Geochemical characterization of surface sediments from the northern Adriatic wetlands around the Po river delta. Part I: Bulk composition and relation to local background

•Geochemical characterization of surface sediments in the Po river deltaic system•Mixture of carbonate and clay fine grained sediments, organic matter variable and influential•The trace elements higher than the background in some sites: Ba, Cr, Cu, Sr, Pb, Zn, V•Two lagoons closer to the town of Ravenna are contaminated by Cr, Cu, and Zn.•Lead shot can explain highest levels of Pb in some sites for a long time devoted to hunting.

The impact of heavy metal pollution on coastal wetlands is a matter of concern worldwide. In the Po Delta (Italian North Adriatic coast) human presence around wetlands has increased considerably in recent years. This study assessed the geochemical composition of surface sediments of several wetlands within the historical Po deltaic system, and the influence of anthropogenic activities on the metal levels in the sediments. Eighty-nine samples were collected from 7 sites, and analysed for major and 16 trace elements using X-ray fluorescence and the results compared to background values obtained from bottom cores drilled near the wetlands. The Enrichment Factors (EFs) were calculated to evaluate metal contamination. In general, sediment composition were found to be consistent with a mixture of carbonate and clay, in agreement with the background composition. However there were some exceptions with some samples found to be enriched in organic matter (OM) and a few samples richer in carbonate than the background. The bulk composition is mainly characterized by the fine-grained fraction. The concentrations of Ba, Cr, Cu, Pb, Rb, Sr, Zn, and V exceeded background values in one or more sites. Copper and Zn enrichments were of anthropogenic origin, high concentrations of Ba, Rb, Sr, and V were the consequence of natural processes, while Cr peaks were likely to be a result of both natural and anthropogenic causes, depending on the site. Lead was generally high, reaching some unexpected high median EFs and a number of peaks. Lead in many sites, and Cu and Zn enrichments in the most polluted sites are preferably controlled by OM. One of the most polluted sites showed alarming peaks of Cr, and contamination of Cu and Zn involves the southern lagoons, due to industrial inputs from Ravenna and local settlements. Lead shot are widely dispersed in all wetlands and this may explain the highest levels found of Pb in the study area.