Simulating estuarine nitrous oxide production by means of a dynamic model

We describe a dynamic model developed from a commercially available modeling package (ECoS-III) to simulate estuarine dissolved inorganic nitrogen (DIN) dynamics, and consequent N2O production and atmospheric flux on the timescale of tidal cycles. Simulated model state variables were NH4+, NO3- and N2O concentrations, and salinity. Model outputs were evaluated through comparison with summer field data for the Tyne estuary, UK. The model adequately reproduced the observed axial profiles of NH4+, NO3- and N2O concentrations. Nitrification was shown to be the dominant N2O source and estimates of the ratios nitrification to DIN load and N2O emission to DIN load are considerably lower than the corresponding values adopted in global scale models of estuarine N2O emissions based on DIN transformations. Hence our results are consistent with the requirement imposed by atmospheric N2O growth rate constraints that the amount of atmospheric N2O arising from agriculturally related sources, including estuarine transformations of N, be revised downward.