Geochemical characteristics of inner shelf sediments along the Adriatic ialian coastline

Grain size and geochemical data of surface shelf sediments collected in the database of the Sistema Difesa Mare (Si.Di.Mar.) of the Ministry of the Environment for the whole Italian Adriatic coastline were analysed for the period 2001-2006 in order to define base level concentration of trace elements vs. anthropogenic signature according to sedimentary characteristics (e.g. grain size and organic carbon) and location of the investigated stations. Determination of major (Al and Fe) and trace elements (Zn, Cr, Ni, Pb, Cu, V and Hg) allow evaluation of the deposition of various chemical elements normally associated with anthropogenic activities. The median of measured values was obtained for each station for the investigated period and used for comparison. In order to compensate for the natural sediment variability (grain size and source area), trace element were normalised to mud and Al.According to geomorphological characteristic and depositional environment, the sampling stations can be subdivided into 4 groups: 1) Friuli and Veneto = 10-20m water depth, high mud (>50%) and OC (0.5-1.5%) content, Al (63-20g/kg) and Fe (135-11g/kg); 2) Emilia Romagna (ER) and Marche = 7-12m water depth, high (ER=>50%) to medium (Marche =ca. 30%) mud content and high OC (0.5-1.5%) content, Al (17-4 g/kg) and Fe (22-9 g/kg); 3) Abruzzo and Molise = 4-7m water depth, low mud content (<20%) and very low (Abruzzo=<0.3%) to high OC (Molise=1-1.5%) content, Al (4-1g/kg) and Fe (9-5g/kg); 4) Puglia = 3-10m water depth, very low (<10%) mud content except for Gulf of Manfredonia (MN) stations (>75%) and high (1-2%) OC content, Al (0.1-0.03g/kg) and Fe (4-1g/kg).Al and Fe are very well correlated in all stations, but the regression line follows two different paths possibly reflecting different geochemistry of the drainage basins (Friuli and Veneto vs. other regions). Friuli always shows the highest concentrations for Cr, Ni, V, Pb and Zn. Cu shows high concentrations in Friuli, Veneto and ER and to a lesser extent in Marche and muddy stations of Puglia (MN). Veneto shows high values for Zn, Cu and V and lower concentrations of Cr, Pb and Ni except for P.to Lido Nord (LN) always showing very high concentrations of all trace elements. ER shows high concentrations of Cu, Ni and Zn and lower for Cr and Pb. Marche shows relatively high Zn, Ni and Cu and lower Cr, V and Pb. Abruzzo and Molise show similar high concentrations of Zn and V. Puglia (MN) displays high values similar to Marche for Cu, Zn and Ni.Cr, Cu, Ni, Pb, Zn show a direct correlation with mud concentration whereas for Cd, Hg, V and As the correlation is not straightforward. Generally, samples with mud content <50% show low to medium trace elements concentrations. Samples with mud content >70% show very different contentrations from low to medium values as in Puglia (MN high only for Cu and Zn) to very high values as in Friuli and Veneto (in particular LN) and to a lesser extent ER.After normalisation for mud to overcome grain size influence, LN station still shows very high metal concentrations in the N Adriatic. On the contrary, in the central Adriatic, Abruzzi and Molise show an enrichment of V, Zn, Ni and Pb. Puglia stations result very high (no muddy sediment) for all metals, in particular at Bari (BA), Brindisi (BR) and Barletta (BL).Al shows the highest concentrations in Friuli then progressively decreases southward to almost null values in Puglia. Hg and As results not correlated with Al as well as Cd. V shows direct correlation with Al in Friuli and Veneto while Zn, Ni and Pb in ER, Veneto, Friuli, Marche and Abruzzo. Cr shows good a correlation in ER and Friuli ad Cu in ER, Marche and Abruzzo.After normalisation for Al, only Molise and Puglia and LN in Veneto show high concentrations of heavy metals. From ER southward, Ni, Cu Cr and Zn still show high concentrations suggesting the influence of the "anthropic" load of the Po River, while V increaes from the Marche southward.