Biogeochemical Cycles (DP IB Environmental Systems & Societies (ESS))

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