TY - JOUR T1 - Impact of urban effluents on summer hypoxia in the highly turbid Gironde Estuary, applying a 3D model coupling hydrodynamics, sediment transport and biogeochemical processes A1 - Lajaunie-Salla,Katixa A1 - Wild-Allen,Karen A1 - Sottolichio,Aldo A1 - Thouvenin,Benedicte A1 - Litrico,Xavier A1 - Abril,Gwenael AD - Univ Bordeaux, CNRS, Environm & Paleoenvironm Ocean & Continentaux UMR, Lab EPOC, Pessac, France. AD - LyRE, SUEZ Res Ctr, Bordeaux, France. AD - CSIRO Marine & Atmospher Res, Hobart, Tas, Australia. AD - IFREMER, Plouzane, France. AD - Univ Fed Fluminense, Dept Geoquim, Niteroi, RJ, Brazil. UR - https://doi.org/10.1016/j.jmarsys.2017.05.009 DO - 10.1016/j.jmarsys.2017.05.009 KW - Hypoxia KW - TMZ KW - Gironde Estuary KW - Wastewater KW - Oxygen KW - Modeling N2 - Estuaries are increasingly degraded due to coastal urban development and are prone to hypoxia problems. The macro-tidal Gironde Estuary is characterized by a highly concentrated turbidity maximum zone (TMZ). Field observations show that hypoxia occurs in summer in the TMZ at low river flow and a few days after the spring tide peak. In situ data highlight lower dissolved oxygen (DO) concentrations around the city of Bordeaux, located in the upper estuary. Interactions between multiple factors limit the understanding of the processes controlling the dynamics of hypoxia. A 3D biogeochemical model was developed, coupled with hydrodynamics and a sediment transport model, to assess the contribution of the TMZ and the impact of urban effluents through wastewater treatment plants (WWTPs) and sewage overflows (SOs) on hypoxia. Our model describes the transport of solutes and suspended material and the biogeochemical mechanisms impacting oxygen: primary production, degradation of all organic matter (i.e. including phytoplankton respiration, degradation of river and urban watershed matter), nitrification, and gas exchange. The composition and the degradation rates of each variable were characterized by in situ measurements and experimental data from the study area. The DO model was validated against observations in Bordeaux City. The simulated DO concentrations show good agreement with field observations and satisfactorily reproduce the seasonal and neap-spring time scale variations around the city of Bordeaux. Simulations show a spatial and temporal correlation between the formation of summer hypoxia and the location of the TMZ, with minimum DO centered in the vicinity of Bordeaux. To understand the contribution of the urban watershed forcing, different simulations with the presence or absence of urban effluents were compared. Our results show that in summer, a reduction of POC from SO would increase the DO minimum in the vicinity of Bordeaux by 3% of saturation. Omitting discharge from SO and WWTPs, DO would improve by 10% of saturation and mitigate hypoxic events. Y1 - 2017/10 PB - Elsevier Science Bv JF - Journal Of Marine Systems SN - 0924-7963 VL - 174 SP - 89 EP - 105 ID - 49903 ER -