NUTRIENT CYCLES

What is a Nutrient Cycle?

The nutrient Cycle also known as Biogeochemical Cycle is an ecological process that involves movement of major nutrients through Earth ecosystems. It is responsible for maintaining continuity & stability of environment by ensuring availability of nutrients that support life processes.

The cycle connects living (biotic) & non-living (abiotic) components contributing to ecosystem stability & productivity. The balance of these cycles is important for ecological sustainability & health of planet. This article by APTI PLUS UPSC Coaching details into concept of nutrient cycle, its importance, types & discussions of specific cycles such as Carbon Cycle, Nitrogen Cycle, Water Cycle (Hydrological Cycle), Phosphorus Cycle & Sulphur Cycle.

Types of Nutrient Cycles

Gaseous Nutrient Cycle

The Atmosphere serves as primary reservoir for these nutrients. Important gaseous nutrient cycles include Carbon Cycle, Nitrogen Cycle, Water Cycle (Hydrological Cycle).

Sedimentary Nutrient Cycle

Earth crust serves as primary reservoir for these nutrients. Important sedimentary nutrient cycles include Phosphorus Cycle, Sulphur Cycle.

These cycles differ in way nutrients are stored & move through ecosystem with gaseous cycles being faster & sedimentary cycles often taking longer due to slower movement of nutrients through rocks & soil.

1. Carbon Cycle

Carbon Cycle describes movement of carbon through Earth Atmosphere, biosphere, oceans & lithosphere. Carbon is key element in organic compounds & is essential for life. The carbon cycle helps regulate concentration of carbon dioxide in Atmosphere & plays role in climate regulation.

Key Steps of Carbon Cycle

Photosynthesis Plants, algae & some bacteria take in carbon dioxide from Atmosphere & convert it into glucose using sunlight through photosynthesis. This carbon is then stored in plant tissues.

Respiration Organisms including plants, animals & microbes release carbon back into Atmosphere through respiration. During respiration glucose is broken down to release energy & CO2 is a byproduct released into Atmosphere.

Decomposition When plants & animals die decomposers (bacteria, fungi) break down organic matter releasing carbon in form of CO2 & methane into Atmosphere or soil.

Combustion The burning of fossil fuels (coal, oil, natural gas) & biomass (wood, agricultural residues) releases large amounts of CO2 into Atmosphere. This accelerates buildup of greenhouse gases contributing to climate change.

Ocean Uptake & Release Oceans play a important role in carbon cycle by absorbing carbon dioxide from Atmosphere & storing it in form of dissolved carbonates. Marine organisms also use carbon to form shells & skeletons which eventually become part of ocean floor.

Sedimentation Over long periods carbon in dead organisms & shells can become buried in sediments eventually forming fossil fuels (coal, oil, natural gas) or becoming part of limestone rock formations.

2. Phosphorus Cycle

Phosphorus Cycle describes movement of phosphorus through Earth biosphere & lithosphere. Unlike nitrogen & carbon, phosphorus does not have a major gaseous phase & primarily exists in rocks & minerals.

Key Steps of Phosphorus Cycle

Weathering of Rocks Phosphorus is released from rocks & minerals through weathering (physical & chemical breakdown of rocks). This phosphorus then enters soil as phosphate ions that plants can absorb.

Absorption by Plants Plants take up phosphate from soil & incorporate it into their tissues. Herbivores in turn absorb phosphorus by eating plants.

Transfer through Food Chain Phosphorus moves through food chain as animals consume plants & other animals. Phosphorus is essential for DNA, RNA & energy molecules like ATP.

Decomposition When plants & animals die decomposers break down their organic matter releasing phosphorus back into soil in form of phosphate.

Sedimentation Phosphorus not taken up by organisms or dissolved in water can be deposited as phosphate in sediments often in marine environments. Over geological time, this phosphorus may become part of new rocks.

Runoff Phosphorus can also be washed into rivers & oceans through runoff from agricultural fields, sewage & industrial waste. This can lead to nutrient pollution in water bodies, causing issues like eutrophication.

