• The role of lichens in the fight against air pollution

When it comes to air pollution, we often think of the biggest culprits as being carbon dioxide (CO2) and carbon monoxide (CO). However, nitrogen pollution is also an equally critical environmental issue that needs to be considered. 

Nitrogen pollution is primarily driven by human activities that disrupt the natural nitrogen cycle. The widespread use of synthetic fertilisers, industrial processes, and emissions from transportation contribute to an excess of reactive nitrogen in the environment. This surplus leads to severe ecological consequences, including eutrophication of water bodies, which results in harmful algal blooms and creates hypoxic ‘dead zones’ where aquatic life cannot survive. 

The United Nations Environment Programme (UNEP) has highlighted nitrogen pollution as one of the most pressing pollution challenges facing humanity today, affecting not only ecosystems but also human health and economic stability. Elevated levels of nitrates in drinking water can cause methaemoglobinaemia in infants, while ammonia emissions contribute to air quality degradation, exacerbating respiratory issues and other health problems.

Moreover, nitrogen pollution significantly impacts climate change. Reactive nitrogen compounds, particularly nitrous oxide, are potent greenhouse gases with a warming potential far greater than carbon dioxide. They persist in the atmosphere for extended periods, contributing to long-term climate effects. 

The challenge lies not only in mitigating these emissions but also in rethinking agricultural practices and waste management systems to prevent nitrogen loss into the environment. Sustainable nitrogen management strategies are essential for reducing pollution levels and safeguarding both human health and biodiversity while ensuring food security for a growing global population.

Recently, a groundbreaking regional study was conducted by the South Asian Nitrogen Hub in collaboration with Dilmah Tea to measure the impacts of nitrogen pollution through the monitoring of lichens. 

In the world of bioindicators, lichens stand out as some of the most effective natural sensors of air quality. These fascinating organisms – often mistaken for simple moss or fungi – are in fact complex ecosystems capable of surviving in harsh environments and providing invaluable insights into the health of our atmosphere. 

As cities and industries continue to grow, the environmental consequences of pollution, particularly nitrogen pollution, are becoming harder to ignore. Lichens, with their sensitivity to atmospheric changes, offer a unique solution to monitoring these effects. 

The Sunday Morning Brunch sat down with National History Museum of London Lichens and Slime Moulds Senior Curator Dr. Gothamie Weerakoon for a discussion on the threat that nitrogen pollution poses and how studying lichens can help manage nitrogen sustainably. 

What are lichens?

Lichens are remarkable organisms composed of a symbiotic association between fungi and either algae or cyanobacteria. This union allows them to thrive in a variety of environments, from the frozen tundra to the scorching desert. 

As Dr. Weerakoon explained: “Lichens are one of the best symbiotic organisms, capable of surviving without any support. They just need a surface to sit on.” Unlike most organisms, lichens do not rely on soil to grow and can attach themselves to a wide range of surfaces, including rocks, trees, and even man-made structures.

What makes lichens particularly fascinating is their ability to farm their own food. The fungal component of a lichen provides protection and structure, while the algae or cyanobacteria produce food through photosynthesis. 

“Lichens are the world’s oldest farmers – they farm cyanobacteria and algae to make their food,” said Dr. Weerakoon. This symbiotic relationship has existed for millions of years, with some fossilised lichens dating back to the Mesozoic and Cenozoic periods, making them older than dinosaurs.

Lichens as air quality sensors

Lichens are incredibly sensitive to changes in their environment, particularly air pollution. They absorb water and nutrients directly from the air, making them highly susceptible to airborne pollutants. Because of their slow growth and long lifespan, lichens can capture environmental changes over extended periods, making them ideal for monitoring long-term shifts in air quality.

“Lichens are very sensitive to environmental changes. They are one of the good biological indicators; they don’t need expensive equipment or technical methods. Lichens themselves can show us how increasing nitrogen is affecting other animals and plants,” Dr. Weerakoon pointed out.

Nitrogen, while a naturally occurring element, has become a major pollutant in many parts of the world due to excessive fertiliser use and industrial emissions. In South Asia, the problem is particularly acute. 

“In South Asia, the most burning problem is not CO2, it’s nitrogen and ammonia,” Dr. Weerakoon explained. Excessive nitrogen, primarily from agricultural runoff and industrial processes, has dire consequences for biodiversity and human health. 

