Heavy Metals in Sediments from Different Environments of a Northern Adriatic Sea Area, Italy S. GUERZONI, M. FRIGNANI, P. GIORDANI, and F. FRASCARI Istituto di Geologia Marina del Consiglio Nazionale delle Ricerche Via Zamboni 65 40127 Bologna, Italy ABSTRACT / Sediments from different environments of an area di- rectly affected by the discharge of the Po River and 13 other minor rivers have been studied Three main sources of metals and several distribution mechanisms can be identified Concentration profiles of metals in a core allow one to establish background levels of fine- grained sediments for Cd, Hg, Pb, and Zn Seabed sediments do not appear to be very polluted, mainly because of desorption and dilu- tion processes Introduction In the last decades, human activities have increased the quantity of heavy metals circulating in the environment. Since sedimentation of particulate material is one of the most impor- tant fluxes in the aquatic system, a knowledge of trace metal concentration in sediments can play a key role in detecting sources, degree of pollution, and distribution mechanisms, especially in coastal areas. For many years, the Adriatic Sea has been regarded as a heavily polluted sea because of its morphology and dynamics. Furthermore, the influence of the Po River, which crosses highly industrialized areas, has been considered very harmful to the whole basin. Only in the last ten years, however, have quantitative data become available. Stirn and others (1974) summarized the pollution problems of the Adriatic Sea with an interdisciplinary approach. Gran- cini and co-workers (1976) used NAA to determine Cr, Co, Hg, and Zn in seawater and in the sediments collected off the Po River delta and to the north of it. Paul and Meischner (1976) studied the whole basin in terms of heavy metals, organic carbon, and carbonates, also discussing mineralogical and sedimentological considerations. Concentrations of ten metals in water, marine organisms, and sediments from the Adriatic were reported by Kosta and others (1978). Anconelli and others (1980) and Benetti and co-workers (1979) analyzed two different environments of the area: the heavily polluted salt marshes near Ravenna's oil refinery and the unpolluted coastal sediments near Ancona, respectively. Recently, Donazzolo and associates (1981) presented a careful study of the contamina- tion by trace metals in the surface sediments of the Gulf of Venice. Frignani and co-workers (1978) and Frascari and others (1979) provided preliminary results from nearly the same area as that presented in this work. The aim of this study is to provide information on the distribution, enrichment, and transport patterns of 11 trace metals in the surface and core sediments of the area directly affected by the Po River and to assess the relative importance of the minor sources. For a better understanding of the results, some textural and geochemical characteristics of the sediments have also been considered. Study Area The upper Adriatic Sea is a shallow shelf area (maximum depth 50 m). Although the wave-cut slopes next to the shore- line are steep (3.8 m/kin in the first 2 km), a typical profile is characterized by a very gradual increase in depth: the average slope from the shoreline to the 30-m isobath is 1:800 (Nelson 1970). The studied area is the part of the northern Adriatic Sea between Ancona and Chioggia, not extending further than 20 km from the coast (Fig. 1). The coast is characterized by three geomorphological (physiographic) units, from south to north: (a) a rocky coast with small beaches from Ancona to Cattolica (where the Apennines are close to the sea); (b) a long arcuate sandy coast, with the outlets of small minor rivers, from Cattolica to Volano; and (c) the delta region, which protrudes onto the shelf, including the Adige and Brenta mouths at its northern end. The greatest depth encountered in this area was 33 meters. The terrigenous material transported to the sea derives from different petrographic provinces. The sediments of the Brenta and Adige rivers originate in the eastern Alps, where prevailing limestones and outcrops of basic igneous rock are present. The sediments carried by the Po River originate in the central and western Alps and northern Apennines, where outcrops of various types of rock exist. The sediments of some minor rivers debouching to the south of the delta originate in the northern Apennines where terrigenous, incoherent outcrops and subor- dinated limestone prevail. In a shallow basin such as the northern Adriatic Sea, the suspended sediments distribution is due to the general current system and to the meteorological and marine conditions. The hydrodynamics of the area are complex (Nelson 1970). Fresh waters debouching from the Po River delta interact with the cyclonic surface circulation of the marine basin. Water masses generally flow toward the south and east, but different patterns Environ Geol Water Sci Vol 6, No 2, 111-119 9 1984 Springer-Verlag New York Inc