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Human Influences on Ecosystems

Food Supply

  • Modern technology has resulted in increased food production in terms of:
    • agricultural machinery to use on larger areas of land and improve efficiency
    • chemical fertilizers to improve yield
    • insecticides to improve quality and yield
    • herbicides to reduce competition with weeds
    • selective breeding to improve production by crop plants and livestock

Effects of Deforestation on the Environment

  • Extinction
    • Reduction of habitats or food sources for animals, which can result in their extinction. Animal and plant diversity is reduced, and food chains are disrupted
  • Loss of Soil
    • Removal of trees means there are not roots to hold soil, which can result in soil erosion and leaching of minerals. Desertification can eventually occur
  • Flooding
    • Lack of roots and soil flooding and mudslides. Lakes can become silted up
    • Leaching of nutrients into lakes, rivers, and eutrophication
  • Increase of carbon-dioxide in the atmosphere
    • Less CO2 is absorbed from the atmosphere, more CO2 build up and increase in the greenhouse effect
    • Less O2 is produced and atmospheric O2 levels can drop
    • Less transpiration and reduced rainfall
  • Through altering food webs and chains, humans can have a negative impact on habitats


  • The sources and effects of pollution of land and water, e.g. rivers, lakes and the sea, by insecticides, herbicides, and by nuclear fall-out

The Sources and Effects of Pollution of Water by Chemical Waste, Discarded Rubbish, Untreated Sewage and Fertilizers

  • Process of eutrophication of water
    • Nitrate fertilizers will be washed into streams and rivers
    • Fast growth of algae when they are supplied with extra nitrates
    • Light blocked by algae
    • No more photosynthesis, so algae and water plants die
    • There is no oxygen released by plants
    • Algae and plants fed on by decomposed bacteria
    • Bacteria multiply and produce toxins which cause fish to die
    • Aerobic respiration occurs causing low levels of oxygen which cause death

The Effects of Non-biodegradable Plastics in the Environment, in both Aquatic and Terrestrial Ecosystems

  • Plastics that are non-biodegradable are not broken down by decomposers when dumped in landfill sites or left as litter
  • This means they remain in the environment. taking up valuable space or causing visual pollution
  • Discarded plastic bottle can trap small animals; nylon, fishing line, and nets can trap birds and mammals such as seals, and dolphins
  • When plastic is burned it can release toxic gases

The Sources and Effects of Pollution of the Air by Methane and Carbon

The Causes and Effect on the Environment of Acid Rains

  • The main causes of acid rain are processes that release SO2 and oxides of nitrogen into the atmosphere. These include:
    • burning of fossil fuels, such as coal and gas, by power stations
    • combustion of petrol in car engines

Problems Caused by Acid Rain

  • Damage to plant leaves, eventually killing the plants. Whole forests of pine trees have been destroyed by acid rain
  • Acidification of Lakes: As the water becomes more acidic, some animals such as fish cannot survive and fish stocks are destroyed
  • Increased risk of asthma attacks and bronchitis in humans
  • Corrosion of stonework on buildings
  • Release into soil of soluble aluminum ions that are toxic to fish when washed into lakes

Ways of Reducing the Incidence of Acid Rain

  • Changing the types of power stations that generate electricity from coal and oil to gas or nuclear power, or using more renewable energy sources such as wind
  • Using ‘scrubbers’ in power station chimneys – these remove most of the SO2 present in the waste gases
  • Using catalytic converters in car exhausts – these convert oxides of nitrogen to harmless nitrogen

Greenhouse Gases

  • Some gases in the earth’s atmosphere stop heat radiating into space from the earth
  • This is called the greenhouse effect and the gases involved are called greenhouse gases
  • They include: methane, CO2, and water vapor
  • An increased greenhouse effect can lead to global warming and climate change


  • A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not run out
  • Sustainable development is providing for the needs of an increasing human population without harming the environment
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