These may look insignificant but they play a major role as bioindicators

Lichens, symbiotic organisms composed of fungi and algae or cyanobacteria, are sensitive to certain environmental changes, making them excellent bioindicators of air quality. In Baguio City, you see them in areas where trees and plants are abundant. This is because their survival and existence are also dependent on the quality of air a certain area has.

Over the years, multiple research studies have shed light on their utility in this realm. Here’s a look at some pivotal findings.

What are lichens?

Lichens are unique and intricate organisms that arise from a symbiotic relationship between fungi and either algae or cyanobacteria. Unlike most plants, they lack roots, stems, and leaves, and instead obtain nutrients directly from the surrounding environment, particularly from the air. This direct exposure, combined with the absence of protective structures like stomata, makes them highly susceptible to atmospheric changes. As a result, lichens readily absorb pollutants, which can affect their growth, abundance, and diversity. The presence or absence of specific lichen species, as well as changes in their morphology, can thus provide vital clues about the level and types of pollutants in an environment, positioning them as powerful natural sentinels for assessing air quality.

Pertinent research on lichens are bioindicators of pollution

1. Sensitivity to Air Quality: Lichens have no stomata to regulate gas exchange, making them constantly exposed to the surrounding environment. This makes them particularly sensitive to air pollutants. In areas with high pollution, particularly sulfur dioxide (SO₂), lichen diversity tends to decrease. Hawksworth and Rose (1970) were among the pioneers in this field, correlating lichen distribution with SO₂ levels in the UK.

2. Biomonitoring Trace Elements: Lichens can accumulate trace elements from the atmosphere. Garty (2001) found that lichens, due to their ability to accumulate trace elements, can be used as biomonitors for metal deposition and pollution. Elements like lead, copper, and zinc, among others, can be detected at elevated levels in lichens in polluted areas.

3. Indicator of Nitrogen Pollution: Nitrogen pollutants from agricultural runoff, vehicle emissions, and industrial processes can affect lichen communities. Pinho et al. (2017) reported that lichens can be used to gauge nitrogen deposition, with certain lichen species being more prevalent in high nitrogen environments.

4. Correlation with Other Pollutants: Lichens are not only sensitive to SO₂ and trace metals. They also respond to other pollutants like ozone, fluorides, and ammonia. Nimis et al. (2002) showed that the presence or absence of specific lichen species can indicate the levels of multiple air pollutants in a given area.

5. Modern Uses and Geographic Spread: Many countries have adopted lichen-based bioindicator systems for monitoring air quality. The Lichen Diversity Value (LDV) system, used in the UK, is an example where the diversity of lichen species on tree trunks is used to assess local air quality (Bates et al., 2011).

Conclusion: Lichens, with their unique biology and wide distribution, serve as a natural monitor for environmental health. Their sensitivity to various pollutants allows scientists and environmentalists to gauge the quality of air in a given area, providing a clear picture of anthropogenic impact on the environment.

References:

• Hawksworth, D.L., & Rose, F. (1970). Qualitative scale for estimating sulphur dioxide air pollution in England and Wales using epiphytic lichens. Nature, 227, 145-148.
• Garty, J. (2001). Biomonitoring atmospheric heavy metals with lichens: theory and application. Crit Rev Plant Sci, 20(4), 309-371.
• Pinho, P., et al. (2017). Mapping lichen diversity as a first step for air quality assessment. J Appl Ecol, 54(2), 478-486.
• Nimis, P.L., et al. (2002). Monitoring with lichens the impact of heavy metal deposition in northern Italy: first results of a case study. Environmental Monitoring and Assessment, 77, 273–292.
• Bates, J.W., et al. (2011). Loss of Lecanora conizaeoides and other changes in lichen composition on oak in southeast England over 21 years with declining SO₂ concentrations. Environmental Pollution, 159, 1961-1968.