Submitted as: model description paper
28 Dec 2020
Submitted as: model description paper | 28 Dec 2020
Status: this preprint is currently under review for the journal GMD.

LPJmL-Med – Modelling the dynamics of the land-sea nutrient transfer over the Mediterranean region–version 1: Model description and evaluation

Mohamed Ayache1,2, Alberte Bondeau2, Rémi Pagès1, Nicolas Barrier3, Sebastian Ostberg4, and Melika Baklouti1 Mohamed Ayache et al.
  • 1Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France
  • 2Institut Méditerranéen de Biodiversité et d’Ecologie marine et continentale, Aix-Marseille Université, Technopôle Arbois-Méditerranée, 13545 Aix-en-Provence, France
  • 3MARBEC, CNRS, Ifremer, IRD, Université de Montpellier, Sète, France
  • 4Potsdam Institute for Climate Impact Research, Research Domain 1: Earth System Analysis, Telegraphenberg A62, 14473 Potsdam, Germany

Abstract. Land forcing (water discharge and nutrient loads) is reported as one of the major sources of uncertainty limiting the capacity of marine biogeochemical models. Runoff from rivers and coastal plains delivers significant amounts of nutrients to the Mediterranean Sea from agricultural activities and urban wastewater. Several recent studies show that variations in river inputs may play a significant role in marine biogeochemical cycles and the planktonic food web throughout the entire basin. The aim of this study is to estimate the water dischargeas as well as nitrate (NO3) and phosphate (PO4) release into the Mediterranean Sea from basin-wide agriculture and inhabited areas through the implementation of the biogeochemical land-sea nutrient transfer processes within the agro-ecosystem model Lund Potsdam Jena managed Land for the Mediterranean (LPJmL-Med). The representation of the nutrient transfer from land to sea has been introduced into LPJmL-Med by considering the following processes: mineralization, denitrification, adsorption, remineralization, nitrification, and phytoplankton dynamics. A compilation of a new input data set of fertilizer, manure and wastewater nutrient content [1961–2005] has been added to the LPJmL-Med forcing data set. The first basin-wide LPJmL simulation at 1/12° indicates that the model succeeds in simulating the interannual variability of water discharge for the main rivers in the Mediterranean Sea, especially the Po, Rhone and Ebro Rivers. A very high correlation (R-square values higher than 0.94) is found for these three rivers. Results also show a good consistency between the simulated nutrients concentration (NO3 and PO4) and available in-situ data. River outflows of NO3 and PO4 exhibit opposite trends in the Mediterranean Sea. NO3 showed a more or less continuous increase from the beginning of the 1960s until the present in all three rivers. PO4 trends are more heterogeneous. There is a strong increase in PO4 between 1960 and 1980, followed by a decrease in mean annual fluxes from the second half of the 1980s as a consequence of the banning of phosphates in detergents, and the construction of wastewater treatment plants in the different countries. Results show that wastewater strongly contributes to the river phosphate fluxes, while both agriculture and wastewater control the nitrogen (mainly as NO3) fluxes from rivers to the Mediterranean Sea.

Mohamed Ayache et al.

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Mohamed Ayache et al.

Mohamed Ayache et al.


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Short summary
Land forcing is reported as one of the major sources of uncertainty limiting the capacity of marine biogeochemical models. In this study, we present the first basin-wide simulation at 1/12° of water discharge as well as nitrate (NO3) and phosphate (PO4) release into the Mediterranean from basin-wide agriculture and urbanization, by using the agro-ecosystem model (LPJmL-Med). The model evaluation against observation data, and all implemented processes are described in detail in this manuscript.