Chapter 6 — ପ୍ରାକୃତିକ ସମ୍ପଦ ଓ ତାହାର ପ୍ରଦୂଷଣ (Natural Resources and Pollution)

A natural resource is any material or form of energy that exists in nature and is useful to living organisms. Air, water, soil, sunlight, minerals, fossil fuels, forests and wildlife are all natural resources. Nothing that we eat, wear, build with or burn comes from anywhere except the Earth and the Sun. The outermost layer of the Earth where life is possible is called the biosphere. It is made of three interacting parts: the lithosphere (the solid crust with its rocks and soil), the hydrosphere (all the water — oceans, rivers, lakes, ground water and ice) and the atmosphere (the envelope of gases). Living organisms are the fourth component that binds these three together.

Resources are classified in two useful ways. On the basis of whether they can be replenished, they are renewable or non-renewable. Renewable resources are regenerated by natural processes within a human lifetime: solar energy, wind, flowing water, forests, crops, fish and fresh water. Non-renewable resources took millions of years to form and once used are gone for all practical purposes: coal, petroleum, natural gas and metallic minerals such as iron, copper and bauxite. Odisha is rich in non-renewable minerals — iron ore in Keonjhar and Sundargarh, coal in Talcher and Ib valley, bauxite in Koraput — and this makes conservation especially relevant to the state.

On the basis of quantity they are inexhaustible (sunlight, air, water in the oceans, which are practically unlimited) or exhaustible (forests, wildlife, minerals, fossil fuels, which can be finished by overuse). Notice that a renewable resource can still be exhausted: a forest regrows, but not if it is cut faster than it grows. Fresh ground water is renewable through rain but a well goes dry when pumping exceeds recharge.

Another classification is biotic (obtained from living things: forests, animals, fossil fuels which came from ancient organisms) and abiotic (non-living: air, water, soil, minerals). A wise use of resources that meets today's needs without robbing future generations is called sustainable development, and the deliberate protection and careful use of resources is conservation. The whole chapter rests on one idea: the biosphere recycles its materials, and human beings must live within the speed of that recycling.

The atmosphere is the blanket of gases held around the Earth by gravity. Dry air is about 78 percent nitrogen, 21 percent oxygen, 0.93 percent argon and 0.03 to 0.04 percent carbon dioxide, with traces of other gases and a variable amount of water vapour. This composition is remarkable when compared with our neighbours: the atmospheres of Venus and Mars are 95 to 97 percent carbon dioxide, and neither planet supports life. Earth's living organisms have themselves shaped the air — green plants released the oxygen and keep the carbon dioxide low.

The atmosphere does three great jobs. First, it acts as a blanket. Air is a poor conductor of heat. During the day it prevents the Earth from heating suddenly, and during the night it slows the escape of heat into space. The result is that the average temperature on Earth stays fairly steady through the day and through the year. The Moon, which has no atmosphere and is at the same distance from the Sun, swings from about 110 degrees Celsius in daylight to minus 190 degrees Celsius at night. Certain gases — water vapour, carbon dioxide, methane — trap the long-wave heat radiated by the ground; this natural trapping is the greenhouse effect and, in its normal amount, it keeps the Earth about 33 degrees Celsius warmer than it would otherwise be.

Second, the atmosphere supplies the gases of life: oxygen for respiration and combustion, carbon dioxide for photosynthesis, nitrogen that is fixed into proteins. Third, its upper layer contains ozone, which absorbs harmful ultraviolet radiation from the Sun.

The atmosphere is arranged in layers. The troposphere (up to about 10 to 15 km) holds most of the air, all the weather, clouds and water vapour; temperature falls with height here. Above it the stratosphere (up to about 50 km) contains the ozone layer. Then come the mesosphere, the thermosphere (where the ionosphere reflects radio waves) and the thin exosphere that fades into space. Air pressure and density decrease as we go up, which is why mountaineers on high peaks need oxygen cylinders. Understanding this structure is necessary before we study how winds, rain and pollution behave.

