Variabilité spatio-temporelle des nutriments et du carbone et flux associés le long d’un continuum terrestre-aquatique tempéré (Marais poitevin – Baie de l’Aiguillon – Pertuis Breton)

  Coastal zones are key systems in biogeochemical cycle couplings between continents, oceans and the atmosphere. Altered by climate change and anthropogenic pressures, there’s a need to predict potential changes to better manage ecosystem functions and services they provided. This study deals with the carbon and nutrient dynamic over a temperate marsh-coastal continuum (Poitevin Marsh-Aiguillon Bay-Breton Sound). Concentrations of carbon, nitrogen, phosphorus and silica were measured twice a month during a year at various locations: estuaries, channels, coastal sites. This coastal zone shelters important blue mussel farming sites and is under the influence of an anthropized watershed where specific lock managements regulate freshwater inputs. Though reduced in 2017, terrestrial inputs significantly influenced carbon and nutrient coastal water dynamics especially in winter under strong discharges and hydraulic lock managements. Nutrients appeared to limit to a small extent the primary production with solely a real nitrogen limitation in stream and coastal waters in summer. Dissolved inorganic, particulate organic carbon (DIC, POC) and dissolved inorganic nitrogen (DIN) were mainly exported from the watershed according to soil occupation (culture vs grassland) and basin geology (carbonate vs silicate). The exported chlorophyll a was rapidly consumed in coastal waters showing the productive potential of this area. The long-term trend in watercourse discharge decrease and specific lock management could perturb the biogeochemical functioning of this costal area in the short term.