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Dragonfly larvae part of mercury study

October 20, 2012
By MIKE LYNCH - Outdoors Writer (mlynch@adirondackdailyenterprise.com) , Adirondack Daily Enterprise

Scientists are looking at dragonfly larvae from lakes in the Adirondacks and throughout the Northeast as part of a one-year mercury study.

Dr. Sarah Nelson, who is leading the study, said that 74 lakes were surveyed in the Northeast, including 43 in the Adirondacks. Water samples were also taken from lakes in New Hampshire, Vermont, Maine and Massachusetts.

Nelson works for the Mitchell Center at the University of Maine at Orono. The center works on policy-relevant research that provides lawmakers with the data they need to make informed decisions, Nelson said.

Article Photos

A study headed by the Mitchell Center in Orono, Maine, is using dragonfly larvae as part of a study of mercury in the Northeast.
(Photo provided by U.S. Fish and Wildlife)

"We wanted to get a one-time snapshot of how much mercury is in the water and in the dragonflies in this one short time period across broad spacial (area)," Nelson said.

The lakes were chosen because they are already monitored for acid rain studies and there is a lot of data about them available.

"Because we know a lot about those lakes and their chemistry and the landscapes around the lakes, they make a great set of study sites for other research," Nelson said. "This project is really leveraging off the fact that we are already doing work there."

In the Adirondacks, the lakes are studied by the Adirondack Lake Survey Corporation, which receives funding from the state Energy Research and Development Authority, Department of Environmental Conservation and Environmental Protection Agency.

ALSC scientists aided the Mitchell Center by collecting dragonfly larvae samples while they were on site gathering their own samples. Larvae, which are immature dragonflies, are found in the water in the sediment and attached to aquatic vegetation. Similar organizations assisted the Mitchell Center in other states. All the dragonfly larvae samples were collected this summer for the one-year study.

Nelson said as part of the study she will be looking at characteristics of the different lakes to determine what factors play a role in mercury accumulation. Factors that will be studied are: forest types surrounding the lakes, how many wetlands are present and where the water body is located geographically, among other things.

"Does it matter more if you're in New York or Maine, or does it matter that you have a certain amount of wetlands in the watershed?" Nelson said.

The study will also look at whether dragonfly larvae are good indicators of mercury in a water system.

Mercury is a natural element but is found in elevated levels in Maine and many locations across the country, due largely to fossil fuel emissions. Mercury travels far in the atmosphere and often lands in environments distant from where it is emitted, including remote locations worldwide. Scientists are unable to predict which lakes or streams might have high or low mercury because it has a complex cycle both getting to water bodies and once it's in the water.

Dragonfly larvae live in the water for up to five years. They can grow up to 2 inches in length, but most of the ones collected for this study were less than an inch.

Nelson said the idea to use the larvae grew out of a citizen science project that involved students and teachers, during which dragonflies were found in abundance.

"(The larvae) seemed to have characteristics for accumulating mercury and also for the laboratory analysis, so we started looking a little more deeply at them," Nelson said.

Nelson said scientists aren't exactly sure how the larvae accumulate mercury in their systems, but it's believed to come through their food.

The young dragonflies are predators that feed on young fish, tadpoles and other invertebrate.

"They will eat essentially anything that they get in their mouths," Nelson said. "(But) it has to be live food."

 
 

 

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