Scientists are using dragonfly larvae to monitor pollution in Acadia National Park
Mercury is a pollutant that comes largely from burning fossil fuels. Carbon and other organic compounds in the environment can convert mercury into methylmercury, a dangerous neurotoxin that builds up in fish, birds and people.
To gauge the amount of methylmercury in the environment, the National Park Service launched a research project more than a decade ago that measures the toxin in dragonfly larvae.
Some of that research is happening in Acadia National Park.
On a rare rainy morning in August, the research team from the Schoodic Institute at Acadia National Park heads to Eagle Lake to do the annual collection of dragonfly larvae. Hannah Webber, Marine Ecology Program Director, explains that dragonflies are good biosentinels — or indicators — of methylmercury in the ecosystem.
"They're predators, they're always eating other things and so if something's going on in that water body it's probably going to be picked up by something like a dragonfly," Webber says.
Using poles with heavy canvas bags attached, Webber and field technician Jess Moskowitz stir up sediment at the bottom of the lake near lily pads and vegetation the dragonfly larvae feed on, vegetation that Webber says contains methylmercury.
Twenty of the small six-legged larvae are scooped from the sediment using spoons and placed in bags.
"Now that they're in their inner zipper bag they are sealed off from any contaminant that we could cause, so with touching them with our fingers or whatever, so these are now pristine and those inner zipper bags won't be opened again until they get to the lab,"
More than a dozen waterbodies are tested at Acadia each year. And what's concerning to scientists is why some have higher methylmercury levels than others. Hodgson Pond at the western end of the park, for example, has a higher methylmercury content than Seal Cove Pond, which is right next door. And it's not clear why.
"We've just started to look at some of the sites that we have a decade of data and tease out some of those patterns," says Dr. Sarah Nelson, now Director of Research at the Appalachian Mountain Club, who started the Dragonfly Mercury Project while at the University of Maine.
With funding from a broad consortium of federal agencies, including the National Park Service and U.S. Geological Survey, the project expanded testing to more than 120 national parks across the country. The work is only just starting to reveal some answers about how water chemistry and climate can cause mercury cycling to decline in some waterbodies and increase in others.
"We're not at a point where we have a tool box...but we better understand the processes to try water management tools we can use," says USGS scientist Dr. Collin Eagles-Smith, who co-leads the Dragonfly Mercury Project.
Eagles-Smith says the project is focused on trying to determine how different water management actions can stop mercury cycling.
"So there are examples of some systems in lakes where the methylmercury production engine, if you will, has been halted by adding nitrogen to lakes."
Mercury has been a target of policy for some time. The Environmental Protection Agency introduced the Mercury and Air Toxics Standards Rule in 2016 for most coal- and oil-fired power plants. The U.S. is also one of 137 countries that have signed the Minamata Convention, named for a Japanese bay polluted with mercury that wiped out numerous fishing villages. The convention, administered by the U.N., bans new mercury mines and phases out the use of mercury in numerous products.
In the meantime, monitoring and research at places such as Eagle Lake in Acadia National Park continue, as Hannah Webber and her colleague prepare dragonfly larvae samples for shipment to a USGS lab in Oregon.
"Each one of them gets a little tag with where it came from, the date, its length and we'll also get some information about the dragonfly family," Webber says. "There are several different dragonfly families that we have here at Acadia and throughout the country. And then they'll get frozen and it's in the frozen state that they'll get shipped off to the lab for mercury analysis."
Researchers say it will require decades of data collection and analysis to determine if federal policy or the efforts by the United Nations can really curb mercury pollution that is 100 years in the making.