Treatment to curtail bacteria blooms in lakes is not – repeat: not! – a magic bullet

  • Nippo Lake in Barrington. NH Dept Environmental Services

Granite Geek
Published: 5/31/2021 3:56:52 PM

The original plan for today’s column was to dazzle the world by unveiling a magic elixir that solves a yucky environmental problem. Then I talked with David Neils, an aquatic biologist with the state.

“This is not a magic elixir,” he said, flatly.

Not even a little magic? “No.”

Darn those scientists.

The non-elixir in question is a combination of aluminum sulfate and sodium aluminate. Neils and others with the state Department of Environmental Services, where he works, have been putting the mixture into Nippo Lake, a pond in the town of Barrington, to combat the nasty and potentially cyanobacteria blooms which have become an unpleasant part of New Hampshire water bodies in summer.

“It has had blooms for eight out of 10 years, probably more than that,” said Neils.

The aluminum mixture attacks the blooms indirectly by binding with phosphorus in lake-bottom mud so that the algae can’t use that mineral as a food source. You may recall that I wrote a few weeks ago about Dart mouth research indicating that this phosphorus is a bigger factor in cyanobacteria blooms that we used to think.

Normally the phosphorus is bound up by iron, Neils said, but Nippo Lake has a particularly strong case of stratification in summer, when cold water stays at the bottom and warm water stays on top and never the twain shall meet. Stratification can deplete oxygen in the cold bottom water and a lack of oxygen can break the bond between iron and phosphorus, releasing it into the water column.

“That’s the perfect situation for cyanobacteria, which can migrate vertically. They go down to the depths and grab phosphorus, which is a limiting nutrient, brings it back up to the upper layer where they can photosyntheize and bloom,” said Neils.

The aluminum mixture, which at first forms a milky white cloud (known, for some reason, as a “flock”) that settles down to the bottom, should keep the phosphorus out of reach of bacteria for at least a decade, reducing or even eliminating the blooms.

That sounds like a magic elixir, doesn’t it? Pour it into the water and stop worrying!

“I get probably 3 or 4 inquiries each year about magic elixirs that could fix their lake. People want to jump right to it, they don’t want to deal with the other things they need to deal with before that,” Neils said.

Not so fast, though. For one thing, aluminum treatment is expensive – it cost a little over $100,000 for this small lake, half of which came from the Nippo Lake Association and half from a federal grant.

More importantly, however, the treatment is pointless unless you keep more phosphorus from entering the water after the treatment. A certain amount of phosphorus is natural and necessary, arriving via rain or waterfowl, but excess phosphorus from human activity such as leaking septic systems, fertilizer runoff and other pollution can overcome any chemical application.

Getting rid of the excess source requires good planning, continued oversight, lots of work and, hardest of all, cooperation from property owners who may not want to compromise on a green lawn leading down to the water at their lakeside summer-cabin-turned-permanent-home. But only if that is accomplished will adding aluminum compounds succeed.

“Having a watershed-based plan and having dealt with all the external, unnatural phosphorus loads – that component is critical. Otherwise you’re just throwing your money away,” said Neils.

This treatment is used in neighboring states and is fairly common in the Midwest, Neils said. New Hampshire hasn’t used it since 1984, when it was applied in Kezar Lake in Sutton, an application that “has held up quite well since then,” said Neils.

The Nippo Lake treatment, which continues through June, is billed as a demonstration project. It will be monitored for a few years to determine when and whether such treatments should be part of our arsenal against this growing problem.

“Last year there were over 700 days of cyanobacteria advisories around the state. That’s a lot of days,” said Neils. “There are several lakes that bloom pretty much every year.”

Down the road, we might be able to curtail some of those blooms through careful application of what I am most definitely not going to call an elixir.

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



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