The Global Change Research Wetland in Anne Arundel County is not a common marsh. Clear plastic chambers dot the 53 acres of lush wetland, connected by a infrastructure of grated walkways that weave through tall marsh plants.

Each chamber can be treated with different combinations of carbon dioxide or nitrogen gases, designed to mimic future environmental conditions in what the scientists involved say is the longest-running climate change experiment in the world.

“It’s the most elaborate facility of its kind,” lead investigator Pat Megonigal said. “We’ve been manipulating carbon dioxide concentrations in the air, around marsh plants, for over 30 years.”

The research wetland in Edgewater is part of the Smithsonian Environmental Research Center campus. Every year it seeks volunteer help to record data for short- and long-term studies.

Last week a volunteer group of local high school and college students gathered for “Marsh Madness,” an annual two-week citizen science project.

They were assisting Thomas Mozdzer, an assistant professor of biology at Bryn Mawr College, with his study on the invasive phragmites plant — otherwise known as the common reed.

Volunteers scattered about the marsh to catalog the contents of each chamber. They measured plants, harvested leaf samples and put them in small brown envelopes to be sent for lab testing.

Because each chamber is treated uniquely, each yields different levels of plant growth and diversity.

“When we add nitrogen, it can potentially increase resilience to sea level rise because of enhanced growth,” Mozdzer said. Nitrogen naturally comes from nonpoint source pollution, such as the overuse of fertilizers on farms and leaky septic systems.

Mozdzer’s study raises a complicated question: Is carbon dioxide good or bad for wetlands?

Carbon dioxide helps marsh plants grow rapidly, and that’s good because marsh plants create soil, effectively raising the marsh and allowing it to keep up with rising sea levels.

But carbon dioxide also accelerates the spread of invasive species such as phragmites. That’s bad for the Chesapeake Bay because the spread of the plants drives fish, crabs, birds and other organisms essential to the area’s economy and culture from their preferred habitat.

Volunteers vary in their motivation for helping out at the center. Some said they wanted to better understand the impact of humans on the environment.

Alexa Poirier, who graduated from Coastal Carolina University recently with a degree in marine science, said she really enjoys plants and feels people don’t understand “how much they actually affect us.”

Connor Morningred, a rising senior at Arundel High School, said it’s interesting “seeing how humans have impacted the earth and the challenges we’re going to face if we don’t stop.”

Marshes support shellfish, fish, birds and mammals. Fish rely on wetlands to spawn, birds feed and rest there during migration, and small mammals — such as muskrats — live there. Wetlands clean water, and protect homes and infrastructure from storms. “If a storm surge pushes a lot of water to the bay, it creates a huge tide,” Megonigal said. “The marsh slows the tide down and gives it space to flood into.”

Marshes also play a role in climate change driven by increasing carbon dioxide by acting as “carbon sinks.”

almann@capgaznews.com