Crowding on Land Is Harming Our Waterways

Although the quality of waterways overseen by the East Hampton Town Trustees is generally excellent, according to a presentation at Town Hall on Monday, the negative effects of housing density and inadequate septic systems are evident.

Christopher Gobler of Stony Brook University’s School of Marine and Atmospheric Sciences has been monitoring waters here since 2013. His report on the 2015 findings was similar to the report the previous year. This time, however, he included mitigation efforts planned for Georgica and Hook Ponds in East Hampton, both of which had harmful algal blooms last year.

Because the Atlantic Ocean, Gardiner’s Bay, and Block Island Sound are among the cleanest waters in New York State, Dr. Gobler said the quality of the town’s waterways and fisheries should be high, and “generally that is true.” But, he said, “areas that couldn’t be more pristine” coexist with areas of impaired water quality that are strongly impacted by what happens on land. Dramatic changes have occurred in a surprisingly short time, he said, manifested by vanishing eelgrass and the persistent appearance of algal blooms in warm months.

Algae and phytoplankton are critically important to marine ecosystems, Dr. Gobler said, but “too much of a good thing” leads to dense, harmful blooms, including cyanobacteria, or blue-green algae, which appeared in many of the town’s freshwater sites last year, including Georgica and Hook Ponds, Wainscott Pond, and Fort Pond in Montauk. For the second consecutive year, Georgica Pond was closed to crabbing for much of the summer, the algal bloom dissipating only when the pond was opened to the ocean, as the trustees typically do biannually.

Exposure to blue-green algal blooms can cause vomiting or diarrhea; skin, eye, or throat irritation; nausea, or allergic reactions or breathing difficulties. Pets are among the most vulnerable, Dr. Gobler said, referring to a dog that died after ingesting water from Georgica Pond in 2012 and two dogs that experienced gastrointestinal illness after swimming in Fort Pond.

Warm water temperatures and a lack of tidal flushing are blamed for cyanobacteria blooms, but Dr. Gobler also pointed to “strong correlations between nitrogen loading and algal blooms.” Excessive nitrogen and phosphorus from wastewater is blamed for suppressed oxygen levels and consequent fish kills. Sample sites in Three Mile Harbor, he said, showed low levels of dissolved oxygen for extended periods last year. “That’s going to have negative repercussions for marine life.”

Alexandrium, a bacterium that can cause paralytic shellfish poisoning, was detected at the head of Three Mile Harbor during the year, Dr. Gobler said. While the level detected “generally wouldn’t be cause for concern,” a shellfish bed in Shinnecock Bay, where lower levels were measured, had been closed. Very little dinophysis, which causes diarrhetic shellfish poisoning, or cochlodinium, known as rust tide, were detected, however.

Fertilizer is another source of nitrogen, and rainfall was often followed, at some sites, by a spike in fecal coliform, which prompts the state’s Department of Environmental Conservation to close waters to the harvesting of marine life.

Levels of Chlorophyll a, a form of chlorophyll used in oxygenic photosynthesis, are below the Environmental Protection Agency standards in all marine water bodies. Levels of dissolved oxygen, he said, are generally high.

Remediation will come in multiple ways, he said. The county Department of Health Services is “on the verge of approving innovative, alternative wastewater treatment systems for individual homes” that dramatically reduce nitrogen levels reaching groundwater, at a cost similar to typical septic systems. A co-director of the New York State Center for Clean Water Technology, Dr. Gobler said, “Good things are on the horizon on this front.” 

Permeable reactive barriers can intercept nitrogen before it enters waterways, and the town’s Natural Resources Department is in the early stages of identifying sites for them, Dr. Gobler said. A plan to harvest macroalgae from Georgica Pond, which is believed to store excessive nutrients, is slated to begin next month. And the trustees have applied to the D.E.C. for a permit to dredge the cut between the pond and the ocean, which will increase circulation and flushing.