Course review
Review each learning objective in this topic, then open its concept explanation or question set.
Learning objective
• Ensure chemical elements remain available to living organisms • Human impact affects ecosystem sustainability
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Learning objective
• Stores: equilibrium with environment • Sinks: net accumulation • Sources: net release
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Learning objective
• Organic: organisms, crude oil, natural gas • Inorganic: atmosphere, soils, oceans
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Learning objective
• Photosynthesis, feeding, defecation, respiration, death, decomposition
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Learning objective
• Capturing atmospheric CO₂ and storing as solid/liquid • Natural: trees absorb CO₂ → biomass • Fossilization into coal, oil, natural gas
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Learning objective
• Sink: photosynthesis > respiration (e.g., young forest) • Store: balanced (e.g., mature forest) • Source: respiration > photosynthesis (e.g., forest fire)
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Learning objective
• Fossil fuels are stores of carbon with unlimited residence times • They were formed when ecosystems acted as carbon sinks in past eras and become carbon sources when burned • Consider: the concept of fossil fuels but not the detail of how and when coal, oil and natural gas were formed
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Learning objective
• Agricultural systems can act as carbon stores, sources and sinks, depending on the techniques used • Regenerative agricultural methods, such as crop rotation, cover crops and no till, will promote the role of soil as a carbon sink whereas drainage of wetland, monoculture • Cropping over a longer timescale (e.g., timber production) and the subsequent use of harvested products will also affect these roles
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Learning objective
• Carbon dioxide is absorbed into the oceans by dissolving and is released as a gas when it comes out of a solution • While oceans act as a carbon sink, the human use of fossil fuels releases inorganic carbon at a faster rate than oceans can absorb it
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Learning objective
• Increases in concentrations of dissolved carbon dioxide cause ocean acidification, harming marine animals • Small decreases in pH can interfere with calcium carbonate deposition in mollusc shells and coral skeletons
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Learning objective
• Measures are required to alleviate the effects of human activities on the carbon cycle • Consider at least three required measures • These include low-carbon technologies, reduction in fossil-fuel burning/soil disruption/deforestation, carbon capture through reforestation and artificial sequestration
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Learning objective
• The lithosphere contains carbon stores in fossil fuels and in rocks, such as limestone, that contain calcium carbonate • The residence time for carbon in these stores can be hundreds of millions of years
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Learning objective
• Reef-building corals and molluscs have hard parts that contain calcium carbonate that can become fossilized in limestone • Limestone is the largest store of carbon in Earth systems • Not all limestone is formed by fossilization of animal remains; it can also be formed by both biological and non-biological processes • Details of these processes are not required
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Learning objective
• In past geological eras, organic matter from partially decomposed plants became fossilized in coal, and partially decomposed marine organisms became fossilized in oil • Formation of coal, oil and gas was greatest in specific geological eras when conditions were most suitable
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Learning objective
• Methane is produced from dead organic matter in anaerobic conditions by methanogenic bacteria
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Learning objective
• Residence time: ~10 years in atmosphere • Oxidized to CO₂ • Potent greenhouse gas
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Learning objective
• Organic: proteins in organisms and dead matter • Inorganic: atmospheric N₂, ammonia, nitrites, nitrates
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Learning objective
• Nitrogen fixation: N₂ → ammonia • Nitrification: ammonia → nitrates • Denitrification: nitrates → N₂ • Decomposition: amino acids → ammonium
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Learning objective
• Only in anaerobic conditions (waterlogged soils) • Insectivorous plants use insects as nitrogen source
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Learning objective
• Plants cannot fix nitrogen • Require mutualistic associations with nitrogen-fixing bacteria
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Learning objective
• Mineral uptake, photosynthesis, consumption, excretion, death, decomposition, ammonification
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Learning objective
• Deforestation, agriculture, aquaculture, urbanization
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Learning objective
• Industrial production of ammonia for fertilizer • From nitrogen and hydrogen
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Learning objective
• Exceeded due to human activities • Nitrate increases in biosphere • Major cause: inorganic fertilizers for crops
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Learning objective
• Address uncontrolled nitrogen use • Bring nitrogen cycle within planetary boundaries
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