Natural versus anthropogenic influences on the chemical composition of bulk precipitation in the southern Apennines, Italy: a case study of the city of Potenza

This paper presents new data on the chemical composition of precipitation in a selected area of the southern Apennines of Italy; these data are used to assess natural and anthropogenic contributions to the precipitation. The city of Potenza was used as a representative urban site, and the major and minor element (Na+, K+, Ca2+, Mg2+, NH4+,Cl–, NO3–, SO42– and Li+, F-, Br-, PO43-) and trace element (Zn, Fe, Al, Sr, Mn, Ba, Cu, Cr, V, As, Pb, Ni and Cd) concentrations of bulk precipitation from three different sampling sites within the study area were determined between June 2011 and May 2012. The majority of the collected rainwater has pH values higher than 5.6. The composition of this rainwater was dominated by Ca2+ the element with the highest volume-weighted mean concentration (VWA), followed by Na+, Cl–, Mg2+, NH4+, SO42–, NO3– and K+. The VWA of the trace metals decreased in the order Zn>Fe>Al>Sr>Mn>Ba>Cu>As>Pb. Neutralising factor (NFXi) values indicate that Ca2+ is the dominant neutralising cation within this rainwater, with lower contribution from Mg2+ and NH4+. The precipitation analysed during this study has a negligible marine influence as determined using Cl–concentrations as a proxy for the abundance of sea salts. Precipitation Fi values (marine fraction of element i) indicate that Na+ is the element with the highest seawater component, and we found partial marine contributions for the SO42–and Mg2+ concentrations within this rainwater. Enrichment factors (EF) of selected elements were calculated to identify the sources of non-crustal elements: K+, Mg2+, Fe, and Ca2+ are the only elements dominantly sourced from the crust, whereas Mn, Sr and Ba have highly variable EF values (10–100) suggesting that a small proportion of these elements was derived from anthropogenic sources in addition to a more significant crustal contribution. Cu, Pb, Zn, and As, elements that are commonly derived from anthropogenic sources, are highly enriched with respect to average crustal compositions, confirming that the concentrations of these elements within precipitation are significantly controlled by human activities.