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Spatially resolved monthly riverine fluxes of oxidised nitrogen (nitrate and nitrite) to the European shelf seas, 1960-2005

Heath, M.R. and , Fisheries Research Services (Funder) (2007) Spatially resolved monthly riverine fluxes of oxidised nitrogen (nitrate and nitrite) to the European shelf seas, 1960-2005. [Report]

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Abstract

This report documents the methodology developed for statistically modelling the spatial and temporal patterns of oxidised nitrogen (nitrate plus nitrite) riverine fluxes into the coastal waters of northwestern Europe, over the period 1960-2005. The purpose of the study was to provide boundary data for a modelling study of new primary production in European waters. For the UK and Ireland, monthly freshwater discharges to a set of grid cells around the coastline were modelled from rainfall data and calibrated from detailed analyses performed for a subset of years with contrasting climatology. The mean and long-term trends in nitrate and nitrite content of the river discharges were modelled from Harmonised Monitoring Scheme data and flux estimates for each of the years of contrasting climateology. The product of the discharge rate and nitrogen content provided estimates of the monthly flux to each grid cell. Scandinavian inputs of nitrate and nitrite to the North Sea, Skagerrak and Kattegat were assembled from a composite of statistically modelled freshwater discharge, and recent estimates of nitrogen flux from national monitoring agencies. Fluxes of nitrate and nitrite from the rivers flowing into the North Sea from Germany, Netherlands and Belgium during 1960-2005 were assembled from previous analyses by researchers at the University of Hamburg. Nitrate and nitrite fluxes from French rivers flowing into the English Channel, in particular the Seine, were indirectly derived by correlation with the River Scheldt, calibrated from published estimates of annual fluxes. The results show the total oxidised nitrogen input to European shelf seas increasing from approximately 0.6Mt pa. in the 1960's to 1.2Mt pa. in the mid-1980's. Recent estimates of the annual flux since 2000 have been approximately 1.1Mt pa. Around 60-70% of the total annual flux to the northwest European shelf enters via the North Sea. Winter input rates are approximately twice those in the summer in all areas except the Skagerrak/Kattegat.