There’s nothing quite as nice on a day as jumping into a cool clear New Hampshire lake. Unless it has been hit with a cyanobacteria bloom, that is; then it’s gross. And dangerous.

The number of these blooms, which can release toxins that sicken or even kill people and animals, has increased to the point that the state has set up monitoring programs to spot them. But what we’d really like is a way to predict blooms in advance instead of waiting until they become visible – say an app that dings your phone when the chance of toxic blooms at your Town Beach reaches 50%.

Such prediction would require understanding more about all the factors that lead to blooms including, I was surprised to learn, understanding what has happened to the lake-bottom mud over my whole lifetime and even much further back.

“Sediment has been storing phosphorus since the glaciers. … Things that we did in the ‘60s and ‘70s are still there,” said Kathryn Cottingham, Ph.D., a biology professor at Dartmouth College. Mud-stored phosphorus matters because its release can be a major trigger for blooms of cyanobacteria. (If you still call it “blue-green algae” you’re a little behind the curve. “Cyan” is the same as “blue-green” but these cells lack a nucleus so they’re not considered algae in modern terminology.)

Cottingham, who says she has been “interested in the general phenomenon of lakes becoming more productive since I was a grad student 30 years ago,” recently published her findings on this problem the “Journal of Plankton Research” with long-time collaborator Cayelan Carey, Ph.D., who was Cottingham’s student at Dartmouth and is now a professor at Virginia Tech.

Unusually for a research paper, the title makes sense to me: “Predicting the effects of climate change on freshwater cyanobacterial blooms requires consideration of the complete cyanobacterial life cycle,” including how the little buggers survive over winter down in the mud, often in a dormant stage. They argue that we need to move beyond an emphasis on studying cyanobacteria only when its blooming or about to bloom in the upper reaches of the water body.

The usual story for blooms, one that I’ve written a whole bunch of times in my career, is that they result from nutrients such as nitrogen and phosphorus washing into a lake after a rainstorm. The extra food causes a population explosion among bacteria that are already there, and then end up using all the oxygen in the water to the point that they suffocate and die, which makes them release toxins that poison life around them. (Consuming everything and releasing poisons so you destroy yourself and your surroundings – the parallels with humanity are distressing.)

We’re seeing more blooms in our lakes, the story goes, because we’re allowing more runoff and the climate is warming. But predicting blooms isn’t as simple as looking at runoff, Cottingham said. Biology is never that simple.

The research stresses that a key point is how the sediment-dwelling stage makes it back into the water column, and then how the water column mixes to bring them up to the surface where sunlight activates them.

As you’d expect, climate change is part of the picture. It is changing the seasonal patterns of water temperature rise and strong wind and rain events, which affect water mixing in various ways.

And then there’s that mud. Nutrients have been settling into lake bottoms since glaciers carved them out, with a big increase due to human activity. This provides a potential food source that can effect how well cyanobacteria survive, with phosphorus providing to be a particularly significant indicator, Cottingham said.

“Two years ago, we hypothesized that cyanobacteria that can harvest nutrients still in the sentiment will accelerate the process of turning lakes green. That seems to be what’s doing it in the clear-water lakes around here,” she said.

Factoring all these together will be required to successfully predict blooms. But even without that knowledge, Cottingham emphasizes, we can dampen down the number and severity of blooms by reducing the amount of nutrients – especially phosphorus – which gets into the water in the first place. That includes actions like maintaining a vegetation buffer along the water’s edge even though you really want to mow it down to give your lakehouse a better view, and upgrading septic systems so they don’t leak phosphorus into the water table.

“Let’s not put any more fuel on the fire,” she said.

Sensible enough. Unfortunately, they’re also the sort of sensible but self-denying actions that we’ve proven very bad at doing. Maybe fear of cyanobacteria will be more of a prod than fear of COVID.

(David Brooks can be reached at 369-3313 or or on Twitter @GraniteGeek.)

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