Air is never completely still. Its movement, which we call wind, is caused by uneven heating of the Earth's surface by the Sun. Two facts explain everything: hot air expands, becomes lighter and rises; and air always flows from a region of high pressure to a region of low pressure.

Consider a coastal town such as Gopalpur on a summer day. Land heats faster than water because water has a much higher specific heat capacity and because sunlight penetrates deep into the sea, spreading the heat through a large volume. So by afternoon the air over the land is hotter and rises, creating a region of low pressure over the land. Cooler, heavier air from over the sea moves in to take its place — this is the sea breeze. At night the land cools faster than the sea. Now the air over the sea is warmer and rises, and air moves from land to sea — the land breeze. Fishermen of the Odisha coast use the land breeze to sail out before dawn and the sea breeze to return in the afternoon.

On a global scale the same process operates between the equator and the poles. The equatorial region receives the most direct sunlight; air there rises and moves towards the poles at high altitude, while cooler surface air moves towards the equator. The rotation of the Earth deflects these flows and produces the belts of prevailing winds. The monsoon that brings Odisha nearly 80 percent of its rainfall between June and September is a giant sea breeze on a continental scale: the Indian landmass heats up in summer, pressure falls, and moisture-laden winds rush in from the Indian Ocean.

Winds are important in the biosphere. They carry water vapour from the oceans to the land, disperse seeds and pollen, spread heat from the tropics to the temperate regions, and also spread pollutants far from where they are released. Air movement is also the reason that smoke from a factory chimney in one district can cause acid rain in another. Wind energy, harvested by windmills, is one of the cleanest renewable energy sources.

Water is the most abundant substance on the surface of the Earth: about 71 percent of the planet is covered by it. Yet 97 percent is salty ocean water, 2 percent is locked in polar ice and glaciers, and only about 1 percent is fresh water available in rivers, lakes and underground. This tiny fraction is continuously renewed by the water cycle or hydrological cycle, driven entirely by the energy of the Sun.

The cycle has four stages. Evaporation: the Sun heats the surface of oceans, lakes and soil, and water changes into vapour. Plants add a large amount through transpiration from their leaves; a single large tree may release hundreds of litres of water vapour a day. Condensation: warm, moist air rises, expands and cools. When it cools below the dew point, the vapour condenses around tiny particles of dust, salt or smoke in the air — these are called condensation nuclei — and forms droplets that we see as clouds. Precipitation: droplets collide and grow until they are too heavy to remain suspended and fall as rain, or as snow and hail if the temperature is low enough. Collection and run-off: rain water flows over the surface into streams and rivers, seeps into the ground to become ground water, or is taken up by plants, and eventually returns to the sea.

The pattern of rainfall in a region is decided by the prevailing winds and the relief of the land. In Odisha the south-west monsoon winds, heavy with moisture from the Bay of Bengal, are forced to rise over the Eastern Ghats, cool and shed their water — so places like Koraput and Phulbani receive more rain than the coastal plain. Rain that falls through polluted air dissolves oxides of sulphur and nitrogen and becomes acid rain, which we study later.

The water cycle purifies water — evaporation leaves salts and impurities behind — distributes it across the continents, and regulates climate. Deforestation reduces transpiration and hence local rainfall; concrete surfaces in cities prevent seepage and reduce ground-water recharge, which is why rainwater harvesting is now compulsory in many town plans. Every drop of water we use today has been through this cycle countless times.

Soil is the loose upper layer of the Earth's crust in which plants grow. It is a mixture of mineral particles, decayed organic matter, water, air and countless living organisms. Soil is formed over thousands of years by the breaking down of rocks — a process called weathering — followed by the addition of organic material.

Weathering is of three types. Physical weathering is caused by the Sun, water and wind. Rocks heat up and expand by day and cool and contract by night; repeated expansion and contraction cracks them. Water entering the cracks freezes in cold regions and expands, splitting the rock. Flowing rivers grind rocks against each other, and wind carrying sand blasts and wears them down. Chemical weathering occurs when water, carbon dioxide and oxygen react with the minerals of the rock: rain water containing dissolved carbon dioxide slowly dissolves limestone, and iron in rocks rusts. Biological weathering is the work of living organisms. Lichens and mosses growing on bare rock release acids that dissolve the surface; roots of trees push into cracks and widen them. The fine particles so produced mix with dead leaves, animal remains and microbial matter to form humus, the dark, spongy organic part of soil that holds water and nutrients.

