9.14 - Indicator Species

Indicator species for air and water pollution

• An indicator species is a species whose presence or absence can be used as a sign of how polluted an area is.
• Some organisms are very sensitive to environmental changes and only survive where conditions are clean; others are adapted to cope with polluted conditions where most species cannot.
• Looking at which species are present, and in what numbers, lets you judge pollution levels without measuring the pollutant directly.

Indicators of water pollution

• Freshwater invertebrates are used to indicate water pollution.
• Stonefly larvae and freshwater shrimps - Very sensitive to dissolved oxygen concentration, so finding them shows the water is clean and well oxygenated.
• Bloodworms and sludgeworms - Adapted to live in low-oxygen, polluted water, so large numbers show the water is heavily polluted.
• Pollution such as untreated sewage or fertiliser lowers dissolved oxygen because the microorganisms breaking down the extra material use the oxygen up.

Indicators of air pollution

• Lichens are used to indicate air pollution.
• Many lichens are very sensitive to sulfur dioxide, an air pollutant released from sources like car exhausts and power stations.
• Plenty of lichen, especially bushy lichen, indicates clean air; only crusty lichen or none indicates dirtier air.
• Blackspot fungus - Grows on rose leaves and is also sensitive to sulfur dioxide, so its presence indicates clean air too.

Surveying and measuring pollution

• Checking whether an indicator species is simply present or absent tells you whether an area is polluted, but not by how much.
• Counting how many are found in different places lets you compare how pollution levels vary from one area to another.
• Pollution can also be checked directly - for example by measuring the dissolved oxygen concentration or the pH of stream water.