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Biogeochemical Cycles UPSC Notes: Meaning, Types & Significance
IMPORTANT LINKS
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GS Paper |
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Topics for UPSC Prelims |
Carbon Cycle, Nitrogen Cycle, Phosphorus Cycle, Sulfur Cycle, Water Cycle, Photosynthesis, Respiration, Decomposition, Combustion, Carbon Reservoirs, Weathering of Rocks, Volcanic Emissions, Atmospheric Deposition, Evaporation, Condensation, Precipitation, Infiltration, Role of Microorganisms, Deforestation, Climate Change, Eutrophication, Acid Rain |
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Topics for UPSC Mains |
Detailed Mechanisms of Biogeochemical Cycles, Impact of Human Activities on Biogeochemical Cycles, National Action Plan on Climate Change, Climate Change Agreements and Protocols, Pollution Control Policies, Biogeochemical Challenges in India, Role of Microorganisms in Biogeochemical Cycles |
What is Biogeochemical Cycle?
The biogeochemical cycle is the movement and recycling of chemical elements and compounds between the biologic, or living organisms, and the geologic, or earth, components of the environment. This process is propelled by natural cycles, which include biological assimilation, microbial activity, chemical reactions, geologic processes of weathering, and physical phenomena like evaporation and precipitation. The biogeochemical cycles range in scale from cellular processes to global atmospheric interactions. They ensure that nutrients are always available in forms that can be utilized by the different forms of life. In the absence of these cycles, ecosystems would suffer from nutrient limitations. This is a factor that may limit growth, reproduction, and eventually the survival of organisms with implications for biodiversity and ecosystem stability.
Read the article on the Nuclear Fuel Cycle!
Types of Biogeochemical Cycles
Some of the more important biogeochemical cycles for terrestrial existence include those for water, carbon, nitrogen, phosphorus, and sulfur. Although each of these cycles has special processes associated with it, they are still somewhat interdependent in their contribution to the self-regulation of the Earth's environment.
The Water Cycle (Hydrological Cycle)
The water cycle refers to the constant circulation of water between the Earth and atmosphere. This process is important not just to all forms of life but also to weather and climate systems. It involves a few key processes in its operation:
- Evaporation: Solar energy warms up bodies of water, which in turn changes the water into its gaseous state from the liquid. This contributes to about 90% of atmospheric moisture.
- Transpiration: Plants absorb water through their roots and re-evaporate it through leaves, this way making for a huge contribution of moisture into the atmosphere, particularly in the tropics.
- Condensation: Water vapour is cooled down and returned back to droplets of liquid, making up the clouds. This transports the water content from the gas phase into that of a liquid phase.
- Precipitation: Water falls from clouds to the ground in the form of rain, snow, sleet, or hail, thereby recharging surface and groundwater. This step returns water to Earth's surface.
- Infiltration: Part of the precipitation that reaches the ground seeps into the soil, thereby recharging the aquifers that supply fresh water to plants and animals.
- Runoff: Water flows over the land surface and eventually reaches rivers, lakes, and oceans. In doing so, it transports nutrients and sediments from one component of the ecosystem to another.
Read the article on the Rock Cycle!
The Carbon Cycle
The carbon cycle is central to the climate of Earth. It is essentially done through the exchange of carbon dioxide, which controls the strength of the greenhouse effect. The key processes involved in the carbon cycle are:
- Photosynthesis: Plants, algae, and cyanobacteria convert carbon dioxide and sunlight into glucose and oxygen. This absorbs CO2 from the atmosphere and binds it in biomass.
- Respiration: Plants, animals, and microbes break down organic materials to provide energy by using oxygen, returning carbon dioxide and water back to the atmosphere.
- Decomposition: This is when decomposer organisms, like bacteria and fungi, break down dead organic matter to return carbon into the soil and atmosphere.
- Combustion: It involves the burning of fossil fuels—coal, oil, natural gas—and biomass to release stored carbon in the atmosphere as CO2 and other gases.
- Oceanic Exchange: Oceans absorb CO2 in the atmosphere, which is either utilized by marine organisms or stored in the deep ocean waters.
- Carbon Sequestration: Some carbon gets buried away in geologic formations—coal, oil, and other sedimentary deposits—that remain there for millions of years.
The Nitrogen Cycle
Nitrogen is a part of amino acids and nucleic acids, and so is necessary for all living organisms. The nitrogen cycle has several steps:
- Nitrogen Fixation: Atmospheric nitrogen is combined into ammonia or related compounds through natural processes like lightning or biological processes involving nitrogen-fixing bacteria. The latter include legume nodules and some free-living bacteria.
- Nitrification: Specialized bacteria oxidize ammonia into nitrites, then into nitrates, which the plants can absorb and make proteins and nucleic acids from.
- Assimilation: Plants and other autotrophs assimilate nitrates in the form of organic molecules, passing it on through the food web to various consumers.
- Ammonification: By action of bacteria and fungi, decomposers that break down organic nitrogen and return it in the form of ammonia.
