- An indicator species is an organism whose presence, absences or abundance reflects a specific environmental condition.
- Indicator species can signal a change in the biological condition of a particular ecosystem and thus may be used to diagnose the health of an ecosystem.
- For example, plants or lichens sensitive to heavy metals or acids in precipitation may be indicators of air pollution.
- Indicator species can also reflect a unique set of environmental qualities or characteristics found in a specific place such as a unique microclimate.
- If raw sewage or other pollutants containing nitrates are released into a river, the bacterial population in the water increases and uses up the oxygen.
- Some invertebrate animals like stonefly larvae and freshwater shrimps are good indicator for water pollution because they’re very sensitive to the concentration of dissolved oxygen in the water. If you find stonefly larvae in a river, it indicates that the water is clean.
- Other invertebrate species have adapted to live in polluted conditions, so if they are seen they are sign of a problem e.g. blood worms and sludgeworms indicate a very high level of water pollution.
- Air pollution can be monitored by looking at particular types of lichen that are very sensitive to the concentration of sulphur dioxide in the atmosphere (therefore can give an idea about the level of pollution from car exhausts, power stations, etc.)
- The number and type of lichen at a particular location will indicate how clean the air is (if the air is clean there is a lot of lichen).
- Blackspot fungus works similarly. It is found on rose leaves and is also sensitive to the level of sulphur dioxide in the air; therefore its presence will indicate clean air.
- Dissolved oxygen meters and chemical tests are used to measure the concentration of dissolved oxygen in water, to show how the level of water pollution is changing.
- Electronic meters and various laboratory tests are also used to measure the concentration of sulphur dioxide in air, to show how air pollution is changing.