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Environmental change

Indicators of pollution

Human activities can pollute the air and water. The presence or absence of certain living organisms acts as an indicator of the amount of pollution.

Air pollution

The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations. Sulfur dioxide is released if the fuel contains sulfur compounds. This gas contributes to acid rain. Lichens can be used as air pollution indicators, especially of the concentration of sulfur dioxide in the atmosphere.

Factories can cause air pollution

Lichens are plants that grow in exposed places such as rocks or tree bark. They need to be very good at absorbing water and nutrients to grow there. Rainwater contains just enough nutrients to keep them alive. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens, and prevent them from growing. This makes lichens natural indicators of air pollution. For example:

  • bushy lichens need really clean air
  • leafy lichens can survive a small amount of air pollution
  • crusty lichens can survive in more polluted air.

In places where no lichens are growing, it is often a sign that the air is heavily polluted with sulfur dioxide.

Water pollution

an oil slick spill on Haven beach

Oil spills cause a lot of harm to the environment, both at sea and on land

Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas. Many aquatic invertebrate animals cannot survive in polluted water, so their presence or absence indicates the extent to which a body of water is polluted.

Water pollution indicators

level of water pollutionindicator species
cleanmayfly larva
lowfreshwater shrimp
highwater louse
very highrat-tailed maggot, sludgeworm

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