Santa Giusta occupies an area of 8 km2, with a mean depth of 1 m. Rio Pauli Maiori and Rio Pauli Figu are the two primary freshwater inputs, both located on the lagoon’s east side (Fig. 1b). Santa Giusta also experienced substantial human modification during the 20th century, resulting in profound ecosystem alterations. The Pesaria channel, which originally connected the lagoon to the sea through the Tirso River outlet was deepened, widened, and separated from the river. An industrial harbour was subsequently built, which was connected to the lagoon through an industrial canal controlled by bulkheads. A fish catch system was constructed in the final portion of the Pesaria channel. In 1995, a diversion canal for Oristano urban wastes (the main urban town in the catchment) was built. Despite the canal, the high inorganic nutrient concentrations and algal biomass remained unchanged (Sechi et al. 2001). Macrobenthic algae and phytoplankton are the most important primary producers in Santa Giusta. Sechi et al. (2001) reported several fish kill events associated with harmful algal species blooms in this lagoon. Santa Giusta sediments show high levels of TOC and OM, especially in surface layers (1‒2 cm) in the north and south lagoon areas (Magni et al. 2008). Lugliè et al. (2002) showed Santa Giusta sediment grain sizes exhibited a degree of heterogeneity, but the finer fractions were primarily located in the south-central lagoon area, consistent with central and peripheral canals dredged in the 1970s to facilitate seawater flow into the lagoon.
From 1990, the trophic status of the lagoon was always kept under control. It was thus possible to monitor the course of the trophy after the waste was diverted. Even recently (summer 2010) serious events of fish death there were. A long-term series of data is available and derives from high-frequency measurements and samplings to assess environmental and biological parameters. In particular the data concern the main trophic descriptors (Secchi depth, temperature, pH, conductivity, dissolved oxygen and saturation, alkalinity, NH4-N, NO2-N, NO3-N, total nitrogen, soluble reactive phosphorus, total phosphorus, dissolved silica) and phytoplankton abundances, as chlorophyll a, cell densities and biomass, class and species composition.
