Keith Williams, a volunteer with the Highland Lake Association, has been collecting water samples from the lake for years. Photo courtesy of Joe Bickard

Editor’s Note: The April 10 version of this story in the Lakes Region Weekly contained some incorrect information. The corrected version appears below.

WINDHAM — The first scientific study of Highland Lake to use environmental DNA testing lends support to an earlier hypothesis that the 2014-17 algae blooms in the lake were caused by a peculiar and rare type of phytoplankton called pico-cyanobacteria.

The research that began in the spring of 2018 also leads researchers to suspect the sudden drop in the algae blooms’ intensity over the last two years is due to the lake adjusting to the reintroduction of alewives into the lake.

The blooms that have plagued the 623-acre lake in Windham and Falmouth were unusual, according to Karen Wilson, an associate research professor at the University of Southern Maine and a member of the Highland Lake Association’s research team.

“It wasn’t your typical algae bloom. It didn’t smell really strongly, you just couldn’t see well (into the water) and people noticed, Wilson said.

The condition of the lake greatly concerned the lake association, a non-profit volunteer group.

Researchers hope this first scientific study using eDNA testing will help them understand what causes this type of algae bloom and how to prevent it. With eDNA, or environmental DNA, researchers do not have to find an organism itself to test. That’s because eDNA comes from cellular material that is “shed” from an organism into another environment, like a body of water.

Wilson and biologist Jeff Dennis of the Maine Department of Environmental Protection found that the lake was experiencing an algae bloom of pico-cyanobacteria. Algae blooms of cyanobacteria, also called blue-green algae, are common in lakes around the world, Wilson said.

But this was a bloom of pico-cyanobacteria, which is the smallest type of cyanobacteria – often so small, it requires eDNA testing to identify it. Wilson and Dennis said that they are not aware of any other lake in North America with a recorded instance of this type of bloom. And the bloom was happening at almost the same time every year.

“They just aren’t punctual like that,” said Dennis.

Researchers began an intensive study of the lake in May 2018, collecting water samples and other data. They began with a set of hypotheses and went off to “science the heck out of it,” in Wilson’s words.

Then, the bloom didn’t occur to the same degree.

“One of the frustrations of (studying) ecology is that there is a lot of variability from year to year,” said Wilson.

The bloom still occurred, but was not as intense as the four previous years and would only last a few days, rather than a few weeks, before it suddenly cleared up.

“It just didn’t have a chance to develop and something interrupted it,” said Dennis.

Wilson was curious to test her hypothesis that alewives were essentially shifting the balance of the lake’s food web. Alewives eat zooplankton, which eat algae (which, in this case, is the pico-cyanobacteria).

“We think very young alewife may be consuming tiny plankton that effectively consume the pico-cyanobacteria in early summer. When these alewives get bigger, they start eating larger zooplankton, allowing the tiny plankton to get back to eating pico-cyanobacteria,” she said.

Alewives were non-existent in Highland Lake for over 200 years, noted Wilson, until the early 2000s, when the Department of Marine Resources reintroduced alewives captured from another wild population. The alewives did not become abundant until 2012. The changes in the pico-cyanobacteria blooms from year to year may be a clue as to how the complex lake ecosystem is adjusting to this reintroduction.

If the researchers can figure out what is behind the previous years’ blooms – and why it all of a sudden stopped – then they might be able to determine the conditions that cause these blooms in other lakes as well.

While the research remains ongoing, the scientists leading the study and the association’s vice president, Rosie Hartzler, all agree that one thing they can do right now is work to prevent more pollutants from entering the lake.

For Highland Lake, which has one of, if not the most developed watersheds in the state of Maine, according to the Highland Lake Association, stormwater runoff and soil erosion are major concerns. That pollution adds too much phosphorus to the water, which allows an excess of algae to grow.

“In general, Highland Lake will have a healthy system and better water quality (if) phosphorus is less,” said Dennis. “It’ll have worse conditions if (there is) more phosphorus.”

“(We’re) dealing with a very sensitive lake to begin with,” he said.

“We know we can do something about (phosphorus levels) so that’s how we’re focusing our education efforts,” Hartzler said. But otherwise, “2020 is a big question.”

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