Anthropogenic contaminants in Venice Lagoon sediments and their pore fluids: Results from the SIOSED Project

Investigations of sediment geochemistry and interstitial water chemistry during SIOSED (Scripps Institution of Oceanography Sediment Research Project) revealed information about the characteristics and depth range of contamination in sediments associated with dredging operations in the Venice Lagoon, Italy. Results from gravity cores indicate that contamination ranges larger and deeper in sediments associated with Porto Marghera and the Venice Industrial Zone compared with sediments at greater distances from dredged shipping canals or pollution sources. The effects of sediment re-deposition were evaluated from a pore water chemistry study of artificial banks constructed by placing dredged canal sediments on top of background sediments. Rapid decreases in dissolved sulfate associated with increases in alkalinity, sulfide, and nutrients, such as ammonium and phosphate, indicate that sediment dredging led to enhanced bio-chemical diagenesis of organic matter near the surface of the re-deposited sediments. Continued diagenesis of organic matter in re-deposited sediments maintained extrema in alkalinity, dissolved sulfate, sulfide, and ammonium. The artificial banks retained their pore water signatures over the duration of the project. Sediment redistribution can thus cause important changes in pore water profiles, as observed from the chemistry in long cores studied in this program.