A mature soil has layers called horizons: the top soil rich in humus, the sub-soil with clay and minerals, weathered rock, and the parent rock beneath. The texture of a soil depends on the size of its particles — clay (finest), silt and sand (coarsest). A soil that is a balance of the three with plenty of humus is called loam, the best for agriculture. Odisha has red and laterite soils in the plateau districts, black soil in parts of the west, and fertile alluvial soil in the Mahanadi delta.

Soil matters because it grows food, filters and stores rain water, supports the roots that hold the land, and is home to bacteria, fungi, earthworms and insects that recycle nutrients. Humus content, mineral nutrients, depth, water-holding capacity and the microorganisms in it together decide the fertility of a soil. Because a few centimetres of top soil take centuries to form, soil is effectively a non-renewable resource and its loss is a serious matter.

The removal of top soil by wind and water is called soil erosion. In a natural forest the canopy breaks the force of rain, leaf litter absorbs the impact, and roots bind the soil, so erosion is slow. When forests are cleared, the bare soil is struck directly by rain and washed into rivers. Overgrazing by cattle strips the grass cover; ploughing along the slope creates channels for run-off; mining and road building leave loose earth. Erosion by water may be sheet erosion (a thin layer removed uniformly), rill erosion (small channels) or gully erosion (deep ravines). Wind erosion is severe in dry, bare regions. The soil that is lost silts up rivers and reservoirs — the Hirakud reservoir has lost a substantial part of its storage capacity to silt — and raises river beds, worsening floods.

Soil is also damaged by pollution. Excess chemical fertilisers make the soil acidic or saline and kill useful microorganisms; pesticides like DDT persist for years and enter the food chain; industrial effluents deposit heavy metals; plastic waste and untreated sewage dumped on land block air and water movement; mining spoils and fly ash from thermal plants poison the ground. Poor irrigation practice raises the water table and leaves salt on the surface, a problem called salinisation.

Soil conservation means preventing erosion and maintaining fertility. The methods are: afforestation and planting shelter belts of trees against wind; contour ploughing across the slope rather than down it; terracing on hillsides, as the tribal farmers of Koraput have long practised; strip cropping, alternating strips of grain and grass; building check dams and bunds to slow run-off; controlled grazing; mulching the soil with straw; crop rotation with legumes to restore nitrogen; use of organic manure, compost and vermicompost instead of only chemical fertilisers; and biological pest control in place of persistent pesticides. Recycling of waste and proper disposal of plastics protect the soil from pollution.

Soil conservation is not only a rural concern. Every citizen who composts kitchen waste, refuses single-use plastic, or plants a tree is conserving soil. The land that feeds a population of over four crore people in Odisha depends on it.

The chemical elements that make up living matter are not created or destroyed; they circulate between the living (biotic) and non-living (abiotic) parts of the biosphere. These circular pathways are called biogeochemical cycles (bio = life, geo = earth, chemical = the elements). The water cycle is one; the carbon, oxygen and nitrogen cycles are the others we must know.

The carbon cycle. Carbon is the backbone of every organic molecule. It exists in the atmosphere as carbon dioxide (about 0.04 percent), dissolved in water as carbonates and bicarbonates, in rocks as limestone and marble, in fossil fuels, and in the bodies of all living things. Green plants and algae take carbon dioxide from the air or water and, using sunlight, convert it into glucose by photosynthesis. Animals get this carbon by eating plants. All organisms return carbon dioxide to the air by respiration. When organisms die, decomposers break down their bodies and release carbon dioxide. Over millions of years some dead matter was buried and became coal and petroleum; when we burn these fuels, and also wood, the stored carbon is released by combustion. Marine animals build shells of calcium carbonate; these settle and form limestone, from which carbon returns very slowly by weathering and volcanic activity. The balance of this cycle is now disturbed: burning of fossil fuels and cutting of forests add carbon dioxide faster than plants and oceans absorb it, raising its level from about 280 parts per million before industrialisation to over 400 today, and driving global warming.

