The boats at the Portland Boat Works marina looked like they were floating in cherry-flavored Kool-Aid. A tank hummed from the shoreline, slowly injecting 60 gallons of water and red dye.
The scene was part of an experiment conducted by the U.S. Army Corps of Engineers on Sept. 9. The agency is adding dye to five sites along the Connecticut River this year as part of a plan to get rid of hydrilla - an invasive, hard-to-kill plant that threatens fish and other wildlife by lowering water oxygen levels and raising temperatures.
The dye, known as rhodamine water trace, flows in the water the same way that herbicides do, giving scientists a better understanding of how the chemicals that will eventually be used to treat hydrilla might work.
“The dye really mimics what a herbicide might do if applied to the water,” said Keith Gazaille, an aquatic ecologist with SOLitude Lake Management, a national lake and pond management company contracted by the Army Corps to administer the dye. “We’re really kind of understanding where would the herbicide go [and] how long will it be in these areas.”
Ben Sperry, a research biologist with the Army Corps, described the dye study as a helpful practice run before applying the actual herbicides next year, pending federal funding. “It gives us another layer of accuracy when we get to treatment,” Sperry said.
At the Portland marina, the dye’s concentration was measured every five minutes by pipe-like data loggers called sondes, located under buoys. If the concentration of the dye is too low, scientists will have to figure out how to adjust their methods during the treatment phase to make sure there’s enough herbicide in the water to effectively kill hydrilla.
“We want to make sure we hit our target concentration and then hold it there for a sufficient time,” Sperry said.
Hydrilla was first found in the Connecticut River near Glastonbury in 2016. The plant in the river is genetically different from other strains of hydrilla growing in the rest of the United States, according to the Army Corps. The Connecticut River would normally be filled with native plants, but many of those are losing out to hydrilla.
“All we see is hydrilla,” Sperry said. “Not really any other native plants. And it's topped out. It's very dense and makes it hard to navigate a boat through it.”
The Army Corps has released a schedule of dye studies along the Connecticut River in Chester Creek, Hamburg Cove, Portland Boat Works and Agawam, Massachusetts, for August and September. Rhodamine water trace dye is approved by the Environmental Protection Agency and is regularly used in water studies.
Herbicides were applied to Selden Cove and Chester Boat Basin on the Connecticut River in August, but results have not yet been released.
Áine Pennello is a Report for America corps member who covers the environment and climate change for Connecticut Public.
