Biogeochemical Cycle – Its Importance in Ecology and Ecosystems

Biogeochemical Cycles

Have you ever wondered how different nutrients and elements are made available in nature, well they are made available by a process we call the biogeochemical process or cycle, the biogeochemical process or cycle refers to a series of cycles that explains how nutrients are made available in nature. In this article, we will be explaining the concept of biogeochemical cycles and the types and importance of these cycles.

The word “bio” means biosphere, “geo” means geological components and “chemical” means elements that move through a cycle.

Biogeochemical cycles refers to the movement of nutrients and other elements between biotic and abiotic factors. The biotic factors of these cycles refers to the living things while the abiotic factors refers to the non living things in this cycle.

Types of Biogeochemical Cycles

There are two types of biogeochemical cycles and they are;

  1. Gaseous Cycle
  2. Sedimentary Cycle

Gaseous Cycle and the Biogeochemical Cycle

The gaseous cycle is a type of biogeochemical cycle in which the storage space or reservoir is the air or ocean. Cycles under this category are the oxygen cycle, carbon cycle, hydrogen cycle and nitrogen cycle.

Oxygen Cycle and the Biogeochemical Cycle

The oxygen cycle describes the movement of oxygen within the earth. Oxygen is produced by plants through a process called photosynthesis and it is also produced by the reaction of sunlight with water vapor.

Oxygen is used up in respiration, decomposition, rusting and combustion.

Steps of Oxygen Cycle

There are important steps that take place in the oxygen cycle and they are;

  1. Photosynthesis
  2. Respiration


During the process of photosynthesis, plants take energy from the sun, carbon dioxide from the air, and water from the soil to make their food. The food produced is glucose. Oxygen is then released into the air as a by-product of photosynthesis.

During metabolism at night, plants take in oxygen and release carbon dioxide.

Respiration and the Biogeochemical Cycle

The oxygen released by plants is used by humans, animals, and other organisms for respiration. We make use of oxygen to break down simple sugars and produce energy to sustain ourselves. During the process of respiration, organisms take in oxygen and release carbon dioxide into the air.

These processes are being repeated continuously thus forming the oxygen cycle.

Carbon Cycle and the Biogeochemical Cycle

The carbon cycle shows how the carbon in the atmosphere is utilized. The carbon cycle shows how carbon atoms travel from the atmosphere into organisms in the earth and then back into the atmosphere over and over again.

Steps of Carbon Cycle

Carbon cycle consists of four important steps and they are;

  1. Photosynthesis
  2. Decomposition
  3. Respiration
  4. Combustion

Photosynthesis and the Biogeochemical Cycle

Plants are able to make their food during photosynthesis. Photosynthesis is the process whereby plants convert light energy into chemical energy through cellular respiration.

During photosynthesis, plants make use of carbon dioxide gotten from the atmosphere.

Decomposition and the Biogeochemical Cycle

Decomposition is a process where complex organic materials are broken into simple inorganic materials.

In this process, animals die, decay and decompose and their remains are stored in the earth’s crust. Over a large period of time, the layers of sediment build up on each other thereby causing pressure and heat from within the earth’s crust, thus generating fossil fuels.

Effect of Respiration in the Biogeochemical Cycle

Respiration is the process of inhaling oxygen and exhaling carbon dioxide.

Animals rely on plants for food, oxygen and energy. Our cells require the presence of oxygen to break down the food we consume through a process called cellular respiration.

Once oxygen is taken in, carbon dioxide is released into the atmosphere where it is then utilized by plants.

Effect of Combustion on the Biogeochemical Cycle

Combustion is the chemical process in which a substance reacts with oxygen to give off heat. The cars we use release energy by burning fossil fuels and combustion involves burning these fossil fuels to release energy.

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Nitrogen Cycle:

Nitrogen Cycle biogeochemical cycle

Nitrogen is an important element that is present in nature. It is needed for the growth of plants and enrichment of the soil. The nitrogen cycle refers to how the nitrogen elements present in the air are converted to a more usable form.

The nitrogen cycle consists of some very important processes that show how the conversion and utilization of nitrogen takes place.

Steps of Nitrogen Cycle

Here are the steps involved in nitrogen cycle

  1. Nitrogen Fixation
  2. Nitrification
  3. Denitrification
  4. Ammonification
  5. Assimilation

Nitrogen Fixation

Nitrogen fixation is the process whereby the nitrogen(N) present in the air is converted to ammonia(NH3).

During this process of nitrogen fixation, the nitrogen present in the air is converted into a more suitable form for the soil. A symbiotic bacteria which is known as diazotroph, which happens to be present in the soil is responsible for this conversion.


Nitrification is the conversion of ammonia into nitrites and further into nitrates by nitrobacter. This is a very important process in the nitrogen cycle.


The assimilation process of the nitrogen cycle happens when plants take in the nitrogen made available in the soil.


