Lichen: Pollution's Canary In The Coal Mine

Lichens are composite organisms made up of a fungus and an alga and/or cyanobacteria. They are sensitive to air pollution and can be used as bio-indicators of air quality. Lichens absorb water, minerals, and pollutants from the air through rain and dust. They are sensitive to nitrogen and sulphur dioxide, and can be affected by nitrogen oxides, which are created when nitrogen is heated and combined with oxygen, such as in car engines. Nitrogen dioxide is harmful to human health and can cause respiratory issues. Sulphur dioxide is produced by coal burning and industrial activities, and can irritate the mucus lining of the eyes, nose, throat, and lungs. Lichens can also accumulate pollutants such as metals, organic elements, and radioelements. They are used to monitor the quality of their environments and provide insights into potential health risks.

Lichens as bio-indicators

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. The algae in lichens photosynthesise, and both the algae and fungus absorb water, minerals, and pollutants from the air, through rain and dust. They are sensitive to air pollution and make good indicators of air quality. Lichens do not have roots or a protective surface, so they cannot filter what they absorb, and pollutants can accumulate in them and become toxic. Lichens are also sensitive to small changes in nutrient nitrogen availability, and nitrogen deposition can increase the load of nutrients, harming and killing the algae's chlorophyll.

Lichens are used as bio-indicators to monitor environmental quality. Scientists monitor lichen communities, and if there is an increase in nitrogen-tolerant species and a decrease in nitrogen-sensitive species, this may indicate an increase in atmospheric nitrogen deposition. Lichens can also be used to determine the sources and levels of pollution causing detrimental effects. Lichens are easier to study than other bio-indicators like butterflies, nematodes, frogs, and toads, and they respond more quickly to environmental change.

Lichen communities in urban parks closest to Washington, DC, for example, are lowest in species diversity and coverage and have no pollution-sensitive species. Lichens in more rural parks are consistently higher in species richness, highest in coverage of pollution-sensitive species, and lower in element concentration. Lichens from Plummers Island, Maryland, show the dramatic rise in atmospheric lead deposition prior to the early 1980s, coinciding with the completion of a bridge and the phasing out of leaded gasoline in the US.

Lichens are also used to monitor the effects of anthropogenic pollution on natural systems. For example, total annual nitrogen deposition in the US decreased from 2002 to 2015 thanks to policies put in place based on data collected by monitoring lichens. Continued monitoring will help protect sensitive ecosystems and ecosystem services.

Nitrogen-loving lichen species

Lichens are sensitive to air pollution and can, therefore, be used as indicators of air quality. They absorb water, minerals, and pollutants from the air through rain and dust. Nitrogen oxides, which are created when nitrogen is heated and combined with oxygen, can be harmful to human health in high concentrations. Nitrogen-loving lichens, also known as nitrophilous lichens, are able to grow in areas with high levels of nitrogen compounds. They can be found near roads with heavy traffic, farms with livestock, and agricultural areas with high levels of fertilisers.

Nitrogen-loving lichens can quickly colonise and grow on surfaces affected by these man-made nitrogen sources. They can outcompete other lichens that are slower-growing or sensitive to nitrogen. Nitrogen-loving lichens are often found in areas with high levels of nitrogen compounds from vehicle exhaust, artificial agricultural fertilisers, and farm animal waste. Three nitrophilous lichen species are now among the most abundant lichens in Britain. These include Xanthoria parietina (golden shield lichen), which can be found on trees, buildings, and sea cliffs. It is commonly seen on concrete surfaces and painted windowsills.

The presence or absence of certain lichen species can indicate the level of nitrogen pollution in an area. Some lichens, such as oakmoss lichen, are sensitive to nitrogen and are found in areas with clean air, such as on woodland branches. Other lichens, like the golden shield lichen, can tolerate high levels of nitrogen, especially ammonia. The growth of some lichens is negatively affected by high nitrogen availability, while others can thrive in these conditions. Lichens with higher nitrogen uptake may experience a reduction in the rate of thallus expansion.

The response of lichens to nutrient enrichment depends on the species and environmental factors such as nutrient concentration, light availability, and water supply. Some lichens, such as Placopsis gelada, contain both nitrogen-fixing and non-nitrogen-fixing phototrophs. The addition of nitrogen fertilisers can reduce lichen cover, while the addition of phosphorus can have the opposite effect. In certain regions, such as boreal forests, the ratio of nitrogen to phosphorus must be balanced for proper symbiotic interactions.

Overall, nitrogen-loving lichens are well-adapted to environments with high levels of nitrogen compounds and can be used as indicators of nitrogen pollution in an area. They play an important role in understanding the effects of pollution on ecosystems and human health.

Sulphur dioxide and lichens

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are sensitive to air pollution and can be used as bioindicators of sulphur dioxide. Sulphur dioxide dissolves in water to produce acidic ions, which are readily absorbed through the lichen thalli, disrupting their photosynthesis. Sulphur dioxide has also been shown to inhibit the activity of nitrogenase, which is used by cyanobacterial photobionts to fix atmospheric nitrogen.

