Particular species of lichen present on tree bark can indicate the typical sulphur dioxide levels experienced in that area. For example if there are no lichens present, the air quality is very poor zone 1 , whilst generally only crusty lichens such as Lecanora conizaeoides or Lepraria incana can tolerate poor air quality zone 3. In moderate to good air, leafy lichens such as Parmelia caperata or Evernia prunastri can survive zone 6 and in areas where the air is very clean, rare species such as 'the string of sausages' Usnea articulata or the golden wiry lichen Teloschistes flavicans may grow zone It is important to note that the zone chart in Table 1 applies to areas where sulphur dioxide levels are increasing.
If sulphur dioxide conditions are falling, lichens rarely colonise in exactly the same sequence; lichens are slow growing and may take a year or two to recolonise bark or other substrates following a reduction in air pollution levels, and tiny recolonising specimens can be difficult to spot and identify. During the early and mid-twentieth century, air pollution levels were much greater than they are today in towns and cities of the UK.
Sulphur dioxide levels were highest in the inner city areas becoming less polluted out towards the edges of the urban areas. At such times, the lichen zone scale would often highlight zone 1 as the inner city area, moving through the zones to the cleaner air at the edge of the city.
From the s onwards, sulphur dioxide levels have been falling markedly in the central and outer areas of cities, such that there may be no differentiation between levels in central and outer areas of many cities.
The fall in sulphur dioxide levels between the s and the s has led to a number of lichens recolonising in areas from which they had previously been eliminated. Desmococcus viridis , present but confined to base. Hypocenomyce scalaris, Lecanora expallens and Chaenotheca ferruginea often present. Air Pollution. Clean Air for Kids. Glossary Further Reading.
It can be difficult to identify lichen species, even for seasoned naturalists. See the resources listed at the end. Activity : Go for a nature walk around your yard, a park or other favorite natural environment. As you walk, stop to look at the types of lichen present. Lichen is very slow-growing, so try not to disturb it as you examine it to determine if it is crustose, foliose or fruiticose. Older children may want to bring a field journal along to diagram the lichen that they see.
Keep track of the number of different types of lichen you see while on your nature walk. Generally speaking, the more lichen you see in color and quantity the cleaner the air. Analysis : Use the modified Hawskworth-Rose Index below to estimate air quality in the area.
Please write to your representatives and voice your concerns about your local air. Children can write letters, take photographs or draw pictures to convey their ideas. This method was widely used throughout France in many studies between the s and s, during which SO 2 was truly the tracer of air pollution. At the end of the s, the amount of atmospheric sulphur dioxide decreased significantly, lichens began to reappear on the trees of the Jardin du Luxembourg, [4] then in other cities in France Figure 3.
Figure 4. Between and , there was an increase in the number of species observed and a sharp increase in nitrophilic species due to the presence of nitrogen oxides pollutants. Asta] However, in parallel with the decrease in SO2, other air pollutants have increased: nitrogen oxides NOx related to automobile traffic, ammonia compounds in rural areas related to agricultural activities, organic compounds Figure 4.
The Hawksworth and Rose method could therefore no longer be used. It was at this time that an approach no longer based on lichen species, but on the observation of species communities, was introduced, making it possible to establish an eco-diagnostic score , where lichens no longer appear as indicators of a single pollutant but as indicators of air quality. In this method, about 30 species are divided into 7 zones ranging from zone A very poor air quality to zone G very good air quality.
This procedure has been applied in the northern half of France, in the Lyon region, etc. Figure 5. The IBLE values reflect air quality: low values correspond to low to poor air quality, high values to medium to very good air quality.
It can be seen that the majority of the population is located in the sectors where the IBLE is lowest. Asta] These methods are based on the calculation of a pollution index calculated from a mathematical formula that uses different parameters related to corticolous lichenical flora.
The best known is the I. Subsequently, the study of lichen diversity as an indicator of environmental quality was introduced. In , 11 European scientists met to develop a single protocol, defined on a sampling strategy in accordance with statistical rules and avoiding any subjectivity of the observer. Nitrogen oxide pollution favours the development of more or less nitrophilous species, at the expense of acidophilic species.
Figure 6. Photo Physcia adscendens. Asta] Nitrogen dioxide NO 2 pollution from motor traffic has been studied in the Grenoble region Figure 6 and a scale of 3 lichen-sensitivity classes has been established. An identical methodology has been established for ozone for which a sensitivity scale of 4 classes has been established in the Grenoble region [10] , in Switzerland and also in the USA Ohio ….
Figure 7. Decrease in the fluorine concentration of various lichens measured in the Maurienne Valley Savoie between and Hypogymnia physodes , a foliose lichen, and Pseudevernia furfuracea , a fruticulose lichen [Source: Adapted from ref. Remy] Lichens are tested for accumulated pollutants bioaccumulators lichens or physiological or cellular effects biomarkers lichens.
The accumulation of fluoride emitted by aluminium plants in the Alpine valleys was particularly sought after by lichens in the s and s. The work made it possible to highlight the distribution of fluoride in space maps and time Figure 7. Figure 8. Harvesting of Cladonia stellaris contaminated with atmospheric iron from mining operations Quebec, Canada. Agnello] Similarly, lichens allow the accumulation of metallic trace elements to be monitored.
The detection of pollution due to road traffic by lead has been extensively studied in the Paris region in northern France or by other metals in the Pyrenees [12], the Alps or other regions of the world Figure 8. Atmospheric mercury deposition from a chlor-alkali plant was measured in Xanthoria parietina.
The results showed that mercury concentrations decreased as one moved away from the plant with a contamination radius of 2 km Figure 9. Figure 9. Mercury concentrations in soils and lichens around the Jarrie Chlor-Alcali plant after Ref. This work has led to the development of a strategy to be followed when using bioindicators such as lichens to assess environmental pollution by persistent organic pollutants in the atmosphere.
Radioactive elements can also accumulate in lichens. The first work was carried out in the s and s, during which nuclear tests were carried out mainly in the former USSR and the fallout of radioelements into the atmosphere mainly 90 Sr and Cs was analysed.
After the Chernobyl accident, reindeer herds were contaminated as a result of the ingestion of lichens contaminated with radioactive elements. In order to prevent the human population that consumed reindeer meat from becoming contaminated in turn, entire herds were slaughtered.
In areas where lichens are rare or absent, the transplant technique [18] can be applied effectively, especially in the case of corticose lichens. Indeed, it can be used for air pollution monitoring, for example in household waste landfill sites.
It describes the method to be used for sampling and preparing in situ lichen samples for the bioaccumulation of substances characterizing air pollution. At sea, various pollutants such as hydrocarbons and anionic surfactants spread by forming a thin film of a few micrometers on the sea surface.
On the coast, pollutants can reach lichens that show various types of damage. Lichens can be used as bioindicators and bioaccumulators of marine aerosol pollution on the Mediterranean coast.
Figure Lichens in water. Left: Dermatocapon luridum ; right: Vezdaea leprosa. Lagrandie] Lichens such as Dermatocarpon luridum are used as bioaccumulators of metallic elements in water Figure 10A. Some tolerant soil lichens can grow on soils containing metallic elements and are therefore indicative of the presence of these metals. Thus Diploschistes muscorum , Cladonia and Stereocaulon , among others, tolerate high levels of metals in the soil.
Vezdaea leprosa is a species particularly vulnerable to the presence of zinc because it is often found near road safety zinc slides.
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