The flux of dissolved nitrogen from the UK — Evaluating the role of soils and land use

Fluvial dissolved nitrogen (dissolved organic nitrogen [DON], nitrate and ammonium) fluxes from the terrestrial biosphere of the UK to surrounding oceans are explained on the basis of combined predictions of soil to water transfer and in-stream loss. The flux of different nitrogen species from land to surface waters is estimated using an export coefficient model employing catchment soil, land use and hydroclimatic characteristics, fitted to flux estimates derived from the Harmonised Monitoring Scheme between 2001 and 2007 for 169 UK catchments. In-stream losses of DON, nitrate and ammonium were estimated using a transit time filter in the fluvial network. Comparisons of modelled land to water N flux (2125 ktonnes N yr^− 1) with estimates of N fluxes to estuarine and ocean systems at the tidal limit (791 ktonnes N yr^− 1) suggest that significant in-channel N losses occur. These in transit losses are equivalent to up to 55 kg N ha^− 1 yr^− 1.