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The Carbon Cycle

2.3 Biogeochemical Cycles

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Carbon Sequestration

Carbon can be sequestered meaning atmospheric carbon dioxide is captured and transformed into solid or liquid form (e.g. to plant biomass by photosynthesis).

Through fossilisation it can be transformed into coal, oil or natural gas.

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Residence Time

Residence time is the amount of time carbon atoms remain stored.

For fossil fuels (coal, oil and natural gas) the residence time is hundreds of millions of years (without human interference).

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Carbon stores, sinks and sources

A carbon sink is one where net intake of carbon is greater than release.

If photosynthesis outweighs respiration, the system will be a carbon sink.

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Carbon stores, sinks and sources

A carbon sink is one where net intake of carbon is greater than release.

If photosynthesis outweighs respiration, the system will be a carbon sink.

TASK1 :

Draw summary diagrams to outline how a young forest, and mature forest, and trees being felled are carbon sinks, stores and sources respectively.

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Carbon stores, sinks and sources

A carbon sink is one where net intake of carbon is greater than release.

If photosynthesis outweighs respiration, the system will be a carbon sink.

TASK 2

Produce two lists, one of agricultural practices that lead to land becoming a carbon sink, and one list of those that lead to land becoming a carbon source.

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Carbon stores, sinks and sources

Carbon sink practices:

Crop rotation, cover cropping, no till farming.

Carbon source practices:

Wetland drainage, mono cultures, heavy tillage.

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Dissolved carbon in the oceans

Carry out research:

How can increased carbon dioxide level negatively affect marine life?

Hint: shell formation.

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Alleviating human impacts on the carbon cycle

TASK

Describe three methods that can be used to alleviate human impacts on the carbon cycle.

Consider:

  • Low carbon technologies
  • Reducing practices that emit carbon dioxide
  • Carbon capture

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Alleviating human impacts on the carbon cycle - Answers

Low carbon technologies

  • Energy generation: solar panels, wind power, hydropower…
  • Energy storage to store energy from renewable sources: new types of battery, thermal storage…
  • Transportation: electric vehicles, hydrogen fuel cells, public transport

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Alleviating human impacts on the carbon cycle - Answers

Reducing practices that emit carbon dioxide

  • Transportation: cycling or walking, using public transport
  • Circular economy: re-use and recycle to avoid producing new materials
  • Any example of reducing energy consumption (use the AC/heating less

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Alleviating human impacts on the carbon cycle - Answers

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Carbon capture

  • Reforestation (allowing trees to trap carbon through photosynthesis)
  • Techniques to capture carbon emitted from industrial processes e.g. Boundary Dam Project (Canada) - capture CO2 from a coal fired power station and injects it into underground reservoirs

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Carbonate rocks

Reef-building corals and molluscs in the ocean produce hard shells containing calcium carbonate.

As they fall to the bottom of the ocean and become buried over millions of years they form limestone.

This is a storage of carbon with a residence time of millions of years.

This is an example of carbon stored in the lithosphere.

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Methane

In anaerobic (no oxygen) conditions, dead organic matter is decayed by methanogens, releasing methane (CH4).

These conditions occur in swamps, rice paddies, and the stomachs of cattle.

Methane has a residence time of about 10 years in the atmosphere. It is a strong greenhouse gas (it traps heat).

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