Biogeochemical Cycles (HL IB ESS OLD COURSE - IGNORE)

Revision Note

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

Diagram of the stores, sinks & sources for IB HL Environmental Systems and Societies
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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Alistair Marjot

Author: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

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