Which lichens indicate pollution

The most widely used was created by Hawksworth and Rose in England in 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. The scientists have drawn up an index of atmospheric purity IAP using lichens to classify levels of pollution in various areas of Haldia. Both the lichen constituents are affected by gaseous and particulate pollutants.

Matter accumulates in the tissues bringin bout degenergation and a number of morphological changes. Mitra and Santra also discovered more pollution-tolerant species, like Bacidia convexula and Parmelia caperato, are found in areas with higher sulphur dioxide levels, while more sensitive species like TrypetheIium trot m and Gyrostomum scyphiliferum are found where pollution levels are lower.

Rainwater contains just enough nutrients to keep them alive. Air pollutants dissolved in rainwater, especially sulphur dioxide, can damage lichens and prevent them from growing. This makes lichens natural indicators of air pollution. For example:. In places where no lichens are growing it is often a sign that the air is heavily polluted with sulphur dioxide. 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.