ABSTRACTNitrogen‐isotope values (δN15) of ground‐water nitrate on Long Island, New York, correlate with δN15ranges of nitrate sources which contribute to the ground‐water systems. The δN15of nitrate in water from the upper glacial aquifer, the water‐table aquifer on Long Island, shows a shift from lighter values in the eastern part of the island where land is used predominantly for agriculture, to heavier values toward New York City where land is used for suburban residences with septic systems or sewers. δN15values for inorganic fertilizer, unfertilized cultivated fields, and animal wastes show a similar shift from low to high values: −3 ‰ to +2 ‰+ 2 ‰ to + 8 ‰ and +10 ‰ to +20 ‰, respectively.Nitrogen‐isotope ratios of nitrate in water from the deeper Magothy aquifer indicat
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