Chesapeake Bay nutrient and plankton dynamics. 2. Sources and sinks of nitrite1

Abstract

The transformations of inorganic nitrogenous nutrients that can lead to the frequently observed high levels of nitrite in the Chesapeake Bay and York River were investigated by a combination of 15 N tracer techniques and assays of the concentrations of chemical constituents (NH 4 + , NO 2 ‒ , NO 3 ‒ , O 2 , N 2 O, and CH 4 ). During destratification, uptake and remineralization of NH 4 + in the York River followed a diel cycle, but nitrification was not as closely coupled to the light regime. The distributions of N 2 O, NO 2 ‒ , and CH 4 in the York River suggest that the primary source of N 2 O and NO 2 ‒ , both produced during nitrification, was in the water rather than in the sediments. Rates of nitrification inferred from N 2 O gas flux calculations are consistent with measured in situ rates. Experiments at a series of stations in the mid‐Chesapeake Bay were designed to look at transformations among N pools. The yield of N 2 O‐N relative to NO 2 ‒ ‐N during nitrification ranged from 0.2 to 0.7%, in agreement with previously published laboratory results. Our 15 N data indicate that oxidized N can be formed in the water of the bay when physical events cause the mixing of NH 4 + ‐rich bottom water with more oxygenated surface layers. We also found that N 3 ‒ was reduced to NH 4 + at unexpectedly rapid rates in well oxygenated surface waters. The magnitude and duration of high concentrations of N 2 O and NO 2 ‒ in these estuarine waters during mixing events might be expected to increase if anthropogenic loading of nutrients causes anoxic conditions in the bay to become more widespread.