|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 15N tracer techniques and assays of the concentrations of chemical constituents (NH4+, NO2-, NO3-, O2, N2O, and CH4).
During destratification, uptake and remineralization of NH4+ in the York River followed a diel cycle, but nitrification was not as closely coupled to the light regime. The distributions of N2O, NO2-, and CH4 in the York River suggest that the primary source of N2O and NO2-, both produced during nitrification, was in the water rather than in the sediments. Rates of nitrification inferred from N2O 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 N2O-N relative to NO2--N during nitrification ranged from 0.2 to 0.7%, in agreement with previously published laboratory results. Our 15N data indicate that oxidized N can be formed in the water of the bay when physical events cause the mixing of NH4+- rich bottom water with more oxygenated surface layers. We also found that NO2- was reduced to NH4+ at unexpectedly rapid rates in well oxygenated surface waters.
The magnitude and duration of high concentrations of N2O and NO2- 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.|