Biogeochemical Cycle

Table of Contents

The Biogeochemical Cycle illustrates the movement of nutrients and other elements between biotic and abiotic components of ecosystems. These cycles are essential for preserving ecological homeostasis and guaranteeing the survival of life on Earth. This article will elucidate the Biogeochemical Cycle, providing valuable insights for those preparing for the Environment syllabus in the UPSC Civil Service exam.

A biogeochemical cycle involves the movement of a chemical substance between Earth’s biotic and abiotic components.
The atmosphere, hydrosphere, and lithosphere are all considered biotic components, while the biosphere is categorized as abiotic.
Geology and chemistry are crucial in understanding this process, and the recycling of inorganic materials between living organisms and their environment is termed a biogeochemical cycle.

Nutrient Cycling

A nutrient cycle is a cyclic mechanism facilitating the recycling and utilization of nutrients.
The pathway of a nutrient cycle encompasses cells, organisms, communities, and ecosystems.
The speed of nutrient cycling is affected by various biotic, physical, and chemical variables.
Nutrient cycles in nature, involving the cyclical movement of elements from the environment to living creatures and back, are termed biogeochemical cycles.

Nutrient Cycling – Types

Replacement Period:
- Perfect Cycle: Nutrients are replenished at the same rate as they are utilized in an ideal nutrient cycle. Most Gaseous cycles are considered perfect.
- Imperfect Cycle: Sedimentary cycles are imperfect as some nutrients are lost and trapped in sediments, rendering them unavailable for immediate cycling.
Nature of the Reservoir:
- Gaseous Cycle: The atmosphere or hydrosphere serves as the reservoir in the gaseous cycle.
- Sedimentary Cycle: The Earth’s crust is the reservoir in the sedimentary cycle.
Gaseous Cycles:
- Water, carbon, and nitrogen are the three most significant gaseous cycles.

Gaseous Cycles

Water, carbon, and nitrogen are the three most significant gaseous cycles.

Water (Hydrologic) Cycle

The water (hydrological) cycle is the solar-driven, uninterrupted circulation of water in the Earth-atmosphere system.
Atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater serve as crucial reservoirs for water on Earth.
Evaporation, transpiration, condensation, precipitation, deposition, runoff, infiltration, and groundwater flow are processes facilitating the movement of water between reservoirs.
It encompasses the continuous flow of water across the land surface, oceans, and subsoil, as well as among species.
The evaporation of water from the ocean’s surface initiates the hydrologic cycle.

The Carbon Cycle

Carbon, predominantly in the form of carbon dioxide (CO2), exists in the atmosphere.
The ongoing transfer of carbon between the atmosphere and organisms is termed the carbon cycle.
Photosynthesis is the process that moves carbon from the atmosphere to green plants and, subsequently, to organisms.
It reenters the atmosphere through the processes of respiration and decomposition of dead organic matter. It is primarily a short-term cycle.

The Nitrogen Cycle

Nitrogen serves as a fundamental building block for all living tissues and is a crucial component of proteins, constituting approximately 16 percent of protein weight.
The nitrogen cycle involves three key phases: nitrogen fixation, nitrification, and denitrification.
The atmosphere, hydrosphere, and lithosphere are integral parts of this cycle.
Nitrogen fixation is an anaerobic process that transforms atmospheric nitrogen (N2) into NH3, carried out by nitrogen-fixing bacteria.
Nitrification is a two-step process, initially reducing ammonium ion (NH4+) to NO2 and then further oxidizing it to produce NO3, with soil bacteria playing a pivotal role.
Denitrification involves the conversion of nitrates to nitrogen gas, with denitrifying bacteria functioning similarly to nitrogen-fixing bacteria.

Sedimentary Cycle

Sedimentary cycles are biogeochemical cycles with the Earth’s crust serving as their reservoir.
Iron, calcium, phosphorus, sulfur, and other elements bound to the Earth are involved in the sedimentary cycle.
These cycles vary based on the element, featuring a solution (or water-related) phase and a rock (or sediment) phase.
Sedimentary cycles have an extended duration for completion.
The Phosphorus cycle and Sulfur cycle are the most significant among sedimentary cycles.

Phosphorus Cycle

Phosphorus undergoes a cycle involving rocks, water, soil, sediments, and organisms.
Rain and weathering over time release phosphate ions and other minerals from rocks.
The resulting inorganic phosphate is then dispersed into the soil and water.
Plants uptake the inorganic phosphate from the soil, which can be consumed by animals.
Once within the plant or animal, phosphate integrates into organic molecules such as DNA.
When a plant or animal dies, decomposition releases organic phosphate into the soil.
Bacteria play a role in the process of mineralization, breaking down organic materials into inorganic forms of phosphorus, making organic phosphate available to plants.
Phosphorus from the soil can eventually find its way into streams and oceans.
Over time, it may be absorbed into sediments at this location.

