Carbon, nitrogen, and sulphur isotope analysis of the Padanian Plain sediments: Backgrounds and provenance indication of the alluvial components

This work reports an ab initio study on the carbon (C), nitrogen (N), and sulphur (S) elemental and isotope compositions of the Padanian Plain sediments collected in the province of Ferrara (Northern Italy). The investigated sediments were already characterized by previous research that highlighted a bimodal provenance, as some sediments are from the Alpine chain and were conveyed to the plain by Po River, whereas others are from the Apennine chain and were conveyed to the plain by the Reno River. This information was obtained considering the concentration of heavy metals retrieved from hundreds of X-ray fluorescence analyses available in the literature, whereas CNS elemental and isotope compositions are unknown. These tracers are generally considered scarcely useful to identify the sediment provenance, as influenced by multiple environmental factors. However, this work challenges these assertions observing that 13C/12C, 15N/14N, 34S/32S are significantly different in Po and Reno River sediments. Our hypothesis is that the CNS geochemical signal is 1) mainly regulated by the organic fraction included in the alluvial sediments, and 2) these organic fraction have in turn a specific composition in the distinct source catchments. More in general, the presented data increase the knowledge on the local elemental and isotopic backgrounds. This is important because many pollutants contain significant CNS concentration and specific isotope composition. Therefore, they serve as baseline and will provide new tools to recognize possible anthropogenic anomalies in the studied area.