Change over time in water and carbon cycle

• Land use changes- urbanisation

  -When land is changed from rural to urban the artificial surfaces are largely impermeable so they allow little or no filtration

  -high proportions of water from precipitation flows quickly into streams and rivers leading to rise in water level

  -urban development on flood plains reduces water storage in drainage basins increasing river flow and flood risk

  -also causes change to carbon cycle, the removal of vegetation and its replacement if urban surfaces results n reduced amounts of organic carbon
• land use changes- farming

  -the clearance of forest for farming reduces carbon storage in above and below ground biomass

  -losses through harvesting crops with only small amounts of organic matter returned to soils

  -erosion by wind and water is most severe when crops have been lifted and soils have little protective cover

  -crop irrigation diverts surface water from rivers and groundwater to cultivated land

  -ploughing increases evaporation and soil moisture loss
• the river kennet- impact on regional water cycle

  -rates of groundwater extraction gave exceeded rates of recharge

  -lower flows have reduced flooding and temporary areas of standing water and wetlands

  -lower groundwater levels have caused springs and seepages to dry up and reduced the chance of saturated overland flow
• aquifers

  -permeable porous water bearing rocks such as chalk
• artesian basins 


  -where sedimentary rocks form a basin-like structure it is confined between impermeable rock layers may contain groundwater which is under artesian pressure.
• Fossil fuels and the carbon cycle

  they impact significantly on the size of the atmosphere, ocean and biosphere carbon stores
• sequestration of waste carbon

  -the combustion of fossil fuels and the transfer of carbon from geological store to the atmosphere and the oceans is the main driver of present day global warming

  -one possible solution is to capture and store co2 released by industry (carbon capture storage)

  -involves separating the emissions and then compressing the co2 and transported by pipeline to storage areas

  -finally its injected into porous rocks deep underground where it is stored permanently

  -the Dax project in Yorkshire designed to transport the carbon by pipeline to the North Sea
• what are the limitations of carbon capture storage

  -involves big capital costs

  -uses large amounts of energy

  -requires storage reservoirs with specific geological conditions
• Feedback in the water cycle- positive

  -rising temperatures affect the water cycle, when its warmer evaporation increases and the atmosphere holds more vapour

  -this results in greater cloud cover and more precipitation

  -this creates a positive feedback effect

  -because water vapour is a green house has more vapour in the atmosphere increases absorption of long wave radiation further rising temperatures
• feedback in the water cycle- negative 


  -in drainage basins inputs and outputs of water are in equlibrium

  -the main input is precipitation and is balanced by outputs of evapotranspiration and run-off

  -the system responds to above average precipitation by increasing river flow and evaporation and increase water storage in permeable rocks
• negative feedback water cycle-small scale

  -in drought years shallow rooted trees like silver birch becomes stressed, water lost in transpiration is not replaced by a similar uptake of water from the soil

  -the tree responds by reducing transpiration losses by shedding some or all of its leaves
• negative feedback- carbon fertilisation

  -excess co2 is extracted from the atmosphere and stored in the biosphere

  -eventually much of this carbon would find its way into long term storage in soils and ocean sediments

  -however its conditional on the availability of other requirements for photosynthesis such as sunlight
• carbon cycle- positive feedback

  -global warming will intensify the carbon cycle, speed up decomposition and release more co2 to the atmosphere, thus amplifying the greenhouse effect
• Diurnal changes

  -significant changes occur within 24hrs of the water cycle, lower temperatures at night reduce evaporation and transpiration

  -flows of carbon vary, during the day time co2 flows from the atmosphere to vegetation. At night the flux is reversed

  without sunlight photosynthesis switches of
• satellite technology to monitor changes to the water and carbon cycle

  -arctic sea ice level- measures microwave energy radiated from earths surface

  -ice caps/ glaciers- measures surface height of ice sheet and glaciers using laser technology

  -sea surface temperatures- radiometers measure the wave band of radiation emitted from the ocean surface

  -deforestation- measurements of reflectivity of earths surface and land change uses
• seasons variations in the carbon cycle

  -shown by the net primary productivity of vegetation

  -durning the northern hemisphere summer trees are in full foliage and there is a net global flow of co2 from the atmosphere to the biosphere

  -at the end of summer as photosynthesis ends the flow is reversed with natural decomposition releasing co2 back to the atmosphere
• long term changes

  -the climate record over the last million shoes the earths climate has been highly unstable with large fluctuations in global temperature occurring at regular intervals

  -the the past 400,000 years there has been 4 major glacial cycles with cold glacials followed by warmer inter glacials
• changes to the water cycle during glacial period

  -the net transfer of water from the ocean reservoir to storage the the ice sheets, glaciers and permafrost

  -as ice sheets advance equator wards they destroy extensive tracts of forest and grassland , the area covered by vegetation and water stored in the biosphere shrinks
• changes to the carbon cycle during the glacial period

  -dramatic reduction in co2

  -possible that access co2 finds its way from the atmosphere to the deep ocean

  -changes in ocean circulation means that it brings up nutrients to the surface and stimulate phytoplankton growth, they absorb large amounts of co2

  other changes occur in the terrestrial biosphere

  -the carbon pool in vegetation shrinks during glacials as ice sheets advance and occupy large areas of the continents