| Summary: | International audience Biogeochemical watershed models are now prompted to reconcile both the need to expand their spatial extent up to the regional scale where coastal damages are observed, and to increase their spatial and temporal resolution to accurately depict the transformation, elimination/immobilization of carbon and nutrients during their in-stream transfers. While regional prospective analysis are still greatly supported by statistical approaches, the newly developed biogeochemical pyNuts-Riverstrahler model rises up the challenge of a mechanistic representation of microscopic processes operating in the aquatic continuum, scalable and compatible with regional up to continental domains. This generic model was successfully implemented and validated over the last decade for all the north-east Atlantic rivers (more than 350000 km of drainage network) from the Rhine to the Guadalquivir, including some major and highly perturbed systems. A European atlas of land based nutrient emissions, developed in this modelling framework, was used to build a set of gradual scenarios, first fully applying current environmental regulations requirements, then assuming deeper societal and agricultural changes (improved human diet, reconnected production, etc.). Impact assessment includes the capacity of western EU-rivers to recover good water quality standards, the analysis of nutrient ratios and the estimation of riverine fluxes delivered to the sea. Impact on marine systems will be briefly shown to illustrate the necessity of river-ocean integrated modelling approaches.
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