## 2 Study Areas and Historical Information
### The Venice Lagoon  
The Venice Lagoon (Figure 1b) is part of the Adriatic Sea in northeastern Italy. It has a surface area of 550 km\({}^{2}\), an average depth of 0.6 m, and a salinity of about 25-36% [37]. The water exchange with the Adriatic Sea (1.6-5.2 \(\times\) 10\({}^{8}\) m\({}^{3}\) day\({}^{-1}\)) occurs through tidal cycles at three entrance channels that divide the lagoon into three basins (Lido, Malamocco, and Chioggia), while freshwater (30.7 m\({}^{3}\) s\({}^{-1}\)) enters the lagoon through about 24 tributaries [37; 38]. The morphology is characterized by a network of canals of various depths, mud flats, tidal marshes, and islets that were first created during the maximum Holocene transmission 6000 years BP [39]. The sediment deposition rate in the lagoon is quite variable, and is higher in the northern sector, due to the supply from the Lido inlet [40; 41]. Bottom sediments are composed almost exclusively of very fine sand and silt. Clay contribution is higher in the inner part of the lagoon and reflects the water dynamic: maximum at the inlets and within the main canals, and lower close to the mainland [38].  
Figure 1: Location of study areas and sampling sites: (**a**) Augusta Bay with sampling sites, dredged and disposal areas, and locations of industrial settlements; (**b**) Venice Lagoon, with a snapshot over the Industrial Area of Porto Marghera. Satellite images are taken from Google maps.  
The Venice Lagoon is a unique shallow aquatic ecosystem whose complex morphology has been profoundly modified over time by human interventions. In particular, during the last century it has experienced a general degradation with the deepening of tidal flats (present rates of sediment loss are estimated to be 0.8 Mm\({}^{3}\) y\({}^{-1}\)) and the reduction of salt marsh areas (from 168 km\({}^{2}\) in 1930 to 60 km\({}^{2}\) in 2002) [39; 42]. In addition, the development of economic activities on the mainland have led to further changes: (1) the construction of the 1 st Industrial Area of Porto Marghera at the beginning of the 20 th century; (2) the excavation of the navigation canal Vittorio Emanuele III in 1930; (3) the building of the trans-lagoon bridge in 1934; (4) the development of the 2 nd Industrial Area after World War 2; (5) the excavation of the navigation canal Malamoco Marghera, in 1969 [28]. More recently, the construction of the controversial _Modulo Sperimentale Elettromecanico_ (MOSE, Italian for Experimental Electromechanical Module) began in 2003 at the lagoon's inlets, with the aim of protecting the city of Venice from high tides (_Acqua alta_ in Italian) through isolation from the adjacent Adriatic Sea [43] and is now fully operative.  
Until the 1970s, Porto Marghera was one of the most important industrial areas in Italy, with plants for the production of chloro-alkali, sulfuric acid, ammonia, fibers, fertilizers from phosphoric, glass, coke, paints, detergents, firebricks, Al from bauxite, and the recovery of Zn and Cd from sphalerites [6; 28; 38]. The contamination of lagoon waters and sediments began soon after the first economic development, when industrial, urban, and agricultural discharges were disposed freely into the lagoon [41]. The situation became so serious that, at the end of the 1990s, a trial against managers of the petrochemical plants began. The defendants were charged with pollution and environmental disaster by polychlorodiphenyl dioxins and furans (PCDD/Fs) in the industrial area of Porto Marghera and in the whole Venice Lagoon. The main subject of the lawsuit was the production of vinylchloride monomer (VCM) that, at that time, was considered the principal industrial source of PCDD/Fs in this region. Researchers from CNR-ISMAR Bologna were involved for their expertise in order to provide scientific evidence in support or against this hypothesis, and the results of their studies served in the court hearing as a technical report.