-A species of organism that can indicate an area of pollution by its presences or absence in that specific area.
Lichen – How does it indicate air pollution?
Lichen is a moss like plant that grows on exposed areas such as on rocks and on trees. Lichen relies on nutrients that it absorbs from rainwater to survive. However rainwater can also contain pollutants such as dissolved sulphur dioxide, which if absorbed can damage the lichen and prevent it from growing. This makes lichen a natural indicator of air pollution as it will only grow well in areas of clean air. If there is only crusty lichen or no lichen in an area, this suggests the area has high levels of air pollutants.
Invertebrates – How do they indicate water pollution?
Water pollution is caused by the removal of harmful chemicals and substances into rivers, lakes or into the ocean. This means that a lot of the invertebrates that cannot live in these polluted conditions so the pollution levels can be determined by which species are living there.
| Level of Pollution | Indicator Species |
| Unpolluted | Mayfly Larva |
| Low | Freshwater Shrimp |
| Medium | Water louse |
| High | Sludgeworm |
