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Lichens reveal pollution from WA coal-fired p -

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Meenu Vitarana: I wonder how many people notice lichens, the organisms that look like splashes of paint found on tree bark, rocks and sometimes even roof and garden tiles. But have you ever wondered what they are? Lichens are not a single organism, they are an association between fungi and algae that live together in a mutual symbiosis, a relationship enabling them to thrive even in very harsh environments.

Lichens play a key role in the weathering of rocks to form soil, and they are good indicators of air quality. Scientists have been using lichens as tools to monitor air pollution for decades. My name is Meenu Vitarana, I am a PhD candidate at the Centre for Ecosystem Management at Edith Cowen University in Perth. I have been studying lichens as air pollution monitors here in Australia where they have not been studied in this context before.

What makes lichens such effective air pollution monitors? Lichens lack true roots and they are dependent on the atmosphere for their nutrients and have developed mechanisms for the efficient uptake of material from the air. If the air around them is polluted, lichens will absorb these pollutants too, and the concentrations of pollutants in lichen tissue reflect their surrounding environment. This simple theory is applied when monitoring the air we breathe.

There are several ways of measuring pollution using lichens. One is to count the number of lichen species and their abundance in a defined area of a natural surface, such as a tree trunk. The more pollution, the fewer species of lichens. A second more direct approach is to collect lichen tissue from sites located at different distances from industrial sources and analyse them.

A third approach is to collect lichens from unpolluted environments, loosely pack them in a nylon mesh bags and hang them on trees in areas suspected to have been polluted. These transplanted lichen bags are collected after specific time intervals and analysed for pollutants. Lichens can be used to measure pollutants such as nitrogen dioxide and sulphur dioxide, and also toxic metals such as arsenic, cadmium, chromium, mercury and nickel. The main advantage of the lichen bio-monitoring approach is that it doesn't require sophisticated field equipment, which saves money and makes it easy to measure pollution over a wide area.

For my PhD I designed a project to explore the use of lichens in relation to coal mining and coal power plant emissions in the Shire of Collie in Western Australia, 200 kilometres south of Perth. Coal power generation is known to emit toxic heavy metals into the environment, and no studies have measured these emissions in Collie. For my PhD I used all three lichen bio-monitoring approaches across 36 study sites in the surrounding native jarrah forest.

I measured nine metals known to be emitted by coal-fired power plants using the beard lichen, Usnea inermis. I used this data to generate pollution dispersion maps around Collie. These maps identify areas impacted by pollution plumes from the power stations. I found low concentrations of most metals in lichen tissue, but clear dispersion patterns were found in the forest, indicating an influence of the coal-fired power plants adding metals to the Collie area. The wet winter season was found to be the best time for lichen biomonitoring. Mapping the dispersion of air pollutants identified impact areas not previously known.

The results from my PhD research have shown that bio-monitoring with the humble lichen can be very useful in identifying areas of air pollution in the Western Australian environment. Thank you.

Robyn Williams: And thank you. Meenu Vitarana from the Edith Cowan University in Perth.