←
General Science Supplement for Forest Beat Officer · Chapter 7

Environment, Pollution and Water Management

What to remember

  • An ecosystem has biotic (living) and abiotic (non-living) parts linked by food chains, energy flow and nutrient cycles. Energy flows one way; nutrients cycle.
  • Pollution is the addition of harmful substances to air, water or soil beyond natural limits. Each pollutant has a known source, effect and control method.
  • Water management means conserving, harvesting and cleaning water. Watershed development, rainwater harvesting and wastewater treatment are the key tools.

Ecosystem basics

An ecosystem is a community of living things interacting with their physical environment. Parts:

  • Producers: green plants and algae that make food by photosynthesis.
  • Consumers: herbivores (primary), carnivores (secondary and tertiary), omnivores.
  • Decomposers: bacteria and fungi that break down dead matter and return nutrients to the soil.

A food chain is a single path of food transfer, for example grass → grasshopper → frog → snake → eagle. A food web is many food chains linked together. The steps are trophic levels.

Ten percent law: only about 10 percent of the energy at one trophic level passes to the next. The rest is lost as heat in respiration. So food chains are short, usually three to five levels.

Biomagnification: harmful chemicals such as DDT and mercury that do not break down become more concentrated at each higher level of the food chain. Top carnivores are affected most.

CycleKey processKey organisms
Carbon cyclePhotosynthesis takes in CO₂; respiration and burning release itPlants, animals, microbes
Nitrogen cycleFixation, nitrification, denitrificationRhizobium, nitrifying bacteria
Water cycleEvaporation, condensation, precipitationNot applicable

Types of ecosystem: forest, grassland, desert, aquatic (pond, lake, river, ocean, estuary) and artificial (crop field, aquarium). Mangroves grow in saline tidal coasts and protect the shore from storms. The Godavari and Krishna deltas have mangrove stretches along the Andhra Pradesh coast.

Biodiversity and conservation

Biodiversity is the variety of living things at gene, species and ecosystem levels. In-situ conservation protects species in their natural habitat: national parks, wildlife sanctuaries, biosphere reserves, sacred groves. Ex-situ conservation protects species outside the habitat: zoos, botanical gardens, seed banks, gene banks. Hotspots are regions rich in species that are also threatened. The Western Ghats is a global hotspot. The Eastern Ghats, which cross Andhra Pradesh, hold important forests.

Threats: habitat loss, poaching, pollution, invasive species and climate change. Endangered species are listed in the Red Data Book. Wildlife is protected in India under the Wildlife (Protection) Act, 1972.

Air pollution

Major air pollutants: carbon monoxide, sulphur dioxide, oxides of nitrogen, particulate matter, ozone at ground level, lead, and volatile organic compounds.

  • Carbon monoxide (incomplete combustion) binds with haemoglobin and cuts oxygen supply.
  • Sulphur dioxide and nitrogen oxides cause acid rain, which has pH below 5.6. It damages buildings, soil, forests and lakes. The Taj Mahal marble is attacked by acid rain.
  • Particulate matter (PM2.5, PM10) harms lungs.
  • Smog is smoke plus fog. Photochemical smog forms in sunlight from vehicle exhaust.

Greenhouse effect: gases such as carbon dioxide, methane, nitrous oxide, water vapour and CFCs trap heat in the atmosphere. Increase in these gases causes global warming, melting of ice, sea level rise and changing rainfall.

Ozone layer: it lies in the stratosphere and absorbs harmful ultraviolet (UV-B) radiation. Chlorofluorocarbons (CFCs) damage it. The Montreal Protocol controls ozone-depleting substances. The Kyoto Protocol and the Paris Agreement deal with greenhouse gases.

Water pollution and water quality

Sources: sewage, industrial effluents, agricultural runoff with fertilisers and pesticides, oil spills, and thermal discharge.

  • BOD (biochemical oxygen demand) is the oxygen needed by microbes to break down organic matter in water. High BOD means more pollution and low dissolved oxygen. Clean water has low BOD.
  • Eutrophication: too many nutrients (nitrates and phosphates) cause algal bloom. When the algae die, decomposition removes oxygen and fish die.
  • Waterborne diseases: cholera, typhoid, dysentery, hepatitis A. Fluoride in excess causes fluorosis; arsenic in excess causes toxic effects.
  • Mercury poisoning in Japan was called Minamata disease. Cadmium poisoning was called Itai-itai.
  • Drinking-water pH is between about 6.5 and 8.5.

