Study: Wind may be behind algae blooms

Researchers believe that a decrease in wind caused by climate change could be responsible for the amount of blue- green algae blooms at Candlewood Lake.

Their paper uses 30 years of data for Candlewood and was recently published in Geo: Geography and Environment, a publication of the Royal Geographic Society of London.

“For me, it helps bring some closure in understanding what’s going on,” said Larry Marsicano, former executive director of the Candlewood Lake Authority and now principal partner at Aquatic Ecosystem Research

Candlewood Lake is one of many lakes that have been plagued by bluegreen algae, or cyanobacteria blooms. The blooms are worrisome because the cyanobacteria can produce a toxin that is harmful to people and pets, especially if ingested.

This year, blooms at Kettletown State Park in Southbury and Jackson Cove in Oxford kept the beaches closed to swimming from Aug. 3 to the end of the season.

Scientists are still trying to get a handle on what’s causing the blooms.

The leading theory was nutrients, such as phos- phorus and nitrogen found in fertilizers, that enter the water. But the last paper published using this dataset showed Candlewood’s nutrient levels and other water quality benchmarks were actually improving over time.

This prompted the group, which also included Mitch Wagener, of Western Connecticut State University, and Peter Siver and Anne- Marie Lott, of Connecticut College, to look at other variables, especially temperature and climate data.

Siver said the air temperature didn’t really increase, and instead the most significant change in data was a drop in wind speeds of about 35 to 38 percent for spring and summer months over that time. During that period more blooms tended to appear in years with a lower average wind speed.

Wind plays a role in the cyanobacteria because it helps the water column mix, especially in the spring, when all of the water is generally the same temperature throughout the lake, Siver said.

“They’ve been growing all of the time in the lake, but when you turn the wind off, they accumulate in one spot,” Siver said. “It doesn’t mean there are more of them, it means it allows them to accumulate near the surface and cause people to panic more about them.”

Lakes in this part of the world stratify, meaning the water column is separated based on temperature, with the cold water at the bottom because it’s denser. This density plays a role in determining which organisms can survive at various parts of the water column.

Cyanobacteria has an advantage over other microscopic organisms in the lake because it can regulate its buoyancy, allowing it to stay closer to the top to feed off the nutrients from below and still get the sun from above.

“The more wind you have in the spring, the warmer it will be on the bottom in the summer,” Siver said.

With less spring wind, less heat is mixed down to deeper depths and stronger stratification can occur earlier in the season, resulting in an average drop of about 3 degrees Celsius in summer bottom temperature during the last 30 years or so.

The colder bottom temperatures could be a good thing, though, because nutrients aren’t released from the soil as easily when it’s cold, Siver said.

Climate change plays a role because wind speeds are a result of the air traveling from high to low pressure. If other places are warming due to climate change, then it closes that gap, which slows the wind.

“It’s telling me more areas locally or regionally are similar in temperatures, and so you have that loss in wind,” Marsicnao said.

The paper uses data from 1985 to 2015, but Marsicano said the bad blooms in 2016, followed by the two recent clear years, are further evidence the blooms are caused by something that shifts and is climatic, more than a constant factor, such as nutrients.

“Now we can move forward knowing what is happening at Candlewood and determine what the next course of action is,” Marsicano said, adding there are ways to help mix the lake, but they are expensive.

Siver cautioned there are many factors at play when it comes to the blooms and the wind isn’t the only thing responsible.

“The take- home message is lakes, like any ecosystem, are very complex,” he said. “When we start to break down and point to single variables, it can be misleading. It’s often a combination of variables.”