The oxygen cycle. Oxygen is 21 percent of the air and is also present in water, in carbon dioxide, in oxides of rocks, and in every organic molecule. It is removed from the atmosphere by respiration of all organisms, by combustion, and by the formation of oxides such as rust. It is returned by one process alone — photosynthesis, in which water is split and oxygen released. Forests and oceanic phytoplankton are thus the lungs of the planet. Oxygen also forms ozone in the stratosphere. Since oxygen is a product of photosynthesis and carbon dioxide is its raw material, the carbon and oxygen cycles are two halves of one process that runs in opposite directions in plants and in animals.

Nitrogen makes up 78 percent of the air, and every living cell needs it for proteins, nucleic acids (DNA, RNA), chlorophyll and vitamins. Yet plants and animals cannot use nitrogen gas directly. The two nitrogen atoms in N₂ are joined by a very strong triple bond, and only a few kinds of organisms and a few physical processes can break it. The nitrogen cycle is the story of how this inert gas is converted into usable compounds and eventually returned to the air.

Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia or nitrates. It happens in three ways. Biological fixation: free-living soil bacteria such as Azotobacter and blue-green algae such as Anabaena and Nostoc in paddy fields fix nitrogen, and Rhizobium bacteria living in the root nodules of leguminous plants (gram, pea, moong, groundnut, soybean) fix nitrogen in exchange for food from the plant. Atmospheric fixation: during lightning the very high temperature makes nitrogen combine with oxygen to form oxides of nitrogen, which dissolve in rain and reach the soil as nitrates. Industrial fixation: the Haber process combines nitrogen and hydrogen to make ammonia for fertilisers such as urea.

Plants absorb nitrates from the soil through roots and build them into amino acids and proteins — this is assimilation. Animals get their nitrogen by eating plants or other animals. When organisms die or excrete, bacteria and fungi break the proteins down into ammonia; this is ammonification. In the soil, nitrifying bacteria convert ammonia first to nitrites (Nitrosomonas) and then to nitrates (Nitrobacter) — the process of nitrification — making nitrogen available again to plants. Finally, denitrifying bacteria such as Pseudomonas in waterlogged soils convert nitrates back to nitrogen gas, which returns to the atmosphere, completing the cycle. This is why farmers drain fields — waterlogging loses nitrogen.

The nitrogen cycle explains several farming practices: growing legumes in rotation, ploughing green manure into the field, and the use of blue-green algae as biofertiliser in paddy. It also explains a pollution problem: excess nitrate fertiliser washed into ponds causes explosive growth of algae, called eutrophication, that we shall meet under water pollution.

Pollution is any undesirable change in the physical, chemical or biological characteristics of air, water or soil that harms living organisms or damages property. The substances or forms of energy that cause it are called pollutants. A pollutant may be a natural substance present in an unnatural amount (carbon dioxide, nitrates, dust) or a substance that nature never made (plastics, DDT, chlorofluorocarbons). Pollution is the price of activities that improve human life — industry, transport, agriculture, urban living — when their wastes are released faster than the environment can neutralise them.

Pollutants are classified in several ways. By their fate in nature they are biodegradable (decomposed by microorganisms within a reasonable time: sewage, paper, vegetable waste, cotton) and non-biodegradable (not broken down, or broken down over centuries: plastics, glass, heavy metals like lead and mercury, pesticides like DDT, radioactive waste). Non-biodegradable pollutants accumulate and pass along food chains, becoming more concentrated at each step — a phenomenon called biomagnification. By their origin, pollutants are primary (released directly: sulphur dioxide, carbon monoxide, dust) or secondary (formed in the environment by reaction of primary pollutants: ozone in smog, sulphuric acid in acid rain). By their state they are gaseous, liquid or solid, and some forms of energy — noise, heat, radiation — are also pollutants.