Unlike carbon dioxide, which has been widely studied and is the focus of many environmental policies, nitrogen pollution often flies under the radar. Dr. Weerakoon emphasised that “nitrogen is 300 times worse than CO2 and CO” in terms of its impact on ecosystems and health.

Lichens react visibly to nitrogen pollution. As nitrogen levels rise, lichens may exhibit discolouration, reduced growth, or even die off completely. 

“Like corals in marine environments, lichens lose their natural colour when stressed – they bleach. This is the first morphological appearance that we see,” she said. In extreme cases, entire populations of lichens can die off, serving as a stark warning of the deteriorating air quality.

Lichens in South Asia: A case study on nitrogen pollution

Dr. Weerakoon’s research focuses on the growing nitrogen pollution problem in South Asia, particularly in Sri Lanka. Since 2022, she has been part of a collaborative research project aimed at monitoring the effects of nitrogen pollution on lichens in the region. This research is particularly important because South Asia has one of the largest nitrogen footprints in the world, driven by widespread agricultural practices that rely heavily on fertilisers.

“We have been monitoring lichens for two years in a permanent forestry monitoring plot in Sri Lanka. We measure how much excess nitrogen is in the atmospheric air and observe changes in the lichens over time – changes in colour, reduction of growth, and even some dying,” she explained. 

The project has already yielded alarming findings. In many urban areas, nitrogen levels have reached critical points, threatening not only lichen populations but also human health. “We know which areas are good for air quality and which are not. We have identified critical levels of nitrogen that can harm human tissue and animal tissue. Nitrogen is very bad for human health and animal health,” she continued.

Lichens are not just passive indicators of pollution; they can also help track changes in air quality over time. By studying lichen growth and morphology, scientists can determine how much pollution has accumulated in a given area and how the environment has changed over the years. 

“Because they grow so slowly, lichens are capable of capturing changes over a very long time,” Dr. Weerakoon said. This ability makes them invaluable tools for environmental monitoring, particularly in regions where long-term data on pollution is scarce.

Managing nitrogen pollution

The research conducted by Dr. Weerakoon and her team has significant implications for environmental policy, particularly in countries like Sri Lanka, where nitrogen pollution is a growing concern. 

“This can be promptly applied by policymakers,” she said. “Government and other policy-making agencies can use our findings to make a nitrogen mitigation roadmap or policy in Sri Lanka.” Such policies could help regulate fertiliser use in agriculture, promote cleaner industrial practices, and establish stricter emissions standards for vehicles and factories.

However, addressing nitrogen pollution will require more than just local policies. Dr. Weerakoon argued that a regional approach was necessary. “The South Asian nitrogen footprint is 300 times bigger than its carbon footprint,” she said. 

Given the interconnected nature of pollution, it is crucial for countries in the region to work together to develop a comprehensive strategy for nitrogen mitigation. Collaborative research projects, like the one Dr. Weerakoon is part of, are a step in the right direction. The project is funded by UK Research and Innovation and involves researchers from Sri Lanka, Bhutan, Nepal, and the Maldives. 

“If all these South Asian countries can come to one platform and make a roadmap for nitrogen pollution mitigation, it will make a big difference,” she emphasised.

One of the key drivers of nitrogen pollution in South Asia is the overuse of fertilisers in agriculture. Many farmers believe that applying more fertiliser will result in higher crop yields, but this is not the case. Plants can only absorb a limited amount of nitrogen and any excess is released into the atmosphere or leaches into water systems, where it can cause severe environmental damage. 

“The future is going to be really unpredictable if we continue using fertilisers the way we do now,” warned Dr. Weerakoon. “The population in South Asia is increasing, and in the next 50-100 years, most of our agricultural fields and crops will collapse because the soil is too unhealthy.”

To prevent such a collapse, she advocates more sustainable farming practices, including proper fertiliser application methods that minimise nitrogen runoff. “The agricultural, industrial, and plantation sectors need to understand what the maximum level of fertiliser application should be, especially for tea, rubber, and vegetable cultivation,” she said.

By reducing the amount of nitrogen released into the environment, it is possible to protect not only the soil and water but also the air we breathe. By paying attention to the signals that lichens are sending us, we have the opportunity to make meaningful changes before it is too late. As Dr. Weerakoon shared: “If we continue the way we are going, the future is going to be unpredictable. But if we act now, we can change that.”