The Physical Environment (AS); Biogeochemical Cycles (Complete)

Nutrients are processed, converted and recycled. Interlinked cyclical processes mean that small # of material continually recycled can support ecosystems over long time. Biogeochemical cycles show processes moving particular elements between their reservoirs in biosphere, atmosphere, hydrosphere and lithosphere

In state of dynamic equilibrium so little/no change in # of carbon in each reservoir of cycle Atmosphere- CO², methane, CO Hydrosphere- hydrogen carbonate ions, dissolved CO²; surface waters 500 Gt + deep ocean 35,000 Gt Biosphere- Carbs (cellulose,starch, etc), proteins,lipids; living organisms 470 Gt + 3700 Gt Lithosphere- Carbonaceous rocks like limestone 20m Gt, fossil fuels 10,000 Gt

Photosynthesis- captures light energy using pigments like chlorophyll. Makes CO² & H²O into carbs, could be converted into proteins & lipids Respiration- Releases energy captured in photosynthesis to drive metabolic processes. Aerobic returns carbon to atmosphere as CO² & breaks down organic compounds more completely and w/ more energy than anaerobic- which allows some organisms to survive + use food sources in O²-deficient environments. usually returns CO² to atmosphere as methane.

Food webs- Some carbs, proteins,lipids made by plants are eaten by herbivores; may then be eaten by carnivores. Feeding relationships combine to make food webs Fossilisation- Incomplete decomposition of dead organic matter, often in anaerobic conditions; can make substances forming long-term carbon stores (e.g fossil fuels) Organisms like molluscs make exoskeletons including calcium carbonate. Can make rocks like limestone- now contain most of carbon in lithosphere Combustion- Burning of organic materials releases CO². Natural fires in forests may start by lightning

Many human activities alter rates of movement of Carbon through cycle. Can unbalance natural dynamic equilibrium of cycle + change distribution of Carbon in reservoirs of cycle. Things humans affect: - changes in photosynthesis - changes in aerobic respiration - changes in anaerobic respiration - carbonic acid concentration in sea - methane releases from fossil fuels - combustion - biomass movements

• Deforestation ↓ movement of Carbon from atmosphere → biomass • afforestation ↑ movement of carbon from atmosphere → biomass • marine pollution w/ toxic materials ↓ phytoplankton populations =↓ absorption of dissolved CO² . Some naturally sink to seabed after dying,↑# of carbon in marine sediments.

Carbon in dead organic matter in soil → gradually released as CO² by aerobic respiration of soil organisms, esp bacteria + fungi Ploughing ↑O² supply to decomposers living in soil so aerobic decomposition = more rapid. # of carbon in soil dead organic matter store ↓ & amount in atmosphere ↑.

Absence of O² → respiration by anaerobic soil organisms releases methane. If released into atmosphere → gradually oxidised to CO² Anaerobic environments made by human activities: - rice paid fields -landfill sites - anaerobic sediments in reservoirs - livestock intestines Anaerobic environments destroyed by drainage: - waterlogged fields - marshlands - peat bogs

Humans don’t directly cause CO² to dissolve/ exsolve but their activities affecting concentration of CO² in atmosphere will after these processes, making a new equilibrium. Dissolved CO² is in equilibrium w/ carbonic acid which dissociates, making hydrogen carbonate + hydrogen ions. Conc of hydrogen ions affects pH of sea = ↑ in dissolved CO² = ↓ pH of water. As atmospheric CO² conc ↑ dissolved CO² conc. ↑, so hydrogen ion conc. ↑→ sea more acidic.

Combustion of fossil fuels & wood releases large # of CO² into atmosphere. Methane may be released into atmosphere during fossil fuel extraction.

Humans don’t directly move large # of carbon in biomass betw. areas, but they can produce local changes w/ environmental impacts: - addition of compost/ mulch to improve soil fertility; - deforestation & crop harvesting → reduced soil organic matter & soil erosion; - movement of biomass into sea when sewage is discharged; - movement of marine biomass → terrestrial system by fishing/aquaculture

A range of strategies of sustainable management: - conservation of biomass carbon stores - use of alternatives to fossil fuels - Carbon sequestration - carbon capture and storage (ccs)

Habitats like peat bogs & forests have huge # of Carbon - protecting these from exploitation/damaging land-use change = important to prevent even↑CO² releases Renewable energy resources & nuclear power make ↓CO² emissions than fossil fuels.

Large-scale tree planting could remove a lot of CO² from atmosphere & slow/reverse ↑CO² conc. Once tree reaches full size there’ll be no further net storage of Carbon but standing tree = carbon reservoir. If trees were harvested & kept as wood → replanting would make + Carbon storage as new tree grows.

Involves capturing carbon, usually as CO² , so that its not released into atmosphere

-Changing the fuel used, or the way it is combusted Gasification → converts fuel like coal into gaseous hydrogen and CO² CO² → can be removed for storage. Hydrogen → distributed for vehicle use/homes/ industry. When burnt, exhaust gas have water vapour but no CO² Oxy-fuel combustion systems use pure oxygen so only CO² & water vapour are made. Water vapour can be removed by cooling gases so it condenses. Capture of CO² = easier as not mixed w/ other gases.

-It may be expensive & require development of new technology -May also make removal of CO² easier and more efficient. - May not be practical for many small sources like small vehicles -Would be better if fuel was modified at large-scale facility where carbon is captured before fuel is used, so it wouldn’t release CO² when burnt

CO² can be removed from the exhaust gases of fossil fuel combustion w/ several methods; - dissolving it in a solvent - high pressure membrane filtration - absorption/desorption processes - cryogenic separation - graphene adsorption None of these methods are fully developed & large scale costs = uncertain.

-Most proposals involve storage underground in suitable geological structures like depleted aquifers, oil/gas fields. -Can also be injected into oil reservoirs to provide pressure needed in secondary oil recovery -Research shows CO² pumped into fractured basalt may react w/ minerals in rock, making solid carbonate materials

It is a component of many essential biological molecules

Atmosphere- N gas (N²) Biosphere- Living organisms; DNA, proteins (cell membranes, hormones,etc) Dead organic matter; proteins- release ammonium compounds as decompose Lithosphere- Soil; ammonium compounds, nitrites, nitrates Rocks; minerals with nitrogen Hydrosphere- Dissolved nutrients & ammonium ions

Processes like lightning & meteor trails give energy for atmospheric nitrogen & oxygen to react—> make oxides of nitrogen

Some micro-organisms can chemically reduce nitrogen to ammonia, which may be free-living bacteria in soil or may live symbiotically in root nodules of legumes

Nitrogen passes between organisms as amino acids & proteins into food