Ria Formosa is a large (c.a. 100 km2) mesotidal lagunary system with intertidal areas with conflicting uses
such as fisheries, aquaculture, tourism and nature conservation. Its watersheds cover an area of
approximately 864 km2, with a perimeter of 166 km and a maximum altitude of 522 m. Land use may be
classified into six major groups: 1) urban, 2) agricultural, 3) forest, 4) rangeland and pastures, 5) wetlands
and 6) water bodies. The main objectives of this work are to: (i) Evaluate the relative importance of land
drainage, waste water treatment plants (WTP) and water exchanges across the lagoon inlets, for nutrient
dynamics; (ii) Analyse management scenarios related to changes in lagoon bathymetry and their potential
effects on system dynamics. The Soil and Water Assessment Tool (SWAT model) has been applied to the
catchment areas in order to simulate water discharges into Ria Formosa providing forcing to a twodimensional
vertically integrated coupled physical-biogeochemical model, implemented with EcoDynamo –
an object oriented modelling software. This model includes water column and sediment processes as well as
their interactions and several biological sub-models (e.g. phytoplankton dynamics and bivalve growth).
Obtained results suggest that the river network may have a significant effect on lagoon concentrations, in
spite of the relatively low river flows, due to the high ammonium and nitrate loads. Scenarios reflecting
increases in lagoon bathymetry through dredging operations suggest an increase in lagoon water washout
time with potential impacts on water quality and impacts at a scale of tens of km. The obtained results are
being used by the Ria Formosa Natural Park authority for management purposes and may be useful to
feedback future updates of the watershed management plans, within the scope of the European Union Water
Framework Directive. The use of a lagoon scale models is therefore justified in this wor
