Santuit Pond continues to be impacted by cyanobacteria blooms. An advisory from the Mashpee Board of Health—the second of the year for the pond—has been in place since the end of August.
Cyanobacteria, a type of blue-green algae that grows in freshwater bodies, can produce toxins that are harmful to humans and pets.
Mashpee Director of Natural Resources Richard York said that cyanobacteria blooms on Santuit Pond extended into December last year. As of Thursday, November 14, he observed that the blooms were present at the surface of the pond.
Staff with the Association to Preserve Cape Cod shot aerial photographs of cyanobacteria blooms on the pond last week.
While Mr. York said that the cyanobacteria species observed in Santuit Pond are less toxic than some species, when the toxic algae floats to the top and become concentrated, they can still present a threat to public health.
“The biggest risk is for dogs lapping up those surface films,” Mr. York said. People should not swim in or swallow the water, and pets should be kept away from the water, the advisory states.
Fed by excess phosphorus leached into the water from septic systems, fertilizer runoff and stormwater, the algal sheets can shade out other plant life and, when the algae dies off, form a muck of decomposing material which consumes oxygen at the bottom, potentially causing fish kills.
“Santuit Pond in Mashpee has been experiencing a cyanobacteria bloom for several weeks now. This is no doubt due to excess nutrients and the fact that we’ve experienced the warmest month of October on record,” said Bryan Horsley, the coordinator of the APCC’s cyanobacteria monitoring program.
While the Santuit’s cyanobacteria problem has never gotten to the point of causing fish kills, it continues to hinder recreation on the pond even as the mitigation efforts are underway.
Since 2012, six solar water circulators—known as SolarBees after the company that makes them—have been circulating oxygenated water to the bottom of the pond, helping to prevent phosphorus trapped in the muddy pond-bottom from escaping into the water.
A seventh SolarBee was installed earlier this year.
The load of phosphorus trapped in the mud of the pond is “the cumulative impact of all the decades of runoff into the pond and it’s now the biggest source [of phosphorus],” Mr. York said.
“The SolarBees are helping,” he said.
But, even as the SolarBees seem to have helped in keeping the phosphorus contained in the mud, seven inches of rain earlier this summer brought in more nutrients, leading to the reemergence of the bloom in late August after an earlier bloom in June had subsided.
Mr. York, who attended the Harmful Algal Bloom Symposium in Alabama last week, noted that the cyanobacteria and algae problem “is definitely getting worse worldwide.”
“It’s theorized that global warming and human development are contributing to that,” he said.
In Mashpee, the failure to remove nutrients such as phosphorus and nitrogen from wastewater has led to the impairment of the town’s bays, inlets, ponds and rivers.
Mashpee’s wastewater management plan, which was published in 2015, includes sewering parts of town to help reduce the nutrients polluting the town’s water bodies. The area nearest to Santuit would not be sewered until phase three of the five-phase plan.
Sewering for phase one has yet to begin.
Methods gleaned from the conference Mr. York attended could also help reduce the problem, he said.
In particular, Mr. York pointed to a way of harvesting the algae from the top of the water as something that Mashpee is likely to try in coming months.
Mr. York noted that one company, Algix, is turning harvested algae blooms into performance foams that can be used in footwear.
Companies like Adidas are using that algae foam in sneakers, he said.
Dredging of Santuit Pond could also help, Mr. York said, noting that the Army Corp of Engineers is conducting a feasibility study for dredging the pond. That project is headed by the Mashpee Wampanoag Tribe’s natural resources department, he said.
While Santuit Pond has displayed the worst cyanobacteria blooms in Mashpee in recent years, Ashumet Pond has had low levels of the blue-green algae float to the top and form surface mats and Mashpee-Wakeby Pond is also impaired, due to excess phosphorus.