Simulating estuarine nitrous oxide production by means of a dynamic model

Abstract

We describe a dynamic model developed from a commercially available modeling package (ECoS-III) to simulate estuarine dissolved inorganic nitrogen (DIN) dynamics, and consequent N 2O production and atmospheric flux on the timescale of tidal cycles. Simulated model state variables were NH 4 + , NO 3 - and N 2O 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 NH 4 + , NO 3 - and N 2O concentrations. Nitrification was shown to be the dominant N 2O source and estimates of the ratios nitrification to DIN load and N 2O emission to DIN load are considerably lower than the corresponding values adopted in global scale models of estuarine N 2O emissions based on DIN transformations. Hence our results are consistent with the requirement imposed by atmospheric N 2O growth rate constraints that the amount of atmospheric N 2O arising from agriculturally related sources, including estuarine transformations of N, be revised downward.