Soil, noise and solid waste

  • Soil pollution results from excess fertiliser, pesticides, plastics, and mining waste. Soil erosion is reduced by afforestation, contour ploughing and terracing.
  • Noise is measured in decibels (dB). Long exposure to loud noise causes hearing loss.
  • Solid waste: biodegradable waste (food, leaves) can be composted. Non-biodegradable waste (plastic, glass) needs recycling. E-waste from old electronics contains lead and mercury and needs special handling. Sanitary landfills, composting, vermicomposting and incineration are the common methods.
  • Biogas is made from cattle dung and organic waste by anaerobic digestion. It contains mostly methane.

Water management

Key ideas: conserve, harvest, treat and reuse.

MethodDescription
Rainwater harvestingCollecting and storing rain from roofs or land in tanks or recharge pits
Check damsSmall barriers across streams to slow water and recharge groundwater
Percolation tankPond that lets water soak into the ground
Drip irrigationWater delivered drop by drop at plant roots; saves water
Watershed managementTreating an entire drainage area with soil and water conservation

Traditional systems such as tanks (cheruvu), step wells and ponds have supported villages for centuries. Rivers like the Godavari and Krishna support irrigation and drinking supply across Andhra Pradesh, and the Polavaram project is a major irrigation scheme on the Godavari. Groundwater is a shared resource and must not be over-extracted.

Treatment of drinking water: sedimentation, coagulation with alum, filtration, then disinfection with chlorine. Sewage treatment has primary (screening and settling), secondary (biological, using microbes) and tertiary stages. Treated water can be reused for gardens and industry. Hardness is reduced by boiling (temporary hardness) or by adding washing soda.

Laws and bodies

  • Water (Prevention and Control of Pollution) Act, 1974. Air (Prevention and Control of Pollution) Act, 1981. Environment (Protection) Act, 1986.
  • Forest (Conservation) Act, 1980 controls diversion of forest land.
  • The Central Pollution Control Board and State Pollution Control Boards enforce pollution laws.
  • World Environment Day is on 5 June. World Water Day is on 22 March. Earth Day is on 22 April.

Climate and forests

Forests act as carbon sinks: trees take in carbon dioxide during photosynthesis and store carbon in wood and soil. Cutting and burning forests releases this stored carbon and adds to global warming. Afforestation means planting trees where there was no forest; reforestation means replanting where forest was cut. Forests also check soil erosion, hold rainwater, protect catchments and give shelter to wildlife.

Forest fires damage soil and wildlife. Fire lines (cleared strips) and early warning by satellite help to control them. Many wild animals and plants in the Eastern Ghats and Nallamala forests depend on healthy forest cover and clean streams.

Human impact and sustainable living

Sustainable development means meeting present needs without harming the ability of future generations to meet theirs. Ways to live sustainably: save electricity, use public transport, avoid single-use plastics, compost kitchen waste, plant trees and conserve water. Renewable energy from the sun, wind, water and biomass cuts carbon emissions. Using an energy-efficient LED bulb instead of an incandescent bulb saves electricity.

Exam traps

  • 1. Producers are the first trophic level; herbivores are the second.
  • 2. About 10 percent of energy passes to the next level, not 90 percent.
  • 3. Biomagnification increases concentration up the chain; it is not dilution.
  • 4. Ozone depletion is from CFCs; global warming is from greenhouse gases like CO₂ and methane.
  • 5. High BOD means polluted water, not clean water.
  • 6. In-situ means in the natural habitat; ex-situ means outside it (zoo, seed bank).
  • 7. Acid rain has pH below 5.6, not below 7 only.
  • 8. Eutrophication is caused by excess nutrients, not by lack of them.

One-liners

  • 1. Ozone absorbs UV-B radiation.
  • 2. The Montreal Protocol deals with ozone-depleting substances.
  • 3. Carbon monoxide reduces oxygen carrying capacity of blood.
  • 4. Biogas is mainly methane.
  • 5. DDT shows biomagnification.
  • 6. World Environment Day is 5 June.
  • 7. Mangroves protect coasts.
  • 8. Rhizobium fixes nitrogen in legume roots.
  • 9. Alum is used for coagulation in water treatment.
  • 10. Chlorine is used to disinfect water.
  • 11. Drip irrigation saves water.
  • 12. Decomposers are bacteria and fungi.

Worked examples

  • 1. Energy at the fourth level if producers hold 10,000 J: 10 percent each step gives 1,000 J, 100 J, then 10 J. The fourth level has 10 J.
  • 2. A solution has [H⁺] = 10⁻⁵ mol/L: pH = 5, which is acidic like acid rain (below 5.6).
  • 3. A pond receives 2,000 L of water with BOD of 6 mg/L: oxygen needed = 2,000 × 6 = 12,000 mg = 12 g.
  • 4. Roof area 100 m² and rainfall 0.05 m: volume = 100 × 0.05 = 5 m³ = 5,000 L (ignoring losses).

Practice questions

  1. Green plants in an ecosystem are called

    1. consumers
    2. parasites
    3. decomposers
    4. producers
    Answer

    D. producers

    Plants make food by photosynthesis.

