Lichen's Sensitivity: Air Pollution's Impact

Lichens are sensitive to air pollution and can be used as indicators of air quality. They are composites of a fungus and an algae, and they absorb water, minerals, and pollutants from the air through rain and dust. Nitrogen and sulphur dioxide are two major air pollutants that affect lichen growth. In the presence of nitrogen, some lichens will die, while others will thrive. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs, and has killed many lichens in the past. Lichens are also sensitive to other pollutants such as nitrogen, acidity, halogens, heavy metals, and ozone. As a result of industrialization, many lichen species have become extinct in large areas. Lichens are not found in air-polluted habitats due to their sensitivity to pollutants, which can cause structural changes, reduced growth, and even death.

Nitrogen dioxide and sulphur dioxide are two pollutants that affect lichen growth

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

Nitrogen is a harmless gas that makes up a large part of the Earth's atmosphere. However, when heated and combined with oxygen, as it is in a car engine, nitrogen oxides are formed, and nitrogen dioxide is created. Nitrogen dioxide is a powerful pollutant that is harmful to human health in high concentrations. It can inflame the lining of the lungs, causing respiratory symptoms such as coughing and shortness of breath. Farms also emit nitrogen pollutants from fertilisers, farm machinery, and livestock waste. Certain lichens, such as the oakmoss lichen, are sensitive to nitrogen in the air and will die in its presence. However, other species, like the golden shield lichen, can thrive in areas with high levels of nitrogen, especially ammonia.

Sulphur dioxide is another pollutant that has killed many lichens in the past. It is produced by coal burning and industrial activities. In high concentrations, it can irritate the mucus lining of the eyes, nose, throat, and lungs, causing coughing and tightness in the chest. Sulphur dioxide has been responsible for the decline in lichen diversity, with species like Usnea lichens (old man's beard) being unable to grow in areas with sulphur dioxide pollution.

The presence and health of lichens are strongly influenced by the levels of nitrogen and sulphur dioxide in the atmosphere. These pollutants can cause structural changes in lichens, including reduced photosynthesis and bleaching. They can also lead to the death of the lichen algae, discolouration, and reduced growth of the lichen fungus. By studying lichen communities and their responses to these pollutants, we can gain insights into the effects of air pollution on ecosystems.

Lichens are sensitive to air pollution and make good air quality indicators

Some sensitive lichen species develop structural changes in response to air pollution, including reduced photosynthesis and bleaching. Air pollutants that affect lichen growth include nitrogen and sulphur dioxide. Nitrogen dioxide can inflame the lining of the lungs and cause respiratory symptoms such as shortness of breath and coughing. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs, and may cause coughing and tightness in the chest.

Lichens have been used as sensitive bioindicators of air quality for over a century in Europe. They exhibit a range of sensitivities to pollutants, with some species being remarkably tolerant. For example, the golden shield lichen can live in areas with high levels of nitrogen, especially ammonia. It is commonly found near farmland and on trees, buildings, and sea cliffs. The presence of certain lichen species can indicate typical SO2 levels—for instance, leafy lichens can survive in moderate to good air, while rare species may grow in very clean air.

Scientists monitor lichen communities to determine the sources and levels of pollution. If there is an increase in pollution-tolerant species and a decrease in sensitive species, it may signal a rise in atmospheric pollution. Lichens can also reveal the effects of air pollution on ecosystems, such as ecological community changes, and the potential decline of species due to pollution.

Some lichens will die in the presence of nitrogen, while others will thrive

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are found in a variety of habitats and climates, from deserts to alpine tundra and tropical rainforests. They are sensitive to air pollution, particularly nitrogen and sulphur dioxide, and can be used as indicators of air quality.

While some lichens are sensitive to air pollution and may die in the presence of nitrogen, others are more tolerant and can even thrive in areas with high levels of nitrogen. The golden shield lichen (Xanthoria parietina), for example, can survive in environments with high levels of nitrogen, especially ammonia. It is commonly found on trees and buildings near farmland and on sea cliffs where seabird droppings provide nitrogen.

