Nantucket voters may soon be asked to spend up to $4 million to dredge Miacomet Pond and remove as much as 100,000 cubic yards of material from the 46-acre pond.
Jeff Carlson, town of Nantucket’s Natural Resources Department director, can talk about the science behind dredging material to improve the health of the pond. But the analogy he used to break it down in layman’s terms seemed to hit the mark for those of us not trained in biology.
“It’s like playing Nintendo in the old days,” Carlson said. “You’d get mad and hit the reset button and start over.”
The $4 million dredging project could represent a reset for Miacomet Pond by removing a thick benthic layer full of nitrogen and phosphorus from years of fertilizer use and septic systems around the pond. The accumulating muck has leached those nutrients back into the water, Carlson said, fueling the harmful algal blooms and invasive species that have plagued Miacomet Pond.
“By removing the benthic layer that causes the nutrients to recycle into the pond, you’re removing that source front the pond itself and kind of resetting the pond to some degree,” Carlson said.
The possibility of dredging Miacomet Pond to remove existing nutrients in the sediment had been proposed as long ago as 2005, when it was among the conclusions of a study of the pond by then-town biologist Keith Conant.
The first-of-its-kind project for the island would be a sort of proof-of-concept effort to demonstrate that dredging can, in fact, improve the health of Miacomet Pond, and perhaps be a water quality solution for Nantucket’s larger ponds.
Last year at Town Meeting, voters endorsed $300,000 for the surveying, design and permitting work for the dredging, and the entire project was recently put out to bid. During the May 2023 Annual Town Meeting, the dredging project is expected to be on the warrant as a $4 million debt exclusion override, which would also have to be approved at the polls.
The logistics of the project also still need to be worked out - specifically, where would 100,000 cubic yards of material go?
“That’s a good question,” Carlson said. “We’d have to dewater it and remove it, do testing to make sure there’s nothing really bad in it as we go. Some of it may be able to be reused, or blended in for top soil because it will be nutrient rich.”
At about one-mile long, Miacomet Pond has a maximum depth of 11 feet near its southern end and the mean depth of the pond is 4.8 feet, according to town records. The pond is where approximately 1,284 acres of the surrounding landscape drains into, so it has numerous sources of nutrients that have had harmful effects.
Carlson added that dredging the pond would also represent an alternative to using an alum (aluminum sulfate) treatment for nutrient binding, another way communities sometimes deal with excessive nitrogen and phosphorus.