On the Geochemistry of Venice Lagoon Sediments. Scripps Institution of Oceanography SEDiment Research Program – SIOSED. A Background Report

In order to understand the biogeochemical processes of involved in the relocation of dredged channel sediments in the Venice Lagoon, Italy, the SIOSED (Scripps Institution of Oceanography SEDiment research group) has carried out a research program from March 2005 to November 2007. Sediments were cored at various locations in the Venice Lagoon. In addition sediments were dredged from a navigation channel and transplanted directly into banks at two shallow sites. The monitoring program was essential since sediment in the Venice Lagoon is often contaminated with various metals and organic pollutants in different concentrations; consequently, most of the sediment in the lagoon has been evaluated as potentially hazardous. The sediment classification of the lagoon is organized into three categories based on the concentration range of various contaminants. Concentrations of the categories are based on total concentration values and on potential toxicity of each single contaminant; therefore, the occurrence of only one contaminant above the range characteristic of a specific category associates the sediment to the next more contaminated category. As part of this multi-disciplinary program, potential changes in the geochemistry of sediments were studied in relation to their dredging and reuse, including both the chemistry of solid phases and of interstitial fluids of the sediments. The present program of studies has emphasized the study of both major elements and trace metals in the sediments. Results of SIOSED sponsored studies on the distribution of Hg and the processes involving the generation of pollutants such as methyl-mercury have been already been publishe