The main types of pollution are named after the medium affected: air pollution, water pollution, soil (land) pollution and noise pollution. Thermal pollution (hot water from power plants discharged into rivers), radioactive pollution and light pollution are other forms. The sources are usually grouped as natural (volcanic eruptions, forest fires, dust storms, pollen) and man-made or anthropogenic (industries, vehicles, agriculture, domestic waste, mining, deforestation). Sources are also described as point sources, such as a factory pipe, whose output can be measured and treated, and non-point sources, such as fertiliser run-off from thousands of fields, which are much harder to control.

The effects of pollution are felt at every level: on human health, on animals and plants, on the climate, on buildings and monuments, and on the economy. The following topics examine each type in turn — its sources, its effects and the measures that control it — because control begins with understanding.

Air pollution is the presence in the atmosphere of gases, particles or other substances in amounts harmful to living organisms and materials. Its major man-made sources are: burning of fossil fuels in thermal power stations, factories and vehicles; industrial processes such as smelting, cement making and refining; burning of biomass — wood, dung, crop residue — in rural kitchens and fields; mining and construction that raise dust; and agriculture, which releases methane from paddy fields and cattle and ammonia from fertilisers. Natural sources include volcanoes, forest fires and dust storms.

The important pollutants and their effects are best learnt in a table.

Smog is a mixture of smoke and fog. The classical London smog of 1952, caused by coal smoke and sulphur dioxide trapped by fog, killed thousands within a week. Photochemical smog, common in sunny cities with heavy traffic, forms when nitrogen oxides and hydrocarbons react in sunlight to produce ozone and other irritants; ozone at ground level is a poison though it is a protector in the stratosphere.

Air pollution attacks health (respiratory and heart diseases, cancers, reduced lung growth in children), plants (yellowing and death of leaves, reduced yield), animals (fluoride poisoning of cattle near aluminium works), materials (corrosion of metals, blackening of buildings, the yellowing of the marble of the Taj Mahal by sulphur dioxide from the Mathura refinery, attacked by acid rain) and the climate itself. Indoor air pollution from cooking with wood and dung in poorly ventilated kitchens is a leading cause of illness among rural women and children in India, which is why clean cooking gas programmes are a public health measure as much as a convenience.

Four consequences of air pollution are so large in scale that they affect the whole planet.

Greenhouse effect and global warming. Sunlight passes through the atmosphere and warms the ground; the ground radiates heat back as long-wave infrared radiation. Gases such as carbon dioxide, methane, nitrous oxide, water vapour and CFCs absorb this radiation and re-emit it, keeping the lower atmosphere warm — just as glass keeps a greenhouse warm. This natural effect makes life possible. But burning of fossil fuels, deforestation, cattle rearing, paddy cultivation and landfills have raised the concentration of these greenhouse gases, trapping more heat. The result is global warming: the average temperature of the Earth has risen by about 1.1 degrees Celsius since 1900. The consequences are melting of glaciers and polar ice, rising sea level threatening low-lying coasts such as Odisha's own Satabhaya villages already swallowed by the sea, more frequent and violent cyclones like Fani and Phailin, erratic monsoons, droughts, floods, spread of disease-carrying mosquitoes to new areas, coral bleaching and loss of species. The change in long-term weather patterns is called climate change.

Acid rain. Sulphur dioxide and oxides of nitrogen released by burning coal and petroleum dissolve in the water droplets of clouds and form sulphuric acid and nitric acid. Rain water, normally slightly acidic (pH about 5.6) because of dissolved carbon dioxide, then falls with a pH of 4 or lower. Acid rain acidifies lakes and kills fish and other aquatic life, leaches nutrients such as calcium from the soil and releases toxic aluminium, damages leaves and stunts forests, corrodes iron bridges and railings, and dissolves marble and limestone buildings — the corrosion of the Taj Mahal is the famous Indian example. The pollutants can travel hundreds of kilometres on the wind, so acid rain falls far from its source.

