Abstract

 Sediment and heavy metal accumulations were studied in the Venetian canal of Rio di S. Angelo, that has typical characteristics of medium-to-small canals with respect to dimensions, boat traffic and pollution sources. The tidal dynamics are particularly weak in this ~5 m-wide canal. Four cores were collected across a section and five additional cores were collected from the longitudinal axis. The canal was dredged in the late 1950s, and therefore the collected cores represent approximately 40 years of deposition. Excess 210Pb and 137Cs inventories are greater toward the canal margins than in the centre, indicating enhanced deposition along the margins. The margin cores show a 137Cs peak at 35 - 50 cm depth that we attribute to input from the 1986 Chernobyl accident. Two of the cores are sufficiently long to show increases of 137Cs at depth, probably related to the 1963 global fallout input. The 137Cs patterns are consistent with accumulation rates of 3 to 4 cm/y toward the canal margin and <2 cm/y in the centre. Long-term rates (based on the 137Cs trend at depth in the cores) are ~2 cm/y along the canal margins, suggesting that rates have increased over time. As the canal shoaled with sediment deposition, increases in re-suspension of sediment by boat traffic along the canal centre likely produced increased deposition along the margins. Excess 210Pb activities show little variability in the upper 25 - 45 cm of the margin cores, and decrease by a factor of ~2 over the next ~30 cm of the cores. These patterns are consistent with the increase in accumulation rate over time suggested by the 137Cs profiles. Concentrations of heavy metals fall within the average of values determined for the whole canal network. Arsenic, Cd, Cu, Pb, Zn show clear increases with depth, suggesting a reduction of contaminant inputs starting from the 1970s.