By Craig LeMoult
On Tuesday afternoon, a team bolted together two dozen large structures off Magazine Beach in Cambridge, assembling an island like a floating puzzle.
“It’s a seven hundred square foot, human-made island, planted with 3,000 native wetland plants that we are about to tow down the river to just past the Longfellow Bridge, where it will be anchored,” said Laura Jasinski, executive director of the Charles River Conservancy.
The floating wetland is part of a research project aimed at improving the water quality by cutting down on toxic blooms of algae called cyanobacteria that have become an annual summer problem in the Charles.
The project will restore a bit of nature to an area of the river that doesn’t feel all that natural now.
“Where this is going to be, it’s a bulkhead or sea wall,” Jasinski said. “So we don’t have a river bank the way we’re used to in that area. So we’re trying to add that back, effectively, to try to boost the food chain and the river to help it be more adaptable to changing conditions.”
Jasinkski rattled off a list of the 22 native plant species planted on the floating island.
“So we have things like Rose mallow and Sweet flag, Swamp milkweed, Seaside goldenrod, Spotted Joe Pye, Monkey flower,” she said. “So lots of lots of fun things.”
Over time, the roots of the plants will penetrate the structure, creating a hydroponic garden. The floating wetland be there for two years as researchers study what happens around those roots.
“This project is all about understanding what we can do from ecological perspective to kind of help create a river that’s healthy and doesn’t have cyanobacteria blooms,” said Northeastern University PhD student Max Rome, who’s leading that research.
Those toxic blooms have become an annual problem in the Charles.
“What we’ve been seeing… is very distinct blooms that last for about seven to 14 days,” Rome said. “And it tends to occur as the water temperature reaches about 25 degrees Celsius, 77 degrees Fahrenheit. And that usually happens in late July or August.”
Rome says one way to fight cyanobacteria is by cutting pollution.
“But we think another piece that might be important is to add habitat that can help the river support higher population of the creatures that eat algae.”
Those creatures are called zooplankton. Rome will track if the floating island results in more and larger zooplankton around the roots of the plants that grow down into the river.
“It’s going answer some really fundamental questions for us about how the ecosystem changes around the floating wetland,” Rome said. “And then with that data, we’re going to be able to do some modeling and do some estimation to see at what scale could floating wetlands or restored shoreline really make an impact in terms of cleaning up the Charles River.”
Jasinski says the cyanobacteria outbreaks are only expected to get worse as temperatures rise.
“The reason we’re seeing the increased algae blooms in the river is a symptom of the rising temperatures of climate change,” she said. “So we’re looking [at this project] as an intervention to help treat that.”
And she says she hopes as people see the island, it will serve as a way to engage people in those issues.
“We really want to use this as a platform to talk to people about how polluted [the Charles River] was, how far we’ve come, but also the increasing challenges we’re seeing with climate change, rising temperatures, increased heavy rainfall that is still posing a threat to the river that we need to continue to innovate and try to protect.”