Management oriented mathematical modelling of Ria Formosa (South Portugal)

Abstract

1 - Ria Formosa is a large (c.a. 100 km²) mesotidal lagoon system included in a Natural Park, with large intertidal areas and several uses such as fisheries, aquaculture, tourism and nature conservation. Its watersheds cover an area of approximately 864 km2, with a hydrographic network of small and, mostly, ephemeral rivers. 2 - The Soil and Water Assessment Tool (SWAT model) has been applied to the catchments in order to simulate water discharges to Ria Formosa, providing forcing to a two-dimensional vertically integrated model, implemented with EcoDynamo – an object oriented modelling software – including hydrodynamics, water column, sediment biogeochemistry and growth models for some important benthic species. 3 - The main objectives of this work are to: (i) Analyse model performance in the light of available data; (ii) Evaluate the effects of dredging operations and changes in biomass densities of cultivated clams, on lagoon biogeochemistry and water quality. 4 - This work is part of a larger project where many possible management scenarios are being analysed following concerns expressed by the project end-users – Ria Formosa Natural Park authority. 5 - Results obtained so far suggest that bivalve rearing areas are probably being exploited close to their carrying capacity. Furthermore, it is apparent that some improvement on water quality could be achieved by reducing bivalve densities, without significant losses of harvest yields.