Biogeochemical Cycles

Introduction

Biogeochemical cycles transport elements in diverse forms from nonliving (abiotic) to living (biotic) components of the biosphere and back. All of the chemical elements that make up live cells must be recycled continuously for the living components of a significant ecosystem to exist. Each biogeochemical cycle has a reservoir (nutrient) pool—a bigger, slower-moving, mainly abiotic element—and an exchange (cycling) pool—a smaller, more active portion concerned with the rapid exchange of biotic and abiotic aspects of an ecosystem

Types of Biogeochemical Cycle

There are two types of biogeochemical cycles

• Gaseous cycles  – Carbon, Oxygen, Nitrogen and the Water cycle.

• Sedimentary cycles – Includes Sulphur, Phosphorus, Rock cycle, etc.

Energy enters ecosystems in two directions: sunshine for phototrophs and inorganic compounds for chemoautotrophs. Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur are the six most prevalent elements associated with organic molecules. They occur in various chemical forms in the atmosphere, on land, in water, and beneath the Earth’s surface. 

The cycling of elements on Earth is influenced by geologic processes such as erosion, river drainage, continental plate movement, and weathering. Recycling inorganic materials between living species and their nonliving environment are called a biogeochemical cycle because geology and chemistry play important roles in studying this process. Let us have a look at each type of biogeochemical cycle:

Water Cycle

The water from the many bodies of water evaporates, cools, condenses, and falls as rain.

These biogeochemical cycles are in charge of keeping meteorological conditions stable. Water interacts with its surroundings in numerous forms, changing the temperature and pressure of the atmosphere.

This process is aided by another mechanism known as evapotranspiration (i.e. vapour created by leaves). Water evaporates from leaves, soil, and water bodies into the atmosphere, condensing and falling as rain. The Sun’s energy heats the seas and other surface waters, which drives the water cycle. 

This causes liquid surface water to evaporate (water to water vapour) and frozen water to sublimate (ice to water vapour), releasing vast volumes of water into the atmosphere as water vapour. Water vapour condenses into clouds as a liquid or frozen droplets over time, eventually resulting in precipitation (rain or snow) that returns water to the Earth’s surface. Rain that reaches the surface of the Earth may evaporate, flow over it, or seep into the Earth. Surface runoff is the freshwater flow from rain or melting ice that is most easily noticed.

Carbon Cycle

Carbon is exchanged among the biosphere, geosphere, hydrosphere, atmosphere, and pedosphere in one of the biogeochemical cycles.

Photosynthesis is carried out by all green plants using carbon dioxide and sunshine. As a result, the plant stores carbon. When green plants die, they are buried in the soil, transformed into carbon-based fossil fuels. When fossil fuels are burned, carbon dioxide is released into the atmosphere.

Animals that eat plants also get the carbon stored in the plants. When these animals decompose after death, the carbon is released back into the atmosphere. Carbon is also returned to the environment by animals’ cellular respiration.

Vast amounts of carbon dioxide are created and stored as fossil fuels (coal and oil). They can be harvested for various commercial and non-commercial applications. When these fuels are burned in factories, the carbon is discharged back into the atmosphere.

Nitrogen Cycle

This is among the biogeochemical cycles in which nitrogen is transformed into various forms and circulates throughout the atmosphere and diverse ecosystems, including terrestrial and marine ecosystems. Nitrogen is a necessary component of life. It consists of five steps:

1. Nitrogen fixation (N₂ to NH₃/ NH₄⁺ or NO₃⁺)

2. Nitrification (NH₃ to NO₃⁻)

3. Assimilation (Incorporation of NH₃ and NO₃⁻ into biological tissues)

4. Ammonification (organic nitrogen compounds to NH₃)

5. Denitrification(NO₃⁻ to N₂)

The nitrogen-fixing bacteria found in the root nodules of leguminous plants fix nitrogen in the atmosphere and make it available to the soil and plants.

This nitrogen gas is converted into a helpful molecule called ammonia by bacteria found in the roots of plants. Plants are also given ammonia in the form of fertilisers. 

Nitrites and nitrates are formed from ammonia. 

Denitrifying bacteria convert nitrates to nitrogen, then released into the atmosphere.

Oxygen Cycle

Another biogeochemical cycle flows through the atmosphere, lithosphere, and biosphere. Oxygen is an abundant element on our planet. It is found in the atmosphere in the elemental form of 21%.

Photosynthesis causes plants to release oxygen. Humans and other animals breathe oxygen and exhale carbon dioxide, which plants absorb anew. They use this carbon dioxide to make oxygen through photosynthesis, and the cycle repeats.

Phosphorus Cycle

In this biogeochemical cycle, phosphorus flows through the hydrosphere, lithosphere, and biosphere. The weathering of rocks extracts phosphorus. Phosphorus is washed away in the soil and water due to rain and erosion. Plants and animals get phosphorus from the soil and water and thrive. 

Phosphorus is also required for the growth of microorganisms. When plants and animals die, their stored phosphorus is released into the soil and water bodies. It is devoured by plants and animals again, and the cycle repeats. Phosphorus is also transferred between marine organisms and phosphate dissolved in the water. The phosphate transport from the ocean to the land and soil is extraordinarily sluggish. The typical phosphate ion has an oceanic residence period of 20,000 to 100,000 years.

Excess phosphorus and nitrogen from fertiliser runoff and sewage infiltrate these habitats, causing excessive algal development. The death and degradation of these species deplete dissolved oxygen, which causes aquatic organisms like shellfish and finfish to perish.

Sulphur Cycle

Human actions have significantly impacted the global sulphur cycle’s equilibrium. More hydrogen sulphide gas is released into the atmosphere when significant volumes of fossil fuels, particularly coal, are burned. Acid rain occurs when rain falls through this gas, causing damage to the natural environment by decreasing lakes’ pH and killing many local plants and animals.

This grouping of biogeochemical cycles flows through rocks, water bodies, and life systems. Weathering of rocks releases sulphur into the atmosphere, which is then transformed into sulphates. Microorganisms and plants absorb these sulphates and convert them to organic molecules. Animals consume organic sulphur through their diet. Sulphur is returned to the soil when animals die and disintegrate. It is acquired again by plants and bacteria, and the cycle repeats. Sulphur is an essential component of the macromolecules of all living things. Protein synthesis plays a crucial role as a component of the amino acids cysteine and methionine. It is found in various vitamins needed to make important biological components like coenzyme A.

Conclusion

Hence, according to biogeochemical cycles, the matter on Earth is conserved and present in atoms. Because matter cannot be generated or destroyed, it is recycled in numerous ways throughout the Earth’s system. All other elements are present in a closed system. The Earth receives energy from the Sun, radiated back as heat.