Nutrient Dynamics of the Seine Estuary, France

With ever-increasing human pressures from human uses of fluvial and estuarine systems, an understanding of the links between the suspended sediment component and nutrient (bio)availability is a major global challenge for effective ecosystem management. For example, the effect of eutrophication is estimated to cost the UK ’£114 million per annum. The relationship between particle transport and nutrient cycling is poorly understood, and presents challenges of spatial and temporal variability in addition to prevailing weather and climate forcing. On an estuarine scale, this variability is controlled by the flow velocity and turbidity of the water, together with the dominant salinity and temperature regime. To address these issues, an integrated approach was undertaken to assess the sedimentary flux of macro-nutrients (nitrogen and phosphorus) from a physico-chemical perspective, in a pilot study conducted on the River Seine (France). In this work, hydrodynamic data, collected using ADCP and CTD apparatus, was compared with the nutrient concentrations and sediment characteristics of the upper and lower water column. Profiles of the master variables, temperature, salinity and turbidity, were obtained hourly or 2-hourly over a tidal cycle in the freshwater zone and the turbidity maximum. Current velocity and sediment flux data were recorded continuously by ADCP while nutrient concentrations, (nitrate, nitrite, ammonium, total dissolved nitrogen, dissolved reactive phosphorus and total dissolved phosphorus) were determined in the laboratory post-collection. The results are presented here and highlight the importance of understanding the relationships between sediment properties and nutrient availability with implications for water quality and estuarine management that are applicable to other turbid, macrotidal estuaries.