earths life support systems

• Importance of water


  • Moderates temperatures by absorbing, storing and slowly releasing heat
  • Ice crystals in clouds reflect 1/5th of solar radiation and lower surface temperatures
  • Water vapour is a greenhouse gas that absorbs long-wave radiation helping maintain global temperatures
  • Makes up 65-95% of living organisms
  • Used in respiration, photosynthesis and transpiration in plants
  • Plants use water to maintain rigidity and to transport minerals from soil
  • Water is the medium for all chemical reactions in humans/animals
  • Evaporation, sweating and panting use water as a way of cooling
  • Economic resource - irrigation, electricity, recreational features, manufacturing e.g, food, brewing, paper making etc
• Roles of water


  • Moderating temperatures
  • Reflecting solar radiation
  • Absorbing long-wave radiation
  • Component of living organisms
  • Enabling plant processes
  • Enabling chemical reactions
  • Cooling mechanism
  • Economic resource
• importance of carbon 


  economic resource - fossil fuels e.g., coal, oil and gas.

  oil used as raw material in manufacturing of plastics, paints and synthetic fabrics

  agricultural crops and forest trees store carbon used for food, timber, paper, textiles etc
• key stores in global water cycle

  atmosphere

  oceans

  land

  biosphere
• key processes in global water cycle

  precipitation

  evaporation

  run-off

  groundwater flow
• main processes in carbon cycle

  photosynthesis

  respiration

  oxidation (decomposition and combustion)

  weathering
• key stores in carbon cycle

  atmosphere

  oceans

  sedimentary rocks

  terrestrial biomass
• stores of water in size order (% of global water)

  oceans - 97%

  polar ice and glaciers - 2%

  groundwater/aquifers - 0.7%

  lakes - 0.01%

  soils

  atmosphere

  rivers

  biosphere
• global water cycle budget

  505,000 km cubed circulated a year
• inputs and outputs of water

  input to atmosphere - evapotranspiration (water vapour evaporated from oceans, soils, lakes and rivers, and vapour transpired from plants)

  output from atmosphere - precipitation and condensation

  output from glaciers, ice sheets and snow fields - ablation
• global carbon stores in size order

  sedimentary rocks - 60k to 100million billion tonnes

  oceans - 39,000 billion tonnes

  sea floor sediments - 6000 billion tonnes

  fossil fuels - 4100 billion tonnes

  soils/peat - 2300 billion tonnes

  atmosphere - 600 billion tonnes

  land plants - 560 billion tonnes
• slow carbon cycle


  carbon stored in rocks, sea-floor sediments and fossil fuels>

  circulates 10-100million tonnes/yr

  CO2 diffuses from atmosphere into oceans where marine organisms fix dissolved carbon and calcium to form calcium carbonate and make shells/skeletons

  on death remains sink and accumulate, form sedimentary rocks over years of heat and pressure

  on land - partly decomposed organic matter buried beneath younger sediments to form carbonaceous rocks = fossil fuels
• typical residence time of sedimentary rocks - slow carbon cycle


  150million years
• exposure of sedimentary rock - slow carbon cycle

  subducted into upper mantle at tectonic boundaries and vented into atmosphere in eruptions

  exposure at/near to surface by erosion and tectonic movements are attacked by chemical weathering - carbonation
• fast carbon cycle


  circulates most rapidly between atmosphere, oceans, living organisms and soil

  transfers between 10-1000x faster than slow carbon cycle

  land plants and phytoplankton absorb CO2 and use it in photosynthesis.

  respiration releases co2 to atmosphere

  decomposition returns co2 to atmosphere

  natural sequestration in oceans - 350 years
• key processes in water cycle (local)

  precipitation

  evaporation

  transpiration

  percolation

  throughflow
• transpiration


  responsible for 10% of water in atmosphere
• environmental lapse rate


  vertical temperature profile of he lower atmosphere at any time
• dry adiabatic lapse rate


  rate at which a parcel of dry air cools

  around 10 degrees/KM
• saturated adiabatic lapse rate


  rate at which a parcel of saturated air cools

  around 7degrees/KM due to latent heat released by condensation
• formation of clouds


  air warmed by contact with ground/sea surface rises freely through atmosphere due to atmospheric instability

  as air rises and pressure falls air cools by adiabatic expansion = convection

  when internal temp reaches 8 degrees - dew point - clouds form via condensation

  air masses move horizontally across relatively cooler surface = advection

  air masses rise as crossing mountain barrier or due to turbulence `

  relatively warm air mass mixes with cooler one
• 4 factors affecting interception loss


  interception storage capacity

  wind speed

  vegetation type

  tree species
• affect of interception storage capacity on interception loss 


  before rain, vegetation surfaces are dry and ability to retain water is max.

