WASTE WARS, episode 7: The pollutant menace
Lichenoindication
We are living in a changing world. In a long run there are no stable conditions anywhere on the planet Earth, and here is no such thing as natural equilibrium. In northern Europe we are now heading for the next glaciation meanwhile living the greenhouse age. Lately, also we human beings (Homo) have begun to affect our surroundings in a large scale. Since the beginning of industrialization we have released such amounts different gases into the atmosphere, that it affects our health.
To find out where we are going, environmental scientists have developed, and are developing, bioindication methods. Bioindicator is an organism, its part or a set of organisms that can be used to study the quality of environment. To fulfil this requirement, bioindicator is characterised by following things:
- its biology is known
- it is easy to determine and has large dispersal
- it has clear positive or negative dependence on some physical or chemical environmental factor
- it reacts rapidly and always the same way to change of that factor
Benefits of bioindicator methods include:
- they usually do not need sophisticated equipments
- the result tells the biological meaning of pollution
- because of accumulation, low contents of elements can be measured
In Finland (western Siberia), one of the most used bioindication method is lichenoindication on Pinus sylvestris, determining the effects of aerial pollution by epiphytic lichens. Pinus is chosen, because it occurs virtually everywhere. The lichens take all their nutrients from the air or rainwater. One important aspect is that they are exposed also in wintertime. The species are rather easily identified and we know, how the sensitivity of different species varies: Usnea-species are very sensitive to airpollution, Pseudevernia is less sensitive. Platismatia is fairly tolerant, Hypogymnia is tolerant and Scoliciosporum benefits from nitrogen. To make it short, the fruticose lichens dislike dirty air and crustaceous like it.
Lichenoindication contains both qualitative and quantitative aspects. Besides just collecting species lists we can measure the coverage of different species (that is point frequency method) and we can estimate also the degree of injury.
The preparing fieldwork includes selecting the site and the trees. The Pinus forest should be homogenous for at least one hectare, with no road, houses or other emission sources nearer than one hundred meters. There should not be clearcut near the site, peat and bedrock soils are not allowed and the place should not be on a top of a hill or on a depression. The investigated ten trees have to be at least 20 cm in diameter at the height of 1,3 meter (”chest height”), they should be branchless up to three meters height and they must not be injured or too old. The meaning is, that same trees are investigated every five years as long as possible.
The occurrence of lichen species is observed between the heights of 0,5 and two meters – approximately from knees to as high as hands can grab. The condition of Hypogymnia is studied by five class standard from well growing to dead stands. When suffering from pollution, Hypo has black spots. The overall condition of lichens is also divided to five classes especially according to the occurrence and outlook of fruticose species versus the green lichens (Scoliciosporum) and Algae (Desmococcus).
In point-frequency method we observe the quantity of Hypogymnia and Usnea. Hypo is our most common lichen and Usnea is the first to disappear under stress. We use a plastic frequency table, that is nailed on two sides of the trunk: SW and NE. The size of the plastic table is 40 square centimetres divided into hundred squares, from which the covering percentage is calculated.
The lichenoindication standard for Picea abies is a bit different due to less rich epiphytic flora.
The results of lichenoindication can be summarised to IAP meaning Index of Atmospheric Purity. It is a parameter, counted as follows:
IAP = S(Q · f) / 10
where Q is the mean amount of epiphytic species, f is the frequency of lichen species on the site (0-10).
