Lyme ― In a state that’s been described as ground zero for a unique strain of the pernicious aquatic weed known as hydrilla verticillata, Selden Cove remains on the front lines of efforts to better understand and eradicate the threat.

Jeremiah Foley IV, an assistant agricultural scientist with the Connecticut Agricultural Experiment Station, said contractors with Massachusetts-based SOLitude Lake Management will apply an herbicide treatment to Selden Cove and four other sites on the lower Connecticut River starting in late July through early August.

The hydrilla strain was first discovered in the Connecticut River in 2016, according to a study by Foley and his colleagues on the spread of the weed. By 2021, the northern strain was found in over 70 miles of the Connecticut River.

Foley emphasized this new strain of hydrilla is uncharted territory. That’s because it’s genetically distinct from other known subspecies.

“We’ve got to write the book of knowledge on what the biology of this plant is, and the types of management that are going to be used,” he said.

The dense mats of vegetation ― decried by U.S. Sen. Richard Blumenthal, D-Conn., at a June press conference as “the worst invasive aquatic species known to man” ― have rendered the cove impassable during late summer for the past several years, according to residents. Power boating, fishing and swimming have fallen victim to the invasion.

Hydrilla degrades water quality, chokes out native plant species and can destroy the habitat for migratory fish like shad and herring, according to the Connecticut River Conservatory.

The Connecticut River Hydrilla project, overseen by the U.S. Army Corps of Engineers in partnership with the Connecticut Agricultural Experiment Station and the Lower Connecticut River Valley Council of Governments, is intended to determine which herbicides ― and in what quantities ― will best control the spread. All herbicides being used are registered for aquatic use by the U.S. Environmental Protection Agency.

Foley said the most appropriate herbicides and how they’re administered will vary in locations ranging from Portland Boat Works on the main trunk of the river to areas like Selden Cove, where the freshwater gets closer to the sea.

Last year, the cove briefly ran red as an airboat commissioned by the Army corps pumped fluorescent rhodamine dye through hoses into the weed-choked cove to mimic the flow of herbicide. The length of time the colorant remained in the water helped determine the concentrations that would attack hydrilla without risking beneficial native plants such as eel grass, coontail and pickerel weed.

Foley said the cove will be treated with dipotassium of endothall, which he identified as one of roughly a dozen aquatic herbicides approved for use by the U.S. Environmental Protection Agency. Several state and federal permits are required to ensure the project does not negatively affect wildlife and native plants.

According to the state Department of Energy and Environmental Protection’s Nuisance Aquatic Vegetation Management manual, the chemical does not have any apparent short-term effects on fish and has no significant adverse effects on aquatic invertebrates.

Questions of hydrilla and climate change

Among the little-understood aspects of this unique hydrilla plant is one that could contribute to global warming if left unchecked, according to Foley.

He said work by Michigan State University biochemistry professor Kelly Aho revealed the northern hydrilla is able to thrive in areas where native plants aren’t as successful, such as parts of the Connecticut River where the weathering of rocks produces carbon in the form of bicarbonate rather than the carbon dioxide typical in water systems.

Data so far indicates hydrilla is “tremendously” able to use bicarbonate in a way most native plants can’t, Foley said. The bicarbonate is absorbed into the hydrilla, which grows all season and then dies out before releasing bicarbonate as carbon dioxide through decomposition.

He said a grant from the National Science Foundation for $190,000 will allow Michigan State University and the Connecticut Agricultural Experiment Station to capitalize on the Army Corps herbicide study by looking at the effect hydrilla is having on the carbon cycle. Monitoring stations will document carbon dioxide and bicarbonate levels at sites treated with herbicides and sites that have not been treated.

“Our hypothesis is the quicker we treat hydrilla, the quicker we can get ahead of it before it starts to alter the carbon cycle that much more and contribute to climate change,” he said.

The experiment station is also hoping to benefit from the $5 million in funding in the 2024 federal budget to address hydrilla infestations in Lake Champlain and the Connecticut River.

Environmental advocates have cited the strain’s arrival in water bodies outside of the Connecticut River ― including Amos Lake in Preston and Lake Pocotopaug in East Hampton ― as evidence of the urgent need to get the situation under control.

Hydrilla can spread to other water bodies on boats if the vessels aren’t properly cleaned, drained and dried before being placed in the water.

“Make sure as a hobbyist lobbyist to clean, drain and dry your boat,” Foley said. “It’s up to the public to prevent the spread of this plant. Preventing that establishment is a lot cheaper than actually treating an established population.”

e.regan@theday.com