Contaminated sediments from dredging activities as modern turbidites: geochemical signatures in box-core sediments from the Augusta area, Ionian Sea, Sicily

The Augusta area (SE Sicily) is one of the most industrialized and contaminated coastal environments in the Mediterranean region, having a relatively high influx of unregulated industrial effluents. Valuable sets of geochemical data (major elements and trace metals), obtained from box-core sediments collected along a transect from the Sicilian coastal zone seawards of Augusta and dated via 210Pb and 137Cs, indicated increased metal contamination (notably Hg) since ca 1940-1950, related to the industrial development of the area. Metal enrichment is considerable in the coastal sediments, being significantly in excess (for Hg and Pb) of background values estimated for the Strait of Sicily. Moreover, investigations of benthic foraminifera assemblages showed a reduction in foraminiferal abundance, increasing percentages of tests with various morphological deformities, and dominance of opportunistic species in more recent sediments. These findings can be correlated to the strong anthropogenic impact. The results obtained support the idea that the pollutant impact is not only confined to the coastal area, but has also affected the open sea environment. At offshore core sites, repeated abrupt Hg enrichments are roughly concurrent with positive Gd anomalies and significant increases of TOC with substantial proportions of land-derived organic material, indicating that the region experienced changes in natural sediment source/composition induced by repeated discharge of contaminated dredged materials from polluted coastal areas. Consistent with the geochemistry of recent turbidites, these anomalous sedimentary inputs have induced changes in the sediment redox environment, shown by distinct Mn peaks and negative Ce anomalies.