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Fish Kill Causes Identified

By
Christopher Walsh

Three fish kills in the Peconic River last summer were the result of rising water temperatures, elevated levels of nitrogen, and harmful algal blooms, according to a study by the New York State Department of Environmental Conservation, the Suffolk County Department of Health Services, and researchers at Stony Brook and Cornell Universities.

High levels of nitrogen suppress dissolved oxygen in water, which the study blames for the asphyxiation of some 300,000 Atlantic menhaden in the river. A large population of bluefish at the mouth of the river also served to trap the fish, also known as bunker, according to the study.

The kills occurred at different locations along the two-mile tidal portion of the river between May and June. The highest concentration was reported near the river’s mouth off Indian Island County Park in Riverhead and in the waters between County Route 105’s bridge and the Riverhead Yacht Club.

The Peconic River has a history of degraded water quality and fish kills. As many as 3 million fish died in September 1999; another 750,000 died the following August, while 100,000 died in separate events in May 2008 and May 2009. But the 2015 kill was unique in the algal blooms’ timing and intensity. Spring blooms and the consequent oxygen decline occurred much earlier than usual. The blooms and rising water temperatures combined to prolong periods of extremely low dissolved oxygen.

Secondary factors, including damage to the menhaden’s gills by exposure to the algal blooms, and resulting exposure to a virus, may have contributed to the fish kills, according to the study.

The Suffolk County Comprehensive Water Resources Management Plan, released in May 2015, identified nitrogen, pesticides, fertilizers, and volatile organic compounds as the principal contributors to degraded water quality, and established a framework for addressing wastewater management. The county entered into an agreement with the Town of Riverhead for a pilot program to test facilities with sanitized wastewater discharges. The county also awarded Riverhead $8 million and the state has offered the town more than $18 million in financing to upgrade its advanced wastewater treatment facility, including construction of a new sewage treatment plant.

The D.E.C. also is to spend $1 million to develop a nitrogen reduction plan for the Peconic Estuary on top of the $5 million in Gov. Andrew M. Cuomo’s budget to fund programs to develop such a plan for Long Island.

 

 

 

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