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A comprehensive investigation of the nitrogen cycle in the Delaware River was carried out using 15 N tracers to measure rates for important transformations of nitrogen. Daily, depth‐averaged 15 N rates for the principal inorganic nitrogen species were consistent with rates derived from longitudinal profiles of concentration in the river. The data indicated that nitrification was a rapid, irreversible sink for NH 4 + , with export of the product NO 3 − from the study area. Utilization of NO 3 − by primary producers was negligible, owing to low irradiance levels and to high NH 4 + concentrations. The oxygen sag near Philadelphia was found to result from oxygen demand in the water column, with only minor benthic influence. Reaeration provided the major oxygen input. Nitrification accounted for about 1% of the net oxygen demand near Philadelphia but as much as 25% farther downstream.
Lipschultz et al. (Tue,) studied this question.