MEPS 543:107-125 (2016)  -  DOI:

Eutrophication modelling chain for improved management strategies to prevent algal blooms in the Bay of Seine

Paul Passy1,2,*, Romain Le Gendre3,7, Josette Garnier1,4, Philippe Cugier5, Julie Callens1, François Paris3,6, Gilles Billen1,4, Philippe Riou3, Estela Romero1

1CNRS & Université Pierre et Marie Curie, FIRE FR-3020, 4 place Jussieu, 75005 Paris, France
2Department of Geography, National University of Singapore, 1 Arts Link, Singapore 117570
3IFREMER, LER/N, Avenue du Général de Gaulle, 14520 Port en Bessin, France
4CNRS & Université Pierre et Marie Curie, UMR 7619 Metis, 4 place Jussieu, 75005 Paris, France
5IFREMER, Ctr Bretagne, Dyneco-LEBCO, CS 10070, 29280 Plouzané, France
6BRGM, Coastal Risks and Climate Change Unit, Risks and Prevention Division, 3 Av. C. Guillemin, BP 36009, 45 Orléans, France
7Present address: IFREMER, Unité de Recherche Lagons, Écosystèmes et Aquaculture Durable (LEAD-NC), BP 2059, Nouméa 98846, New Caledonia, France
*Corresponding author:

ABSTRACT: Eutrophication of the Seine estuary and the Bay of Seine is a crucial environmental issue for the management of ecosystems and economic activities related to fisheries and tourism in the region. A large quantity of nutrients, especially nitrogen, is brought to the coastal zone by the Seine River, the main input into that area, but also by smaller rivers along the Normandy coast. This large delivery of nitrogen leads to an imbalance between nitrogen (N), phosphorus (P) and silica (Si), which affects the growth of planktonic organisms and can exacerbate the occurrence of harmful algal blooms (HABs). These events can be damaging for shellfish fisheries, an important economic resource for the region. The study describes a new modelling chain coupling a riverine and a marine model (the Seneque/Riverstrahler and the ECO-MARS3D, respectively), which allows us to explore the effects on the coast of 2 scenarios of watershed management. The first one, focused on an upgrade of wastewater treatment plants, decreases the P fluxes by 5 to 35 kg P km–2 yr–1 on average over the 2000 to 2006 period, depending on the watershed, and would reduce about 3-fold the concentration of dinoflagellates in the adjacent coastal zone. The second one explores a hypothetical scenario of generalisation of organic farming in all agricultural areas of the basin. Although this is not realistic, it shows the best theoretical results we can achieve. With this scenario, the N fluxes decrease by almost 50%, and the dinoflagellate blooms and thus possibly the Dinophysis spp. blooms are drastically reduced by a factor of 20 to 40. Nevertheless, diatoms, which are the main primary producers in the bay and sustain the marine food web, are not significantly affected by this drastic scenario.

KEY WORDS: Eutrophication · Harmful algal blooms · Nutrient load · Modelling · Water quality · Seine

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Cite this article as: Passy P, Le Gendre R, Garnier J, Cugier P and others (2016) Eutrophication modelling chain for improved management strategies to prevent algal blooms in the Bay of Seine. Mar Ecol Prog Ser 543:107-125.

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