The Falmouth Conservation Commission on Wednesday, November 6, took under advisement the town’s plans to clean up Mill Pond in East Falmouth.
The plan would include managing the macrophytes, or aquatic weeds, that cover the surface of the pond as well as improving its oxygen concentration.
“I don’t have a problem with this,” said commission member Elizabeth H. Gladfelter. “I think this is a logical intermediary gap to deal with this problem.”
In the summer, the plants pop up and blanket Mill Pond, and when they start to die near the end of summer, they produce a strong odor. The plan would involve trimming the plants using a blade and then hauling that material out, said Kristen Rathjen, a technical consultant for Science Wares, Inc., who gave the presentation to the commission at the meeting.
Science Wares is the technical consultant on the project for the Water Quality Management Committee, which initiated the project.
“People have seen a decline in the water quality of the pond,” Ms. Rathjen said. “We have abundant community support.”
After the 2015-2018 study on the pond by the University of Massachusetts Dartmouth’s School of Marine Science and Technology found that the pond was nutrient-impaired, the Water Quality Management Committee looked at the university’s recommendations to see what is feasible, Ms. Rathjen said.
The university recommended management of the macrophytes through mechanical harvesting, which would be the majority of the town’s project. It would involve “mowing the lawn,” except on the water, this involves trimming the stems of the plants, Ms. Rathjen said.
The plan also aims to improve the oxygen concentration on the bottom of the pond to allow denitrification to occur naturally in the sediment.
“When all of these surface plants die off and all of the organic matter sinks into the sediment, the process of decay uses up all of the available oxygen in the pond,” Ms. Rathjen said.
Ms. Rathjen said that by removing the surface vegetation, the wind will hit the open surface and add oxygen to the pond.
The project would also implement diffuser discs that would deliver oxygen and facilitate mixing at the bottom of the pond.
“It would give the water a good turnover and get the oxygen where it needs to be,” she said.
The more plants that are removed from the surface leads to less fertilization for next year’s plants, Ms. Rathjen said, so over time the number of plants covering the pond’s surface will decrease.
When harvesting the macrophytes, the town would dam the water to ensure that nutrients would not travel into Green Pond. Because Mill Pond directly discharges into Green Pond, the town wants to make sure Mill Pond is not negatively impacting it, Ms. Rathjen said.
If the project is approved, the team would haul the macrophytes out and measure the amount of nitrogen in order to calculate the amount of nitrogen that has been removed from the pond, and subsequently other water streams.
For the first year, they are planning on harvesting the plants twice, although the plants will probably return within three weeks, Ms. Rathjen said.
“These proposed activities are not going to be a permanent solution for the pond,” Ms. Rathjen said.
The University of Massachusetts also recommended in its study the altering of cranberry bog practices upstream from the pond. Some changes include switching the types of fertilizer that are used and gradually releasing the floodwaters, instead of releasing them all at once.
The Town of Falmouth wants to work with cranberry bog owners nearby to better manage the nutrient level coming to Mill Pond.
“It took Mill Pond a long time to reach the state that it’s in,” Ms. Rathjen said. “And it’s going to take a while for it to get back to a healthy balance.”
The pond can be reached from the lawn of the East Falmouth Public Library, Ms. Rathjen said, and the town has also received permission to access the pond via the property of a couple of residents.