The role of inorganic nutrients and dissolved organic phosphorus in the phytoplankton dynamics of a Mediterranean bay: A modeling study

18 pages, 9 figures, 7 tables

The effect of Dissolved Organic Phosphorus (DOP) availability and nutrient limitation of phytoplankton growth in an estuarine bay (Alfacs Bay, NW Mediterranean) have been studied by means of a zero-dimensional ecological model including nitrogen, phosphorus (organic and inorganic), two groups of phytoplankton (diatoms and flagellates), one group of zooplankton, and detritus. Simulations with and without DOP as an extra source of phosphorus for phytoplankton growth suggest that DOP plays an important role in the dynamics of the Alfacs Bay ecosystem. DOP is indeed necessary to simulate the observed draw-down of nitrate and build up of phytoplankton biomass. Two non-exclusive mechanisms allowing DOP availability for phytoplankton are possible: direct uptake, or remineralization to Dissolved Inorganic Phosphorus. Including both gives a better agreement with the observations. Inclusion of DOP in the model leads to predominance of phosphorus limitation of phytoplankton growth in fall and winter, and of nitrogen limitation in late spring and summer. Simulations with and without sediment resuspension suggest that this process does not significantly affect the nutrient budget in the bay

This work was funded by projects TURECOTOX (CTM2006-13884-CO2-00/MAR9, Ministerio de Ciencia e Innovacion, Spain) and CANESP (a joint project between the National Research Council of Canada and the Ministerio de Asuntos Exteriores of Spain), and by the CSIC. CL was supported by a fellowship of the Spanish National Research Council, CSIC (Beca CSIC Predoctoral I3P-BPD2005), and during the last months for a postgraduate grant of La Fundación Caja Madrid. The modeling was performed during CL's internship in the College of Oceanic and Atmospheric Sciences at Oregon State. We thank Tim Cowles for hosting CL during her first stay in the US and for his help and support during the first stages of the model development. JS was funded by Proyecto Intramural Especial del CSIC, “Desarrollo de algoritmos y validación de productos en el Centro Experto SMOS en Barcelona” (200430E530). We are grateful to Maximinio Delgado for kindly providing phytoplankton data, to Elisa Berdalet, Esther Garcés and Mariona Segura for valuable advice and information, and Francisco Rueda for his help during the process of implementation of the physical model Si3D to Alfacs. IRTA (Institut de Recerca i Tecnologia Agroalimentàries, Generalitat de Catalunya) sponsored the collection of time series of environmental data in Alfacs Bay. The Servei Meteorològic de Catalunya and the Instituto Nacional de Meteorología provided meteorological data. We also acknowledge the valuable comments of Annie Chapelle and an anonymous reviewer

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