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Lichen as Bioindicators of Air Quality Essay

Lichen as Bioindicators of Air Quality Essay

 Lichen as Bioindicators of Air Quality Essay


Men in big white space suits, complicated laboratory equipment, meters and computers. These are visions of scientists collecting data about pollution. Although the space suits and the expensive equipment are used to monitor pollution, sometimes scientists use simpler methods. Often, the organisms that make their homes in the ecosystem can provide scientists with clues to the health of the area in question. Different species can act like indicator organisms or biomonitors. For example, the recent rapid decline of amphibian populations, which are very sensitive to environmental changes, has caused many scientists to investigate possible damage to the environment from increased UV radiation.

Lichens are a unique living system – two different organisms, a fungus and an algae, that live a very close mutualistic symbiosis. The lives of the fungus and the algae are interwoven so much so that a lichen appears to be one single organism. In the lichen partnership, Algae photosynthesize, providing food for the fungus, and the fungus provide a habitat in which the algae can survive out of water.

So who cares about lichens? Being particularly sensitive to certain environmental factors, such as air pollution, lichens are excellent bio-indicators. The presence or absence of certain types of lichens can be good predictors of air quality (especially the level of sulfur dioxide, the prerequisite for acid rain). In this labs you will be classifying types and amounts of lichens in an area. Based on your data you will be able to make an analysis of the air quality in the area you are investigating.

Types of Lichens

Lichens are classified into three forms or types, based on their appearance. There are three forms of lichens; crustose, foliose and fruticose. There is a description of these forms on the Ch. 7 Lab Aid. Look at these pictures, they will help you identify the lichens in the field.

Crustose – have a flat, rough surface, adhering close to the material that the lichen is growing on. Crustose lichens are more pollution tolerant of the lichen species.

Foiliose – flat but leafy, more ruffled, with some of the “leaves”, not directly adhering to the surface.

Fruticose – usually small stalks or branches.


  • Clear transparency sheet. You can use any clear sheet of plastic about the size of a piece of paper. Transparency sheets can be purchased at copy shops. You can also use a clear folder which can be purchased at office/school supply shops.
  • washable marker (nonpermanent)
  • permanent marker
  • metric ruler
  • note book and pen or pencil

Procedure (adapted from: Environmental science activities, D.B. Rosenthal, John Wiley & Sons, New York, 1995)

Initial preparations

  1. Locate two different sampling areas. The areas should be ones that you suspect vary in the amount of air pollution. For this exercise you will be evaluating air quality based on two parameters; 1) by the types of lichens that you find in the area; 2) by the amount of lichens you find in the area. You should be doing both procedures as you go along.
  2. Conduct the following procedures at each of your locations.
    1. Identifying lichen forms: Be sure to look at the color lichen guide. You will have to identify lichen forms and looking at these pictures first will help you.
    2. Creating a measurement grid – Using your permanent marker, the transparency, and a ruler draw a grid – 20cm x 20cm with 1 cm square blocks on your transparency or clear plastic sheet.

Part 1: Evaluating air quality based on the types of lichens found in the area

  1. Search for lichens on rocks, walls, tree branches or anywhere else you can find them.
  2. Identify the lichens you find according to the chart below. Record, using the scale below the probable air quality in the area based on the lichen types you find.
  3. You may find more than one type of lichen. The air quality is based on the lichens that indicate the best air quality. For example, in the area you look you may find grey-green crustose lichens (#2 on the scale below) and foliose lichens (#4 on the scale below). You would decide that that air quality is pretty good because of the presence of the foliose lichens. Now if you only found the grey-green crustose lichens (no foliose) then you would conclude the air quality was poor (a #2 on the scale).
  4. Table 1. Air quality based on lichen tolerance to pollution. Crustose lichens are the most tolerant, fructicose the least and foliose in the middle. The air quality scale runs from left to right with 1 (left side) being the most polluted and 5 (right side) being the cleanest air. Compare the types of lichens you find in the area to the chart below. Look at the number above the description, this will give you a rough estimate of air quality in that area.

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