Ozone layer depletion. In the stratosphere, 15 to 35 km up, oxygen molecules are split by ultraviolet light and recombine to form ozone (O₃). This ozone layer absorbs most of the Sun's harmful ultraviolet-B radiation. Chlorofluorocarbons (CFCs), once used in refrigerators, air conditioners, aerosol sprays and foam, drift up to the stratosphere where ultraviolet light frees their chlorine atoms; each chlorine atom destroys thousands of ozone molecules. A thinning called the ozone hole was discovered over Antarctica in 1985. More ultraviolet reaching the ground causes skin cancer, cataracts, weakened immunity, damage to crops and death of phytoplankton. The Montreal Protocol of 1987, signed by India, phased out CFCs, and the ozone layer is slowly recovering — a rare example of the world solving a pollution problem together.

Air pollution cannot be undone once a pollutant is released into the wind; it must be prevented at the source. Control measures work at three levels — technology, law and personal behaviour.

Industrial control. Factories and thermal power stations must remove pollutants from their flue gases before release. Electrostatic precipitators give dust and fly ash particles an electric charge and collect them on oppositely charged plates, removing over 99 percent of particulate matter. Scrubbers spray the gases with water or a lime solution that absorbs sulphur dioxide. Cyclone separators and bag filters trap coarse and fine particles. Tall chimneys disperse residual gases high in the atmosphere where they are diluted, though this does not remove them. Using low-sulphur coal, washing coal before use, and switching industries to natural gas or electricity reduce emissions. Industries should be located away from residential areas and surrounded by green belts of trees that absorb gases and trap dust.

Vehicular control. Catalytic converters fitted to exhausts convert carbon monoxide, unburnt hydrocarbons and nitrogen oxides into carbon dioxide, water and nitrogen. Unleaded petrol, low-sulphur diesel, compressed natural gas (CNG), ethanol-blended petrol and electric vehicles reduce emissions. Regular engine servicing, the Pollution Under Control certificate, the Bharat Stage emission standards, and above all fewer vehicles through good public transport, car-pooling and cycling, cut the total load.

Domestic control. Replacing wood and dung stoves with LPG, biogas or improved smokeless chulhas removes the largest source of indoor pollution; solar cookers and lamps help further. Burning of leaves, garbage and crop residue must stop — composting is the alternative.

Afforestation. Trees are the cheapest air purifiers: a mature tree absorbs many kilograms of carbon dioxide a year, releases oxygen, and its leaves trap dust and sulphur dioxide. Planting neem, peepal and banyan along roads and a green belt around every town is an effective long-term measure.

Law and monitoring. India's Air (Prevention and Control of Pollution) Act 1981 and the Environment (Protection) Act 1986 empower the Central and State Pollution Control Boards to set emission standards and prosecute offenders; the Odisha State Pollution Control Board monitors air quality in Angul, Rourkela, Paradip and other centres. The National Air Quality Index tells citizens each day how safe the air is. Internationally, the Montreal Protocol on CFCs and the Paris Agreement on greenhouse gases are the framework. Ultimately, every unit of electricity saved, every kilometre walked instead of driven, is air pollution prevented.

Water pollution is the contamination of water bodies — rivers, lakes, ponds, seas and ground water — with substances that make the water unfit for its intended use, whether drinking, bathing, irrigation, fishing or supporting aquatic life. Water is called the universal solvent; that same property makes it the easiest resource to pollute.

Sources. Domestic sewage from towns carries human excreta, detergents, food waste and disease-causing microorganisms; most Indian towns discharge it untreated into the nearest river — the Kathajodi at Cuttack and the Gangua nala at Bhubaneswar are examples. Industrial effluents from paper mills, tanneries, textile dyeing, chemical and fertiliser plants, sugar mills and mines carry acids, alkalis, dyes, oils, cyanide and heavy metals such as mercury, lead, cadmium, chromium and arsenic. Agricultural run-off washes chemical fertilisers (nitrates and phosphates) and pesticides from fields into ponds and rivers and down into wells. Thermal pollution occurs when power plants return cooling water to rivers several degrees hotter. Oil spills from tankers and offshore drilling coat the sea surface. Solid waste and plastic dumped in drains reach rivers and the sea. Religious and cultural practices — immersion of painted idols, dumping of flowers and ashes — add to the load. Natural sources include silt, arsenic and fluoride dissolved from rocks: fluoride in ground water is a known problem in parts of Nuapada and Nayagarh districts.