Much like how nutrient cycles continuously replenish resources APTI PLUS IAS Academy in Kolkata refreshes & adapts study materials to keep aspirants up to date with latest syllabus changes & exam trends.

3. Sulphur Cycle

Sulphur Cycle describes movement of sulphur through environment. Sulphur is component of proteins & vitamins & plays an important role in regulating Earth climate & health of ecosystems.

Key Steps of Sulphur Cycle

Volcanic Emissions & Decomposition Sulphur is released into Atmosphere through volcanic eruptions, geothermal vents & decomposition of organic matter (like dead plants & animals). This sulphur is primarily in form of sulphur dioxide which can form sulfuric acid in Atmosphere.

Absorption by Plants Plants absorb sulphur in form of sulphate ions from soil which is then used to form amino acids & other important molecules.

Transfer through Food Chain Animals obtain sulphur by eating plants or other animals. Sulphur is a component of proteins & enzymes.

Decomposition & Mineralization When plants & animals die decomposers break down sulphur containing compounds & release sulphur back into soil in form of sulphate ions.

Emission of Hydrogen Sulphide Some bacteria in soil & wetlands reduce sulphate to hydrogen sulphide gaseous form of sulphur. H2S can escape into Atmosphere & contribute to acid rain.

Sedimentation Sulphate ions from rainwater & other processes can be deposited in ocean & on land becoming part of sedimentary rock layers.

4. Oxygen Cycle

Oxygen Cycle describes movement of oxygen through Atmosphere, biosphere & lithosphere. Oxygen is essential for respiration in most living organisms & is also involved in various chemical processes including combustion.

Key Steps of Oxygen Cycle

Photosynthesis Oxygen is produced as a byproduct of photosynthesis. Plants, algae & cyanobacteria take in carbon dioxide & release oxygen into Atmosphere.

Respiration Animals, plants & microorganisms take in oxygen for respiration process in which glucose is broken down to release energy producing carbon dioxide & water as byproducts.

Decomposition When organisms die decomposers break down their organic matter using oxygen releasing carbon dioxide & other gases in process.

Combustion Burning of organic matter (like fossil fuels & biomass) consumes oxygen & produces carbon dioxide, water vapor & heat.

Ozone Formation & Depletion In stratosphere ozone is formed by reaction of oxygen molecules with ultraviolet light from sun. Ozone absorbs harmful UV radiation, protecting life on Earth. Ozone is also broken down by chemical reactions contributing to oxygen cycle.

5. Water Cycle (Hydrological Cycle)

Water Cycle is continuous movement of water within Earth & Atmosphere. It is driven by solar energy & involves processes like evaporation, condensation & precipitation.

Key Steps of Water Cycle

Evaporation Water from oceans, lakes, rivers & other bodies of water is heated by sun & changes into water vapor rising into Atmosphere.

Transpiration Plants release water vapor into Atmosphere through transpiration from their leaves, contributing to movement of water in Atmosphere.

Condensation As water vapor rises & cools it condenses into tiny droplets to form clouds in Atmosphere.

Precipitation When clouds become heavy with water, they release it as precipitation in form of rain, snow, sleet or hail which falls back to Earth.

Infiltration & Runoff Some water that falls to Earth infiltrates into soil & replenishes groundwater supplies. The rest runs off into rivers, lakes & oceans continuing cycle.

Groundwater Flow Water infiltrating into soil can flow through underground aquifers eventually discharging back into rivers, lakes or oceans.

6. Nitrogen Cycle

Nitrogen is an essential element for all living organisms because it is a component of amino acids, proteins & nucleic acids (DNA & RNA). However nitrogen in its atmospheric form is not directly usable by most organisms which is why nitrogen cycle is so important for making nitrogen available in forms that can be absorbed & utilized by plants & animals.

Key Stages of Nitrogen Cycle

Nitrogen Fixation is process by which nitrogen gas from Atmosphere is converted into a form that plants can use such as ammonia or ammonium ions.

Biological Nitrogen Fixation bacteria like those in Rhizobium genus live symbiosis with legume plants (such as peas & beans) in root nodules. These bacteria convert nitrogen gas into ammonia which is then absorbed by plant & used to build proteins.

