Example 1
A forest gains 90 tonnes of carbon by photosynthesis and loses 65 tonnes through respiration and decay in one year. Find the net change.
Change =90−65=+25 tonnes of carbon. The forest store grows by 25 tonnes.
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Year 9
Combustion and carbon budgets
Calculate changes in carbon stores from supplied input and output fluxes.
Method and worked examples
Combustion of carbon-containing fuels transfers carbon to the surroundings, commonly as carbon dioxide when oxygen is sufficient. Fossil fuels store carbon that was buried over geological timescales. Burning them can release that carbon much faster than natural long-term storage replaces it. Forest fires also transfer biomass carbon; regrowth can remove some atmospheric carbon later, depending on conditions and land management.
A carbon budget compares inputs and outputs for a specified reservoir and time interval. Change in store = total inputs − total outputs. Positive values mean the store grows; negative values mean it shrinks. Use the same units and count each flux once. A reservoir can gain carbon while carbon remains conserved overall, because another reservoir supplied it. These simplified budgets use supplied data.
Example 1
Example 2
An air reservoir receives 18 units from combustion and 12 from respiration, while photosynthesis removes 24. Find its change.
Inputs =18+12=30. Change =30−24=+6 units. Its carbon store increases.
Watch out: Carbon has moved from other reservoirs. Conservation applies to the full system, not to one store in isolation.