- Denitrification: Denitrifying bacteria reduce the nitrate back to nitrogen gas, N2, which is released into the atmosphere, completing the cycle.
Read the article on the Significance of Weathering!
The Phosphorus Cycle
Unlike other cycles, there is no significant gaseous phase in the phosphorus cycle, and it appears to be a slow-moving cycle. Phosphorus is definitely an element that is an essential nutrient and part of important molecules such as DNA, RNA, and ATP. The major steps involved are:
- Weathering: The phosphate rock, present in the Earth's crust, undergoes weathering to release phosphate ions into the soil and water bodies.
- Absorption: Plants absorb phosphates from the soil, which are then utilized in the synthesis of organic molecules.
- Consumption: Animals take up phosphorus as they ingest plants or other animals. This takes the phosphorus through the food web.
- Decomposition: In this step, when plants and animals die, decomposers break it down into organic matter in inorganic phosphate, returning it to the soil or aquatic systems.
- Sedimentation: On geological timescales, phosphorus can precipitate and become buried in sedimentary rocks that may subsequently be uplifted to begin the cycle again.
The Sulfur Cycle
The atmospheric and terrestrial sulfur cycles are important for protein synthesis as sulfur is part of the amino acids which build proteins. It involves:
- Mineralization: Organic sulfur in decaying organic material is mineralized into hydrogen sulfide and released back to the environment.
- Oxidation: Hydrogen sulfide becomes oxidized into elemental sulfur or sulfate ions by chemotrophic bacteria.
- Assimilation: These sulfates are then assimilated by plants and microorganisms into surroundings for the synthesis of organic compounds, for example, amino acids.
- Reduction: Under lack of oxygen, sulfate-reducing bacteria reduce sulfate back to hydrogen sulfide.
- Weathering: Sulfur can also be released through weathering of rocks, contributing to the pool of available sulfur in the ecosystem.
Read the article on Biochemical Techniques!
Significance of Biogeochemical Cycles
The function and importance of biogeochemical cycles is beyond debate. They are pretty essential for the following:
- Supply of Nutrients: These cycles ensure continuous supply and recycling of nutrients, like carbon, nitrogen, phosphorus, and sulfur, that are crucial for the survival of living organisms. They prevent nutrient depletion in ecosystems.
- Soil fertility: The nutrients that are recycled through these cycles constitute the content for soil fertility and promote the growth of plants, hence agricultural productivity.
- Climatic controls: Biogeochemical cycles regulate the global climate through moderation of greenhouse gases, such as carbon dioxide and methane, in the atmosphere. An example is the carbon cycle, which plays a very important role in mitigating the power of climate change.
- Ecosystem Health: Through nutrient fluxes, the cycles support diverse and productive ecosystems, which are essential for biodiversity and ecosystem services.
- Detoxification: Quite frequently, microbial actions associated with these cycles detoxify certain harmful substances, making environments habitable to higher life forms.
- Energy Flow: These cycles are also related to the energy flow in ecosystems. For instance, the carbon cycle is strictly linked to energy production and consumption by photosynthesis and respiration.
Read the article on Biochemical Techniques!
Conclusion
Biogeochemical cycles are intrinsic natural processes that sustain life on Earth by perpetually re-supplying and recycling essential elements. They join living organisms to their physical environment and equilibrate them in such a manner that is deemed necessary for ecological stability. Human activities like deforestation, industrialization, and agriculture have strongly influenced these cycles; therefore, their understanding and protection have become very vital in the light of environmental sustainability. Correct knowledge of biogeochemical cycles is needed when formulating plans with regard to mitigating climate change, conserving biodiversity, and safeguarding the health of worldwide ecosystems.
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Key Takeaways for UPSC Aspirants
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Biogeochemical Cycles UPSC FAQs
What are the 4 major biogeochemical cycles?
It involves four important processes: biological processes, that is, the activities of living organisms; geological processes, that is, activities involving the Earth's crust; physical processes, such as state changes in water; and chemical processes, that is, reactions between the chemicals in the cycles.
How many components of a biogeochemical cycle are there?
It is divided into four parts, namely reservoirs, fluxes, pathways, and sinks. Reservoirs are the places or in other words, the natural sinks of a particular element or substance. Fluxes refer to the movement of an element or substance in and out of a given reservoir. Pathways refer to the routes taken by the substance while in the cycle. Sinks refer to areas where an element or a substance is assimilated and stored for a relatively long period.
What is the biological cycle?
It refers to the continuous changes and processes involving living organisms through which essential elements are transformed and moved throughout ecosystems.
What is a biogeochemical cycle?
A biogeochemical cycle is the natural process by which elements and compounds move between living organisms and the physical environment in a way that facilitates their re-use and recycling.
What are the 7 steps of carbon cycle?
Those through which carbon is cycled include photosynthesis, respiration, decomposition, ocean uptake, fossil fuel combustion, sedimentation, and volcanic release.