  2. Bacteria and fungi that break down dead matter are

    1. producers
    2. herbivores
    3. carnivores
    4. decomposers
    Answer

    D. decomposers

    They return nutrients to the soil.

  3. Increase in concentration of a non-degradable chemical at higher trophic levels is called

    1. bioremediation
    2. biomagnification
    3. photosynthesis
    4. eutrophication
    Answer

    B. biomagnification

    DDT and mercury are classic examples.

  4. Which layer of the atmosphere contains the ozone layer?

    1. Thermosphere
    2. Mesosphere
    3. Stratosphere
    4. Troposphere
    Answer

    C. Stratosphere

    Ozone in the stratosphere absorbs UV-B.

  5. Which chemicals are mainly responsible for ozone layer depletion?

    1. Nitrogen
    2. Methane
    3. Carbon dioxide
    4. Chlorofluorocarbons
    Answer

    D. Chlorofluorocarbons

    CFCs release chlorine atoms that destroy ozone.

  6. Which international agreement controls substances that deplete the ozone layer?

    1. Basel Convention
    2. Ramsar Convention
    3. Kyoto Protocol
    4. Montreal Protocol
    Answer

    D. Montreal Protocol

    The Montreal Protocol targets ozone-depleting substances.

  7. Which gas, produced by incomplete combustion, reduces the oxygen-carrying capacity of blood?

    1. Carbon dioxide
    2. Carbon monoxide
    3. Methane
    4. Nitrogen
    Answer

    B. Carbon monoxide

    CO binds haemoglobin strongly.

  8. Acid rain has a pH value lower than about

    1. 8.5
    2. 7
    3. 5.6
    4. 6.5 to 8.5
    Answer

    C. 5.6

    Normal rain is slightly acidic at about 5.6.

  9. Acid rain is mainly caused by oxides of

    1. calcium and sodium
    2. argon and neon
    3. carbon and hydrogen
    4. sulphur and nitrogen
    Answer

    D. sulphur and nitrogen

    SO2 and NOx form sulphuric and nitric acids.

  10. Excess nitrates and phosphates in a lake cause

    1. ozone depletion
    2. biomagnification
    3. eutrophication
    4. acid rain
    Answer

    C. eutrophication

    Algal bloom then oxygen depletion.

  11. A high BOD value of a water sample indicates

    1. very clean water
    2. high dissolved oxygen only
    3. hard water
    4. heavy organic pollution
    Answer

    D. heavy organic pollution

    Microbes need more oxygen to decompose more organic matter.

  12. Which is the main gas in biogas?

    1. Oxygen
    2. Methane
    3. Nitrogen
    4. Hydrogen
    Answer

    B. Methane

    Anaerobic digestion of dung produces methane.

  13. Conservation of species in their natural habitat is called

    1. in-situ conservation
    2. ex-situ conservation
    3. captive breeding
    4. gene banking
    Answer

    A. in-situ conservation

    National parks and sanctuaries are examples.

  14. Which of these is an ex-situ conservation method?

    1. Biosphere reserve
    2. Wildlife sanctuary
    3. Botanical garden
    4. National park
    Answer

    C. Botanical garden

    It protects plants outside their natural habitat.

  15. Which chemical is used to coagulate suspended particles in water treatment?

    1. Chlorine
    2. Alum
    3. Sodium hydroxide
    4. Common salt
    Answer

    B. Alum

    Alum makes particles clump and settle.

  16. Which chemical is commonly used to disinfect drinking water?

    1. Sand
    2. Alum
    3. Chlorine
    4. Lime water
    Answer

    C. Chlorine

    Chlorine kills germs.

  17. World Environment Day is observed on

    1. 5 June
    2. 16 September
    3. 22 March
    4. 22 April
    Answer

    A. 5 June

    22 March is World Water Day.

  18. Which Act of India deals with control of water pollution?

    1. Air Act, 1981
    2. Water (Prevention and Control of Pollution) Act, 1974
    3. Forest Conservation Act, 1980
    4. Wildlife Protection Act, 1972
    Answer

    B. Water (Prevention and Control of Pollution) Act, 1974

    It created the pollution control boards.

  19. Drip irrigation helps in

    1. soil erosion
    2. increasing runoff
    3. flooding fields
    4. saving water
    Answer

    D. saving water

    Water is given drop by drop at roots.

  20. If the energy at the herbivore level is 500 J, the energy available to the secondary carnivore is

    1. 5 J
    2. 0.5 J
    3. 50 J
    4. 500 J
    Answer

    A. 5 J

    Next level 50 J; one more step gives 5 J.

  21. A water sample has [H+] = 10^-4 mol/L. Its pH is

    1. 10
    2. -4
    3. 4
    4. 7
    Answer

    C. 4

    pH = -log10 [H+] = 4.

