Particle transfer along the modern mud-wedge of the Adriatic Sea by down-core sediment-bound metal distributions

In the marine environment, anthropogenic contaminants are mostly adsorbed onto the particulate matter, which mainly accumulates close to the source areas. Their concentrations and inventories gradually decline with increasing distance from the inputs. In many sedimentary systems, such as the Adriatic Sea, the magnitude of along-shelf particulate transport is much greater than the corresponding across-shelf component. In these systems, the riverborne contaminated material follows the dispersion pattern controlled by the main currents and accumulates when and where the energy of water mass decreases. Thus, the study of the contaminant fate can contribute to elucidate the depositional processes of river-borne material from the riverine source to the final sink into the sedimentary record. High Zn and Pb concentrations have been previously found in the northern Adriatic sector and related to anthropogenic influences. In this study, we used the vertical profiles of Pb and Zn, measured in 210Pb-dated sediment cores collected along the modern mud wedge of the western Adriatic Sea, to reconstruct their historical evolution during the last century. The temporal trends of trace metals in the Adriatic sediments coincided with the industrial production activities and their past use. Our results showed that Zn and Pb concentrations started to increase from the World War I. The increasing contamination signal of these trace metals propagated southward as far as 450 km with a growing delay. A reduction of trace metals from mid-1980s was also observed, related to the implementation of stricter environmental regulations on chemical wastewaters. Based on the delay of propagation of the signal of the onset and decreasing shift of Zn and Pb recorded in sediment cores collected along the Po River dispersion system, a first estimate of ~10 years is provided for the mean transfer time of particles travelling from the Po River mouth to the Gargano subaqueous delta.