Biogeochemical Cycles (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Introduction to Biogeochemical Cycles
Biogeochemical cycles are natural processes that circulate the chemical elements necessary for life
They include cycles such as:
The carbon cycle
The nitrogen cycle
The hydrological cycle
These cycles ensure that these elements continue to be available to living organisms
This means they play a very important role in maintaining the balance of ecosystems and supporting life on Earth
Human impact
Human activities such as burning fossil fuels, deforestation, urbanisation and agriculture can disrupt biogeochemical cycles
This can lead to environmental imbalances and threaten the sustainability of ecosystems
For example, deforestation can disrupt the carbon cycle by reducing the number of trees available to absorb carbon dioxide from the atmosphere
Components of biogeochemical cycles
Biogeochemical cycles are made up of:
Stores
Sinks
Sources
A component in a biogeochemical cycle can be described as a store, sink or source depending on the size of its net input relative to its net output
Stores:
Also known as storages
They are "reservoirs" where elements are held for varying periods of time
They represent areas where the element remains in equilibrium with the environment i.e. the total input of the element is equal to the total output
Examples include oceans, atmosphere, soil and living organisms
For example, the ocean serves as a major store of carbon in the carbon cycle, with dissolved carbon dioxide being absorbed by seawater
At the same time, an equivalent amount of carbon dioxide is released back into the atmosphere, maintaining equilibrium
They can either be natural or artificial
Sinks:
Sinks represent parts of the cycle where a particular element accumulates over time
They are areas where the total input of the element is greater than the total output
This results in the net accumulation of the element
For example, fossil fuel deposits act as sinks for carbon in the carbon cycle, storing carbon that was once part of living organisms
They can either be natural or artificial
Sources:
Sources release elements into the cycle
They represent parts of the cycle where the total output of the element is greater than the total input
This results in net release of the element
For example, volcanic eruptions release large amounts of carbon dioxide into the atmosphere, acting as a source in the carbon cycle
They can either be natural or artificial
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