Lichen's Vulnerability To Air Toxins And Pollutants

Lichens are composite organisms consisting of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. They are highly sensitive to air pollution, especially nitrogen and sulphur dioxide, and are therefore used as bio-indicators of air quality. Lichens absorb water, minerals, and pollutants from the air, through rain and dust. Air pollutants can cause structural changes in lichens, including reduced photosynthesis and bleaching, and can even lead to the death of the lichen algae, discoloration, reduced growth, or the complete death of the lichen. Lichens are also important for other plants and animals, as they can grow in barren places, allowing other organisms to grow in the organic material they leave behind when they break down. They are a source of food for many animals and have potential medicinal uses for humans.

Nitrogen dioxide and sulphur dioxide are two major air pollutants that harm lichen

Nitrogen dioxide (NO2) is a powerful air pollutant that can harm both human health and lichens. It is created when nitrogen is heated and combined with oxygen, such as in a car engine. In high concentrations, nitrogen dioxide can irritate the lining of the lungs, causing respiratory symptoms like shortness of breath and coughing. It can also decrease the body's immune response to lung infections, making people with asthma more susceptible to attacks. Certain lichens, such as oakmoss lichen, are sensitive to nitrogen in the air and can be used as indicators of nitrogen pollution levels.

Sulphur dioxide (SO2) is another significant air pollutant that has historically killed many lichens in the UK. It is produced by coal burning and industrial activities. In the past, when coal was more widely used, sulphur dioxide pollution was a major issue for lichens. However, with the reduction in coal burning, lichens are beginning to return in some areas. Sulphur dioxide can irritate the mucus membranes of the eyes, nose, throat, and lungs, leading to coughing and tightness in the chest. Usnea lichens, also known as old man's beard, are particularly sensitive to sulphur dioxide and are absent in areas with this type of pollution.

Both nitrogen dioxide and sulphur dioxide emissions contribute to the deposition of nitrogen-containing pollutants in the atmosphere. These pollutants have the potential to cause significant harm to vegetation and aquatic ecosystems, especially in regions like the Pacific Northwest of the United States. The presence and health of lichens can provide valuable information about the effects of air pollution on ecosystems and help us understand how ecological communities are being impacted.

Overall, nitrogen dioxide and sulphur dioxide are two key air pollutants that have detrimental effects on lichens. Their presence in the atmosphere can cause lichens to die, change their growth patterns, or alter their species composition. By studying lichens and their response to these pollutants, we can gain insights into the quality of the air we breathe and the health of our ecosystems.

Lichen are sensitive to air pollution and can be used to indicate air quality

Lichens are sensitive to air pollution and can be used as bio-indicators of air quality. They are miniature ecosystems composed of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. The fungus gains constant access to nourishment through this relationship, allowing it to thrive.

Lichens are found in both natural and human-made environments, including rocks, trees, barren earth, metal, and concrete. They receive all their nutrients and water from the atmosphere, making them valuable as indicator species. Their sensitivity to air pollution means they can indicate the effects of air pollution on ecosystems, not just the number of pollution particles in the air.

The two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide. Nitrogen deposition can increase the load of nutrients, and too much nitrogen can harm and kill the algae's chlorophyll, which is used to produce sugars to feed the lichen. Sulphur dioxide pollution comes from coal burning and industry, and in the past, it has killed many lichens in the UK. However, as coal burning has decreased, lichen populations are beginning to recover.

Different lichen species have different sensitivities to air pollutants, and this variation is considered when calculating and representing the air quality index. For example, the Dutch method of classifying lichens categorises them as either "nitrophyte" or "acidophyte". Nitrophyte lichen species thrive in high-nitrogen environments and on tree bark with high pH, while acidophyte lichen species prefer the opposite. This method has been used to map and monitor nitrogen and ammonia pollution patterns across Europe.

Lichen communities dominated by nitrogen-loving, pollution-tolerant species have developed over time

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are highly sensitive to air pollution and can be used as indicators of air quality.

In the NCR, a baseline inventory of bark-dwelling lichens conducted from 2004 to 2006 and in 2009 identified 45 species of bark-inhabiting lichens, with a dominance of nitrogen-loving, pollution-tolerant species. Pollution-sensitive species were infrequently found in most parks, especially in urban parks closest to Washington, DC.

