Lichen Growth: Pollution's Impact And Resilience

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacterium. They are sensitive to air pollution and can be used as indicators of air quality. Lichens absorb water, minerals, and pollutants from the air through rain and dust. Certain lichen species are more tolerant of pollution than others, and their presence or absence can indicate the level of air pollution in an area. For example, the presence of crusty lichens like Lecanora conizaeoides or Lepraria incana indicates poor air quality, while leafy lichens like Parmelia caperata or Evernia prunastri suggest moderate to good air quality. Lichens can also accumulate pollutants, which can lead to structural changes, reduced growth, or death. They are important for studying the effects of pollution on ecological communities and have been used to assess air pollution levels in various parks and urban areas.

Lichens are sensitive to air pollution

Some sensitive lichen species develop structural changes in response to air pollution, including reduced photosynthesis and bleaching. Pollution can also cause the death of the lichen algae, discoloration, and reduced growth of the lichen fungus, or even kill the lichen completely. Lichens can be used as indicators of air pollution, as the species of lichen present in a location and the concentration of pollutants measured in those lichens can tell us a lot about air quality. For example, in the 1970s and 1980s, SO2 and fluoride pollution dominated air pollution chemistry, and a lichen zone pattern was described in large towns and cities corresponding to the mean levels of SO2. In general, crustier lichens tend to be more tolerant of pollution than hairy lichens. The golden shield lichen (Xanthoria parietina), for instance, can live in areas with high levels of nitrogen, especially ammonia.

Lichens are also sensitive to ozone, and some species are more resilient than others. They can be killed by toxic compounds, such as those found in commemorative plaques on boulders, and by wind-blown pollutants, which have greater effects on higher, exposed areas. Lichens can also be affected by nitrogen pollutants, which may be more important than the overall N dose, and the long-term N load may become significant due to N accumulation. Lichens growing in remote, pristine environments can experience N limitation, and nitrogenous air pollution can influence the occurrence of acid-loving lichen species, threatening natural populations.

In the 20th century, the reduction of coal fires and the implementation of clean air policies led to a decrease in sulphur dioxide levels in various cities, which has resulted in an increase in the number of lichen species in previously polluted urban centres. However, in some cases, the lichen 're-invasion' has been limited to nitrogen-tolerant species due to high levels of nitrate or ammonium deposition.

Some lichens tolerate poor air quality

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. They are sensitive to air pollution, and pollutants can accumulate in them, becoming toxic very quickly. However, some lichens are more resilient than others and can tolerate poor air quality.

Crustier lichens, for instance, tend to be hardier than hairy lichens. The golden shield lichen (Xanthoria parietina) can survive in areas with high nitrogen levels, especially ammonia. It is commonly found near farmland and on sea cliffs where seabird droppings provide nitrogen. Similarly, Flavoparmelia caperata, a pollution-tolerant lichen, has been found in several national parks.

Some lichens can tolerate sulphur dioxide (SO2) pollution, which is caused by coal burning and industrial activities. In the past, SO2 pollution killed many lichens, but with the reduction in coal fires and the implementation of clean air policies, SO2 levels have decreased, allowing lichens to return. However, nitrogen pollutants may prevent the recolonization of certain lichen species. Crustose lichens like Lecanora conizaeoides and Lepraria incana can tolerate poor air quality with respect to SO2.

Nitrogen-loving, pollution-tolerant lichen communities have developed in regions with poor air quality. In the Netherlands, high ammonia levels caused the disappearance of acid-preferring lichen species, leading to communities dominated by nitrophytic species. Epiphytic lichens, which grow on trees, have been studied for their tolerance of nitrogenous gases and acidity. Lichens on Atlantic Oak trees in areas of high rainfall and low gaseous pollutant levels are highly sensitive to nitrogen.

While some lichens can tolerate poor air quality, it is important to note that pollution can still cause structural changes, reduced photosynthesis, bleaching, discoloration, and even death in sensitive lichen species.

Lichens absorb pollutants from the air

Lichens are miniature ecosystems made of fungus and algae and/or cyanobacteria. The algae or cyanobacteria photosynthesize, creating food from sunlight energy, and the fungus provides a home. Lichens are durable and can grow on tree bark and bare rock, yet they are sensitive to pollution and air quality. They absorb water, minerals, and pollutants from the air, through rain and dust.