Ammonification is the process of the conversion of the nitrogen present in organic matter to ammonium.


Denitrification is a process that involves the conversion of nitrite into atmospheric nitrogen.

Water Cycle and Its Relationship with the Biogeochemical Cycle

Water Cycle

The water cycle, also called the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the earth.

Steps of Water Cycle

Here are the steps involved in water cycling.

  1. Evaporation
  2. Condensation
  3. Precipitation
  4. Runoff and Percolation


The first step to understanding the water cycle is knowing how the process of evaporation works. Water exists in three phases: solid, liquid, and gas. Evaporation is the process of water changing from a liquid form to a gas form.


Condensation is the process where water vapor turns back to liquid water.

When water evaporates into the atmosphere, it cools and turns back to tiny water droplets which in turn form clouds. When the clouds get full, we enter the next step of the water cycle.

Effect of Precipitation on the Biogeochemical Cycle

Precipitation is the process whereby any liquid or frozen water present in the atmosphere falls back to the surface of the earth.

Eventually, the clouds become too full of water droplets. And as they become too full, the water droplets fall, thus forming rain or snow or some other type of precipitation.

Runoff and Percolation

Percolation is the movement of water through the soil. Some amount of the water stays on the earth’s surface in reservoirs, lakes and oceans. Others seep down into the ground. It takes nine days to complete the water cycle.

Relationship Between the Sedimentary Cycle and the Biogeochemical Cycle

The sedimentary cycle is a biogeochemical cycle that involves the weathering of rocks and erosion of minerals with its circulation to the environment. The reservoir of the sedimentary cycles is the earth’s crust.

Cycles under this category are the sulphur cycle, phosphorus cycle etc.

Sulfur Cycle:

Sulfur Cycle

The sulfur cycle is a biogeochemical cycle in which sulfur moves between waterways, rocks, and living systems.

Steps of Sulfur Cycle

The following are the important steps of the sulfur cycle:

  1. Decomposition of organic compounds
  2. Oxidation of Hydrogen Sulfide to Elemental Sulfur
  3. Oxidation of elemental Sulfur
  4. Reduction of Sulfates

Decomposition of Organic Compounds

Protein degradation produces sulfur-containing amino acids. Desulfotomaculum bacteria convert sulfates to hydrogen sulfide (H2S).

Oxidation of Hydrogen Sulfide to Elemental Sulfur

Elemental sulfur is formed when hydrogen sulfide oxidizes. The oxidation process is initiated by photosynthetic bacteria from the Chlorobiaceae and Chromatiaceae families.

Oxidation of Elemental Sulfur

Plants cannot directly utilize the element sulfur found in the soil. As a result, chemolithotrophic bacteria convert it to sulfates.

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Reduction of Sulfates

Desulfovibrio desulfuricans converts sulfates to hydrogen sulfide. This happens in two steps:

First Step: Using ATP, the sulfates are first converted to sulfites.

Second Step: Sulfite is reduced to hydrogen sulfide.

Phosphorus Cycle:

Phosphorus Cycle

The biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere is known as the phosphorus cycle.

Steps of Phosphorus Cycle

The following are the important steps of phosphorus cycle:

  1. Weathering
  2. Absorption by Plants
  3. Absorption by Animals
  4. Return to the Environment through Decomposition

Weathering Processes in the Biogeochemical Cycle

Phosphorus can be found in abundance in rocks. Because of this, the phosphorus cycle begins in the earth’s crust. The phosphate salts are extracted from the rocks. These salts are washed away into the ground and mixed with it.

Absorption of Phosphorus by Plants in the Biogeochemical Cycle

Plants absorb phosphate salts that have been dissolved in water. However, the phosphorus content of the soil is very low. That is why farmers use phosphate fertilizers on their agricultural land.

Aquatic plants absorb inorganic phosphorus from the bottom layers of bodies of water. Because phosphate salts do not dissolve properly in water, they have an impact on plant growth in aquatic ecosystems.

Absorption of Phosphorus by Animals in the Biogeochemical Cycle

The animals obtain phosphorus from plants or from plant-eating animals. When compared to rocks, plants and animals have a faster phosphorus cycle.

Return of Phosphorus Back to the Ecosystem in the Biogeochemical Cycle

When plants and animals die, microorganisms decompose them. The organic form of phosphorus is converted into the inorganic form, which is recycled to soil and water during this process.

Soil and water will end up in sediments and rocks, which will then weather and release phosphorus. As a result, the phosphorus cycle begins again.

These cycles demonstrate the way in which energy is utilized in the ecosystem.

In Summary

The biogeochemical cycle is the way that conserved matter moves between the biotic and abiotic parts of Earth’s systems. Matter can be stored for long periods in what are called reservoir pools or held for shorter amounts of time in what are called exchange pools.