  most rain initially intercepted however increasing saturation means outputs of water through stemflow and throughflow increases

  dependant on duration and intensity of rain event
• effect of wind speed on interception loss


  higher wind speed increases rates of evaporation
• effect of vegetation type on interception loss


  interception losses greater from grasses > agricultural crops and trees > grasses
• effect of tree species on interception losses


  losses greater from evergreen conifers than deciduous trees>
• two flows that rain falling to ground and not entering storage follows


  infiltration by gravity into soil and lateral movement/throughflow to stream and river channels

  overland flow across ground surface as sheet or as trickles to stream and river channels
• saturated overland flow


  overland flow that occurs when the soil becomes saturated and the water table rises above the surface
• carbon flux from atmosphere to plants and phytoplankton via photosynthesis per year

  120 GT
• chemical weathering transfers

  0.3 billion tonnes to atmosphere and oceans
• burning of fossil fuels carbon transfer

  10GT a year to atmosphere, oceans and biosphere
• physical/inorganic pump


  co2 enters oceans via diffusion

  surface ocean currents transport water and co2 polewards where it cools, becomes more dense and sinks = downwelling

  carbon may remain in ocean depths for centuries

  deep ocean currents transport water to areas of upwelling, where cold carbon rich water rises to surface and co2 diffuses back into atmosphere
• biological/organic pump


  50GT/yr drawn from atmosphere via biological pump

  phytoplankton on ocean surface fix carbon

  consumed or die naturally, carbon locked in phytoplankton either accumulates in sediments on ocean floor or released into ocean as dissolved co2

  other marine organisms extract carbon and calcium ions to produce shells, skeletons etc

  most of this material ends up in ocean sediments and ultimately lithifies into chalk and limestone
• land-use changes affecting water and carbon cycles

  urbanisation

  farming

  forestry
• impact of urbanisation on water cycle

  natural surfaces replaced by impermeable surfaces such as concrete/brick

  little to no infiltration and provide minimal water storage capacity to buffer run off

  urban areas have drainage systems = high proportion of water flows quickly into streams/rivers = rapid rise in water level

  encroaches on floodplains reduces water storage capacity in draining basins
• impact of farming on carbon cycle

  clearance of forest reduces carbon in both above and below ground biomass stores

  ploughing reduces soil carbon store due to exposure to oxidation

  harvesting = little amounts of organic matter returned to soil

  little protective cover of soils = erosion and weathering

  lack of biodiversity and short growing seasons = carbon exchanges via photosynthesis decreased
• impact of farming on water cycle


  crop irrigation diverts water from rivers and groundwater

  interception of rainfall by annual crops is less than forest/grassland ecosystems

  ploughing increases evaporation and soil moisture loss

  furrows act as downslope drainage channels, accelerating run-off and soil erosion

  infiltration due to ploughing greater in farming systems, while artificial underdrainage increases rate of water transfer to streams/rivers

  heavy machinery compacts soils = increased surface run-off
• impacts of forestry on water cycle

  higher rates of rainfall interception in plantations in natural forests

  increased evaporation

  reduced run-off and stream discharge. high interception and evaporation rates and water absorption by roots = drainage basin hydrology altered

  transpiration rates increased

  felling to harvest timber = sudden but temporary changes to local water cycles - increased run off and stream discharge, decreased evapotranspiration
• impacts of forestry on carbon cycle

  changing land use from farmland, moorland and heath to forestry increases carbon stores by 10 times

  forest trees sequester carbon for hundreds of years

  ?? only become active carbon sink after 100 years and forestry trees are usually felled after 80-100 years
• impacts of water extraction on regional water cycle - River Kennet catchment

  rates of groundwater extraction exceed rates of recharge = falling water table = reduced flows by 10-14%

  lower flows reduced flooding and temporary areas of standing water and wetlands on floodplains

  lower groundwater levels = springs and seepages dried up = reduced incidence of saturated overland flow