Dry spells followed by downpours lead to more cyanobacteria in NH, experts say

Aug. 20—When it rains, it pours in New Hampshire, which according to experts, causes more cyanobacteria blooms when met with the ongoing drought.

The N.H. Department of Environmental Services has issued three cyanobacteria advisories in the Monadnock Region this summer — on Island Pond in Stoddard in June, Halfmoon Pond in Hancock last week and on Forest Lake in Winchester, which began in late July and remains in effect, according to the department.

So far this year, the state has issued a total of 28 cyanobacteria advisories. In 2021, the state issued 33. David Neils, DES' chief aquatic biologist, said that since 2018, DES has issued more than 20 a year, and between 2003 and 2018, only three years exceeded 20 advisories.

Cyanobacteria are naturally occurring bacteria that get energy from the sun and are present in all lakes. Some cyanobacteria can produce toxins that are released upon cell death. Exposure to these toxins can cause mild to serious adverse health effects, according to DES.

With nearly all of the state experiencing some level of drought conditions, on top of patterns of heavy rains, Andrea LaMoreaux, president of NH LAKES, said this makes it more difficult for the ground to absorb the water, leading to more runoff going into lakes.

"When it rains hard, the ground can't absorb the water very fast," LaMoreaux said in an interview Wednesday. This can wash soil, nutrients, fertilizer and polluted runoff into lakes, exacerbating cyanobacteria blooms, she added.

"Every waterbody is different," Neils said in an email. "For some waterbodies, drought can exacerbate the risk of blooms because 'fresh' water is not being carried into the lake."

Neils added that drought along with warm air temperatures tend to result in higher-than-normal water temperatures, increasing production of cyanobacteria in lakes and ponds.

"However, lack of rain can also reduce the risk of cyanobacteria blooms as less stormwater (from rain) is carried to lakes," Neils said. "Stormwater typically has much higher nutrient concentrations."

At least part of the increase in cyanobacteria blooms could stem from New Hampshire residents getting better at spotting them and reporting them to the state, N.H. Public Radio has reported.

LaMoreaux said NH LAKES, a nonprofit dedicated to the preservation and restoration of lakes statewide, thinks climate change is driving the increase in reported cyanobacteria blooms.

"New Hampshire's climate is getting warmer and wetter," she said. "With shorter winters, and milder winters, we have a shorter period of ice cover on our lakes and our lakes are warming up more quickly and warming up more. The increased temperature increases the growth of the cyanobacteria."

Kelli Hanzalik, a member of the board of directors with Spofford Lake Association, said the organization is helping to mitigate cyanobacteria blooms.

The nonprofit uses education and wastewater management, such as bringing septic systems up to date, to help reduce the amount of polluted runoff going into Spofford Lake.

Hanzalik explained that cyanobacteria blooms can make people nervous using the lake for recreation.

"People are not comfortable using the lake until they know it's safe," she said.

Lake-goers who suspect a bloom can call or text the DES hotline at 848-8094. After receiving a report, DES samples the potential bloom to determine if cyanobacteria levels are above the state's standard of 70,000 cells per milliliter. If they are above the standard, a lake warning will be issued and the water will be tested and monitored until levels are below standards.

DES recommends not swimming or wading in cyanobacteria contaminated water, especially close to blooms.

The state also recommends not allowing pets and livestock near the water, as dogs are especially vulnerable to toxic cyanobacteria.

This article has been changed to correct the capitalization of NH LAKES.

Tom Benoit can be reached 352-5993 or tbenoit@keenesentinel.com.