Three future agro-food system scenarios were specified for the territory draining into the Seine Bight, comprising Paris megacity and the Seine watershed. The first scenario assumes the pursuit of the current trend of opening and specialization of agriculture, as well as of the concentration of population within the Paris agglomeration. The second scenario assesses the generalization of agroecological practices and a healthier human diet. A third hybrid scenario was elaborated assuming that agroecological practices were implemented only in some protected areas (about one-third of the total watershed area). We use a unique modelling chain (GRAFS-Riverstrahler-ECOMARS3D) that couples the biogeochemical functioning of the river basin, the estuary, and the adjacent bay. It allows consistently exploring the implications of changes in terrestrial activities throughout the aquatic continuum and assessing to what extent changes in population, agricultural practices, food consumption, and sanitation may sustain the current recovery trend or increase stress on the system. Results show that only the full agroecological scenario would restore good water quality everywhere in the river network and significantly decrease the risks of toxic algal blooms in the coastal zone. Intermediate situations, such as the protection of specific areas, however attractive as a solution, are not enough to offset the impacts of intensive human activities unless the protected areas dedicated to compensating for damage are sufficiently large.

Primary Presenter: Estela Romero, CREAF (estela.romero@creaf.uab.es)

Authors:

Estela Romero, Global Ecology Unit, CREAF, Bellaterra, SPAIN  (estela.romero@creaf.uab.es)

Josette Garnier, UMR Metis 7619, Sorbonne Université - CNRS, Paris, FRANCE   (josette.garnier@sorbonne-universite.fr)

Romain Le Gendre, Unité de Recherche Lagons, Ecosystèmes et Aquaculture Durable, IFREMER, Nouméa, NEW-CALEDONIA  (romain.le.gendre@ifremer.fr)

Gilles Billen, UMR Metis 7619, Sorbonne Université - CNRS, Paris, FRANCE  (gilles.billen@sorbonne-universite.fr)