Experiment Begins In Mill Pond's Waters

An experimental treatment of a portion of Mill Pond with a mineral that the Southampton Town Trustees hope eventually will help improve water quality in the entire pond began this week.

Using a modified leaf blower mounted on the bow of a small boat, a company contracted by the Trustees spread 160 pounds of a granular, clay-like modified mineral called Phoslock into a narrow creek at the western corner of Mill Pond in Water Mill on Monday morning. The hope is that the mineral, which is primarily naturally occurring clay, will bond with phosphorus in the water and sink it to the bottom of the pond, where it cannot feed destructive algae blooms that have plagued the pond for years.

If the test convinces the Trustees that Phoslock could be an elixir for the pond’s woes, a broader application could be conducted in the entire pond as early as next spring, which the developers of Phoslock say would have an immediate and dramatic impact on the algae blooms.

“The results at this time of year will be subtle,” said Shaun Hyde, an engineer at SePro, the consulting company that designed the experimental Phoslock treatment. “When you have very high free phosphorus levels, you will see a big drop, immediately, in a matter of an hour or hours.”

Phosphorus in fertilizers, pesticides and other chemicals is carried into the lake primarily through runoff from nearby roads, lawns and farm fields. It is also created by decaying plant life within the pond ecosystem. Once suspended in the water column, the phosphorus becomes food for blue-green algae, fueling the summertime blooms that choke the pond of oxygen and the sunlight that native plants need to thrive. When the algae dies with the first chill of autumn, the dying blooms return a heavy dose of phosphorus to the system, restarting the cycle.

In 2008, the die-off of a very large algae bloom suffocated thousands of fish in the pond, giving new urgency to years of pleas of pondfront residents for the Trustees to address the chronic water quality issues in the pond.

“This breaks the cycle,” said Eddie Edmunds, the CEO of Phoslock Water Solutions, the Australian company that developed Phoslock, while standing at the edge of Mill Pond on Monday morning.

Mr. Edmunds said that Phoslock is made from naturally occurring Bentonite clay, which makes up much of the substrate on the South Fork. The granules of clay have been modified to boost levels of lanthanum, a metallic chemical element that is found naturally in bentonite clay, to increase the amount of phosphorus that will bind to the granules.

“It’s a natural product, not a chemical or pesticide,” Trustee Fred Havemeyer said as the test began. “To me, it’s the same thing as taking Alka-Seltzer for an upset stomach.”

Once phosphorus interacts with the granules of Phoslock, it is permanently bonded to it and can no longer be consumed by plants or algae. The Phoslock granules also will continue to bond with new phosphorus as it enters the pond.

Mr. Hyde said that water sampling conducted before the test and over the coming winter will give his company an idea of how much phosphorus is entering the pond each year, allowing them to calculate how much Phoslock would have to be added in order to neutralize it over time.

If a broader application of Phoslock is approved by the Trustees—an initiative that would cost upward of $400,000 over a period of three years, and as much as $35,000 a year into the foreseeable future—SePro would broadcast thousands of pounds of Phoslock throughout the entire pond, monitoring phosphorus levels over several seasons until a balance is found.

Phoslock will not address other water quality issues in the pond, like groundwater polluted with nitrates from decades of pesticide applications on the farms that once surrounded the pond or invasive plant species. Last year, the Trustees hired commercial fishermen to begin an annual program of netting thousands of carp, a foraging fish that eats native plant species, allowing invasives to flourish.

Phoslock is the second, and more expensive, of two mineral applications the Trustees have been considering as possible treatments for water quality problems, the other being an aluminum derivative known as Alum. A vocal group of residents who live along the pond have also pushed for, and offered to help fund, other proactive steps, including the use of aerators and natural enzymes to dissolve the amount of plant material in the bottom of the pond—an approach the Trustees have been wary of since water circulators placed in the pond in 2007 may have contributed to the 2008 fish kill.

SePro and consultants from Inter-Science Research Associates, a Southampton firm, will take water samples from the test area, which has been separated from the rest of Mill Pond by a cloth curtain, 24 hours after the test and again at seven days, 28 days and 56 days, to track the impacts on phosphorus levels.