Chapter 29A Freshwater Resources

NIOS Class 12 Environmental Science Chapter 29A

INTEXT QUESTIONS 29.1

1. What fraction of total water available on Earth is fresh water?

Ans: About 2.7%

2. Water covers about three-quarters of the Earth’s surface, but how much of it is fresh water?

Ans: More than 1400 million km³

3. Name the three resources of fresh water.

Ans: Lakes, rivers, groundwater

INTEXT QUESTIONS 29.2

1. Why does usable water require treatment?

Ans: Because water is used for drinking, bathing, washing, cleaning, etc., and to protect the health of the community.

2. Name the steps in water treatment.

Ans: Steps of water treatment

I. Clarification or sedimentation
- Coagulation and fluoridation
- Filtration
II. Disinfection
- Chlorination
- Ozone

3. What is fluorosis?

Ans: Fluorosis is a crippling and painful disease caused by the intake of fluoride.

4. How is water rid of iron at the community level?

Ans: By using a sequential process of aeration, reaction-cum-setting, and filtration. Water from the hand pump is sprinkled from the top. This will ensure contact with air for complete aeration. A major part of iron is oxidized here. Then the water is made to react with oxidizing media (limestone). The remaining iron is oxidized in this chamber. By aeration and further oxidation, the dissolved iron is converted to insoluble ferric hydroxide. The insoluble iron can thus be easily removed through filtration. Then it is passed through filter media (sand and gravel filter). The filtrate water contains iron in an acceptable range.

5. What harm does arsenic cause if consumed with water contaminated with it?

Ans: It may cause several skin disorders or even cancer.

INTEXT QUESTIONS 29.3

1. What is meant by ‘water quality’?

Ans: Water quality is defined as those physical, chemical or biological characteristics of water by which the user evaluates the acceptability of water.

2. State one example to express that concept of water quality differs with the purpose of using water.

Ans: It is based on the physical, chemical, or biological quality of water, removal of toxic substances for the sake of human health, we require a water supply by pure, wholesome, and potable.

3. Name any two major water quality issues of our country.

Ans: Water scarcity is wholesome and potable. Pathogenic pollution, oxygen depletion, etc., or any other.

4. What is eutrophication?

Ans: Enrichment of nutrients like phosphates and nitrates promotes excess growth of algae in water bodies.

5. Why do certain aquatic areas require special protection?

Ans: A large number of areas in our aquatic environment support rare species of aquatic and amphibious plants and animals, and are, therefore, ecologically very sensitive. They need special protection.

INTEXT QUESTIONS 29.4

1. State an abstractive use and an instream of water.

Ans:

The different abstractive uses include domestic water supply, irrigation, and industrial use of water.
The in-stream uses of water include hydropower, fisheries, navigation, community bathing and washing, and cattle bathing and watering.

2. Of what benefit are dams and canals drawn from rivers?

Ans: Ample water for irrigation, production of electricity.

3. State two causes of long-term ecological damage to our river.

Ans: Diversions of the river stream and long-term environmental damage, pollution.

TERMINAL EXERCISE

1. Describe the distribution of freshwater on Earth.

Ans: About 97.3% of this water is in the oceans. Of the 2.7% that is fresh, 2.14% lies frozen in the polar regions. Thus, all the water in the lakes and rivers, all the moisture in the atmosphere, soil, vegetation, and all the water underground amounts to about 0.5% of the total. Of this 0.5% (that is, liquid fresh water), more than 98% is in the form of groundwater, half of which may lie more than 1000 meters below the surface, and thus only 0.1% is in the rivers.

2. Explain in brief the water resource distribution of India

Ans:

From precipitation alone, India receives 4000 billion cubic meters (BCM), including snowfall. Of this ,3⁄4 part occurs only during the monsoon.
A good part of it is lost through the process of evaporation and plant transpiration, leaving only half of it on the land for us to use.
After allowing for evapotranspiration losses, the country’s surface flow is estimated as 1880 BCM.
Due to topographical, hydrological, and other constraints, it is assessed that only about 700 BCM of surface water can be put to beneficial use.
The annual replenishable groundwater resources are assessed to be about 600 BCM, of which the annual usable resources are estimated at 420 BCM.

3. How is water purified for drinking?

Ans: For drinking water supply, surface water is treated, whereas groundwater can be used directly with disinfection. Impurities in water are either dissolved or suspended. The drinking water treatment involves coagulation, filtration, followed by disinfection.

