Sarah J. Nelson Does Mercury Research in Acadia

Mercury is a heavy metal that can appear in several forms. It can appear as a vapor, a liquid metal or as methylmercury as found in fish. Scientists have been studying mercury for years trying to learn its effects on the environment, in animals and in the human body. University of Maine Research Professor Sarah Nelson specializes in the study of mercury in the environment.

Mercury is both naturally occurring in the environment and also a product of coal burning across the globe. The United Stats receives most of its mercury from emissions put out from factories in Asia. The mercury travels in the air and then settles here in trees, dirt and water.

Nelson has done extensive mercury testing in the Acadia region. It was found that Acadia actually contains fairly high levels of mercury, despite being viewed as a pristine national park. This prompted scientists to study the Acadia landscape to see if it plays a roll in the storage of mercury. Starting in 1998 a watershed research project began in Acadia.

The scientists picked two watersheds to study. A watershed is an area of land that collects rainwater and then funnels that rain out through a stream. Scientists picked an area that was burnt in a wildfire in 1947 and also picked an area that was not burned. They studied the levels of mercury going in and out of these two watersheds. Mercury enters the water through the forest canopy. This is the area underneath a tree where water drips off it and onto the ground.

Nelson and her team discovered that softwood trees, such as pine trees and spruce, which there are a lot of at Acadia, are better at “scavenging mercury from the atmosphere,” Nelson says, “Even when it’s not raining, there are dry mercury particles and dust floating around and those trees capture it.” The mercury sticks to the foliage. These trees have foliage on them year-round, meaning there is more time for the foliage to gather mercury. Hardwood trees such spruce and maples do not have foliage in the winter months, this cuts down on the mercury they collect. They also have less surface area, which also reduces the amount of mercury they can collect.


Nelson also looked at mercury in wetlands. Wetlands are very important because they are great ecological systems. They retain water and prevent flooding from happening. They are great for both animals and plants, but because they are a special environment and contain anoxic places, places without oxygen, they can be a “hot spot” for mercury methylation, the conversion of mercury into its most toxic form.


Nelson and her team also decided to investigate the presence of mercury in snow at Acadia. Not much research had been done, and the theory was that there was no mercury in snow. Because this hadn’t been extensively tested Nelson decided to do her own research into the issue. “The going statement from some scientists was that they didn’t think there was very much mercury in snow,” says Nelson, “So we wanted to test that for sure because nobody had explicitly checked.”

They put up samplers to collect snow and went out as quickly as possible after every snowstorm to collect the samples. They were set up under various types of forests. They also left one sampler out for the entire winter and collected some snow samples off the ground. They tested and compared the various samples for mercury.

They found that when snow was collected right away, it contained the highest levels of mercury, much higher than the other samples. They think it is because “mercury can turn into a gas and volatilize, or blow right back up into the atmosphere when it is it by UV light, or it could have something to do with heating,” according to Nelson. By collecting the samples right away and closing up the samplers, they trapped the mercury inside. The samples that were left out, or collected from the ground had time for the mercury to escape into the atmosphere as a gas.