Greta Jimenez
Lichens are composite organisms that grow in all environments except the high seas, on live animals, and in highly polluted areas. They are sensitive to air pollution and can be used to determine air quality in a given area. Lichens are especially sensitive to nitrogen and sulphur dioxide. Sulphur dioxide, in particular, has killed many lichen species in the UK, though its decline since the 1980s has allowed the return of lichens sensitive to this pollutant. The Usnea lichen, also called old man's beard, does not grow in areas with sulphur dioxide pollution. The golden shield lichen, on the other hand, can live in areas with high levels of nitrogen. The oakmoss lichen is sensitive to nitrogen in the air and can be found on woodland branches where the air is clean.
| Characteristics | Values |
|---|---|
| Common Name | Old man's beard |
| Scientific Name | Usnea ceratina |
| Sensitivity | Very sensitive to sulphur dioxide |
| Habitat | Does not grow in areas with sulphur dioxide pollution |
| Nitrogen Sensitivity | Tolerant |
| Ammonia Sensitivity | Tolerant |
| Use as Bio-Indicator | Used to track levels of air-borne lead over a 100-year period |
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What You'll Learn
Lichens as bio-indicators
Lichens are composite organisms composed of a single fungus species (mycobiont) and one or more algae species (phycobionts). The algae in lichens photosynthesize, creating food from sunlight energy, while both the algae and fungus absorb water, minerals, and pollutants from the air, through rain and dust. Due to their unique biology and sensitivity to contaminants, lichens have emerged as valuable tools for biomonitoring. They are especially sensitive to nitrogen and sulphur dioxide.
Lichens are bio-indicators of environmental pollution because of their sensitivity to various contaminants. They are capable of responding to ecological toxins, thus functioning as bio-indicators. Lichens are also durable and can grow on tree bark and bare rock. Their gradual growth rate allows them to accumulate substances, and they exhibit exceptional nutrient cycling, contributing to ecosystems from a local to a regional scale. Lichens are widely recognized as bio-indicators of environmental pollution, especially in mountainous regions.
Lichens are sensitive to atmospheric pollution such as nitrogen (N) because they receive all their nutrients and water from atmospheric deposition (fallout). 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. Some lichens will die in the presence of nitrogen, while others will thrive. By learning a few common lichen species, you can judge the nitrogen pollution levels in your area.
The presence or absence of certain lichen species can indicate the overall health of an ecosystem, and changes in lichen populations can be an early warning sign of environmental problems. Lichens can absorb heavy metals from the soil, helping to detoxify polluted areas, contributing to environmental sustainability. Lichens have been used to track levels of airborne lead over a 100-year period, for example, in Maryland in the early 20th century, where they showed a dramatic rise in atmospheric lead deposition. Lichens have also been studied in South Korea to assess their response to heavy metal pollution in their native ecosystems.
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Nitrogen pollution
Lichens are very sensitive to air pollution and can be used as indicators of air quality. They are composite organisms comprising a fungus and an algae species. Lichens absorb water, minerals, and pollutants from the air through rain and dust. Some lichen species are more sensitive to nitrogen pollution than others.
Nitrogen is a harmless gas that makes up a large part of the Earth's atmosphere. However, when nitrogen is heated and combined with oxygen, nitrogen oxides are created. Nitrogen dioxide is a powerful pollutant and is harmful to human health in high concentrations. Farms, road traffic, and machinery are some sources of nitrogen dioxide.
The oakmoss lichen is sensitive to nitrogen in the air and can be found on woodland branches where the air is clean. Some lichens will die in the presence of nitrogen, while others will thrive. The golden shield lichen, for example, can live in areas with high levels of nitrogen, especially ammonia. It is commonly found near farmland and on sea cliffs where seabird droppings provide nitrogen.
Lichens growing on Atlantic Oak trees in areas of high rainfall but low levels of dry deposition (gaseous pollutants) are highly sensitive to nitrogen. In Europe and the UK, the lichen flora of oak trees in agricultural areas has changed from communities dominated by species preferring acid bark to species that tolerate and benefit from nitrogen.
Scientists monitor lichen communities to assess the levels of nitrogen deposition. If there is an increase in nitrogen-tolerant species and a decrease in nitrogen-sensitive species, it may indicate rising nitrogen deposition. Lichens act as "canaries in the coal mine" for nitrogen deposition, and their decline or change in species composition can signal potential ecosystem decline due to nitrogen pollution.
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Sulphur dioxide pollution
Sulphur dioxide is a major air pollutant that has been shown to be harmful to lichens. Sulphur dioxide dissolves in water to produce acidic ions, which are readily absorbed through the lichen thalli, disrupting their photosynthesis. Sulphur dioxide has also been shown to inhibit the activity of nitrogenase, which is used by cyanobacterial photobionts to fix atmospheric nitrogen.
