Lichen As Air Pollution Monitors: Nature's Solution

Lichens are composite organisms made of a fungus and an algae and/or cyanobacteria. They are sensitive to air pollution because they absorb nutrients directly from the atmosphere. This makes them valuable as indicator species, providing information on the condition of their environment. Lichens have been used by scientists to determine the air quality in a given area, specifically to monitor nitrogen and sulphur dioxide levels. They are also used to monitor the effects of nitrogen pollution from tea estates in Sri Lanka and in the forests of the Himalayas.

Lichen species variety

Lichens are composite organisms that consist of a symbiotic association of photosynthetic algae or cyanobacteria and one or two fungi. They are not plants, but they may appear plant-like. Lichens can be found in a variety of shapes, sizes, and forms, including tiny, leafless branches (fruticose), flat leaf-like structures (foliose), crust-like growths that adhere tightly to a surface (crustose), and powder-like appearances (leprose). They can be found in a variety of habitats and climates, from hot, dry deserts to alpine tundra and tropical rainforests. There are approximately 20,000 known lichen species, with about 3,600 of those found in North America.

Lichens are sensitive to air pollution and can act as good indicators of air quality. They absorb nutrients, water, and pollutants from the air through rain and dust. The presence of certain lichen species in an area can indicate the level of air pollution, as some species are more tolerant of pollution than others. For example, Flavoparmelia caperata is a pollution-tolerant lichen species, while Usnea ceratina is sensitive to pollution.

Some lichen species are more commonly found in certain regions or habitats. For example, oakmoss lichen is found on woodland branches where the air is clean, while Cladina arbuscula, also known as reindeer moss, is rare in Colorado. Lichens can also be used to study the effects of pollution on ecosystems, such as the impact of nitrogen pollution from tea estates in Sri Lanka and the forests of the Himalayas.

The diversity of lichen species in an area can also indicate the level of air pollution. As a rule of thumb, an area with a smaller size and less variety of lichens indicates a more polluted environment. For example, urban parks closest to Washington, DC, have lower species diversity and no pollution-sensitive species, while Prince William Forest Park has higher species richness and a greater presence of pollution-sensitive species.

In addition to their use in monitoring air pollution, lichens have also been used as a food source in some cultures. For example, Iceland moss (Cetraria islandica) was once an important food in northern Europe, and Bryoria fremontii (edible horsehair lichen) was consumed in parts of North America. Lichens have also been used in traditional Korean and Japanese cuisine.

Nitrogen and sulphur dioxide levels

Lichens are useful for monitoring air quality as they are sensitive to pollutants and absorb nutrients directly from the air. They are composites of a fungus and an algae, with the algae photosynthesising to create food from sunlight energy. Lichens are affected by nitrogen and sulphur dioxide, two of the main air pollutants.

Nitrogen is a harmless gas that makes up a large part of the Earth's atmosphere. However, when heated and combined with oxygen, nitrogen oxides are created. Nitrogen dioxide is a powerful pollutant and is harmful to human health in high concentrations. It can inflame the lining of the lungs, causing respiratory symptoms such as shortness of breath and coughing. Nitrogen dioxide can also decrease the body's immune response to lung infections, and people with asthma may experience more frequent attacks. Some lichens will die in the presence of nitrogen, while others, such as the golden shield lichen, can live in areas with high levels of nitrogen, especially ammonia.

Nitrogen oxides are created by car engines, and in UK cities, around half of nitrogen dioxide air pollution comes from road traffic. Farms also emit nitrogen pollutants from fertilisers, farm machinery, and livestock waste. Tea growers in Sri Lanka use fertilisers containing nitrogen in the form of ammonia, which then enters the surrounding ecosystems. Researchers are using lichens as indicators to monitor the effects of nitrogen air pollution in Sri Lanka and the Himalayas.

Sulphur dioxide is another pollutant that has killed many lichens, particularly in the UK. It is produced by coal burning and industry. Sulphur dioxide dissolves in water to produce acidic ions that are readily absorbed through the lichen thalli, disrupting photosynthesis. It also inhibits the activity of nitrogenase, which is used by cyanobacterial photobionts to fix atmospheric nitrogen. Sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs, and may cause coughing and tightness in the chest. People with asthma are more sensitive to sulphur dioxide pollution. Usnea lichens, also called old man's beard, do not grow in areas where there is sulphur dioxide pollution.

Lichen growth and health

Lichens are organisms that consist of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria. The fungus provides shelter for the algae, and the algae provide food for the fungus through photosynthesis. Lichens are durable and can grow on tree bark, bare rock, barren earth, metal, and even concrete.

