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The analysis of nutrient concentrations in surface sediments is a reliable tool for assessing the trophic status of a water body. Nitrogen and phosphorus concentrations are strongly related to the sediment characteristics but are mainly driven by anthropogenic impacts. The results of the determination of total nitrogen and total inorganic and organic phosphorus in surface sediments of the lagoons and ponds of the northwestern Adriatic Sea (Marano-Grado, Venice, Po Delta, Comacchio Valleys, Pialassa della Baiona) show the merit of this approach. Indeed, when previous data are available, the ratio between the actual and background values can provide useful information on the trophic changes that have occurred in the most recent times, and the results can also explain the conditions present in less studied environments. In this context, numerous studies performed in the Venice lagoon since the second half of the 20th century during different environmental scenarios provide mean concentration ranges and propose the main causes of changes. The results of single datasets available for the other lagoons fall into scenarios that occurred in the Venice lagoon. At present, the most eutrophic basins are Pialassa della Baiona, the Po Delta lagoons and ponds and the Comacchio valleys due to industrial effluents, fish farming and clam harvesting, respectively, whereas the Venice lagoon is now experiencing environmental recovery.

The Lagoon of Venice covers a surface area of about 550 km2, roughly 80% of which is covered by water, about 10% by salt marshes and 5% by islands. The mean depth of the water column is about 1.2 m, with only 5% of the lagoon deeper than 5 m. It is connected to the Adriatic Sea through three inlets (Lido, Malamocco, Chioggia), which allow tidal flushing twice a day. The mean tidal range is 61 cm (calculated on 1986-2004), the largest in the Mediterranean. The majority of the lagoon can be classified as mixoeuhaline/mixopolyhaline according to the "Venice System" (Anonymous, 1959), with a mean salinity of about 30, ranging from marine (around 37), to mesohaline (5 ��� 18) near the bay-head river mouths (Zirino et al., 2014). Because of the shallowness of the lagoon, water temperature follows the seasonal trends of air temperature, with very low values during winter, although seldom freezing, to above 30��C during summer. From the biological point of view, the benthic communities of this meso/eutrophic ecosystem, mainly belong to the "Lagunaire Euryhaline et Eurytherme (L.E.E.)" biocenosis as defined by Peres and Picard (1964). These benthic communities are characterized by seagrass meadows (Zostera noltei, Zostera marina, Cymodocea nodosa), over than 300 species of macroalgae and over 800 species of macroinvertebrates. The phytoplankton communities are dominated by diatoms and phytoflagellates, while the zooplankton communities are characterized by the predominance of copepods and different larval forms of e.g. bivalves, echinoderms or benthic crustaceans. The nektonic communities are made both by resident species and by species that spend only a part of their life cycle in the lagoon (migratory and occasional visitors). The avifauna is characterized by ornithic communities nesting in salty grasslands and wintering throughout the whole lagoon basin. The research activities in the Venice Lagoon, that include analyses of environmental parameters and the study of biodiversity and ecology of phyto- and zooplankton, phyto- and zoobenthos and ichthyo- and avifauna, are aimed at understanding the long-term variability of the structure and the relationships between the components of this ecosystem and the resulting processes