Non-Biological Nitrogen Fixation Lightning & industrial processes (like Haber-Bosch process) also convert nitrogen gas into usable forms like nitrates & ammonia.

Nitrification is a two step process in which ammonia (NH3) or ammonium ions (NH4+) are converted into nitrate ions (NO3-) form that plants can easily absorb.

Assimilation refers to process by which plants & animals take up nitrogen in form of nitrate (NO3-) or ammonium ions (NH4+) from soil or water & incorporate it into amino acids, proteins & other nitrogen containing organic compounds.

Ammonification (Decomposition, also called mineralization) is process by which nitrogen in organic matter (like dead plants, animals & waste) is broken down by decomposers (bacteria & fungi) into ammonia or ammonium ions.

Denitrification is final step of nitrogen cycle, in which nitrates are converted back into nitrogen gas by denitrifying bacteria such as Pseudomonas & Clostridium. This process occurs in oxygen poor environments like waterlogged soils & wetlands—the released nitrogen gas returns to the atmosphere where it can again enter the cycle through nitrogen fixation.

Comparison of Six Major Nutrient Cycles

Nutrient Cycle	Major Reservoirs	Role in Ecosystem	Human Impact
1. Nitrogen Cycle (N)	Atmosphere (78% N₂) Soil (Ammonia, Nitrates, Nitrites) Water Bodies	Essential for DNA, proteins, ATP Helps plants grow & maintains soil fertility	Overuse of fertilizers → Eutrophication & dead zones Nitrogen oxides (NOₓ) from industries → Acid rain & air pollution Nitrate contamination → Blue Baby Syndrome
2. Carbon Cycle (C)	Atmosphere (CO₂ gas) Oceans (Dissolved CO₂, Carbonates) Fossil Fuels (Coal, Oil) Forests & Living Organisms(Biomass)	Carbon is building block of life Regulates Earth’s temperature(Greenhouse effect)	Deforestation reduces CO₂ absorption Burning fossil fuels increases CO₂ → Climate change Ocean acidification from CO₂ harming marine life
3. Oxygen Cycle (O₂)	Atmosphere (21% O₂) Oceans & Water Bodies Living Organisms(Organic molecules, O₂ in blood)	Essential for respiration & energy production Maintains atmospheric balance	Deforestation reduces oxygen production Pollution reduces dissolved oxygen → Fish die in water bodies
4. Water Cycle (Hydrological Cycle, H₂O)	Oceans (97% of Earth’s water) Rivers, Lakes, Glaciers Groundwater, Atmosphere	Regulates climate & temperature Supports all life forms	Deforestation reduces transpiration, affecting rainfall Climate change disrupts rainfall patterns → Floods & droughts Pollution contaminates drinking water
5. Phosphorus Cycle (P)	Rocks & Minerals(Phosphate deposits) Soil & Water Bodies (Phosphates in sediments) Living Organisms(DNA, ATP, Bones, Teeth)	Essential for DNA, ATP & bones Key for plant growth & energy transfer	Fertilizers & detergents → Excess phosphorus in water → Algal Blooms Mining phosphate rocks depletes reserves Soil erosion washes away phosphorus
6. Sulphur Cycle (S)	Soil & Rocks(Sulphur minerals) Volcanoes (Emit SO₂ gas) Oceans (Dimethyl sulphide from plankton) Atmosphere (SO₂ & H₂S gases)	Helps build proteins & enzymes Regulates climate via sulphate particles	Burning coal & oil releases SO₂ → Acid Rain Mining & industrial emissions increase sulphur pollution Deforestation reduces sulphur absorption in soil

Conclusion

Nutrient Cycles are important for maintaining Earth ecosystems. Understanding them allows us to address environmental challenges like climate change, deforestation & pollution. By adopting sustainable practices we can preserve these cycles for future generations. Just as nutrient cycles ensure continuous flow of essential elements in ecosystems APTI PLUS UPSC Coaching ensures a steady supply of knowledge & resources to IAS aspirants.