Three levels of salinity (5, 20 and 35 psu) were fully crossed with three levels of nutrients enrichment (NH4–N concentration was 32 μmol l−1 in all treatments, while three levels of PO4–P were tested: 6.4 μmol l−1; 2 μmol l−1 and 0.8 μmol l−1). Seawater nutrient concentrations were neglected, as they were relatively low (Table 1) compared to added nutrient concentrations. The tested salinity levels were obtained diluting the seawater with demineralised water. In all experiments, the nutrient enrichment as well as the tested salinity values were based on the values measured in the Mondego estuary between 1993 and 2002 (Table 1; Lillebø et al., 2005).
Higher nutrient concentrations were also tested in order to simulate a more eutrophic system.