The presence or absence of certain lichen species in an area can indicate the level of nitrogen pollution. For instance, the oakmoss lichen is sensitive to nitrogen and can be found in woodlands with clean air. In contrast, nitrogen-loving, pollution-tolerant species dominate the bark-inhabiting lichen communities in the National Capital Region (NCR).

The response of lichens to nutrient enrichment, including nitrogen, depends on the species and environmental factors such as nutrient concentration, light availability, and water supply. Lichens with both nitrogen-fixing and non-nitrogen-fixing phototrophs, such as Placopsis gelada, can also exhibit varying responses to nitrogen availability.

The study of lichens can provide valuable insights into the effects of air pollution on ecosystems. For example, researchers are using lichens to investigate nitrogen pollution from tea estates in Sri Lanka and the forests of the Himalayas. By understanding how nitrogen pollution from fertilisers used on tea farms is impacting the ecology of the region, scientists can help develop strategies to mitigate these effects and promote sustainable practices.

Lichens are composites of a fungus and an algae, both of which absorb pollutants from the air

Lichens are composite organisms made up of a symbiotic relationship between a fungus and an alga. Lichens are very sensitive to air pollution and can act as indicators of air quality. They absorb water, minerals, and pollutants from the air through rain and dust. The two main air pollutants that affect lichen growth and development are nitrogen and sulphur dioxide.

Nitrogen deposition can increase the load of nutrients, and while lichens need nitrogen to survive, too much can harm and kill the algae's chlorophyll, which is used to produce sugars to feed the lichen and its fungi. Lichens that are more sensitive to nitrogen include the oakmoss lichen, which can be found on woodland branches where the air is clean, and Usnea lichens, also called old man's beard, which do not grow in areas where there is sulphur dioxide pollution.

Sulphur dioxide is a pollutant that has killed many lichens in the UK, though they are beginning to return as coal burning has decreased. In high concentrations, sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs, and may cause coughing and tightness in the chest. Some lichens, such as the golden shield lichen (Xanthoria parietina), can live in areas with high levels of nitrogen, especially ammonia.

Lichens can be used to monitor the effects of anthropogenic pollution on natural systems. Scientists monitor lichen communities and pair this bio-monitoring data with atmospheric deposition data to determine the sources and levels of pollution causing detrimental effects. Lichens from Plummers Island, Maryland, for example, show the dramatic rise in atmospheric lead (Pb) deposition prior to the early 1980s, which coincided with the completion of the American Legion Memorial Bridge.

Lichens are bio-indicators of nitrogen deposition and can signal the potential decline of an ecosystem

Lichens are composite organisms made up of a fungus and an alga and/or cyanobacteria. They are highly sensitive to air pollution, especially nitrogen and sulphur dioxide. This is because they absorb water, minerals, and pollutants from the air through rain and dust. 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.

Lichens are, therefore, bio-indicators of nitrogen deposition. Scientists monitor lichen communities, and if there is an increase in nitrogen-tolerant species and a decrease in nitrogen-sensitive species, it may indicate a rise in atmospheric nitrogen deposition. Lichens are the "canaries in the coal mine" of nitrogen deposition, and their decline in health and shift in species composition can signal the potential beginning of an ecosystem's decline due to nitrogen deposition.

For example, in the mid-Atlantic region of the United States, there has been a dramatic rise in atmospheric lead deposition observed through the study of lichens. The highest lead values were recorded after the completion of a bridge that carries Interstate 495 traffic. At the same time, leaded gasoline was phased out in the U.S., and subsequent measurements of lead concentrations in lichens declined sharply. This demonstrates how lichens can indicate the presence of harmful pollutants and their decline over time.

Additionally, in urban parks near Washington, D.C., lichen communities are lowest in species diversity and coverage, with no pollution-sensitive species present. In contrast, Prince William Forest Park has higher species richness, including pollution-sensitive lichens, and lower pollutant concentrations. This indicates that the urban parks are experiencing higher levels of air pollution, which is detrimental to the growth of pollution-sensitive lichen species.

By learning about common lichen species and their tolerance or sensitivity to nitrogen, we can judge the nitrogen pollution levels in an area. Lichens, therefore, provide valuable information about air quality and the potential decline of an ecosystem due to nitrogen deposition.

Frequently asked questions