Lichen: Nature's Air Pollution Indicator?

Lichens are composite organisms that consist of a symbiotic relationship between a fungus and an algae or cyanobacteria. They are highly sensitive to air pollution, specifically nitrogen and sulphur dioxide, and are therefore used as bio-indicators to determine air quality in a given area. The presence or absence of lichens, as well as the species composition and health of lichen communities, can indicate the levels of pollution in the environment. Lichens are particularly useful as bio-indicators because they absorb water, minerals, and pollutants from the air and can exhibit structural changes in response to air pollution, such as reduced photosynthesis and bleaching.

Lichens are sensitive to nitrogen and sulphur dioxide

Lichens are sensitive to air pollution and are therefore useful as indicators of air quality. They are especially sensitive to nitrogen and sulphur dioxide. Lichens are organisms that consist of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. Fungi are incapable of photosynthesis as they do not possess chlorophyll, but algae and cyanobacteria do.

Nitrogen deposition can increase the load of nutrients. While nitrogen is necessary for lichens to survive as it supports them in producing necessary proteins and organic acids, too much nitrogen can harm and kill the algae's chlorophyll, which is used to produce sugars that feed the lichen. Certain species of lichen are more tolerant of nitrogen than others. 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.

Sulphur dioxide is a compound that easily dissolves in water, which the lichen can then absorb, and is prevalent in the air in its gaseous state as well. Sulphur dioxide interferes with the cyanobacteria's ability to fix nitrogen and destroys the chlorophyll of the algae, thus inhibiting photosynthesis. Sulphur dioxide also impedes lichen reproduction and spore germination across certain species. In high concentrations, sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs. Exposure to sulphur dioxide may cause coughing and tightness in the chest. People with asthma are more sensitive to sulphur dioxide pollution.

They are good indicators of air pollution

Lichens are indeed sensitive to air pollution and make excellent indicators of air quality. Lichens are organisms that consist of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. They are found in nature and in human-made environments, including rocks, trees, barren earth, metal and concrete.

Lichens are sensitive to air pollution because they absorb water, minerals, and pollutants from the air through rain and dust. They receive all their nutrients from the atmosphere, which makes them valuable as indicator species. They are especially sensitive to nitrogen (N) and sulphur dioxide (SO2) pollution. Nitrogen deposition can harm and kill the algae's chlorophyll, which is used to produce sugars to feed the lichen. Sulphur dioxide interferes with the cyanobacteria's ability to fix nitrogen and destroys the chlorophyll of the algae, inhibiting photosynthesis.

The presence and health of lichens can indicate the level of pollution in an area. Scientists monitor lichen communities, and if there is an increase in nitrogen-tolerant species and a decrease in nitrogen-sensitive species, it may indicate rising nitrogen deposition. This shift in species composition and health can signal the potential decline of an ecosystem due to nitrogen deposition. Lichens can also be used to study the effects of air pollution on ecosystems, not just the number of pollution particles in the air.

In addition to nitrogen and sulphur dioxide, lichens are also sensitive to other acidic pollutant gases, heavy metals, and photo-oxidants. Different lichen species have varying sensitivities to air pollutants, so the diversity of lichen species in an area is considered when calculating the air quality index. Lichens are easier to study than other indicator species and respond quickly to environmental changes, making them ideal for monitoring air pollution and its effects on ecosystems.

Lichen variety indicates air quality

Lichens are sensitive to air pollution and can therefore be used as indicators of air quality. They are composite organisms consisting 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 and can thus thrive.

Lichens are found in nature and in human-made environments, including rocks, trees, barren earth, metal, and concrete. They receive all their nutrients and water from the atmosphere, which makes them valuable as indicator species. The two main 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 it and the fungi. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs, causing coughing and tightness in the chest.

The variety of lichen species in an area is indicative of the air quality. As a rule of thumb, the smaller the size and the less variety of lichens in an area, the more polluted the environment. Scientists monitor lichen communities, and a shift in their species composition and health can exemplify the potential beginning of ecosystem decline due to nitrogen deposition. For example, in the Netherlands, high levels of ammonia have led to the complete disappearance of acid-loving lichen species, resulting in communities dominated by nitrogen-loving species.

Lichens are easier to study than other indicator species such as butterflies, nematodes, frogs, and toads, and they respond quickly to environmental changes. By learning a few common lichen species, people can judge the nitrogen pollution levels in their area. For instance, the golden shield lichen can live in areas with high levels of nitrogen, especially ammonia, and is commonly found near farmland. The oakmoss lichen, on the other hand, is sensitive to nitrogen and can be found in clean, woodland areas.

Lichens are sensitive to acidic gases and heavy metals

Lichens are sensitive to air pollution and are therefore useful as indicators of air quality. They are miniature ecosystems made of a fungus and an algae and/or cyanobacteria. Lichens receive all their nutrients from the atmosphere, which makes them valuable as indicator species.

Lichens are sensitive to nitrogen (N) and sulphur dioxide (SO2) in particular. Nitrogen deposition can harm and kill the algae's chlorophyll, which is used to produce sugars to feed the lichen. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat and lungs, causing coughing and tightness in the chest. It also interferes with the cyanobacteria's ability to fix nitrogen and destroys the chlorophyll of the algae, inhibiting photosynthesis.

Lichens are also sensitive to other acidic pollutant gases, heavy metals and photo-oxidants. They can be affected by the presence of heavy metals such as copper, which is trapped and concentrated by mosses, which are often found growing with lichens.

The presence of lichens can indicate the air quality of an area. For example, the lichen Usnea, also called old man's beard, does not grow in areas where there is sulphur dioxide pollution. If you see Usnea on your walk, it probably means that coal has not been burnt in the area for some time. Similarly, 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.

Some lichens are more sensitive than others

Some lichens are more sensitive to air pollution than others, and this is due to a variety of factors, including the specific species of lichen, the type and concentration of pollutants, and local environmental conditions.

Lichens are a combination of algae or cyanobacteria and fungi living in a symbiotic relationship. This unique partnership allows lichens to survive in a wide range of habitats, from the arctic tundra to the tropics and from rocky outcrops to tree bark. However, this also means that their tolerance to environmental stressors, such as air pollution, varies greatly.

For example, the species of photobiont (algal or cyanobacterial partner) within a lichen can greatly influence its sensitivity to air pollution. Lichens containing green algae are generally more sensitive to pollutants, particularly those that impact their ability to photosynthesize, such as sulphur dioxide and ozone. In contrast, lichens containing cyanobacteria can tolerate higher levels of pollution and may even be absent in areas with high pollution levels, as they are outcompeted by more pollution-tolerant lichens.

The specific pollutants present in the air can also play a role in lichen sensitivity. For example, nitrogen dioxide, commonly emitted by vehicles, can cause damage to lichen tissue, particularly in humid conditions.

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