The statement seems straightforward: Septic systems add 65 percent of the watershed nitrogen in the South Shore Estuary Reserve [“A blueprint for Suffolk water quality,” News, Dec. 21]. However, its simplicity may confuse the public into thinking that septic-sourced nitrogen is the cause of all harmful algal blooms.

For 13 years, the National Atmospheric Deposition Program, a cooperative that measures effects on the environment, has measured nitrogen that falls in precipitation on Peconic Bay in Southold. This is called acid rain or wet nitrogen. Additional nitrogen drifts down from clear skies; this is called dry nitrogen. The nitrogen enters the high atmosphere as a byproduct of burning fuels to generate electricity, along with other industrial and natural sources. Other nitrogen enters Peconic Bay from its watershed.

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Data show that nitrogen from atmospheric deposition accounts for 70 to 80 percent of the nitrogen entering Peconic Bay. While septic systems contribute the majority of nitrogen from watersheds, septic-sourced nitrogen actually contributes about 16 percent of the total.

Perhaps we don’t hear much about the nitrogen that rains down on us from the skies because we cannot locally control the sources. However, if we are to accept that too much nitrogen is the cause of harmful algal blooms, how can we ignore the impacts of the largest contributor?

Roger C. Tollefsen, Hampton Bays

Editor’s note: The writer is president of the New York Seafood Council, which represents the seafood industry, including harvesters and processors.