Similarly, in Europe and the UK, the lichen flora of oak trees in agricultural areas has shifted from communities dominated by species preferring acid bark to those that tolerate and benefit from nitrogen. High levels of ammonia in the Netherlands, for example, have led to the disappearance of acid-preferring species and the dominance of nitrophytic species.

Over time, as air pollution increases, sensitive lichen species may be replaced by pollution-tolerant species. This phenomenon is observed in locations with high levels of nitrogen oxides, sulphur dioxide, and other pollutants. As a result, the overall number of lichen species starts to decline, and it becomes challenging to find any lichens at all in highly polluted areas.

Lichen are sensitive to atmospheric deposition, which can increase the load of nutrients

Lichens are composite organisms consisting of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. They are sensitive to air pollution, particularly nitrogen (N) and sulphur dioxide (SO2), because they absorb water, minerals, and pollutants from the air through rain and dust. As lichens receive all their nutrients from the atmosphere, they are valuable as indicator species for air quality.

Nitrogen deposition can increase the load of nutrients, which can be harmful and even kill the algae's chlorophyll, which is used to produce sugars to feed the lichen. This can cause the death of the lichen algae, discoloration, and reduced growth of the lichen fungus, or even kill the lichen completely. Lichens that grow on Atlantic Oak trees in areas of high rainfall but relatively low levels of dry deposition (gaseous pollutants) appear to be highly sensitive to nitrogen. In Europe and the UK, the lichen flora of oak trees growing in agricultural areas has changed from communities dominated by species preferring acid bark to species that tolerate and benefit from nitrogen.

Lichen communities in urban parks closest to Washington, DC, for example, are lowest in species diversity and coverage and have no pollution-sensitive species. However, lichens in Prince William Forest Park are consistently higher in species richness, highest in coverage of pollution-sensitive species, and lower in element concentration than those from other parks. Lichens from Plummers Island, Maryland, show a dramatic rise in atmospheric lead (Pb) deposition before the early 1980s, with the highest lead values observed after the completion of the American Legion Memorial Bridge.

Some lichens are more tolerant of nitrogen than others. For example, the golden shield lichen (Xanthoria parietina) 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. Nitrogen-tolerant lichens are also found in the Netherlands, where high levels of ammonia have led to the disappearance of acid-preferring species, resulting in communities dominated by nitrophytic species.

Lichen are valuable as indicator species, but they have their limitations

Lichens are valuable as bio-indicator species because they are sensitive to air pollution and can indicate the typical levels of sulphur dioxide and nitrogen in the atmosphere. Lichens are miniature ecosystems made of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. The fungus gains constant access to nourishment through this relationship, allowing it to thrive. Lichens are found in both nature and human-made environments, including rocks, trees, barren earth, metal, and concrete. They receive all their nutrients and water from wet and dry atmospheric deposition, which makes them valuable as indicator species.

However, lichens have their limitations as indicator species. Firstly, they can only be used to monitor nitrogen and sulphur dioxide levels, while there are many other pollutants that pose ecological and health threats. For example, sulphur dioxide pollution comes from coal burning and industry, and has killed many lichens in the past. In addition, indicator species like lichens cannot provide immediate feedback on exact pollution levels, only averages over a longer period of time. This limitation makes it difficult to source, control, manage, and improve air quality in real-time.

Another limitation of lichens as indicator species is that their sensitivity to pollution varies depending on the species. For example, crustier lichens tend to be more tolerant of pollution than hairy lichens. Additionally, the golden shield lichen (Xanthoria parietina) can live in areas with high levels of nitrogen, especially ammonia, and is commonly found near farmland. This variation in sensitivity among lichen species must be considered when interpreting data on air quality.

Furthermore, lichens may not recolonize in the same magnitude or place after being affected by pollution. For example, following a decline in SO2 and fluoride pollution, some lichen species have returned but have not recolonized to the same extent. This may be due to the presence of nitrogen pollutants, which can cause structural changes in sensitive lichen species, such as reduced photosynthesis and bleaching.

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