NEWBURYPORT - If the scientists who presented their research on the local marsh ecosystem at a symposium yesterday looked a little young, there's a reason: some of them are fourth-graders.

Despite their age, the elementary, middle and high schoolers from Ipswich, Essex, and Newburyport did all the work of professional researchers at a scientific conference. They outlined their field research, explaining their hypotheses and experimental methods, and then presented their data in great detail before attempting to draw some conclusions for their results.

The seventh Annual Coastal Science Conference, held at the headquarters of the Parker River National Wildlife Refuge, is a long-standing collaboration between marsh scientists and local schools.

"It's a good experience for the kids, because it gets them out of the classroom and shows them what this kind of research is all about," said John Halloran, a former teacher at the Nock Middle School who helped to start the collaboration. "But it's also good for the scientists, because with a steady supply of student researchers they can get longterm data that wouldn't be gathered otherwise.

Much of the students' research focused on phragmites, an invasive reed that ecologists fear could destroy the diversity of the great marsh, turning it into a monoculture. To everyone's surprise, the students' research has called into question one of the central assumptions about phragmites. For decades, it has been assumed that phragmites thrive in relatively fresh water with low salinity, but are unable to proliferate in waters with salinity over 30 parts per thousand. But student research shows that phragmites are only marginally affected by salt levels.

"Salinity is not as big an issue as we thought at first," said David Burdick, an assistant research professor at the University of New Hampshire's Jackson Estuary Lab. "That may have real implications for how we try to fight phragmites. We scientists wouldn't be able to get this kind of depth of data without the kids' help."

Getting a middle-schooler to stand knee-deep in a marsh while measuring plant heights might sound like an uphill battle, but many of the students see an important mission behind their classwork.

"I want to keep this marsh alive," said Newburyport seventh-grader Skyler Wack. "If we don't work to save it, it could be gone in 10 years. I want other people to be able to see this marsh in the future, and our research is helping make that possible."

Comments like Wack's are music to Halloran's ears.

"We want them to learn science, but we also want them to learn to take civic action," Halloran said.

A team of nine former Nock students enjoyed their introduction to marsh ecology so much they wanted to continue their research. With help from Halloran, they secured funding from the Gulf of Maine Institute, or GOMI, which encourages youth leadership and environmental stewardship from Nova Scotia to Massachusetts.

The students, now in high school, are now conducting research not on phragmites, but on another invasive species, perennial pepperweed. A major problem in western states, pepperweed populations in this area are low enough that the students believe they can be controlled and even eliminated.

Last spring, the team recruited 69 volunteers from among their Newburyport High School classmates and uprooted about 3,000 pounds of pepperweed from the area around the Plum Island Turnpike. They are planning to expand their program into other communities this summer.

"It's very labor-intensive, but what we're finding is that if you pull the plants two years in a row, they really don't come back," Halloran said. "It's encouraging. It's also encouraging that the kids are really the ones taking the lead on this."