Lichen's Response To Air Pollution: A Natural Indicator

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are highly sensitive to air pollution, which makes them excellent indicators of air quality. Lichens absorb all their nutrients and water from the air, and since they lack physical protection, they cannot filter what they absorb. As a result, pollutants can accumulate in lichens and become toxic. Sulphur dioxide and nitrogen dioxide are two major air pollutants that affect lichen growth. Sulphur dioxide is produced by coal burning and industrial processes, while nitrogen dioxide is created when nitrogen is heated and combined with oxygen, such as in car engines. The presence or absence of lichens, as well as the specific species of lichens in an area, can indicate the level of air pollution. Scientists monitor lichen communities to assess the health of the lichens and pair this data with atmospheric deposition data to determine the sources and levels of pollution.

Lichens are good indicators of air quality

Secondly, lichens are very sensitive to air pollutants and respond quickly, so changes in their health or species composition can indicate potential ecosystem decline due to pollution. For example, the presence of sulphur dioxide (SO2) in the atmosphere can be determined by studying lichens. SO2 is a pollutant produced by coal burning and industrial processes, and certain lichens cannot survive extended exposure to it. Thus, the absence of lichens or the presence of only crusty lichens (which are more tolerant of poor air quality) indicates high levels of SO2.

Thirdly, lichens are easy to study and can be found in a variety of environments, making them convenient indicators of air quality. They can be studied through direct observation, or by taking samples and analysing them for the presence of pollutants. Scientists can also transplant lichens to test areas to specifically study the effects of pollution on their physiology.

Finally, lichens can indicate not just the number of pollution particles in the air, but also the effects of air pollution on ecosystems. This is important for understanding how air pollution is changing ecological communities and what that means for the people who rely on them.

Overall, the presence or absence of lichens, as well as the specific species of lichens present in an area, can provide valuable information about the level of air pollution and its impacts on the surrounding environment.

Lichens absorb pollutants and can become toxic

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 indicators of air quality. Lichens absorb nutrients and water from their surroundings, and because they lack a protective surface, they cannot filter what they absorb. This means that when exposed to air pollutants, lichens absorb them and can become toxic.

Lichens are like sponges, absorbing rainwater and air through their entire thallus, which is essential for gas exchange, photosynthesis, and respiration. The dust is trapped between the mycelium filaments, and lichenic acids fix pollutants. Fruticose lichens, with their bushy structure, have a higher surface-to-volume ratio, making them more effective at recovering air pollutants present as aerosols. Foliose lichens, with their leaf-like shape, are more efficient at recovering compounds that are deposited through gravity, such as particles and air pollutants.

The two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide. Nitrogen dioxide is formed when nitrogen is heated and combined with oxygen, such as in car engines. It is a powerful pollutant that can harm human health by irritating the lungs and causing respiratory issues. Sulphur dioxide is produced by coal burning and industrial processes. While sulphur dioxide levels have decreased in some regions due to reduced coal usage, it still affects lichens and can irritate the mucous membranes of humans, causing coughing and chest tightness.

Lichens respond quickly to pollution, and their presence or absence can indicate air quality. The diversity and health of lichen species in an area can provide information about the levels of pollution. Some lichen species are more tolerant of pollution, while others are more sensitive. Scientists monitor lichen communities to detect changes in species composition and health, which can signal potential ecosystem decline due to increased pollution.

Lichen transplants are also used to assess air quality in areas where lichens are scarce. Healthy lichens are transferred to test areas, and the effects of pollution exposure are studied. This helps scientists understand the impact of pollution on lichen physiology and element accumulation. By observing the distribution and health of lichens, we can gain valuable insights into the presence and effects of air pollutants on ecosystems and human health.

Nitrogen dioxide is a powerful pollutant and harmful to human health

Lichens are miniature ecosystems composed of fungi and algae and/or cyanobacteria. They are highly sensitive to air pollution, absorbing nutrients, water, minerals, and pollutants from the air through rain and dust. This makes them excellent indicators of air quality.

