From environmental evaluation to the dynamics of agrarian systems on a 'green algae' watershed

The article presents the Acassya project conducted in the Lieue de Grève coastal watershed (Brittany, France) to address water quality degradation from intensive livestock farming. It assesses nitrogen compartments and fluxes in breeding zones, develops an agro-hydrological model that integrates farm constraints, spatial practices, and landscape structure, and co-constructs realistic, low-emission farming scenarios with local stakeholders. Methodologies include historical land-use and production system analysis, surveys for agro-socio-economic typology, pilot farm trajectory monitoring with simple indicator guides, and iterative scenario simulation using the CASIMOD’N model. Results demonstrate the feasibility of combining productive agriculture with very low nitrogen emissions.