Natural Resources

Air, water, and soil are the three natural resources on which all life depends — and all three are under unprecedented pressure from human activity. Climate change (air), water crisis, and land degradation directly shape India's development challenges and appear in virtually every UPSC GS3 mains paper. This chapter builds the scientific foundation for those policy debates: why greenhouse gases warm the Earth, how the nitrogen cycle underpins agriculture, why topsoil loss threatens food security. No UPSC aspirant can afford to skip this chapter.

PART 1 — Quick Reference Tables

Atmospheric Composition

Layers of the Atmosphere

Soil Components

Biogeochemical Cycles — Summary

PART 2 — Detailed Notes

1. Air — Composition and Importance

The atmosphere is a thin gaseous envelope held by gravity. Its composition is remarkably stable because biological processes (photosynthesis, respiration, nitrogen fixation, decomposition) continuously cycle elements.

Air is essential for:

• Respiration (O2 for aerobic organisms)
• Photosynthesis (CO2 as raw material)
• Weather and climate (water vapour, temperature regulation)
• Protecting Earth from UV radiation (ozone layer in stratosphere)

Wind is caused by unequal heating of different parts of Earth's surface. Land heats and cools faster than water. During the day, air over land is warmer and rises; cooler air from over the sea moves in — sea breeze. At night, the reverse occurs — land breeze. Seasonal patterns of heating give rise to the Indian monsoon.

Air pollution occurs when harmful substances enter the atmosphere. Sources: fossil fuel combustion (coal, petrol, diesel), industrial emissions, crop burning. Primary pollutants: CO, SO2, NOx, particulate matter (PM2.5, PM10). Secondary pollutants form from chemical reactions: ozone (at ground level), nitric acid, sulphuric acid (acid rain). India's National Clean Air Programme (NCAP) 2019 targets 40% reduction in PM2.5 and PM10 levels by 2026 (from 2017 baseline).

2. The Greenhouse Effect and Climate Change

Natural greenhouse effect: Certain gases in the atmosphere (CO2, water vapour, methane, N2O, ozone) trap outgoing infrared radiation from Earth's surface, warming the planet. Without this, Earth's average temperature would be -18°C instead of +15°C — life as we know it would be impossible.

Enhanced greenhouse effect: Since the Industrial Revolution (~1750), human activities have increased atmospheric CO2 from ~280 ppm to ~421 ppm (2024 levels). This enhances the natural greenhouse effect, causing global warming and climate change.

Greenhouse gases by global warming potential (GWP, per molecule over 100 years):

• CO2 — GWP = 1 (the reference)
• Methane (CH4) — GWP = 27–30 (produced by rice paddies, cattle, landfills, natural gas leaks)
• Nitrous oxide (N2O) — GWP = 273 (from synthetic fertilisers, animal waste)
• HFCs/PFCs/SF6 — GWP in thousands (industrial gases)

🎯 UPSC Connect: Paris Agreement and India's NDC

The Paris Agreement (2015) under UNFCCC commits countries to limiting global average temperature rise to 1.5°C above pre-industrial levels. Countries submit Nationally Determined Contributions (NDCs) — voluntary climate targets.

India's Updated NDC (2022):

• Reduce emission intensity of GDP by 45% by 2030 (from 2005 levels)
• Achieve 50% of cumulative electric power installed capacity from non-fossil fuel sources by 2030
• Create additional carbon sink of 2.5–3 billion tonnes of CO2 equivalent through forest and tree cover

India also committed to Net Zero emissions by 2070 at COP26 (Glasgow, 2021).

3. Water — The Universal Solvent

Water covers about 71% of Earth's surface, but only 2.5% is freshwater, and of that, 70% is frozen in glaciers and ice caps. Only about 0.3% of all water on Earth is in liquid freshwater lakes and rivers accessible to humans.

The Water Cycle (Hydrological Cycle):

1. Evaporation — sun heats surface water → water vapour rises
2. Transpiration — plants release water vapour through stomata (collectively, evapotranspiration)
3. Condensation — water vapour cools and condenses on dust particles → clouds form
4. Precipitation — rain, snow, hail fall
5. Surface runoff — water flows over land to rivers and lakes
6. Infiltration — water seeps into soil → recharges groundwater
7. Percolation — deeper movement to aquifers

Importance of water:

• Universal solvent — all biochemical reactions in cells occur in water
• Thermoregulation — high specific heat of water buffers temperature
• Habitat for aquatic organisms
• Agriculture — irrigation

Water pollution: Addition of harmful substances that degrade water quality. Sources: industrial effluents (heavy metals — lead, mercury, cadmium), agricultural runoff (pesticides, fertilisers — eutrophication), sewage, oil spills. India's Jal Jeevan Mission (JJM) targets tap water connection to every rural household by 2024. NMCG (National Mission for Clean Ganga) / Namami Gange programme targets Ganga rejuvenation.

4. Soil — The Living Skin of the Earth

Soil is not inert rock particles — it is a living ecosystem hosting billions of microorganisms per gram. Good topsoil takes hundreds to thousands of years to form.

Soil formation processes:

1. Weathering of parent rock — physical (temperature changes, frost), chemical (oxidation, hydrolysis), biological (lichens, roots breaking rock)
2. Accumulation of organic matter — decomposition of dead plants and animals by bacteria and fungi → humus
3. Leaching — water carries minerals down through soil layers (horizons)
4. Biological activity — earthworms till soil, bacteria fix nitrogen, fungi form mycorrhizal networks

Soil profile (horizons):

• O horizon: Organic litter (leaf litter, partially decomposed material)
• A horizon (topsoil): Humus-rich, most fertile layer; where crops grow
• B horizon (subsoil): Accumulation of minerals leached from above; less organic matter
• C horizon: Partially weathered parent material
• R horizon: Bedrock

Soil erosion — removal of topsoil faster than it forms:

• Water erosion: Rainfall impact, surface runoff, rivers. Forms gullies and ravines. Most severe on slopes.
• Wind erosion: Blowing away of dry, bare topsoil. Major problem in Rajasthan, Haryana, and semi-arid areas.

