The cyanobacteria, or blue-green algae, that have bloomed in Wainscott Pond in recent years produce dangerous toxins known as microcystins, the East Hampton Town Trustees were told on Friday, presenting a hazard to private wells or even those breathing the surrounding air.
Christopher Gobler of Stony Brook University’s School of Marine and Atmospheric Sciences, who monitors water quality for the trustees as well as for the Friends of Georgica Pond Foundation and the recently formed Wainscott Pond Project, delivered to the trustees a “mixed story” on the levels of cyanobacteria and the toxins produced by them in Wainscott Pond between 2016 and this year.
This year “was one of the most toxic years ever for the pond,” Dr. Gobler said. The particular microcystin produced by the cyanobacteria in Wainscott Pond is a hepatotoxin, meaning it causes liver damage.
“Before it had an official name, it was called ‘fast death factor,’ ” he said. “Not only are the blooms persistent every year . . . but there’s a disturbing trend in the last two years of toxin levels increasing, and now getting as high as approaching 10 micrograms per liter,” almost 20 times the drinking water standard and more than double the recreational standard.
There have been instances in which, because of the pumping of groundwater for agricultural or other use, cyanobacteria are entering private wells in the area. “That’s obviously of concern,” Dr. Gobler said. “You could be drinking it, albeit at low levels.”
Another consideration, he said, is groundwater entering the pond and feeding the blooms. “This toxin microcystin is rich in nitrogen,” he said, and research demonstrates that “the more nitrogen these cyanobacteria get, the more of this microcystin they can make.”
Among the dozens of types of cyanobacteria, “we’re seeing a shift amongst the community of different cyanobacteria toward the types that make this microcystin in recent years. . . . It’s a human health risk.” Exposure to toxins in the water is the greater threat, he said, “but there’s also the possibility of aerosolization of these toxins. . . . That would make the zone of concern more than just being in the water.”
With Bryan Grogan of PW Grosser, a Bohemia consultant, Dr. Gobler proposed a groundwater study. Sediment samples taken at 16 points throughout the pond would help identify what’s in the thick layer of silt at the bottom of the pond, Mr. Grogan said, which would direct remediation efforts, such as dredging.
“Then we can quantify what the removal of that material would look like, how much nutrient load we would be removing from the pond, and also how to move forward,” he said. “By doing sampling across the pond, we can see, is there a hotspot in the pond? Maybe we don’t need to dredge the whole pond. . . . We can ascertain a cost-benefit analysis.”
A permeable reactive barrier, a device comprising trench boxes filled with ground woodchips or another reactive substance that intercepts groundwater as it seeps into a water body, might also be installed, Mr. Grogan said.
The six trustees present voted unanimously to approve the proposal to sample the sediment in the pond.