The effects of nitrogen and phosphorus contamination as well as artificial impoundments were topics of concern Monday night at a public meeting called to discuss the recent Mill Brook watershed report in West Tisbury.
After four years of data collection, field work and analysis, the watershed management planning committee presented its report on the watershed to an audience of about 30 people at the town library.
The $41,630 study measured water temperature, quality and flow at several sites along the brook and its tributaries. It also monitored wildlife, rainfall and Mill Pond depth.
Researchers called for continued study, but highlighted the impacts of development and dams in the watershed. The study found high levels of phosphorus throughout the watershed and some high levels of nitrogen, nutrients that can contribute to algae blooms and threaten water quality. The study also found that the ponds contributed to solar heating of still water, raising temperatures to levels lethal to many of the watershed’s historic species. Diversion of water for landscaping, irrigation and firefighting purposes was also identified as a stressor on the watershed system.
At the meeting, George Gay said he owned property along the brook.
“I very much appreciate the amazing work of this body,” he said of the committee, which was made up of volunteers and met more than 70 times over the last four years.
“My big time wish . . . is that the select board does what it has to . . . so there are herring or another breed running by my house in the summertime,” Mr. Gay said.
Nelson Sigelman was one who of many who agreed with Mr. Gay’s request to remove impoundments along Mill Brook. He called the pond, considered by many to be the historic gateway to West Tisbury, a “scenic mud puddle.”
“Is there any reason to think that really, ultimately, the whole goal is not to get rid of all these dams?” he asked the committee.
In response Selena Roman, who served on the watershed planning committee, said the report focused on environmental data, which while useful, is not the only aspect of the watershed.
“We did not address at all any of the multitude of other uses those bodies of water bring to people recreationally, historically and aesthetically. There are many other issues that need to be addressed,” Mrs. Roman said.
But others cautioned that removing dams could contribute nutrient contamination to the Tisbury Great Pond, where sensitive oyster populations have already been affected by algae blooms.
“There might be a short-term flush of nitrogen out of those wetlands if we removed the dams,” said Bill Wilcox, former longtime Martha’s Vineyard Commission water quality planner. He also later said the dams are the clearest factor impeding aquatic life in the streams. “At the very least, I think we need to find a way to get high-quality fish ladders going up every dam in the stream,” Mr. Wilcox said.
Prudy Burt took note of the committee’s suggestion that Mill Pond be separated from a free flowing Mill Brook in order to allow the water to flow without asking the town to sacrifice the historic landscape.
“The idea of having a free flowing stream in that location would eliminate that solar input,” Ms. Burt said. She added that extensive engineering studies and permitting would be necessary.
A principal recommendation was ongoing study of the watershed. The committee discussed the possibility of using community preservation funds to support more research.
“It is obvious that any responsible management plan must rely not just on base data, but data over time,” said selectman and committee chairman Cynthia Mitchell.
Selectmen are expected to officially accept the report Wednesday, and are responsible for deciding on next steps.
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