Coherent assessment framework for eutrophication : model results Deltares

This report describes the results of the modelling work done by Deltares in the framework of the OSPAR Intersessional Correspondence Group on Ecosystem Modelling (ICG-EMO). In this group, an ensemble model approach was started in 2020, with the aim to simulate the effects of anthropogenic nutrient loads on nutrient and chlorophyll concentrations in the NE Atlantic. The final objective of the modelling work is to define harmonized and coherent reference conditions representing a historic pre-eutrophic state, i.e. around the year 1900, for each eutrophication assessment area. These areas have been defined in earlier OSPAR work, using ecological and physical characteristics which go beyond country borders, to improve coherence in assessment outcomes between countries. Threshold values are derived by adding an acceptable deviation of 50% above the modelled historic pre-eutrophic concentrations of nutrients and chlorophyll. The set of coherent threshold values can be applied by OSPAR Contracting Parties in the assessment of eutrophication in the OSPAR area that will contribute to the next OSPAR Quality Status Report (QSR) in 2023. The QSR will in turn serve as the common basis for the 2024 reporting on the status of the marine environment (Marine Strategy Part 1) under the EU Marine Strategy Framework Directive by EU Members States that are also OSPAR Contracting Parties. This report describes the model results of Deltares, with special attention to the results in the Dutch part of the North Sea and provides recommendations for further work by ICG-EMO.