Modeling biogeochemical processes in sediments from the Rhône River prodelta area (NW Mediterranean Sea)
1Laboratoire de Géochimie des Eaux, UMR 7154, Université Paris Diderot – Paris 7 and IPGP, Batiment Lamarck, Case Postale 7052, 75205 Paris cedex 13, France
2Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS UMR 1572, Av. de la Terrasse, 91198 Gif sur Yvette, France
3UMR 5805 EPOC – OASU, Université Bordeaux 1 – CNRS, Avenue des Facultés, 33405 Talence cedex, France
4NIOO-KNAW, Centre for Estuarine and Marine Ecology, Korringaweg 7, 4401 NT Yerseke, The Netherlands
5Laboratoire d'Aérologie, CNRS et Université de Toulouse, 14 avenue Edouard Belin, 31400 Toulouse, France
6Laboratoire des Bio-Indicateurs Actuels et Fossiles, UPRES EA 2644, UFR Sciences 2 bd Lavoisier, 49045 Angers Cedex 01, France
Abstract. In-situ oxygen microprofiles, sediment organic carbon content and pore-water concentrations of nitrate, ammonium, iron, manganese and sulfides obtained in sediments from the Rhône River prodelta and its adjacent continental shelf were used to constrain a numerical diagenetic model. Results showed that (1) organic matter from the Rhône River is composed of a fraction of fresh material associated to high first-order degradation rate constants (11–33 yr−1), (2) burial efficiency (burial/input ratio) in the Rhône prodelta (within 3 km of the river outlet) can be up to 80%, and decreases to ~20% on the adjacent continental shelf 10–15 km further offshore (3) there is a large contribution of anoxic processes to total mineralization in sediments near the river mouth, certainly due to large inputs of fresh organic material combined with high sedimentation rates, (4) diagenetic by-products originally produced during anoxic organic matter mineralization are almost entirely precipitated (>97%) and buried in the sediment, which leads to (5) a low contribution of the re-oxidation of reduced products to total oxygen consumption. Consequently, total carbon mineralization rates as based on oxygen consumption rates and using Redfield stoichiometry can be largely underestimated in such River Ocean dominated Margins (RiOMar) environments.