Spatial distribution of elements in near surface sediments as a consequence of sediment origin and anthropogenic activities in a coastal area in northern Italy

The study reports the results of a geochemical survey in a coastal area of northern Italy with focus on the distribution of chemical elements in near surface sediments as result of both sediment origin and anthropogenic activities. In addition to emphasizing the source-to-sink element dynamics in the area, the main purpose of this paper is to ascertain if anthropic presence could have altered the composition of near surface sediments in urban and industrial areas. We considered 173 sampling sites, and collected soil material from a depth of 90–110 cm. Major and trace elements assessment on milled 2 mm fraction was conducted using WDXRF for Al, As, Ba, Ca, Ce, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Nb, Ni, P, Pb, Rb, Si, Sr, Th, Ti, V, Y, Zn and Zr. In addition, Loss On Ignition (LOI) was determined. Principal component analysis (PCA) and cluster analysis (CA) were performed for data interpretation. The distribution of element concentration is heavily related to sediment origin. The major presence of Al, Fe, K, LOI, Mg, Nb, Rb and V characterizes alluvial plain sediments. These materials of Apenninic origin have a finer texture and a major presence of carbonates in respect to the other sediments of the area. Coastal sediments display a general wider range of variation in element concentrations (i.e. Al, Ca, Cr, K, Mg, Mn, P, Si, Ti and Zr) due to a dual origin. In particular, the greater Cr, Mn and Zr content is related to sediments enriched by heavy minerals (e.g. garnet, chromite, zircon) of Alpine origin, while the lesser concentrations trace back to Apenninic origin. Near surface sediments of urban and industrial areas always contain higher Cu, Pb and Zn concentrations with respect to the same sediments not impacted by urban and industrial settlements. This is likely a consequence of the movement of materials made by men over the last 2000 years. These results suggest that the adopted depth of sampling for the calculation of background values might need to be increased in urban and industrial areas to reach unaltered near surface sediments.