dynamic equilibrium and the water and carbon cycles

  • 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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  • 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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  • 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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  • 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: 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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