Atmospheric Deposition of Trace Metals in North Adriatic Sea

Abstract

Atmospheric bulk deposition of trace metals (Cd, Cu, Ni, Pb) was measured at two coastal urban sites (Cesenatico and Venice) in the north Adriatic Sea. Collection was carried out using polyethylene bulk passive samplers, samples being collected bi-weekly. Annual deposition fluxes of metals were calculated and compared with the Po river supply rates to the north Adriatic sea (surface area=25000 km2) and those of several rivers to the lagoon of Venice (surface area=546 km2). Atmospheric annual deposition at Venice was obtained by averaging data collected in the period 1993–97; Cesenatico values refer to 1995–96 depositions, measured in one coastal station and in one station 10 nautical miles offshore. Average north Adriatic fluxes (Venice+Cesenatico), in mg m−2 year−1, range from 0.15 to 0.22 for Cd, 4.5 to 11.3 for Cu, 1.4 to 3.5 for Ni, and 3 to 21 for Pb, and are similar to French coastal sites data. The atmospheric deposition observed at Venice was 2- to 7-fold higher than that of Cesenatico for Cu, Ni and Pb, and comparable for Cd. Compared with riverine inputs of respectively 0.42, 4.0 and 5.5 tonnes year−1, at Venice one–third of Cd (0.12 tonnes year−1), nearly half of Ni (1.9 tonnes year−1) and an almost equal amount of Cu (6.2 tonnes year−1) are atmospherically derived, whereas the deposition flux of Pb is estimated to be 11.5 tonnes year−1, i.e. 60% higher than the riverine input of 7 tonnes year−1. Comparison with Po river data shows that the atmosphere delivers 70% of Cd, 10% of Ni, 70% of Cu and an amount of Pb 2-fold higher than riverine inputs. The magnitude of the atmospheric input indicates that eolian deposition is an important contribution which cannot be neglected in the study of biogeochemical cycles of anthropic elements introduced in the north Adriatic Sea.