Nitrogen dioxide (NO2) is a powerful pollutant and is harmful to human health. It is one of the six widespread air pollutants with national air quality standards limiting their levels in outdoor air. NO2 is a nitrogen oxide produced from burning natural gas (methane) and is emitted from combustion sources such as gas-fired power plants, industrial sites, and vehicles. In the UK, around half of the nitrogen dioxide air pollution comes from road traffic. Farms also contribute to nitrogen dioxide pollution through fertilisers, farm machinery, and livestock waste.

Nitrogen dioxide can cause a range of adverse health effects. It can irritate and inflame the lining of the lungs, leading to respiratory issues such as coughing, shortness of breath, and increased susceptibility to lung infections. Long-term exposure can cause structural changes in the lungs, including emphysema-like destruction of alveolar walls and enlarged airspaces. It is also associated with an increased risk of asthma, heart problems, and harm to pregnancy and birth outcomes. Children are particularly vulnerable, with higher exposure due to their greater breathing rate relative to body weight and increased time spent outdoors.

In addition to its direct health impacts, NO2 contributes to the formation of other air pollutants, including ozone (O3), nitric acid (HNO3), and nitrate (NO3-) particles. It can react with water to form nitrous acid (HONO), a common indoor and ambient pollutant. While indoor levels of NO2 are often lower due to ventilation, they can still accumulate to unhealthy levels, especially near emission sources such as stoves, dryers, and space heaters.

Overall, nitrogen dioxide is a significant contributor to outdoor and indoor air pollution, posing a range of risks to human health. Its presence and impact are effectively monitored by lichens, which serve as sensitive indicators of air quality in their ecosystems.

Sulphur dioxide has killed many lichens

Sulphur dioxide pollution has historically killed many lichens in the UK. In high concentrations, it can irritate the mucus lining of the eyes, nose, throat, and lungs in humans, causing coughing and tightness in the chest. Similarly, lichens are unable to tolerate high levels of sulphur dioxide. When exposed to this pollutant, they exhibit reduced photosynthesis and bleaching. Sulphur dioxide dissolves in water to produce acidic ions, which are readily absorbed through the lichen thalli, further disrupting their ability to photosynthesize.

The Usnea lichen, also known as old man's beard, is particularly sensitive to sulphur dioxide pollution and is absent in areas where it is present. Other lichen species, such as the golden shield lichen (Xanthoria parietina), are better able to tolerate higher levels of nitrogen, especially ammonia, and can be found in areas with agricultural pollution, such as near farmland or on sea cliffs where seabird droppings are prevalent.

Lichens are excellent indicators of air quality and the health of ecosystems. Their sensitivity to pollutants means they can act as bioindicators, bioaccumulators, and biomarkers of air pollution. By studying the presence or absence of different lichen species and measuring the concentration of pollutants in their tissues, scientists can gain valuable insights into the quality of the environment and potential health risks for humans and other organisms.

While sulphur dioxide pollution from coal burning has decreased in recent times, other sources of air pollution, such as nitrogen oxides from vehicle emissions and agricultural activities, continue to impact lichen populations and the ecosystems they inhabit.

Lichens can indicate typical sulphur dioxide levels

Lichens are excellent bioindicators of sulphur dioxide levels in the lower troposphere. They are sensitive to atmospheric pollution, including sulphur dioxide, which comes from coal burning and industry. Sulphur dioxide can dissolve in the water films on or within moist lichen thalli, yielding various dissolutions.

Lichens are miniature ecosystems made of fungus and algae and/or cyanobacteria. They fix carbon dioxide from the air to build biomass. They get their nutrients from the air, and because they have no roots or protective surface, they absorb everything in their environment. This makes them susceptible to certain pollutants, which can accumulate in the lichen and become toxic very quickly.

Sulphur dioxide, when mixed with rainwater or air, can damage lichens and prevent them from growing. Therefore, the absence of lichens indicates that the area is heavily polluted with sulphur dioxide. Usnea lichens, also called old man's beard, do not grow in areas where there is sulphur dioxide pollution. Sulphur dioxide can also irritate the mucus lining of the eyes, nose, throat, and lungs. Exposure may cause coughing and tightness in the chest.

Lichen diversity can be very high, and consequently, the level of uncertainty in the interpretation of data may arise considerably. This should be considered when planning higher-scale surveys by implementing adequate sampling intensity at the within-site scale.

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