Sulphur dioxide pollution comes from coal burning and industry. This pollutant has killed many lichens around the UK in the past. However, as we burn less coal, lichen populations are beginning to recover. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs.

Lichen communities in urban parks closest to Washington, DC, for example, have low species diversity and no pollution-sensitive species. Lichens in more rural parks, such as Prince William Forest Park, have higher species richness and more pollution-sensitive species.

The sensitivity of lichens to sulphur dioxide varies between species. For example, Evernia prunastri is more sensitive to sulphur dioxide than Ramalina fraxinea. Sulphur dioxide fumigation of both lichen species resulted in changes in net photosynthesis, dark respiration, and chlorophyll content in relation to both concentration and duration of exposure. Net photosynthesis was the most sensitive response variable.

Sulphur dioxide pollution can be estimated qualitatively by studying the lichens growing on trees. A ten-point scale has been constructed and used in pilot surveys in England and Wales, south-east England, and the city of Leicester.

Lichens and air quality

Lichens are miniature ecosystems made up of a fungus and an alga and/or cyanobacteria. They are durable enough to grow on tree bark and bare rock, yet sensitive to air pollution. They are immersed in their environment and do not have protective physical structures, so they absorb anything in the air, water or dust straight inside. This includes pollutants like nitrogen, sulphur, metals, organic elements, and radioelements. Lichens are therefore excellent bio-indicators of air quality.

Lichens are sensitive to atmospheric pollution because they get all their nutrients and water from atmospheric deposition (fallout). Nitrogen deposition, for example, can increase the load of nutrients, and too much can harm and kill the algae's chlorophyll, which feeds the fungi. Some lichens will die in the presence of nitrogen, while others will thrive. The golden shield lichen (Xanthoria parietina), for instance, can live in areas with high levels of nitrogen, especially ammonia. It is common on trees and buildings near farmland and on sea cliffs where seabirds' droppings provide nitrogen.

Sulphur dioxide (SO2) is another pollutant that has been known to kill lichens. It is produced by coal burning and industrial activities. In the past, sulphur dioxide has killed many lichens in the UK, but since we have burned less coal, they are beginning to return. Lichens that are unlikely to be found where SO2 are high include Chaenotheca chrysocephala, Cladonia digitata, Evernia prunastri, Lecanora pulicaris, and Phlyctis argena.

The presence and health of lichens, therefore, indicate the potential beginning of ecosystem decline due to deposition. Scientists monitor lichen communities, and if they observe an increase in tolerant species in combination with a decrease in sensitive species, this may indicate an increase in atmospheric deposition. Lichens can also tell us about the effects of air pollution on ecosystems, not just the number of pollution particles in the air. For example, a baseline inventory of bark-dwelling lichens was conducted in nine parks of the National Capital Region (NCR) from 2004 to 2006 and in 2009. Lichens from Plummers Island, Maryland, show a dramatic rise in atmospheric lead deposition before the early 1980s, coinciding with the completion of a bridge that carries Interstate 495 traffic over the island.

Lichens as sensors of pollution

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are sensitive to air pollution and can be used as bio-indicators of air quality. They are particularly sensitive to nitrogen (N) and sulphur (S) dioxide, which are two widespread ecological concerns in the United States. Nitrogen deposition can increase the load of nutrients, harming and killing the algae's chlorophyll, which is used to produce sugars for the lichen. Sulphur dioxide is produced by coal combustion and industrial development. It can irritate the mucus lining of the eyes, nose, throat, and lungs.

Lichens are immersed in their environment and do not have protective physical structures like plant cuticles, so they absorb whatever is in the air, water, or soil around them. This includes pollutants like nitrogen oxides, sulphur, metals, organic elements, and radioelements. Lichens can respond to pollution in short time frames, and their presence or absence can indicate the level of pollution in an area. For example, the presence of nitrogen-loving, pollution-tolerant lichen species in urban parks closest to Washington, DC, indicates higher levels of pollution than parks with more diverse lichen communities and pollution-sensitive species.

The sensitivity of lichens to nitrogen and sulphur dioxide pollution varies by species. Some lichens will die in the presence of nitrogen, while others, like the golden shield lichen, can live in areas with high levels of nitrogen, especially ammonia. Similarly, some lichens are highly sensitive to small changes in nutrient nitrogen availability or acidity (pH), while others prefer higher nitrogen levels or can tolerate more acidity. As atmospheric deposition increases, the dominant ecologically important species tend to be displaced by less ecologically valuable species.

Scientists can monitor lichen communities to assess the sources and levels of pollution and their potential effects on ecosystems. By studying the presence or absence of different lichen species and their health, scientists can detect the effects of air pollution and map its impacts. Lichens are particularly useful for studying gaseous or particulate air pollution due to their anatomical and physiological characteristics. They can also be used to monitor the quality of the environments in which they live and assess potential environmental and health risks.

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