Carbon, nitrogen, oxygen, phosphorus and sulfur are examples of chemical substances that are recycled by biogeochemical processes. They move in cycles through different geological forms and reservoirs such as rocks, water bodies and living organisms.

Water Cycle

The Water Cycle is a biogeochemical cycle that involves the movement of water and other elements through organisms and nonliving parts of the environment. These cycles help regulate Earth’s climate and the health of terrestrial and aquatic ecosystems.

Essential elements like carbon, nitrogen, oxygen, and phosphorus continuously move between living (bio-) and nonliving (geo-) components of the Earth. These elements form part of the biotic and abiotic parts of ecosystems. Biogeochemical elements may be held for different amounts of time in each of the parts of the ecosystem that they move through. These elements are recycled by these ecosystems to ensure the survival of all forms of life on Earth.

Water is a crucial element for all organisms to survive. The water cycle is a global phenomenon that takes place on, above, and below Earth’s surface. The water cycle includes the processes of evaporation, condensation, precipitation, and re-adsorption. The water cycle is also affected by changes in Earth’s temperature.

Nutrients such as nitrogen, phosphorus, and sulfur are continually cycling between the soil, plants, animals, microorganisms, and the atmosphere in an ecosystem. The cycling process occurs when the organisms consume and return nutrients to the ecosystem through plant growth, death, decomposition, and natural processes such as erosion and floods. The nutrient cycles are controlled by the biogeochemical process of mineralization that converts organic nutrients to mineral forms and back again for reuse.

Carbon Cycle

All the atoms of carbon and nitrogen move around the planet in cycles. These atoms are part of living things like plants and animals, and also non-living things like water and air.

READ MORE: Plant and Animal Cells and Their Functions

These atoms can be stored in the body of an animal, or they can travel through the water, air, and sedimentary rocks. These are called biogeochemical cycles.

When an animal dies, the atoms of carbon and nitrogen can be reabsorbed by the soil or by plants growing in that area. These atoms can then be recombined with water to form glucose or other organic compounds. These are the building blocks of all living things. The recombined molecules can then be used to make the skeleton of an animal or of a rock.

NEON studies the flow of matter and energy in the earth’s system. This includes the major biogeochemical processes that cycle carbon, oxygen, nitrogen and phosphorus. It also includes human activities that impact element fluxes.

All of these cycles are interconnected. They are a result of the harmonious interaction between living and nonliving factors in an ecosystem. This is why the Earth can support life.

Nitrogen Cycle

The elements nitrogen, carbon, and phosphorus are essential to life on Earth. These and many other elements are continuously recycled from the nonliving (abiotic) components of a major ecosystem — such as a lake or forest — to its living components, such as plants and animals. This process is known as a biogeochemical cycle.

Nitrogen is found in both organic and inorganic forms. The organic forms include the proteins in living organisms and dead plants. Inorganic forms include nitrogen gas in the atmosphere and the nitrogen compounds nitrites and nitrates in soil. Some bacteria, such as cyanobacteria, can convert nitrogen from inert gas into the plant-available form ammonia through a process called nitrogen fixation.

Plants absorb the usable nitrogen compounds from the soil through their roots and utilise them for protein production. Animals assimilate nitrogen by eating these plants and other organisms containing nitrogen. The nitrogen then becomes part of the waste products of these organisms, which are decomposed by fungi and bacteria.

These decomposers help make the nutrient compounds available to new plants in the food chain. This is a key function of the decomposition process in all living ecosystems, including humans’. Phosphorus, a very important nutrient for all organisms, is also recycled by these same bacteria in the soil. Phosphorus is a component of calcium phosphates in bones and phospholipids in cell membranes.

Phosphorus Cycle

Phosphorus is a key component of both DNA and RNA and is one of the main ingredients along with nitrogen in artificial fertilizers used for agriculture. It is also essential to plant and animal growth. The phosphorus cycle is closely linked with the carbon and nitrogen cycles.

Like the nitrogen and carbon cycles, phosphate moves in a circular motion from the lithosphere to the atmosphere and back again. It is a natural process that is controlled by the weather and biotic processes. It is also accelerated by human activities such as the mining of phosphate-bearing rock for the production of fertilizers and detergents, and runoff from agricultural land. This accelerated movement causes an overabundance of phosphate in water systems, which leads to the excessive growth of algae populations that reduces oxygen levels and kills other aquatic life.

The phosphate that is not taken up by plants is washed away into the soil and is absorbed by microorganisms, fungi, and bacteria. When these organisms die and decompose, they release phosphate back into the ecosystem. This phosphorus is then reclaimed by plants, and the cycle continues. Like the nitrogen and carbon cycles, this phosphorus cycle is controlled by the weather and biotic and abiotic processes. It is also accelerated by many human activities such as the mining of phosphate-bearing rocks for the production of fertilizers and detergents, as well as the shipping of foods from farms to cities, where they are washed into local water systems.

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