Effects. Water-borne diseases — cholera, typhoid, dysentery, hepatitis A, polio, diarrhoea — spread through sewage-contaminated water and kill more children in India than any other cause. Organic waste is decomposed by bacteria that consume dissolved oxygen; the biochemical oxygen demand (BOD) rises and fish and other aquatic animals suffocate. Nitrates and phosphates cause eutrophication: algae grow explosively into a green scum, block sunlight, and when they die their decay uses up all the oxygen, turning a pond into a stinking dead water body — as happens in many village tanks and in parts of Chilika when nutrient-rich run-off enters. Heavy metals accumulate in fish and reach people: mercury poisoning caused the Minamata disease in Japan, and nitrates in drinking water cause blue-baby syndrome in infants. Pesticides pass along the food chain by biomagnification. Oil films stop oxygen exchange and kill sea birds. Hot water lowers dissolved oxygen and disturbs breeding. Salt water intrusion into over-pumped coastal wells makes them brackish. Polluted water also damages crops when used for irrigation, corrodes pipes and pumps, and destroys the fisheries on which lakhs of Odisha families depend.

Control of water pollution rests on one principle: treat waste water before it reaches a water body, and use every drop wisely so that less waste is produced.

Sewage treatment. A sewage treatment plant works in stages. Primary treatment is physical: screens remove floating rubbish, grit chambers settle sand, and sedimentation tanks let suspended solids settle as sludge. Secondary treatment is biological: the water is aerated in tanks where bacteria decompose the dissolved organic matter (the activated sludge process) or trickled over beds of stones coated with microbial film. This removes most of the BOD. Tertiary treatment removes nutrients and disinfects the water with chlorine, ozone or ultraviolet light before it is released or reused for irrigation and industry. The sludge is digested to produce biogas and dried as manure. Every town needs such plants, and every household in a town without one needs a properly built septic tank rather than a drain into the street.

Industrial control. Industries must have effluent treatment plants that neutralise acids and alkalis, precipitate heavy metals, separate oils and cool hot water in cooling towers before discharge. Cleaner production, recycling of process water, and common effluent treatment plants for clusters of small units cut costs. The Water (Prevention and Control of Pollution) Act 1974 set up the Pollution Control Boards to enforce standards; the Namami Gange and similar river programmes fund treatment plants.

Agricultural control. Judicious use of fertilisers, organic manure, biofertilisers, integrated pest management and drip irrigation reduce the chemicals reaching water. Buffer strips of vegetation along streams trap run-off.

Household water purification. Boiling for several minutes kills microorganisms; chlorine tablets or bleaching powder disinfect wells; filtration through cloth, sand and candle filters removes suspended matter; and reverse osmosis removes dissolved salts. Slow sand filtration and chlorination are the standard steps in municipal water supply.

Conservation of water. Rainwater harvesting — collecting roof water in tanks or directing it into recharge pits — restores ground water; the traditional tanks and ponds of Odisha villages were exactly this. Watershed management, check dams and percolation ponds hold water on the land. Drip and sprinkler irrigation, repairing leaking taps, reusing washing water for gardens, and choosing less water-hungry crops reduce demand. Protecting wetlands like Chilika and mangroves like Bhitarkanika keeps natural water purifiers alive. Water conservation and pollution control are two sides of one coin: clean water saved is clean water not polluted.

Sound is a form of energy, and unwanted, unpleasant or excessively loud sound is noise. Noise pollution is the presence of noise at levels that disturb, harm or annoy people and animals. It is different from other pollutions in that it leaves no residue in the environment; the moment the source stops, the pollution stops. But its effects on the body and the mind are real and are measured by physicians.

