The concentration of inorganic nitrogen was measured in samples from 521 wells in the upper glacial and Magothy aquifers and from 46 streams in Nassau and Suffolk Counties during May 1971. The predominant form of dissolved nitrogen was nitrate. Nitrate concentrations (as N) in the upper glacial aquifer in both counties ranged from 0 to 20 milligrams per liter (mg/L) ; those in the Magothy aquifer ranged from 0 to 20 mg/L but were generally much lower in Suffolk County than in Nassau County. Nitrate concentrations (as N) decreased with depth in both counties; below 400 feet, concentrations ranged from 0 to 0.2 mg/L.
Nitrate concentrations (as N) of streams ranged from 0 to ii mg/L, which is an indication of the general quality of water in much of the upper glacial aquifer, the source of most of the streamflow. Generally, concentrations of total nitrogen in streams draining the sewered area of Nassau County were lower than those in streams draining the unsewered area. Median concentrations of total inorganic nitrogen (as N) were 1.3 mg/L for the sewered area and 7.5 mg/L for the unsewered area. About 5,500 pounds of nitrate (as N) was estimated to be discharged daily in surface flow to tidewater from Nassau and Suffolk Counties.
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USGS Numbered Series
Nitrogen in water in Nassau and Suffolk counties, Long Island, New York, in 1971