Sulphur Cycle

The majority of the world’s sulphur is bound in rocks, salts, or deep within oceanic sediments.
Sulphur is present in the air we breathe, contributed by both natural and human sources.
Volcanic eruptions, microbiological activities, water evaporation, and decomposing organisms are examples of natural sources.
Human activities, particularly industrial processes generating sulphur dioxide (SO2) and hydrogen sulphide (H2S) gases, introduce sulphur into the atmosphere.
Sulphur dioxide reacts with oxygen to form sulphur trioxide gas (SO3) or with other chemicals to create sulphur salts.
In reaction with water, sulphur dioxide can produce sulphuric acid (H2SO4).
Dimethyl Sulphide, emitted by plankton, can also contribute to sulphuric acid formation.
Particles may fall back to Earth or react with rain, resulting in acid deposits.
Plants absorb these particles, releasing them back into the atmosphere, thus restarting the sulphur cycle.

Calcium Cycle

Calcium primarily exists in rock, minerals, or structural calcium within the mineral crystal lattices of soil particles, and it’s not readily available.
The majority of soil calcium is insoluble unless ‘weathered off’ minerals or bacterial breakdown of organic materials makes it soluble.
Some calcium is loosely or securely held in the soil or soil solution, making it available to plants and microbes.
Upon decomposition of animals, microbes, and plants, calcium from their bodies is mineralized and released into the soil.
Roots regularly contribute minerals, carbohydrates, and other chemicals, including calcium, back to the soil.
Due to its positive charge, calcium is adsorbed to the surface of clay and negatively charged organic particles, forming “exchangeable ions” that can be exchanged in the soil solution.
When taken by plants or microbes, calcium enters an organic phase, constantly exchanging between plant roots, microbes, and soil.
Decomposers break down deceased plant, animal, or soil fauna, releasing calcium back into the soil in a soluble form.
Consequently, calcium undergoes alternation between the soluble (and available) and insoluble (and unavailable) phases.

Importance of Biogeochemical Cycle

It is essential for converting nutrients from one form to another to make them usable by various organisms.
For instance, plants need to fix and convert atmospheric nitrogen into ammonium and nitrate before utilizing it.
Biogeochemical Cycles play a crucial role in maintaining ecosystem balance by storing nutrients for future use.
The transfer of elements from one location to another occurs through biogeochemical cycles, such as from air to soil or from water to soil.
Living creatures engage with the abiotic components of their surroundings through biogeochemical cycles.

Conclusion

Biogeochemical cycles play a crucial role in ecosystems, facilitating the continuous movement of essential nutrients like carbon, nitrogen, and phosphorus.
Nutrients are often in motion, with essential elements held in reservoirs where they can be temporarily removed from circulation and stored for extended periods.
The biogeochemical cycle serves as a recycling system in nature, ensuring the efficient use and movement of essential elements.

FAQs on Biogeochemical Cycle

Question: Is the nutrient cycle and biogeochemical cycle the same?

Answer: No, they are not the same. While both involve the movement of nutrients through ecosystems, the nutrient cycle specifically focuses on the pathways of a particular nutrient, such as carbon or nitrogen. On the other hand, the biogeochemical cycle encompasses the larger concept of nutrient cycles and includes the interactions between living organisms and their abiotic environment.

Question: What is the difference between the nitrogen cycle and the phosphorus cycle?

Answer: The nitrogen cycle and the phosphorus cycle are distinct biogeochemical cycles. In the nitrogen cycle, nitrogen undergoes processes like fixation, nitrification, and denitrification, moving through the atmosphere, soil, and living organisms. Meanwhile, the phosphorus cycle primarily involves the movement of phosphorus through rocks, soil, water, and living organisms. The key difference lies in the elements involved and the specific processes they undergo.

Question: Why are nutrient and biogeochemical cycles necessary?

Answer: Nutrient and biogeochemical cycles are essential for maintaining the balance and sustainability of ecosystems. These cycles ensure the continuous availability and circulation of crucial nutrients, such as carbon, nitrogen, and phosphorus, among living organisms and their environment. By recycling these nutrients, the cycles contribute to the health and functioning of ecosystems, supporting the growth and survival of various species. Additionally, they play a vital role in regulating environmental processes and preventing nutrient imbalances that could have adverse effects on ecosystems.

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Biogeochemical Cycle – UPSC Notes – Environment