  22. A water sample has a pH of 9. What is its [H+] in mol/L?

    1. 9
    2. 10^-9
    3. 10^9
    4. 10^-5
    Answer

    B. 10^-9

    [H+] = 10^-pH.

  23. The BOD of a water sample is 5 mg/L. How much oxygen in mg is needed for 1,000 L of this water?

    1. 5 mg
    2. 500 mg
    3. 50 mg
    4. 5,000 mg
    Answer

    D. 5,000 mg

    5 mg/L x 1,000 L = 5,000 mg.

  24. A roof of area 50 m2 receives 0.04 m of rain. The volume collected, ignoring losses, is

    1. 2,000 litres
    2. 200 litres
    3. 20,000 litres
    4. 2 litres
    Answer

    A. 2,000 litres

    50 x 0.04 = 2 m3 = 2,000 L.

  25. A rainwater tank holds 6,000 litres. How many cubic metres is this?

    1. 60
    2. 6
    3. 0.6
    4. 600
    Answer

    B. 6

    1,000 L = 1 m3.

  26. A 200 m2 catchment gets 0.1 m of rain with a runoff coefficient of 0.8. The water collected is

    1. 160 m3
    2. 8 m3
    3. 16 m3
    4. 20 m3
    Answer

    C. 16 m3

    200 x 0.1 x 0.8 = 16.

  27. If a food chain is grass -> grasshopper -> frog -> snake -> eagle, how many trophic levels are there?

    1. 5
    2. 4
    3. 3
    4. 6
    Answer

    A. 5

    Each organism is one level.

  28. Sound level is measured in

    1. pascals
    2. decibels
    3. hertz only
    4. lux
    Answer

    B. decibels

    The decibel scale measures sound intensity.

  29. If an energy of 1,000 J is available at the producer level and a loss of 90 percent occurs at each step, energy at the fourth level is

    1. 0.1 J
    2. 100 J
    3. 10 J
    4. 1 J
    Answer

    D. 1 J

    1,000 -> 100 -> 10 -> 1.

  30. A pond of 2,500 L has dissolved oxygen of 8 mg/L. The total dissolved oxygen is

    1. 2,000 mg
    2. 8,000 mg
    3. 20,000 mg
    4. 200 mg
    Answer

    C. 20,000 mg

    2,500 x 8 = 20,000 mg.

  31. Which is a greenhouse gas?

    1. Helium
    2. Argon
    3. Neon
    4. Methane
    Answer

    D. Methane

    Methane traps heat in the atmosphere.

  32. Mangroves are best suited to

    1. dry grasslands
    2. salty coastal tidal areas
    3. deserts
    4. high mountains
    Answer

    B. salty coastal tidal areas

    They tolerate salt and protect coasts.

  33. Which bacteria in root nodules of legumes fix atmospheric nitrogen?

    1. Rhizobium
    2. Streptococcus
    3. Escherichia
    4. Lactobacillus
    Answer

    A. Rhizobium

    Rhizobium lives in legume root nodules.

  34. Which of these is a biodegradable waste?

    1. Plastic bags
    2. Aluminium cans
    3. Glass bottles
    4. Vegetable peels
    Answer

    D. Vegetable peels

    Food waste is broken down by microbes and can be composted.

  35. Consider the statements. 1. Energy flows in one direction in an ecosystem. 2. Nutrients cycle between living and non-living parts. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are standard statements.

  36. Consider the statements. 1. CFCs damage the ozone layer. 2. Carbon dioxide is the main ozone-depleting gas. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    CO2 is a greenhouse gas, not the main ozone depleter.

  37. Consider the statements. 1. A high BOD means cleaner water. 2. A high BOD means more organic pollution. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    High BOD indicates heavy pollution.

  38. Consider the statements. 1. In-situ conservation protects species in their natural habitat. 2. Zoos are examples of in-situ conservation. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Zoos are ex-situ.

  39. Consider the statements. 1. Eutrophication reduces dissolved oxygen in water. 2. Eutrophication is caused by a shortage of nutrients. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    It is caused by excess nutrients.

  40. Consider the statements. 1. Biogas can be made from cattle dung. 2. Biogas is mainly carbon monoxide. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Biogas is mainly methane.

  41. Consider the statements. 1. Check dams slow stream flow and help recharge groundwater. 2. Percolation tanks help water soak into the ground. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are water conservation structures.

  42. Consider the statements. 1. Biomagnification affects top carnivores most. 2. The ten percent law means 90 percent of energy passes on to the next level. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Only about 10 percent passes on.

  43. Consider the statements. 1. Acid rain damages marble monuments. 2. Acid rain has a pH above 7. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Acid rain has pH below 5.6.

Page 1 of 1
‹
›