What you’ll learn25 learning objectivesChoose one objective for a focused lesson, or study the complete topic.2.3.1Biogeochemical cycles purpose• Ensure chemical elements remain available to living organisms• Human impact affects ecosystem sustainabilitySyllabus objective2.3.2Cycle components• Stores: equilibrium with environment• Sinks: net accumulation• Sources: net releaseSyllabus objective2.3.3Carbon stores• Organic: organisms, crude oil, natural gas• Inorganic: atmosphere, soils, oceansSyllabus objective2.3.4Carbon flows• Photosynthesis, feeding, defecation, respiration, death, decompositionSyllabus objective2.3.5Carbon sequestration• Capturing atmospheric CO₂ and storing as solid/liquid• Natural: trees absorb CO₂ → biomass• Fossilization into coal, oil, natural gasSyllabus objective2.3.6Ecosystems as carbon stores/sinks/sources• Sink: photosynthesis > respiration (e.g., young forest)• Store: balanced (e.g., mature forest)• Source: respiration > photosynthesis (e.g., forest fire)Syllabus objective2.3.7Fossil fuels as carbon stores• 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 formedSyllabus objective2.3.8Agriculture as carbon store/source/sink• 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 rolesSyllabus objective2.3.9Ocean carbon exchange• 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 itSyllabus objective2.3.10Ocean acidification• 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 skeletonsSyllabus objective2.3.11Alleviating carbon cycle impacts• 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 sequestrationSyllabus objective2.3.12(HL)—Lithosphere carbon stores• 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 yearsSyllabus objective2.3.13(HL)—Carbonate fossilization• 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 requiredSyllabus objective2.3.14(HL)—Fossil fuel formation• 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 suitableSyllabus objective2.3.15(HL)—Methane production• Methane is produced from dead organic matter in anaerobic conditions by methanogenic bacteriaSyllabus objective2.3.16(HL)—Methane cycle• Residence time: ~10 years in atmosphere• Oxidized to CO₂• Potent greenhouse gasSyllabus objective2.3.17(HL)—Nitrogen cycle stores• Organic: proteins in organisms and dead matter• Inorganic: atmospheric N₂, ammonia, nitrites, nitratesSyllabus objective2.3.18(HL)—Bacterial roles in nitrogen cycle• Nitrogen fixation: N₂ → ammonia• Nitrification: ammonia → nitrates• Denitrification: nitrates → N₂• Decomposition: amino acids → ammoniumSyllabus objective2.3.19(HL)—Denitrification conditions• Only in anaerobic conditions (waterlogged soils)• Insectivorous plants use insects as nitrogen sourceSyllabus objective2.3.20(HL)—Plant nitrogen fixation• Plants cannot fix nitrogen• Require mutualistic associations with nitrogen-fixing bacteriaSyllabus objective2.3.21(HL)—Nitrogen cycle flows• Mineral uptake, photosynthesis, consumption, excretion, death, decomposition, ammonificationSyllabus objective2.3.22(HL)—Human impacts on nitrogen cycle• Deforestation, agriculture, aquaculture, urbanizationSyllabus objective2.3.23(HL)—Haber process• Industrial production of ammonia for fertilizer• From nitrogen and hydrogenSyllabus objective2.3.24(HL)—Nitrogen planetary boundary• Exceeded due to human activities• Nitrate increases in biosphere• Major cause: inorganic fertilizers for cropsSyllabus objective2.3.25(HL)—Global collaboration needed• Address uncontrolled nitrogen use• Bring nitrogen cycle within planetary boundariesSyllabus objective
EduNinja