The suspended material reduces clarity, and the easiest way to remove it is to let the suspended particles settle.
Filtration is a physical process that removes these impurities from water by percolating it downward through a layer or bed of porous, granular material such as sand.
Microstrainers capture solids from water.
Disinfection destroys pathogenic bacteria and is essential to prevent the spread of water-borne disease. It can be used with chlorine or ozone.

4. Why is water required to be purified for drinking?

Ans: Potable water must be free of harmful microorganisms and chemicals. The water should be crystal clear, with almost no turbidity, and it should be free of objectionable colour, odour, and taste.

5. Why is groundwater safe for drinking?

Ans: Groundwater is usually free of microbes and suspended solids because of natural filtration as the water moves through soil, though it often contains relatively high concentrations of dissolved minerals from its direct contact with soil and rock.

6. How is excess fluoride removed from water?

Ans: Defluoridation at the domestic level can be carried out in a container (bucket) of about 60 litre capacity.

The bucket should have a tap 3-4 cm above the bottom for withdrawal of treated water after treatment.
The water for treatment is taken in the container, mixed with an adequate amount of aluminum sulphate (alum) solution, lime or sodium carbonate, and bleaching powder.
Alum solution is added first and mixed well.
Lime or sodium carbonate solution is then added, and water is stirred for 20 minutes, then it is allowed to settle for nearly one hour, and then withdrawn through a tap for consumption.
The settled sludge is discarded.

7. How in stream uses affect water quality?

Ans: The in-stream uses of water are as follows:

(a) Hydro-power: A potential of about 13400 MW has already been created, and three schemes with a total power potential of about 5420 MW are under construction.
(b) Fisheries: Indian water resources are extensively utilized for fish production throughout the country. India has the distinction of being the seventh largest producer of fish in the world and the second largest producer of inland fisheries after China.
(c) Navigation: Inland Waterways Traffic (IWT) (traveling or cruising by ship, boat, etc.) is adversely affected by the withdrawal of water for domestic, agricultural, and industrial uses, etc.
(d) Community bathing and washing: The entire surface water sources are being used for bathing and washing. On particular religious and cultural occasions, when millions of people take a holy dip in several stretches of our riverine system e.g. “Ganga snan”, “Kumbh mela,” etc.
(e) Cattle bathing and watering: Most of the towns and villages along the surface water sources have been using them for cattle bathing and watering/washing.
(f) Water as raw material and not a dumping ground for wastes: With the advent of industrialization and increasing populations, the range of requirements for water has increased, resulting in gradual depletion of water from its sources and degradation in its quality.

8. What are the main water quality issues in India?

Ans: The major water quality issues in the Indian context can be summarized as follows:

(a) Water scarcity: Due to uneven distribution of rainfall in time and space and ever-increasing demand for water for agricultural, industrial, and domestic activities, the water resources are over-exploited. This is resulting in the shrinking or even drying up of many water bodies for considerable periods in a year.
(b) Pathogenic pollution: Water-borne diseases are the most important water quality issues in India, as most of the surface water bodies and many groundwater sources are contaminated.
(c) Oxygen depletion: Sudden oxygen depletion causes heavy fish mortality, which occurs every year during the first flushing after the onset of monsoon.
(d) Eutrophication: Nutrients like phosphates and nitrates. These nutrients promote excess growth of algae in water bodies (algal blooms). This is not desirable for a balanced aquatic ecosystem.
(e) Salinity: The increase in groundwater and surface water salinity reduces the fitness of water for drinking or irrigation. It may also affect the ecosystem in surface water.
(f) Toxic pollution: Discharge of toxic effluents from many industries and increased use of chemicals in agriculture and their subsequent contribution to the water bodies. Many water bodies in the country are polluted due to the presence of toxic substances.
(g) Ecological health: The rare species of aquatic and amphibious plants and animals are ecologically very sensitive. They need special protection.

9. How does agricultural activity affect water quality?

Ans: Increased use of chemicals in agriculture and their subsequent contribution to the water bodies, many water bodies in the country are being polluted due to the presence of toxic substances. The uncontrolled and excessive use of fertilizers and pesticides has long-term effects on ground and surface water resources.

10. How is water quality altered due to dumping of wastes?

Ans: With the advent of industrialisation and increasing populations, the range of requirements for water has increased. This has resulted in a gradual depletion of water from its sources and degradation in its quality. Each water use, including abstraction of water and discharge of wastewater, leads to specific and generally predictable impacts on the quality of the aquatic environment.