The LOICZ biogeochemical budget approach applied to Ria Formosa lagoon, - Algarve, South Portugal

Abstract

The Ria Formosa lagoon is a mesotidal lagoon located in the south coast of Portugal. A single-box, single-layer LOICZ model was applied to data in 1987 and 1999 to estimate the biogeochemical budget of the Ria Formosa lagoon. Water exchange time in the lagoon was estimated to be about 2 days. Both the fluxes of DIP and DIN were negative, indicating that the system acts as sink of both DIP and DIN. Stoichiometric calculations assumed nutrient ratios in both Redfield proportions (C:N:P=106:16:1) and in proportions appropriate for macroalgae (C:N:P=335:35:1). Overall, the lagoon can be consider as “autotrophic”, with a net ecosystem metabolism (p-r) 8.4 mmol C m-2 d-1 considering Redfield ratio. Nitrification dominated over nitrogen fixation since it was positive in both cases. The Ria Formosa lagoon is sensitive to the tide. The water and nutrient budget in the lagoon has strong seasonal variation, especially the dry and rainy seasons. According to the standards of EEA, the Ria Formosa lagoon is between oligotrophic and mesotrophic.