Eutrophication gradients in coastal lagoons as exemplified by the Bassin d'Arcachon and the Étang du Prévost

摘要: The conditions of eutrophication are described in three lagoon systems differing by their structure, catchment area and connection with the sea: Bassin d'Arcachon on Atlantic coast, SW France, semi-artificial fish ponds d'Arcachon, Etang du Prevost Mediterranean. is a shallow semi-enclosed bay, strongly influenced climatic factors tidal currents. receives significant inflow freshwater waters only partially renewed. greatest part primary production due to seagrass Zostera noltii. Although ecosystem remains whole steady state, some evidence potential visible. For instance, flux nitrogen into has increased more than 50% during last 25 years. most change among producers massive development since 1988 green alga Monostroma obscurum. ‘reservoirs’ man-made enclosures designed for extensive aquaculture where water renewal possible certain periods time. Thus, because shallowness confined nature these ponds, acute sometimes observed summer. extremely eutrophic agricultural urban run-off. Red occur periodically warm summer months as consequence ecological events beginning early spring bloom macroalgae (Ulva sp.). In summer, algal biomass degraded aerobic heterotrophic bacteria; oxygen demand encompasses production, leading predominence anaerobic processes dystrophic crisis. From comparison selected sites, stages recognized according conceptual model Nienhuis (1992) describing relation between relative dominance connected availability nutrients. Such macroscopic observations should, now, be explained study microbiological including meiofauna, protozoa, bacteria all components microbial loop.