# Natural Versus Anthropic Influence on North Adriatic Coast Detected by Geochemical Analyses
## 1 Introduction
### Study Area  
The North Adriatic Sea (NAS) is an epicontinental basin characterized by a global cyclonic circulation with seawater inflow to the northwest along the Croatian coast (EAC) and outflow to the southeast along the Italian coast (WAC) [9] (Figure 1). This general pattern is greatly influenced by winds, mainly Bora and Scirocco [11; 12], and by lateral freshwater inputs [13]. Freshwater runoff enters the NAS from eastern Alpine and northern Apennine rivers located mainly along the  
Figure 1: (**A**) Lithologic map of the Po River drainage basin (data from 1:1 Million Surface Geology—European Geological Data Infrastructure: [[https://egdi-v6.geology.cz/?ak=detailall&uuid=5729](https://egdi-v6.geology.cz/?ak=detailall&uuid=5729) ffdf-2558-48 fc-a5d2-645a0a010855]([https://egdi-v6.geology.cz/?ak=detailall&uuid=5729](https://egdi-v6.geology.cz/?ak=detailall&uuid=5729) ffdf-2558-48 fc-a5d2-645a0a010855)). Major Po contributor rivers are also indicated. (**B**) Schematic surface circulation pattern of the Northern Adriatic Sea. EAC: Eastern Adriatic Current; WAC: Western Adriatic Current [9]. Triangles represent S1, E1 (this work, red triangles) and AN2 (grey triangle) [10] coring sites.  
Italian coastline. The largest source of freshwater and sediments is represented by the Po River (mean annual discharge of 1500 m\({}^{3}\) s\({}^{-1}\)) [14; 15; 16]. The Po River catchment extends from the Central and Western Alps up to the northwestern Apennines and includes more than 140 Alpine and Apennine tributaries that discharge water and sediment into the Po River [17] (Figure 1). The hydrologic behavior of the Po River is characterized by the mixed Alpine/Apennine discharge regime resulting in two flooding periods in late fall and spring, due to intense precipitation and snow melting, respectively [18].  
Sediment accumulation rates range 1.2-30 mm/year with the highest value recorded in the study area, and then accumulation rates decrease southward and toward the open sea [15]. Several studies [18; 19; 20; 21] pointed out a decrease of the sediment supply in terms of both suspended and bed loads, from the Po and the Northern Apennines rivers, after 1945. An additional decrease was observed in the 1980s when the _Emilia-Romagna_ region underwent heavy urbanization of both coastal and inland areas, as well as other parts of the Po River plain [18; 19; 22; 23]. The Apennine rivers--which flow into the NAS encompassing the area between Ravenna and Rimini (Reno, Lamone, Bevano, Fiumi Uniti, Savio, Rubicone, Uso and Marecchia)--are characterized by smaller catchments areas. Their courses are almost straight, and their flow rate is subject to the rainfall regime resulting in very low discharges in summer, when hydric demand and evapotranspiration are the highest [20; 24; 25].  
Geochemical characterization of Po Plain late Quaternary deposits [17; 26; 27; 28; 29; 30; 31] document that they preserve fingerprints of the related catchment basins. In detail, nickel and chromium have been used as tracers of sediment provenance since Cr-rich (and Ni-rich) sediments have been found to be representative of the Po River drainage basin, whereas sediments with lower Cr and Ni values have been related to the Apennines supply [26; 28]. Their concentration is due to the contribution of ultramafic rocks in the Po River catchment (Figure 1). Although Cr and Ni could also be affected by anthropogenic sources, they seem to be minor, since comparable results were reported for present day Po River sediments and Holocene marine deposits in the area [27].