How do you track biodiversity loss? Check air filters, say scientists

It's no surprise that along with the wildfire ash, pollen, dust and other particles that can be found floating in the air we breathe, there are also fragments of genetic material from plants and animals.

A new study by Canadian and British scientists reveals a novel way of harnessing that material to help track changes in the environment.

Those genetic fragments that animals and plants shed through skin, scales, fur or excretion are known as environmental DNA (eDNA). They can give researchers clues to the biodiversity of an area by showing what creatures are present there more easily than other methods.

The eDNA can be gathered by installing small air filters, similar to those used to cool computers and 3-D printers, directly in the habitats scientists want to monitor. 

But while these are capable of collecting data on a small scale, researchers at Toronto's York University and two institutions in the U.K. found that there are gadgets monitoring air pollution all around us that have already inadvertently been collecting eDNA on a large scale for decades.

Called air-monitoring stations, they're used by most countries to measure air quality. Canada has nearly 260 of them installed across the country, everywhere from St. John's to Mississauga, Ont., to Burnaby, B.C. 

The researchers behind the study, published in Current Biology Monday, collected samples from two stations in fall 2021 — one in a park in London and the other in a field north of Edinburgh. They found eDNA from 182 different species of plants, fungi, insects, mammals, birds, fish and amphibians.

"It was far more than we expected," said co-author Elizabeth Clare, assistant professor of biology at York University in Toronto. "That was one of the biggest shocks to us."

A trove of data already there

The samples revealed the presence of everything from cabbage to soy beans to the little owl and the red deer.

Clare said she and her colleagues were surprised to find that such a trove of information was under their noses the whole time.

"The idea that there is a system that's out there, collecting it daily over and over and over again, that's basically semi-automated, and that we've never noticed that it exists, that's the thing that is so astonishing, is that this data is already there," she said.

While many air-monitoring stations would not have held onto their air filters over time, the researchers said, some may have records dating back to the 1970s.

Collecting eDNA can help researchers identify the types of organisms living in an ecosystem, known as biodiversity, without having to observe them directly and can paint a picture of what's going on with certain species over time.

International treaties such as the Convention on Biological Diversity commit Canada and other countries to monitoring biodiversity to assess and compare rates of species decline. 

There are lots of ways to measure the biodiversity in the ecosystem other than eDNA. They range from species to species, said Clare, but the use of air-monitoring networks to collect eDNA is one way of standardizing that monitoring. 

"We don't have a single approach to anything," said Clare. "So one of the biggest challenges we have is trying to match up that data on a broader scale, but now, we can collect this data on a global level all at once."

Getting the full picture

Christoph Deeg, a researcher with the Pacific Salmon Foundation and Fisheries and Oceans Canada, relies on eDNA when monitoring the biodiversity of salmon. He said that while he collects most of his information from water, the salmon's ecosystem, he could learn a lot from eDNA in the air as well.

"By combining what we see in the air and the water, we can really capture everything that's going on," he said. "So this is where the study is exciting and really allows us to get a holistic view of entire ecosystems on a continental scale — an overview of biodiversity."

Given how large Canada is and its diverse climate, it's challenging to get a full picture of biodiversity across the country. But if there is historical data collected by these air-monitoring systems and saved, mining some of the historical data might help flesh out that picture.  

"If you were to apply this to the archive samples in Canada, you would already see a drastic change in our diversity," he said.   

"We're losing biodiversity faster than we can catalog, we don't really know what we're losing." 

Not as accurate as field work

Lots of techniques in biodiversity science are time-intensive and done by hand, Clare said; they require people going out in the field every day and a lot of effort to collect the data.

Rebecca Rooney, associate professor of biology at the University of Waterloo, is one the people doing field work as part of her research on biomonitoring and wetland assessment. She said that while the eDNA data is useful, it's not yet as accurate as going out into habitats to measure biodiversity.

"At least we know for certain that these plants are there when we are there physically," she said.

Co-author Joanna Littlefair from Queen Mary University of London agrees that there is still a long way to go to ensure the accuracy of the data collected. 

"This study is still just proving the existence of this method," she said. "And so, yes, there are questions, but also there's a lot of potential, and that's what we hope to see in the next steps."

For example, while the eDNA reveals the types of species in an ecosystem, it is not able to measure the actual population of those species or the nuances between ecosystems. It's also difficult to tell exact locations of species, because the wind can blow molecules far distances. 

"We ask, 'Is the cow 20 metres away or is it a herd of cows that's potentially hundreds of kilometres away?'" Littlefair said.

Importance of preserving historical data

Not all air-monitoring network samples are stored, and the authors hope their study will prompt those operating the networks to preserve the data they collect.

Having a historical picture as well as a current snapshot is key to enabling scientists to compare ecosystems and points in history and keep track of what's being lost, said Deeg. 

At-risk populations in Canada, for example, have declined by almost 60 per cent in the last 50 years and mammal populations have decreased by about half, according to Nature Canada. 

"We should think about opportunities like this and really make sure that we're not missing anything," Deeg said.