WATER A WONDER LIQUID

Natural resource of Class 9

Water occupies a very large area of the Earth’s surface and is also found underground. It is one of the basic necessities of life needed for various activities such as drinking, bathing, washing, etc. It is also needed for irrigation of crops, industries and for navigation.

It is renewable resource. Like air, water is vital to life since for all physiological activities of plants and animals, it is essential. Water is mainly present in two forms:

  1. Surface water.
  2. Ground water.

Types of water resources

Water resources can be classified into two types i.e.

  1. Fresh water resources
  2. Salt water resources
  3. Fresh Water Resources

Fresh water resources range from ponds to lakes and large rivers.

It has following characteristics

  • Fresh water is exhaustible; however it is being made available again by oceans through hydrological cycle.
  • 77.2 % of fresh water is stored in glaciers and ice caps and 22.4 percent is ground water and soil moisture. Remaining 0.36 percent is found in lakes, rivers, streams and swamps etc. Out of total water evaporated from oceans 90 per cent falls to the oceans and remaining 10 per cent falls on the land. This water is utilised by various terrestrial ecosystems.
  • Fresh water is essential for life on earth as well as for survival of human race.
  • The total water in hydrosphere is 1.4 billion cubic kilometers (km)3. Total 97% is ocean water. The ocean water cannot be consumed by human beings. Remaining three percent (fresh water) is available for human consumption.
  • The water resources in India have an average run off in river system of 1,869 km3 and 432 km3 ground water.

Salt Water Resources

India has a very long coast line hence, it has a large source of salt water of seas and oceans.

Oceans can be used in following aspects:

  • Mineral concentrates in the form of mineral nodules can be used for the source of various minerals.
  • To build offshore terminals for ships etc.
  • As a source of food and other edible animals mainly fishes.
  • Shells of mollusks are source of calcium and quicklime’s.
  • For the production of many useful products such as algin, agar, carrageenan, diatomitic etc.
  • It is used for commercial navigation and shipping.
  • For generating power from sea tides.

RAIN WATER HARVESTING

It is a technique used to capture and store rain water by making special water-harvesting structures so that there is an increase in the recharge of underground resources. Dug-out wells, percolation pits, check dams and lagoons can do this job.

Adva​ntages of rain water harvesting

  1. It reduces the run-off loss of rain water.
  2. It is helpful in controlling floods.
  3. It helps to check soil erosion.
  4. It helps to raise the water table.

NECESSITY OF WATER

Water is necessary for the growth and sustenance of both plant and animal lives. Water makes up a large percentage of animal and plant cells.

Importance of water in human life

  • Water dissolves all salts and nutrients present in the food.
  • An aqueous medium is required to carry out all the metabolic reactions.
  • Water helps in regulating our body temperature.
  • Water is required for removal of waste products.

Importance of water in plant life

  • Water helps in germination of seeds and growth of plants.
  • Green plants require water during photosynthesis.
  • Water provides a medium for the transport of minerals and food.

Water pollution and control measures:

The water pollution is caused by the addition of organic and inorganic chemicals as well as the biological materials which change the physical and chemical properties of water. This harmful process is called as water pollution. The water pollution is caused by many sources such as sewage matter, industrial wastage, agricultural wastage, domestic wastage, not water of thermal plants and nuclear reactors etc. water pollution can be caused by the following man made sources :

  1. Household detergents:The household detergents include the compounds ofphosphate, nitrate, ammonium and alkylbenzenesulphonate etc. harmful substances which are gathered in water. Alkyl benzene sulphonate (ABS) is not degradable, so that its concentration increases which is harmful for aquatic life.
  2. Control measures:For the control of this pollution lime, ferric chloride etc. are used to precipitate the phosphate. Zirconium is considered best for this purpose.
  3. Sewage: Sewage contains highest amount of carbonic materials and biological materials. These carbonic materials increase the number of decomposers like bacteria and fungus. The rate of reoxygenation reduced as compared to deoxygenaion in a water reservoirs. The acceleration of microbial activity increases the BOD of water. BOD is very less in pure water. The higher BOD is the indication of water pollution and the water of polluted reservoir can not be utilized and produces a very bad smell spreading around the locality. The infection or disease also takes place. Daphnia and some fishes are sensitive to water pollution and show the intensity of water pollution.
  4. Control measures: To control the water pollution of sewage water it should be left into reservoir after the primary and secondary treatment. The big particles are mainly separated in primary treatment through floatation and sedimentation. Micro organisms are used for secondary treatment such as oxidation chamber or activated sludge process. Oxidation chamber is a shallow reservoir in which the sewage is stored. Algae and bacteria grow very well because of the higher amount of carbonic materials in it. Bacteria decomposes the organic materials and produce CO2 which is utilized by the algae in photosynthesis. Oxygen released by photosynthesis protects the water pollution. Therefore oxidation pond is the example of symbiosis in between algae and bacteria. The infectious bacteria are destroyed during the activity (reactions) in the oxidation pond. So that the simple substances are left after decomposition of organic matter.
  5. Industrial wastes : the wastes of industries are discharged into the running water, rivers and canals, industrial wastes mainly contain inert suspended particles such as dust, coal, toxins like acid, base, phenols, cyanides, mercury, zinc etc., inorganic materials like-ferrous salts, sulphides, oils and other residues of organic material and hot water. The water polluted by mercury, lead etc. causes disorganization of nervous system. It means it produces insanity. The minamata disease is caused in Japan by eating of mercury polluted fishes. So many people died because of this disease.
  6. Control measures: The industrial wastes and toxic components should be made pure before releasing into rivers, lakes, ponds or sea. So that the water pollution of industrial effluents can be controlled by suitable treatment to remove the pollutants.
  7. Bioaccumulation of pesticides: Pesticides like DDT(dichlorodiphenyltrichloroethane) are poisonous chemicals sprayed on crops to protect them frompests and diseases. This increase in concentration of harmful non-biodegradable chemical substances in the body of living organisms at each trophic level of a food chain is called biological magnification.
  8. Eutrophication: the discharger of sewage water and detergents in water bodies promotes excessive growth of phytoplanktons (minute aquatic algae). This excessive growth causes reduction in oxygen level of water. The excessive growth of phytoplanktons brings about a reduction in dissolved oxygen which affects other aquatic organisms. Consequently potential sources of food are highly reduced.

Q. What is the role of water in the life of plants and animals ?

Ans. Water plays several roles in the life of plants and animals

  • In plants water is needed for the germination of seeds, for photosynthesis, for absorption and transport of minerals, nutrients and fertilizers from the soil.
  • In animals water is the chief component of blood and other body fluids.
  • Water is required for the transport of gases and nutrients, for excreting waste materials and for reproduction and development in several animals.
  • For animals like fish, many invertebrates, several bacteria and algae water is the medium in which they live.
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