erosion.
List water pollutants.
Some water pollutaants are :
(i) Microorganisms e.g., protozoans, bacteria and viruses
(ii) Eggs or larvae of disease causing vectors like mosquitos.
(iii) Oil spills.
(iv) Fertilizers and pesticides.
(v) Radioactive wastes.
(vi) Industrial wastes.
(vii) Sewage disposals and domestic wastes.
When do we use the term water pollution. Give examples.
The term water pollution is used when there is :
(i) Addition of undesirable substances to water bodies. For example, addition of industrial wastes containing poisonous salts like mercury salts, pesticides, insecticides, etc. Addition of disease causing organisms, like cholera causing bacteria through sewage.
(ii) The removal of desirable substances from water bodies. For example, depletion of dissolved oxygen and nutrients which adversely affects aquatic animals and plants.
(iii) A change in temperature of water in water bodies which adversely affects the organisms living in the water bodies.
List any three human activities which would lead to an increase in the carbon dioxide content of air.
The following activities of human beings may increase carbon dioxide content of air:
(i) Burning of fossil fuels such as petrol, diesel and coal in various activities like transportation and industrial processes.
(ii) Burning of wood and charcoal for heating, cooking, etc.
(iii) Deforestation that reduces the green plant and tree population, consequently utilisation of atmospheric CO2 during photosynthesis.
What are the methods of preventing or reducing soil erosion.
The following are some methods which can prevent or reduce soil erosion:
(i) Keeping the vegetation cover on the ground which reduces soil erosion by wind and water.
(ii) Avoid overgrazing.
(iii) Afforestation, the roots of trees check the flow of running water. Trees also check speed of strong winds. Thus, prevent erosion of soil.
(iv) Intensive cropping.
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