Biogeochemical Cycles

How elements move between living and nonliving components of an ecosystem.

pH levels
Benefits that humans receive from healthy ecosystems

Definition of Biogeochemical Cycles

Biogeochemical cycles are the pathways through which elements move between living and nonliving components of an ecosystem. These cycles involve a reservoir pool, where elements are stored in large amounts, and an exchange pool, where elements are exchanged among organisms or with their environment. These cycles are vital for the continued existence of life on Earth. Some of the best known biogeochemical cycles include the nitrogen cycle, carbon cycle and phosphorous cycle.

The nitrogen cycle involves the conversion of atmospheric nitrogen into usable forms by bacteria in soil and water. This process is known as nitrification, and it allows plants to absorb nitrogen for growth. The carbon cycle involves the transfer of carbon dioxide from atmosphere to land-based ecosystems via photosynthesis before being released back into the atmosphere through respiration or combustion processes such as burning fossil fuels.

The phosphorous cycle involves transferring phosphorus from rocks on land to aquatic systems via runoff before returning to land again when animals excrete waste products containing phosphorus compounds. Understanding these cycles allow us to understand how deeply interconnected life on Earth is, and the ways in which they may be disrupted.

Carbon Cycle

Carbon and, by extension, the carbon cycle is essential to life on Earth All life on Earth is carbon-based: carbon is found in all living things, from plants and animals to bacteria and fungi. It cycles through the environment in a variety of ways, including photosynthesis, respiration, decay, and combustion processes such as burning fossil fuels. Photosynthesis captures carbon dioxide from the atmosphere and converts it into organic molecules that can be used by plants for growth.

Respiration releases this stored energy back into the atmosphere as carbon dioxide when organisms break down these molecules during metabolism. Decay further breaks down organic matter releasing more carbon dioxide back into the environment while also providing nutrients for new plant growth. Combustion processes release large amounts of carbon dioxide directly into the atmosphere which contributes to global warming if not managed properly.

Carbon reservoirs include oceans where dissolved CO2 is stored; soils where organic matter stores large amounts of carbon; rocks containing minerals which incorporate carbon and vegetation which stores significant amounts of atmospheric CO2 via photosynthesis before releasing it again through respiration or decay processes.

Nitrogen Cycle

Nitrogen is an essential element for life, and its movement through the nitrogen cycle plays a vital role in maintaining healthy ecosystems. Nitrogen-fixing bacteria in the soil and oceans convert atmospheric nitrogen into usable forms such as nitrates and ammonium which can be absorbed by plants for growth.

Volatilisation then releases these compounds back into the atmosphere where they are available to be used again. Mineralisation further breaks down organic matter releasing more nitrogen compounds before they are taken up by plants or converted to nitrate via nitrification. Immobilisation occurs when organisms in the soil take up these compounds like nitrates and ammonium from their environment, which results in them being unavailable for plants.

This cycle ensures that there is enough usable nitrogen available for all living things while also preventing it from accumulating in large amounts which could lead to eutrophication of aquatic systems.

Phosphorus Cycle

Phosphorous is essential for life on Earth, forming an important part of DNA among other things. The phosphorous cycle is the pathway through which phosphorus moves between living and nonliving components of an ecosystem. Phosphorus enters the soil from rocks, either in its inorganic form or as organic phosphate compounds. Plants take up this phosphorus for growth, incorporating it into their tissues and passing it up the food chain when they are consumed. It is released back to the environment upon the death and decay of an organism or in the excretion of waste products containing phosphorus compounds.

In addition to being taken up by plants, some forms of phosphorus can be adsorbed onto soil particles making them unavailable for uptake by plants. Bacteria can also convert plant-available phosphates to forms of organic phosphorous unavailable to plants, further limiting the availability of phosphorous to plants and their consumers. The availability of phosphorous may also be affected by pH levels. If soils are too acidic or alkaline, phosphorus can react with elements in the soil, leaving it inaccessible to plants. Understanding how these processes interact with each other is essential for maintaining healthy ecosystems.

Sulfur Cycle

The sulfur cycle is the pathway through which sulfur moves between living and nonliving components of an ecosystem. Sources of sulfur include matter decay in anaerobic environments and geologic sources such as volcanoes, hot springs, and rock-weathering processes. Sulfur combines with oxygen to create sulfates that can be taken up by plants for growth. Once the sulfates are assimilated by plants and bacteria, the sulfur can be passed up the food chain to consumers until it’s recycled through decay.


Certain types of bacteria, known as sulfur-reducing bacteria, can use the reduction of sulfur to create energy – including the specialized bacteria found around deep-sea hydrothermal vents. Bacteria also break down decaying matter containing sulfur so it can be released back into the environment.

