ACCUMULATION RATES AND SOURCES OF SEDIMENT IN A NORTHERN ADRIATIC COASTAL LAGOON BASED ON RADIOISOTOPIC TRACERS (137Cs AND 210Pb)

This paper focuses on sediment accumulation rates determined on sediment cores collected from three locations in a northern Adriatic coastal lagoon in Italy, using bomb fallout and natural radionuclides (137Cs and 210Pbxs) along with supporting measurements of organic carbon (OC). 210Pbxs and 137Cs fluxes measured on sediment cores, and sediment nuclide inventories, maximum detectable depths, and sediment accumulation rates, calculated using both 137Cs and 210Pbxs, are explored. Radiotracer 210Pb, contaminant mercury, and relative and absolute compositions of sediment fluxes are used to infer the contributions of allochthonous sources and autochthonous production of sedimentary particles. Mercury accumulation was enhanced in the pre-1980 sediments decreasing towards present days. These recent sediments with enhanced mercury concentrations come from acetaldehyde synthesis with Hg-based technology, employed in a local petrochemical complex from the 1958 to middle 1970s. Variations in sediment core profiles of Al, Fe, and organic carbon were consistent, indicating changes in bulk sediment composition. The pollution intensity of the lagoon ecosystem was determined by the enrichment factors, which show that the area is moderately polluted to polluted.