Coupled modelling of the interaction between dissolved substances emitted by Minho and Lima estuarine outflows (Portugal)

The Minho and Lima estuaries comprise important and sensitive protected areas valuable for species and habitats conservation, constituting a reference for ecotoxicological and water quality studies. These estuaries, separated only by 20 km, are very productive systems with high metabolic rates that strongly influence the cycle of nutrients and the ecology of NW Iberian coast. This study aims to understand the propagation of Minho and Lima estuarine plumes in order to investigate the effects of buoyancy on the interaction between dissolved substances emitted by their outflows and its impacts on regional productivity. Using the Delft3D model, a deeper analysis of the intrusion and dynamics of outflows of these adjacent estuaries was performed, through the simulation of trajectories of passive tracers emitted in each estuary, considering river discharges and wind stress. The results show an interaction between these estuaries, both during the summer and the winter seasons. Both estuarine outflows tend to move southward in response to the predominant north wind in the summer season, while in winter the opposite is observed. The northward outflows tend to be transported very close to the coastline, while the southward and westward is diverted offshore. The estuarine outflows interaction promotes exchanges of physical-chemical properties and nutrients between these estuaries, generating ecological advantages for the smaller one. These results showed that the numerical model used accurately describes the dynamical processes in these estuarine systems, being essential for a proper assessment of the effects of forcing drivers and providing relevant information for coastal zone planning and management.