Consequences: Loss of fertility, desertification, silting of reservoirs, flooding.

Conservation measures: Contour ploughing, terracing on slopes, windbreaks (shelterbelts of trees), maintaining vegetative cover, avoiding overgrazing, afforestation.

5. Biogeochemical Cycles

Carbon Cycle: Carbon moves between atmosphere, living organisms, soil, and oceans:

• Photosynthesis: Plants absorb CO2 → organic molecules (glucose)
• Respiration: All organisms break down glucose → release CO2
• Combustion: Burning of fossil fuels and biomass → CO2 release
• Decomposition: Dead organic matter broken down by bacteria/fungi → CO2 released, some becomes humus
• Ocean absorption: Oceans absorb about 25–30% of anthropogenic CO2 → ocean acidification

Nitrogen Cycle: Nitrogen makes up proteins, DNA, and RNA — essential for life. But N2 gas is highly stable and cannot be used directly by most organisms.

Steps in the nitrogen cycle:

1. Nitrogen fixation: Conversion of N2 → ammonia (NH3). Done by: free-living bacteria (Azotobacter in soil; Anabaena in water), symbiotic bacteria in legume root nodules (Rhizobium), lightning (small amount).
2. Ammonification: Decomposition of dead organisms → ammonia → ammonium ions (NH4+).
3. Nitrification (two-step):
   • Nitrifying bacteria Nitrosomonas: NH4+ → nitrites (NO2-)
   • Nitrobacter: NO2- → nitrates (NO3-) — the form plants absorb
4. Assimilation: Plants absorb nitrates → convert to proteins; animals eat plants → nitrogen moves up food chain.
5. Denitrification: Anaerobic bacteria (Pseudomonas, Thiobacillus) convert nitrates → N2 gas — returned to atmosphere. Occurs in waterlogged soils and swamps.

💡 Explainer: Nitrogen Cycle and Agriculture

The nitrogen cycle explains why:

• Legume rotation improves soil fertility — Rhizobium bacteria in root nodules fix atmospheric N2 into ammonia, enriching the soil with usable nitrogen.
• Synthetic fertilisers (urea, DAP) bypass the natural cycle, delivering nitrogen directly — but excess causes eutrophication in water bodies and N2O emissions (a potent greenhouse gas).
• Waterlogged paddy fields are major sources of methane (CH4) and N2O.
• India is the world's second-largest consumer of synthetic fertilisers — significant implications for water quality, soil health, and greenhouse gas emissions.

Oxygen Cycle: Oxygen is produced by photosynthesis and consumed by respiration and combustion. The stratospheric ozone layer is formed when O2 molecules absorb UV radiation and split, then recombine as O3. CFCs (chlorofluorocarbons) catalytically destroy ozone — controlled by the Montreal Protocol 1987 (the Kigali Amendment 2016 extended the Montreal Protocol to phase down HFCs, potent greenhouse gases).

PART 3 — Frameworks & Analysis

Framework: India's Water Stress

India has ~4% of the world's freshwater but ~18% of the world's population. Key facts:

• 54% of India faces high or extremely high water stress (WRI Aqueduct, 2019)
• Groundwater depletion — 89% of India's groundwater is used for irrigation
• 600 million people face high to extreme water stress
• Major rivers are fed by Himalayan glaciers — glacier retreat threatens long-term water security

Framework: Land Degradation in India

About 29.7% of India's land area is degraded (ISRO 2021 assessment):

• Water erosion: 10.98 million hectares
• Wind erosion: 5.55 million hectares
• Salinity/waterlogging (from over-irrigation): 1.43 million hectares

India's commitments: Restore 26 million hectares of degraded land by 2030 under the Bonn Challenge and Land Degradation Neutrality (LDN) target under UNCCD.

Exam Strategy

Prelims traps:

• The most abundant greenhouse gas by mass is water vapour, not CO2. But CO2 is the most important human-influenced greenhouse gas.
• Ozone in the stratosphere is protective; ozone at ground level (troposphere) is a pollutant.
• Nitrosomonas converts ammonium to nitrite; Nitrobacter converts nitrite to nitrate — don't mix up these two nitrifying bacteria.
• Denitrification returns nitrogen to the atmosphere — it is a "loss" from the soil system (occurs in waterlogged conditions).
• The ozone layer is in the stratosphere (20–35 km altitude), not the troposphere.

Mains frameworks:

• Climate change: carbon cycle science → enhanced greenhouse effect → IPCC assessments → Paris Agreement → India's NDC
• Water crisis: hydrological cycle disruption → groundwater depletion → JJM → Namami Gange
• Soil degradation: soil formation → erosion causes → desertification → India's LDN target

Previous Year Questions

Q1 (Prelims 2022): With reference to the nitrogen cycle, consider the following statements about denitrification… (Tests understanding of nitrogen cycle steps and bacteria involved)

Q2 (Prelims 2019): In the context of the carbon cycle, which of the following is/are considered a carbon sink? (Oceans, forests, soil organic matter — all are carbon sinks)

Q3 (Mains GS3 2021): Discuss the impacts of climate change on glaciers in the Hindu Kush Himalayan region and its implications for water security in India. Water cycle science → glacier melt → disrupted hydrology → policy response

Q4 (Mains GS3 2019): What is the significance of the Pradhan Mantri Krishi Sinchayee Yojana (PMKSY)? Explain how it can help in conservation of water. Water cycle → irrigation efficiency → PMKSY → water conservation