Cyanobacteria blooms have forced closures and advisories in 18 ponds around the Cape this summer. The blue-green algae on the water’s surface can produce toxins, but it’s not just the scum that could be worrisome.
On a breezy day at Walker’s Pond in Brewster, graduate student Hailey Carter waded a few feet into the water, toward the sound of a whirring machine about the size of a toaster.
“OK, so this is the CLAM,” said the University of New Hampshire researcher.
The CLAM, a black box outfitted with tubs and nets and a sign that reads, “Please do not disturb, research in progress,” collects cyanobacteria cells straight out of the air.
“So these cyanobacteria, we kind of recently discovered that they have the ability to leave the water and come up into the air,” Carter said, “which is another route of exposure to the cyanotoxins that they can produce.”
Cyanobacteria blooms have traditionally peaked on the Cape in late July to early August, so public health officials encourage people planning to swim in ponds to check local advisories.
In recent summers, these advisories have become fairly routine when scum forms on the surface of the ponds, but little is known about why the cyanobacteria become airborne and what risk that poses to humans and animals.
“Essentially, I'm trying to gather information about how these aerosols work, [and] what drives them,” she said, “so that eventually down the road we can answer, ‘Well, how much are humans actually exposed to them? And is that an issue? Should we be afraid of that?’”
Generally, cyanobacteria are a naturally occurring part of the ecosystem, but it can become a problem when the algae grow unchecked. And locally, the blooms, fueled by nutrients from backyard fertilizers and septic systems, are growing rapidly in ponds warmed by climate change.
Those blooms produce all kinds of toxins, but for years, researchers were only looking for two of them in pond water on Cape Cod: BMAA and microcystin. Then in 2019, Carter discovered a third, called anatoxin.
“Anatoxin acts as a neurotransmitter,” Carter said. “So it causes your muscles to kind of overreact and it can cause … respiratory failure, which is common in a lot of the anatoxin dog deaths and stuff like that that you see.”
Some of the research she’s already done seems to indicate that ponds that look the clearest might still contain the form of cyanobacteria most likely to produce airborne toxins. That could mean that unseen cyanobacteria still pose a danger.
To help with the research, Carter and a team at the University of New Hampshire are working with volunteers from the Brewster Ponds Coalition. They’re helping to collect data on evaporation rates, light intensity, and water temperature and clarity.
It’s a partnership not everyone will understand, admitted Brewster Ponds board member Marty Burke, who knows that the community’s home prices rely on the perception that Cape Cod waters are top notch.
“I understand that you don't want to say there's cyanobacteria in a pond in July and August on Cape Cod,” Burke said. “But if it's there, we have a responsibility to tell people.”
Carter’s research isn’t yet mature enough to help public health officials make risk assessments, but for the rest of this summer, the CLAM air sampler will be whirring as the research continues.