Lichens make great air pollution indicators because they absorb pollutants from the air and are very sensitive to them, responding to changes in a short time frame. Lichens can absorb pollutants like nitrogen, sulphur, and lead. For example, in the 1970s and 1980s, SO2 and fluoride pollution dominated the air due to industrial activities. Lichens were affected by these pollutants, with some species unable to tolerate poor air quality. Similarly, lichens from Plummers Island, Maryland, showed a rise in atmospheric lead deposition before the 1980s, corresponding to the completion of a bridge and the use of leaded gasoline. As leaded gasoline was phased out, lead concentrations in lichens declined sharply.

Nitrogen is an essential element for lichens to survive as it helps them produce necessary proteins and organic acids. However, too much nitrogen can be harmful, causing over-fertilization and the death of certain lichen species. Nitrogen dioxide, formed by heating nitrogen and combining it with oxygen, is a powerful pollutant that can harm human health. Farms emit nitrogen pollutants from fertilizers, machinery, and livestock waste.

The presence or absence of lichens, as well as the species and their health, can indicate the level of air pollution in an area. For example, in urban parks near Washington, DC, there are lower species diversity and coverage, with no pollution-sensitive species. In contrast, Prince William Forest Park has higher species richness and more pollution-sensitive species. The types and health of lichens can provide valuable information about air quality and the effects of pollution on ecosystems.

Pollution can cause structural changes in lichens

Lichens are miniature ecosystems composed of a fungus and an alga and/or cyanobacteria. The alga in lichens photosynthesizes to create food from sunlight, while both the alga and fungus absorb water, minerals, and pollutants from the air, through rain and dust. Due to their unique composition, lichens are highly sensitive to pollution and air quality.

Lichens can absorb pollutants from the air and their presence in an environment can indicate the level of air pollution. Some lichen species develop structural changes in response to air pollution, including reduced photosynthesis and bleaching. For example, sulphur dioxide (SO2) pollution, which comes from coal burning and industry, has killed many lichens in the past. However, as coal burning has decreased, SO2 levels have also reduced, leading to an increase in lichen species in previously polluted areas.

Nitrogen pollutants can also impact lichens, with some species being N-sensitive and experiencing N limitation. Nitrogenous gases and acidity can affect lichens, with nitrogenous air pollution influencing the occurrence of acid-loving lichen species. In the Netherlands, for example, high levels of ammonia caused the disappearance of acid-preferring species, leading to a dominance of nitrophytic species.

Ozone has also been shown to be detrimental to lichens, although some species are more resilient than others. Metal compounds, such as bronze plaques on boulders, can leach toxic compounds that kill lichens in their flow path.

Overall, pollution can indeed cause structural changes in lichens, including reduced photosynthesis, bleaching, and even death. Lichens are valuable indicators of air pollution and can provide insights into the changing ecological communities and air quality of an area.

Lichens can indicate air quality

Lichens are miniature ecosystems composed of a fungus and an algae and/or cyanobacteria. The algae or cyanobacteria photosynthesize and provide the fungus with sugars made from sunlight, and the fungus provides a home. Lichens can grow on tree bark and bare rock, but they are also sensitive to pollution and air quality. They absorb water, minerals, and pollutants from the air through rain and dust. Some lichen species develop structural changes in response to air pollution, including reduced photosynthesis and bleaching.

The study of lichens and their response to pollution can provide valuable information about air quality and ecological changes. Lichens were used to assess the impact of atmospheric lead deposition in Plummers Island, Maryland, and the results showed a decline in lichen diversity and the disappearance of pollution-sensitive species over time. Similarly, a baseline inventory of bark-dwelling lichens was conducted in nine parks of the National Capital Region (NCR) to analyze pollution-tolerant lichen species and their corresponding pollutant levels.

In summary, lichens are useful indicators of air quality due to their sensitivity to pollutants and their ability to absorb them from the atmosphere. The presence or absence of specific lichen species in an area can provide insights into the level of pollution and help assess changes in air quality over time.

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