Hydrodynamical and biogeochemical modelling of the highly vulnerable Mar Menor coastal lagoon

The Mar Menor is the largest hypersaline coastal lagoon in Europe, located in the semi-desertic south-east of the Iberian peninsula. This lagoon provides a variety of ecosystem services and resources to the community but, although it has been traditionally considered oligotrophic, in recent decades it has suffered drastic changes and degradation caused by human activities, including agriculture, mining and tourism. In the early 1990s, the lagoon began to receive high inputs of nutrients and organic matter due to changes in agricultural practices in the watershed. Due to the complexity, heterogeneity, and particular homeostatic mechanism of the system, eutrophication symptoms were not evident until the summer of 2015 and early 2016. Although the system recovered quickly after the first eutrophication crisis, several hypoxic events have happened since (in 2019 and 2021) causing massive death of fishes and moluscs.

In order to better understand and predict the functioning of the Mar Menor, and to provide the necessary tools for risk management, a comprehensive modelling effort has been launched in the framework of the BELICH project. This project, funded by the Framework of Priority Actions for the Recovery of the Mar Menor (MAPMM), aims to both enhance our understanding of the physical and biological processes occuring in the lagoon and to provide short term forecasts to support decission making under extreme events.

The modelling system consists in three modules to represent hydrodynamical, biogeochmical and land hydrology processes. The hydrodynamical module is based on the Symphonie model and uses a very high resolution configuration with curvilinear coordinates to simulate the evolution of circulation, temperature, salinity and sea level. This module feeds ECO3M-S, a biogeochemical model of intermediate complexity which includes several types of phytoplankton with flexible stoichiometry, several groups of zooplankton and bacteria. Finally, the inland waters contribution in terms surface and underground water and nutrient supply is simulated with the WaterpyBal and HEC-HMS models.

After a careful calibration and validation procedure, this system is being used to characterize the evolution of the lagoon under mean conditions and during extreme events potentially leading to ecological crises. Also, the system is being run in a pre-operational mode to produce 3-days forecasts and to produce key indicators that can support stakeholder actions. In the presentation, the main results of the system will be presented and its potential usefulness for decission support will be discused.