New research suggests water quality in Candlewood Lake has modestly improved during the past three decades, challenging a claim made in 2013 that the quality had worsened because of annual winter water drawdowns.

The findings will be shared in an upcoming edition of Lake and Reservoir Management, an international peer-reviewed journal. The paper was written by Larry Marsicano, Candlewood Lake Authority’s executive director, and several professors at Connecticut College and Western Connecticut State University.

“It’s the complete opposite of what was being suggested and presented by others out there,” Marsicano said.

Marsicano said he and Peter Siver, who began data collection on Candlewood in the 1980s while working at Western, decided to study the data further after a lake biologist hired by FirstLight Power Resources said in 2013 deep drawdowns were worsening

water quality and could be the cause of toxic blue-green algae blooms.

“I knew over time we weren’t seeing that,” Marsicano said. ”We wanted to test that with our 28 years of data.”

FirstLight owns and operates Candlewood Lake and has been lowering lake levels up to 10 feet each winter as a way to kill invasive Eurasian watermilfoil.

Marsicano said he and scientists, along with mathematicians who analyzed the data, saw levels of phosphorus and chlorophyll were not increasing and that water clarity was not worsening.

“We found we were trending better,” he said. “Not a great deal, but a little bit.”

Marsicano said water quality was best after deep drawdowns — typically about 10 feet — than with shallower drawdowns, typically 4 to 5 feet.

Marsicano hypothesized the milfoil could release nutrients from the soil into the water, and the more milfoil plants are killed in deep drawdowns, the less such nutrients find their way into the lake.

“If you wipe out the plants in the winter, you have less plants to leak the nutrients in the summer,” he said.

He said the best-practice techniques the authority promotes could also be a factor. The lake authority works with towns and lakeside residents, for example, to improve septic systems and keep phosphorus from entering the lake.

Since phosphorus and chlorophyll levels are not increasing, Marsicano said, there must be another explanation for the rise of blue-green algae blooms, which have closed many beaches in the area.

“We know something else is changing,” he said.

Marsicano acknowledged the lake has experienced higher pH levels and more conductivity from salt, both of which can give the blue-green algae an advantage. He said the way lakewater separates itself into layers by temperature is changing.

He and the other scientists who wrote the paper plan to examine other causes for blue-green algae in their next paper.

“It pushes us in another direction to explain the blooms,” he said.

Marsicano and the group of scientists and mathematicians have been working on the paper for several years. He said it feels good to have the paper accepted by their peers.

“That’s why scientists publis; they want to share information,” he said. “That’s how science moves forward.”

kkoerting@newstimes.com; 203-731-3345