Lichens are sensitive to air pollution because they have no roots or protective surface, so they absorb all their nutrients directly from the air. This means that pollutants can accumulate in the lichen and become toxic very quickly. The two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide. Nitrogen deposition can harm and kill the algae's chlorophyll, which is used to produce sugars for the lichen. Sulphur dioxide concentrations can also affect lichen growth by altering the pH of tree bark, which lichens often grow on.

The presence and health of lichens in an area can indicate the level of air pollution. If there are fewer lichen species and smaller lichens in an area, it is a sign of higher pollution levels. Scientists can monitor the health of lichens and pair this data with atmospheric deposition data to determine the sources and levels of pollution. This information can be used to track the effectiveness of clean air actions and protect sensitive ecosystems.

Different lichen species have different sensitivities to air pollutants. For example, "nitrophyte" lichen species thrive in high-nitrogen environments, while "acidophyte" lichen species prefer low-nitrogen environments. The variety of lichen species in an area is taken into account when calculating the air quality index.

While lichens are useful indicators of air quality, they have some limitations. They can only monitor nitrogen and sulphur dioxide levels, while there are many other pollutants that pose ecological and health threats. Lichens also provide information on pollution levels over a longer period of time, rather than giving immediate feedback.

Air quality index

Lichens are highly effective bioindicators of air pollution and have been used extensively to monitor air quality. They are miniature ecosystems, consisting of a symbiotic relationship between a fungus and an algae and/or cyanobacteria. Lichens are sensitive to air pollution because they absorb all their nutrients from the atmosphere, and cannot filter what they absorb. This means that pollutants can accumulate in the lichen and quickly become toxic.

Lichens have been used to monitor air quality in several ways. One method, developed in the Netherlands, classifies lichens as either "nitrophyte" or "acidophyte". Nitrophyte lichen species thrive in high-nitrogen environments and on tree bark with a high pH, while acidophyte lichen species prefer the opposite conditions. This method has been used to map and monitor nitrogen and ammonia pollution patterns across Europe, and has helped to discover how lichens respond to global warming.

Another method, known as the Ellenberg method, uses "Ellenberg N Values" to estimate the position along a productivity/macro-nutrient availability gradient at which a species reaches peak abundance. This method has been used to indicate species change and colonisation across time.

In the United States, the health of various lichen species is monitored and paired with atmospheric deposition data to identify sources and levels of air pollution. Atmospheric deposition is the process of gases and particles from the atmosphere being transferred to earth. Scientists in the US have used lichens to monitor nitrogen deposition levels and protect sensitive ecological systems.

Lichens have also been used in Germany as bioindicators of air pollution, where they are particularly sensitive to sulphur dioxide, but also to other acidic pollutant gases, heavy metals, and photo-oxidants.

Lichens have been used in environmental impact studies, particularly in Italy, where biological indicators are required to evaluate the quality of the air resulting from industrial plants.

Lichens are also being used to monitor nitrogen levels at tea farms in Sri Lanka and the Himalayan forests. Tea growers use fertilisers that contain nitrogen in the form of ammonia, which can escape into the surrounding ecosystems.

Overall, lichens are a valuable tool for monitoring air quality and pollution levels, and have been used in various methods and countries to gain a better understanding of the atmosphere and its effects on ecosystems and human health.

Lichen as an indicator species

Lichens are composite organisms consisting of a fungus and an algae or cyanobacteria. They are durable and can grow on tree bark and bare rock. However, they are also sensitive to air pollution and can act as an indicator species. Lichens absorb water, minerals and pollutants from the air through rain and dust. They are particularly sensitive to nitrogen and sulphur dioxide.

Lichens have been used to monitor the effects of nitrogen pollution from tea estates in Sri Lanka and nitrogen oxide pollution from traffic in the UK. They have also been used to monitor sulphur and ammonia pollution patterns across Europe. In the US, the National Park Service has monitored lichen communities in national parks to assess air quality.

The presence of certain lichen species in a location can indicate the concentration of pollutants in that area. For example, the oakmoss lichen is an indicator of clean air, while Flavoparmelia caperata is a pollution-tolerant species. The variety of lichen species in an area can also indicate the level of pollution, with fewer lichen species indicating a more polluted environment.

While lichens are useful as an indicator species, they are limited in that they can only monitor certain pollutants, such as nitrogen and sulphur dioxide. They also cannot provide immediate feedback on pollution levels, only averages over a longer period of time.

Overall, lichens are valuable tools for monitoring air pollution and understanding the condition of their environment.

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