dynamic equilibrium and the water and carbon cycles
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- Created by: beaw18
- Created on: 04-05-19 12:21
dynamic equilibrium
- natural systems which have been unaffected by human activity maintain a dynamic equilibrium - inputs and outputs balance each other out, and if they fluctuate, balance is restored
- negative feedback loops restore balance
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urbanisation
- conversion of land use from rural to urban
- artificail surfaces such as tarmac replace natural ones - usually impermeable, no water storage and primarily runoff, no underground water storage
- we have created our own ways to ensure water drainage, including gutters, sewerage systems etc
- as a result large amounts of water flow to rivers, leading to rapid rise in water levels
- urbanisation of floodplains (natural storage areas from water) increases river level and flood risk
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farming
- clearance of forest for for farming reduces carbon storage in soils and trees
- ploughing exposes soil to oxidation - increases evaporation rates
- wind and water erode soils most when crops have been lifted
- where farming replaces natural grasslands, NPP is greater that original
- crop irrigation diverts water to crops
- interception of rainfall is less when forest is replaced, as is evapostranspiration rates
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forestry
- higher rates of rainfall interception in plantations in natural forests
- increased evapotranspiration - water stored on leaf surfaces evaporates into atmosphere
- reduced runoff and stream discharge - high interception and evaporation rates, absorbtion of water by tree roots, drainage basin hydrology altered
- transpiration rates increased
- felling/timber harvesting increases runoff and stream discharge
- increase of carbon stores - mature forest trees conatain an average of 170-200 tonnes, 10x higher than grasslands and 20x higher than heath lands
- trees a carbon sink
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aquifers
- aquifers: permeable/porous water-bearing rocks which are saturated with water
- water extracted from them via boreholes and wells
- aquifers cause springs which feed into rivers/act as the river's source - when surface of ground dips below water table, water fills this space
- upper surface of saturation is called the water table - height fluctuates seasonally, as is also effected by drought/heavy rainfall
- formed by precipitation infiltrating soils and saturating it
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artesian basins
- sedimenatry rocks form basin-like structure (syncline)
- an aquifer confined between impermeable rock layers makes groundwater under artesian pressure
- if groundwater is tapped into, water will flow to surface under its own pressure - spouts like a natural water fountain
- london sits on top of artesian basin
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fossil fuels and the carbon cycle
- coal, oil and gas drive industrialisation
- gloabl economy still relies heavily on fossil fuels despite rise of renewables - 2013: 87% of global energy consumption
- fossil fuel consumption releases 10 billion tonnes of CO2 annually
- since 1750, human activites have total 2000 gigatonnes of carbon - 3/4 of emissions are from the burning of fossil fuels
- in the period between 2000-2009, emissions higher than any previous decade
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fossil fuels and carbon cycle: sequestration of wa
- combustion of fossil fuels and transfer of carbon from geological store to atmosphere and oceans are main drivers of present-day global warming
- possible solution - capturing and storing CO2 released from fossil fuels in industry
- new technology of carbon sequestrian known as 'carbon capture and storage' (CCS)
- CO2 is separated from power station emissions
- CO2 compressed and transported via pipeline into storage areas
- then it is injected into porous rocks deep in ground where it is stored permanently
- could eventaully play an important role in reducing role of fossil fuels in climate change
- problems with CCS
- expensive
- uses large amounts of energy - 20% of a powerplant's input is needed to separate and compress CO2
- requires storage resevoirs with specific geological conditions
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feedback loops in the water cycle
- climate change causes evapoartion increase, atmosphere holds more vapour
- higher cloud coverage and more precipitation
- positive feedback as water vapour is a greenhouse gas - increases warming temps
- more vapour could cause negative feedback - more vapour, more cloud cover, reflects solar radiation back into space, temp falls
- equilibriums of drainage basins can be changed too; system responds to increased preciptation and evaporation - negative: river flow higher, aquifers recharged
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feedback loops in the carbon cycle
- carbon cycle currently under state of disequilibrium due to human emissions
- increased CO2 in atmosphere, more acidic oceans, fluxes between stores
- negative feedback: CO2 stimulating photosynthesis (carbon fertilisation), excess CO2 is stored in biosphere rather than atmosphere
- this would rely on other factors such as sunlight, water, etc
- positive feedback: global warming intensifies carbon cycle, speeds up decomposition, releases more CO2, amplifies greenhouse effect
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