This process is essential for maintaining healthy ecosystems as it ensures there is enough usable sulfur available while preventing its accumulation in large amounts which could lead to acidification of aquatic systems. Additionally, assimilation of sulfates into organic forms allows them to be stored within organisms until they are released again upon death or excretion, further contributing to the cycling of this element throughout an ecosystem.

Hydrologic Cycle

The hydrologic cycle, also known as the water cycle, is a continuous process of evaporation, transpiration, condensation and precipitation. Evaporation occurs when liquid water on the surface of oceans and other bodies of water turns into vapor which rises into the atmosphere. Transpiration is similar to evaporation but it occurs in plants; they release moisture from their leaves through tiny pores called stomata. Condensation happens when warm air cools down and forms clouds or fog droplets that eventually fall back to Earth as rain or snow. Precipitation is any form of water that falls from the sky such as rain, hail or snow. Finally, run-off refers to excess precipitation that flows over land surfaces before entering rivers and streams which then carry it back out to sea where it can start its journey again. The hydrologic cycle plays an important role in maintaining life on Earth by providing fresh drinking water for organisms and regulating global temperatures through evaporative cooling processes.

Oxygen Cycle

The oxygen cycle is the movement of oxygen through the atmosphere, lithosphere and biosphere – simply put, the sky, the Earth and living things. A major source of atmosopheric oxygen through photosynthesis, a process in which plants use sunlight to convert carbon dioxide into glucose and release oxygen as a byproduct. This oxygen then diffuses into the air where it can be taken up by animals during respiration. Bacteria also play an important role in this cycle; they oxidize organic matter during decomposition, gaining energy. The importance of these processes cannot be overstated; without them, life on Earth would not exist as we know it today. Photosynthesis is essential for the flow of both energy and oxygen, while respiration allows us to take in vital oxygen for our cells to function properly. Bacterial oxidation helps keep ecosystems balanced by cycling nutrients between living organisms and their environment.

Human impacts on Biogeochemical Cycles

Humans have had a significant impact on biogeochemical cycles, most notably the nitrogen and carbon cycles. Through activities such as burning fossil fuels, deforestation, and agricultural practices, humans are releasing large amounts of carbon dioxide into the atmosphere. This disruption to the carbon cycle has caused an increase in global temperatures due to the greenhouse effect.

Additionally, human activity has led to increased levels of nitrogen in the environment through fertilizer use and emissions from vehicles and factories. This excess nitrogen can lead to eutrophication – an overabundance of nutrients that causes algal blooms which deplete oxygen levels in water bodies leading to dead zones in the water.

Furthermore, humans have disrupted cycles by actions such as suppressing wildfires. This can cause changes in vegetation composition and soil fertility and affect nutrient cycling within ecosystems as well as species interactions with their environment. Ultimately, it is important for us to understand how our actions are impacting these vital biogeochemical cycles so that we may take steps towards mitigating our impacts on them.

Global Climate Change

Global climate change is a direct result of human activities disrupting the carbon cycle. The burning of fossil fuels and deforestation have caused an increase in atmospheric carbon dioxide, which traps heat from the sun and warms the planet. This process is known as the greenhouse effect, and it has led to rising global temperatures over time.

Other gases such as methane, nitrous oxide, and ozone also contribute to this warming trend by trapping additional heat in our atmosphere. These changes are having profound impacts on life on Earth; melting glaciers are causing sea levels to rise while extreme weather events become more frequent due to changing patterns in precipitation and temperature.

Additionally, ecosystems around the world are being disrupted as species struggle to adapt or migrate away from their current habitats that may no longer be suitable for them. It is essential that we take action now if we want to mitigate these effects before they become irreversible. We must reduce emissions of greenhouse gases through sustainable practices such as renewable energy sources, reforestation efforts, improved agricultural techniques, and increased efficiency standards for vehicles and appliances.

Biogeochemical Cycles and Ecosystem Services

Ecosystem services are the benefits that humans receive from healthy ecosystems, such as clean air and water, food production, climate regulation, and recreational opportunities. These services are provided by a variety of organisms in an ecosystem working together to maintain balance. Biogeochemical cycles play an important role in providing these services; they cycle essential elements like nitrogen and carbon through the environment which is necessary for life on Earth.

For example, photosynthesis uses carbon dioxide from the atmosphere to produce oxygen which we need to breathe. Additionally, nitrogen fixation converts atmospheric nitrogen into usable forms for plants and animals while decomposition recycles nutrients back into soil so that new life can grow. By understanding how biogeochemical cycles work within an ecosystem we can better manage our resources and ensure that these vital services continue to be available for future generations.


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