Loudness is measured in decibels (dB), a logarithmic scale: an increase of 10 dB means roughly a tenfold increase in sound intensity. A whisper is about 30 dB, normal conversation 60 dB, busy traffic 80 dB, a loudspeaker at a wedding 100 to 110 dB, a jet aircraft at take-off 130 dB, and a firecracker at close range 140 dB. Sound above about 85 dB heard for long periods damages hearing, and above 120 dB it causes pain. The Noise Pollution (Regulation and Control) Rules 2000 in India set permissible daytime limits of 50 dB for silence zones (near hospitals and schools), 55 dB for residential, 65 dB for commercial and 75 dB for industrial areas, with lower night limits.

Sources. Road traffic and horns, railways and aircraft, factories and construction machinery, generators, loudspeakers at religious and social functions, firecrackers, and household appliances. Growing urbanisation has made Bhubaneswar and Cuttack markedly noisier in a generation.

Effects. On humans: temporary or permanent hearing loss, tinnitus (ringing in the ears), headache, irritability, loss of concentration and reduced learning in children, sleep disturbance, high blood pressure, increased heart rate and stress hormones, and in extreme cases mental illness. Continuous noise in factories is an occupational hazard. On animals: birds abandon nesting sites, animals in zoos and forests near highways show stress, marine mammals lose their way because ship noise interferes with their echolocation, and fireworks terrify domestic animals. Noise also masks warning sounds and causes accidents.

Control. At the source: silencers on vehicles and generators, well-maintained machines, enclosing noisy machinery, banning pressure horns and limiting loudspeaker hours and volume, restricting firecrackers to quieter varieties and fixed hours. In the path: planting dense rows of trees along roads (a green belt absorbs sound), sound-proofing walls, double-glazed windows, and locating airports and industries away from residential areas. At the receiver: earplugs and earmuffs for workers, and simple personal discipline — not honking at a red light, keeping television and music at reasonable volume. Silence zones around hospitals, schools and courts are enforced by law. Public awareness is the most effective measure of all, because most noise is produced by ordinary people who have not thought about its cost.

The chapter closes where it began: the biosphere recycles its materials at a certain speed, and human survival depends on living within that speed. Conservation is the planned management of natural resources so that they last, remain clean, and are shared fairly with other species and future generations. It is not the same as not using resources; it is using them wisely.

The guiding principle is the three Rs. Reduce: use less — switch off lights and fans, walk or cycle, buy only what is needed, avoid packaging. Reuse: use an article again — cloth bags, glass bottles, both sides of paper, old clothes as dusters. Recycle: convert waste into new material — paper, glass, metal and some plastics are recycled; kitchen waste is composted into manure. A fourth R, Refuse — say no to single-use plastic and to things that are not needed — and a fifth, Recover energy from waste, are often added.

Conservation of forests and wildlife. Forests are the roof of the water cycle, the lungs of the air and the home of biodiversity. Afforestation, social forestry, community protection of village forests as practised by thousands of forest protection committees in Odisha, prevention of forest fires, and controlled felling maintain them. Wildlife is conserved in national parks such as Simlipal, sanctuaries such as Bhitarkanika and Chilika, and through protection of the olive ridley turtles that nest on the Gahirmatha coast. The Chipko movement, in which villagers hugged trees to stop felling, shows what ordinary people can do.

Conservation of energy and minerals. Use energy-efficient LED lamps and star-rated appliances, solar water heaters and cookers; support wind, solar and biogas; recycle metals — recycling aluminium uses only about 5 percent of the energy of making it from bauxite.

Conservation of water and soil has been discussed: rainwater harvesting, drip irrigation, watershed management, contour farming, organic manure and tree planting.

Legal and institutional support. The Wildlife Protection Act 1972, the Water Act 1974, the Forest Conservation Act 1980, the Air Act 1981 and the Environment Protection Act 1986 form India's environmental law. World Environment Day (5 June), Earth Day (22 April) and Ozone Day (16 September) remind us every year. Environmental education in schools, eco-clubs, cleanliness drives, tree-planting campaigns and citizen science are the roots of a conservation culture. A student who carries a steel bottle, segregates waste at home, plants and protects one tree a year, and speaks up when a pond is being filled or a hill is being quarried illegally is already a conservationist. The natural resources of Odisha — its forests, rivers, minerals and coast — are a trust, not an inheritance to be spent.