Human influence on ecosystems

• Intensive Food Production


  • Making food production more efficient with a finite amount of land and other resources
• How modern technology has increased food supply

  1. Agricultural machinery has replaced humans and improved efficiency

  2. Chemical fertilisers improve yields

  3. Insecticides and herbicides kill off unwanted insects and weeds

  4. Selective breeding of animals and crop plants to produce high yields
• Intensive Livestock Farming


  • Keeping large numbers of livestock in an area that would not normally support them
  • Feeding them high energy foods
  • Regularly giving them medication
  • Keeping them in artificially warm temperatures and small spaces
• Advantages of Intensive Livestock Farming

  • Less land required to produce large amounts of food
  • Food can be produced all year round in controlled environments
  • Lower cost of production, so food can be sold at cheaper prices
  • Lower requirement for labour
• Disadvantages of Intensive Livestock Farming

  • Use of herbicides and pesticides can cause environmental issues
  • Ethical issues with cruel treatment of animals
  • Destruction of natural habitats
  • Ecological issues like reduction in biodiversity and soil erosion
  • Large amounts of methane produced by cattle
• Monoculture


  Farming where only one type of crop is grown on a given area of land
• Issues with Monocultures


  • Lower biodiversity
  • Increase in pest populations
  • Overuse of insecticides leading to pollution and pest resistance
• Palm oil production has increased rapidly over the last 30 years
• Biodiversity


  The number of different species that live in a particular area
• Human activities have tended to force biodiversity downwards, whereas high biodiversity is needed for stable ecosystems
• Reasons for Habitat Destruction


  • Increasing human population
  • Making space for other economic activities
  • Pollution from economic activities
• Habitat destruction by humans

  Interrupts food chains and webs, causing more species to die
• Deforestation


  The clearing of trees (usually on a large scale)
• If trees are replaced by replanting it can be a sustainable practice
• Generally the trees are being cleared for the land to be used in a different way (for building, grazing for cattle, planting of monocultures such as palm oil plantations etc) and therefore it is not sustainable
• As the amount of the Earth's surface covered by trees decreases, it causes increasingly negative effects on the environment and is a particularly severe example of habitat destruction
• Undesirable effects of deforestation

  • Extinction of species
  • Loss of soil
  • Flooding
  • Increase of carbon dioxide in the atmosphere
• Extinction/Loss of biodiversity


  • Forest habitats, especially tropical rainforests, have a huge range of biodiversity and as habitat is destroyed it causes the loss of large numbers of plant and animal species
  • Many of these species are only found in these areas and therefore will become extinct
• Soil erosion


  • Tree roots help to stabilise the soil, preventing it from being eroded by rain
  • Trees will usually take up nutrients and minerals from the soil through their roots
  • Without trees, nutrients and minerals will remain unused in the soil so will be washed away into rivers and lakes by rain (leaching)
  • This loss of soil nutrients is permanent and makes it very difficult for forest trees to regrow, even if the land is not cultivated with crop plants or grass for cattle
  • Without trees the topsoil will be loose and unstable so will be easily washed away by rain, increasing the risk of flash flooding and landslides
• Increased carbon dioxide in atmosphere

  • Trees carry out photosynthesis during which they take in carbon dioxide and release oxygen
  • The removal of significant numbers of trees means less carbon dioxide is being removed from the atmosphere (and less oxygen released)
  • When areas of land in forests are cleared for land use, the trees are often burned as opposed to being cut down. This releases carbon dioxide (it is an example of combustion), further increasing carbon dioxide levels in the atmosphere and contributing to global warming
• Water pollution


  Human activities have led to the pollution of land, water and air
• Sources of pollution


  • Untreated sewage
  • Chemical waste
  • Discarded rubbish
  • Fertilisers
  • Insecticides & herbicides
  • Nuclear fallout
• Untreated sewage


  Lack of sewage treatment plants in inhabited areas (due to poor infrastructure / lack of money) meaning sewage runs / is pumped into streams or rivers
• Effect of untreated sewage


  • Provides a good source of food for bacteria which increase rapidly, depleting the oxygen dissolved in the water (as they respire aerobically) and causing death of aquatic organisms such as fish - known as eutrophication
• Chemical waste


  Chemicals such as heavy metals like mercury can be released from factories into rivers and oceans or leach into land surrounding the factories
• Effect of chemical waste

  • Many heavy metals and other chemicals are persistent - they do not break down and so can build up in food chains (known as bioaccumulation), poisoning the top carnivores
• Discarded rubbish


  Much rubbish consists of plastic that is either discarded or buried in landfills
• Effect of discarded rubbish

  • Much rubbish, such as that made from plastic, is non-biodegradable and remains in the environment for hundreds of years. Animals also eat the plastic as it breaks into smaller pieces (especially in the ocean) and it can get into food chains this way
• Fertilisers


  Runoff from agricultural land if applied in too high a concentration
• Effect of fertilisers


  • Causes algal blooms which then die and provide a good source of food for decomposing bacteria which increase rapidly, depleting the oxygen dissolved in the water (as they respire aerobically) and causing death of aquatic organisms such as fish known as eutrophication
• Insecticides & herbicides


  Sprayed on crops to prevent damage by insects and growth of weeds
• Effect of insecticides & herbicides

  • Bioaccumulation, loss of biodiversity, damage to beneficial insects, can build up in soil to toxic concentrations and harm other organisms
• Nuclear fallout


  Radioactive particles that get into the environment from accidental leakage from nuclear power plants or detonation of a nuclear bomb
• Effect of nuclear fallout

  • Some radioactive particles have long half-lives and can remain in the environment for many years. They can cause increased risks of cancer and smaller particles can be carried by winds hundreds of miles from the original site of exposure
• Methane


  Produced from cattle farming, rice fields, landfills
• Effect of methane


  • Methane is a greenhouse gas which contributes to the enhanced greenhouse effect that is causing climate change
• Carbon dioxide


  Produced when fossil fuels are burnt, also released when trees are burnt to clear land for human use
• Effect of carbon dioxide

  • Carbon dioxide is a greenhouse gas which contributes to the enhanced greenhouse effect that is causing climate change
• Eutrophication


  1. Runoff of fertiliser from farmland enters the water and causes increased growth of algae and water plants

  2. The resulting 'algal bloom' blocks sunlight so water plants on the bottom start to die, as does the algae when competition for nutrients becomes too intense

  3. As water plants and algae die in greater numbers, decomposing bacteria increase in number and use up the dissolved oxygen whilst respiring aerobically

  4. As a result there is less oxygen dissolved in water, so aquatic organisms such as fish and insects may be unable to breathe and would die
• Sequence of events causing eutrophication in lakes and rivers

  1. Excessive nutrients from fertilisers run-off from the land into water

  2. Algae show rapid growth

  3. Algal bloom prevents sunlight reaching aquatic plants

  4. Water oxygen levels fall

  5. Decomposition rate increases

  6. Aerobic respiration of decomposers reduces dissolved oxygen

  7. Death of organisms requiring dissolved oxygen in water