Sacca di Goro Lagoon

The Sacca di Goro is an eutrophic lagoon located along the North Adriatic coast of Italy in the southernmost part of the Po River delta. The lagoon was investigated in 1992, when annual and monthly budgets were estimated with a single-box, single-layer LOICZ model. Exchange flows were obtained from the application of COHERENS (COupled Hydrodynamical Ecological model for REgioNal Shelf seas) 3-D model. A mean water residence time of 2 days was estimated. The annual mean ΔDIP was positive (0.01 mmol m-2 d-1) whereas ΔDIN was negative (-20 mmol m-2 d-1), thus the system can be considered as a source of DIP and a sink of DIN. Budgets for DOP and DON were calculated from April onwards (except October). Dissolved nutrients from marine and freshwater sources were dominated by the organic forms of P and the inorganic forms of N. In 1992, the lagoon acted as a net sink of DOP and a net source of DON. The imbalance between input and output of nutrients conformed to the seasonal trends of macroalgal biomass growth and decomposition. From March to June macroalgal blooms were coupled to negative ΔDIP (except for April), ΔDOP and ΔDIN. In July and August, during the decay phase of macroalgae, ΔDIP, ΔDOP and ΔDON were positive indicating a high organic matter mineralisation and a release of inorganic and organic dissolved nutrients. The C, N and P budgets were estimated considering the C:N:P ratios of both macroalgae and phytoplankton. On an annual basis, the lagoon can be considered as slightly autotrophic, with a net ecosystem metabolism (p-r) of about 3 mmol C m-2 d-1. The net nitrogen budget (nfix-denit) was negative, indicating a dominance of denitrification over N-fixation even with values much higher than those expected in this ecosystem.