Lichens are very sensitive to sulphur dioxide pollution and respond to it in short time frames. Sulphur dioxide pollution comes from coal burning and industry. This pollutant has killed many lichens around the UK in the past. However, due to reduced coal burning, lichen populations are beginning to recover.
Usnea lichens, also called old man's beard, do not grow in areas with sulphur dioxide pollution. If you see Usnea lichens on your walk, it means that coal probably hasn't been burnt in the area for some time. People with asthma are more sensitive to sulphur dioxide pollution, which may cause coughing and tightness in the chest. In high concentrations, sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs.
Lichens are excellent indicators of air pollution and can tell us about the effects of air pollution on ecosystems. They are miniature ecosystems made of fungus and algae and/or cyanobacteria. The algae or cyanobacteria provide the fungus with sugars made from sunlight, and the fungus provides a home. Lichens are durable enough to grow on tree bark and bare rock, yet sensitive to air pollution.
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Lichen species diversity
Lichens are composite organisms comprising a single species of fungus (mycobiont) and one or more algal species (phycobionts). The fungus provides structure and protection for the algae, which reciprocates by providing energy through photosynthesis. This symbiotic relationship is so close that the algae sit inside the fungus.
There are about 20,000 known species of lichen, with approximately 3,600 species in North America alone. Lichens are found all over the world, in a vast diversity of habitats and climates, from deserts to alpine tundra, tropical rainforests, and even inside solid rock. They are a major component of high-latitude ecosystems and play an important role in nutrient cycling. They are a keystone species in many ecosystems and benefit trees and birds.
Lichens are highly sensitive to environmental conditions, including airborne contaminants, substrate chemistry, and climate. They are particularly sensitive to air pollution, which makes them good indicators of air quality. Sulphur dioxide and nitrogen are two major air pollutants that affect lichen growth. Some lichens will die in the presence of nitrogen, while others will thrive. The golden shield lichen, for example, can live in areas with high levels of nitrogen, especially ammonia. It is commonly found near farmland and on sea cliffs where seabird droppings provide nitrogen. Usnea lichens, also called old man's beard, do not grow in areas with sulphur dioxide pollution.
Lichens have been used to study air quality and pollution levels over time. For example, lichens collected from Plummers Island, Maryland, in the early 20th century, showed a dramatic rise in atmospheric lead deposition prior to the 1980s, coinciding with the completion of a bridge and the phasing out of leaded gasoline in the US. Present-day lichen communities in this region are less diverse and contain fewer sensitive species than in the past.
Lichen inventories and studies have been conducted in various national parks in the US and Europe, contributing to our understanding of lichen biodiversity and providing baseline data for resource management and ecological monitoring. These studies have discovered new lichen species and rare or endangered lichen populations.
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Lichen observation methods
One of the earliest methods of observing lichens was developed by Nylander, a Finnish lichenologist, in the 19th century. Nylander made observations of the trees in the Luxembourg Garden in Paris and found that the disappearance of lichens was due to the presence of sulphur dioxide (SO2) from coal combustion and industrial development.
In the 1970s and 1980s, the Hawksworth and Rose method was widely used in France. This method classified about 80 lichen species into 11 pollution levels, with level 0 corresponding to the maximum pollution level and level 10 to the maximum purity level. However, with the decrease in SO2 emissions, other pollutants such as nitrogen oxides became more prevalent, and the Hawksworth and Rose method could no longer be used.
An alternative approach was introduced, focusing on the observation of species communities rather than individual lichen species. This method, known as the IBLE (Biological Index of Lichens Epiphytes) method, divides about 30 species into 7 zones ranging from very poor to very good air quality. This procedure has been applied in the northern half of France, including the Lyon region.
Other methods for observing lichens include qualitative and quantitative approaches. Qualitative methods involve developing lichen-pollution/air quality correspondence levels, while quantitative methods involve calculating an air quality index, such as the nitrogen air quality index (NAQI). Scientists can also monitor the health of lichens and pair this data with atmospheric deposition data to determine the sources and levels of pollution causing detrimental effects.
Additionally, field manuals and mobile apps have been developed to assist in lichen observation and identification, providing step-by-step methods for determining the levels of risk from gaseous nitrogen pollution and assessing air quality.
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Frequently asked questions
While all lichens are sensitive to pollution, some are more so than others. Usnea lichens, also called old man’s beard, don’t grow in areas where there’s sulphur dioxide pollution. Other lichen species that are sensitive to pollution include Usnea hirta, Usnea ceratina, Bryoria capillaris, B. fuscescens, Imshaugia aleurites and Chaenotheca ferruginea.
Lichens are organisms consisting of a symbiotic relationship between a fungus and a chlorophyll-containing partner, either algae or cyanobacteria.
Lichens are immersed in their environment and receive all their nutrients from the atmosphere, which makes them valuable as indicator species. Lichens can indicate the presence of sulphur dioxide, nitrogen, heavy metals, organic elements, and radioelements.
