Spatial variability of organic matter and phosphorus cycling in Rhône River prodelta sediments (NW Mediterranean Sea, France): a data-model approach
|Temporal extent||2018-05-21 -2018-06-02|
|Author(s)||Ait Ballagh Fatima Ezzahra1, 2, Rabouille Christophe2, Andrieux Francoise3, Soetaert Karline4, Lansard Bruno2, Bombled Bruno2, Monvoisin Gaël5, Elkalay Khalid1, Khalil Karima1, Brethous Laurie2, Villedieu Anouk2|
|Affiliation(s)||1 : Laboratory of Applied Sciences for the Environment and Sustainable Development, Essaouira School of Technology, Cadi Ayyad University, Km 9, Route d’Agadir, BP. 383, Essaouira Aljadida, Morocco.
2 : Laboratoire des Sciences du Climat et de l'Environnement, Laboratoire Mixte CEA-CNRS-UVSQ, IPSL et Université Paris-Saclay, CEA-Orme des Merisiers, 91191, Gif sur Yvette, France.
3 : Ifremer – DYNECO PELAGOS, ZI Pointe du Diable, 29280 Plouzané, France.
4 : Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research (NIOZ) and Utrecht University, P.O. Box 140, 4400 AC Yerseke, The Netherlands.
5 : GEOPS, Université Paris-Saclay et CNRS, Campus d’Orsay, Orsay, France.
|Keyword(s)||Phosphorus, Rhône River prodelta, Sediment, Diagenetic modelling, Mineralization pathways, DIP recycling|
The Mediterranean Sea (MS) is a large oligotrophic sea. Its productivity may be sensitive to riverine nutrient inputs. Understanding its productivity involves quantifying phosphorus (P) river supply which is crucial for calculating P mass balances in the anthropogenically disturbed sea. Yet the precise role of the deltaic filter is not known, especially concerning the differential trapping/recycling of nutrients in deltaic sediments. A benthic dataset from the Rhône River prodelta was coupled to an early diagenetic model, including the benthic P cycle. The dataset comprised porewater oxygen, nitrate, sulfate, dissolved inorganic carbon, ammonium, dissolved reduced and total iron, dissolved inorganic phosphorus (DIP) and solid data (organic carbon, Fe-bound P, Ca-bound P and organic P) for 9 stations from the Rhône River prodelta. The model results indicated that the intensity of biogeochemical processes occurring near the sediment–water interface decreased from the river mouth to the adjacent continental shelf. This decrease occurred according to OC fluxes to the seafloor, sedimentation rates and integrated rates of OC mineralization (from 160 mmol C m-2 d-1 near the mouth to 10 mmol m-2 d-1 on the shelf). The organic P mineralization was intense, especially near the river mouth (1196 µmol m-2 d-1), and its contribution to DIP release was large (> 90%). Fe-bound P had a key role in promoting Ca-bound P precipitation in anoxic sediments. These sediments played an important role as a source of regenerated DIP.A significant part of DIP was recycled to the overlying waters (72-94%), representing 25% of the riverine discharge input of DIP. While 6-28% of produced DIP was buried as Ca-bound P, which represented 3-6% of the riverine inputs.
|Acknowledgments||We would like to thank the captain and the crew members of N.O. Tethys II (INSU/CNRS) for their assistance during sampling at sea. Florian Caradec and Emilie Rabiller are acknowledged for their help during P-speciation measurements at IFREMER’s laboratory. This work was supported by the INSU/EC2CO-MissRhoDia project, the French State program "Investissement d'avenir" run by the National Research Agency (AMORAD project ANR-11-RSNR-0002) and the CEDoc cooperation research project between Morocco and France.|