Topic 3

• Exponential growth


  1. Human population growing

  2. Rate of increase is increasing
• Reasons for population increase

  • Better farming means we have more food
  • We can treat and prevent many diseases
  • We have no natural predators
  • Better housing has meant we have better sanitation
• Bigger Population

  farming:

  • More land use
  • Deforestation & soil erosion
  • Pollution from fertilisers and pesticides
  • Overfishing
• Industry


  • Burns fossil fuels -> pollution
  • Uses non-renewable resources
  • Produces other toxic waste
• Building


  • More land used
  • Brownfield sites are expensive
  • Greenfield sites are being used
• Quarrying & Mining


  • Destroys habitats
  • Uses up limited resources, including non-renewable energy sources
• Waste

  • More waste produced = more landfill sites
  • more sewage and pollution
• Acid rain (weak acid)

  having a pH lower than 5.5

  1. sulfur dioxide released for burning fossil fuels (coal) + nitrogen released from car exhausts
  2. SO2 and NOx react with H2O to form sulphuric and nitric acid
  3. can be carried hundreds of miles in the atmosphere
  4. precipitation has a lower pH than normal and can damage trees lakes and soil
• Sulphur and nitrogen

  Sulphur dioxide + water -> sulphuric acid

  Nitrogen oxide + water -> nitric acid
• Neighbouring countries

  sulphur dioxide and nitrogen oxide are carried by prevailing winds which makes the “green” countries get the acid rain and the associated problems
• Acid rain and trees and plants and soil

  Damages leaves reducing their ability to photosynthesise

  Acidification of the soil causes leaching of mineral ions, so plants can’t grow as well and lowers the pH of the soil and increases the acidity of where the plant grows
• Acid concentration on seedling

  Cell is no longer turgid so it wilts

  the acid damages the root hair cells so it can’t absorb nutrients and damages leaves and can’t photosynthesise

  Independent variable - the concentration of acid

  Dependent variable - the amount of seeds

  Control variables - size of pot, where we kept them

  Next time use more seeds and different species
• How to prevent acid rain

  1. Use less fossil fuels

  2. Use catalytic converters

  3. International agreements to reduce sulfur dioxide pollution

  4. Increase energy efficiency to reduce coal burning for electricity

  5. Use ultra low sulfur petrol

  6. Use alternative energy sources like natural gas, solar, wind farms and nuclear power
• Deforestation


  Trees cut down that were supposed to remove CO2 from atmosphere are cut + trees release CO2 when cut = increase in CO2 in atmosphere
• Methane


  Natural : rotting plants in marshland

  Manmade : cattle ranching, rice growing, anaerobic bacteria decaying rubbish in landfill sites
• Carbon dioxide


  Burning fossil fuels

  Peat bags burned and destroyed

  Deforestation: reduced photosynthesis, releases CO2 when wood is burned or decomposes (respiration of microbes)
• Other greenhouse gases


  Nitrous oxide - car fumes and fetilisers

  CFCs - aerosols and fridges

  water vapour
• people clear forests for:

  Cattle ranches (majority)

  Small scale agriculture

  Fires, mining, urbanisation, construction

  Illegal and legal logging

  Large scale agriculture
• Deforestation


  Large scale Removal of forests
• The trees:


  are Used for resources

  No longer photosynthesise

  Burnt, left to rot and release CO2
• Leaching


  Removal of mineral ions from the soil by water running out of the soil
• Nitrates


  • Very soluble in water
• Plant roots


  1. Slow leaching Down

  2. Keep the nutrients in the soil

  3. So the plants can absorb them
• When plants are removed

  Mineral ions are quickly leached from the soil
• Soil erosion


  The removal of soil from an area, by water running over & through the soil
• Soil erosion


  • The soil is exposed due to the lack of tree cover (canopy)
  • The soil is blown or washed away
• Soil erosion

  Soil can be washed into rivers, causing rising water levels and loading
• Other impacts of deforestation

  • Reduction in soil quality as when land is used for crop plants, minerals are not cycled back into the soil
  • Reduce biodiversity
  • Disruption of the water cycle
  • Destroying a valuable source of medicinal drugs
  • Leaching leading to chemical weathering and the release of nutrients from rock
• Very few trees, few leaves
• Change in composition of soil
• Rapid loss of nutrients by leaching results in acidic soil
• Deforestation

  Before: Many trees offering protection from rain erosion -> many leaves fall to the floor which form a layer of nutrients of top soil (humus) -> soil retains water, increase in chemical weathering and release of minerals from rocks -> few nutrients lost by leaching, which leads to very nutritious soil -> nutrient rich soil allows quick plant growth
• How can we reduce deforestation?

  • Introduce laws to protect forests, making deforestation illegal
  • Afforestation where trees are planted to replace those felled
  • Using sustainable sources of wood from coppicing and pollarding
• Deforestation


  After: not many trees providing protection from rain erosion -> not many leaves dropped as littler so less humus produced -> loss of nutrients by leaching which leads to acidic soil -> less mineral ions and low pH of soil means it is infertile -> Infertile soil means very little vegetative growth
• Coppicing


  Cutting back trees to ground level periodically to stimulate growth (usually in late Autumn)
• Pollarding


  Cutting of the top and the branches of a tree to stimulate new growth while controlling the height of the main stem
• Eutrophication

  1. Nitrates enter water system, could be from organic waste (faeces) or from fertilisers that are leached from soil
  2. nitrates cause algae to grow very quickly
  3. algal bloom doesn’t let light penetrate further into water so underwater plants cant photosynthesise and so they die
  4. the algae also runs out of nitrates and so they die
  5. the bacteria that feed on the dead organic matter use up lots of oxygen in respiration
  6. the water becomes anoxic and aquatic life either die or swim away
• Temperature affecting eutrophication 


  Warm weather means an increase in algal growth because it increases the rate of decomposition as the can photosynthesise
• rate of water flow and eutrophication


  faster and more water flow moves algal bloom. Makes water more dilute and brings oxygen
• light intensity and eutrophication

  More light means the algae can photosynthesise more