Green and Ominous
The Edgartown Great Pond is in trouble, its brackish waters out of balance and at the outer limit of their capacity to carry nitrogen. This is a well-known fact, thoroughly documented in the Massachusetts Estuaries Project draft report for the pond which was obtained by this newspaper, published on its Web site and written about a year ago this summer.
Now fact has come into living color with a summer algae bloom that calls to mind Little Shop of Horrors. A layer of bright green slime eight inches thick has spread across the pond, coating rocks and threatening shellfish beds with potentially fatal anoxic conditions. Identified last week by the Smithsonian Institution, the algae occurs most commonly in freshwater ponds and is known to thrive on nitrogen.
Nitrogen-rich groundwater is seeping into the Great Pond, which covers some eight hundred acres. The nitrogen is coming from septic systems and also from the Edgartown sewage treatment plant. The plant was upgraded some years ago, but a plume of polluted groundwater is still headed for the pond, left over from earlier days when methods for sewage treatment were not as sophisticated as they are today.
The algae bloom is a call to arms for all residents and scientists who have been hard at work studying the Edgartown Great Pond over the last two decades, from the old harbor study group which was ahead of its time in targeting the pond for data collection and special protection some twenty years ago, to the more recent Great Pond Foundation made up of a group of riparian owners. The foundation has raised money and is taking an active role in improving the health of the pond, among other things hiring graduate students to do water sampling and testing this summer. The foundation also last year leased a small dredge to test its usefulness on the pond; the experiment was a success and the foundation is now set to buy its own small dredge.
In the end the best measures for correcting the problems in the Great Pond are also the simplest: improve circulation (read: oxygen) by dredging and increase the salinity by mechanically breaching the pond to the sea.
These measures are immediately achievable. The Edgartown selectmen would be wise to step in and devise an emergency plan, in concert with the town shellfish committee and shellfish constable Paul Bagnall.
The Great Pond is one of the town’s most pristine resources; there is no reason to wait.