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Grain-size and redox potential distributions in sediments were used as tracers to investigate environmental conditions in a shallow water area of the Venice Lagoon subjected to summer anoxic events. Data are presented showing different environmental characteristics within the study area. The results illustrate the reliability of these tracers to acquire a preliminary knowledge of the aquatic ecosystem behavior. Even small differences in morphology and hydrodynamics are observable because of the marked influence they exert on sediment parameters.

Sediment and heavy metal accumulation in a small canal, Sediment and heavy metal accumulation were studied in a canal of Venice (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 210 Pb and 137 Cs are present throughout the sediment cores and inventories of both radionuclides are greater toward the canal margins than in the center, indicating enhanced deposition along the margins. The margin cores show a 137 Cs peak at 30 to 45 cm depth that we attribute to input from the 1986 Chernobyl accident. Two of the cores are sufficiently long to show increases of 137 Cs at depth, probably related to the 1963 global fallout input. The 137 Cs profiles are consistent with accumulation rates of ∼2 to 3 cm y −1 . Excess 210 Pb activities show little variability in the upper 25 to 45 cm of the margin cores, and decrease by a factor of ∼2 over the next ∼30 cm of the cores. As the canal shoaled with sediment deposition, resuspension of sediment by boat traffic along the canal center likely produced increased deposition along the margins. Concentrations of heavy metals fall within the average of values determined for the whole canal network. Arsenic, cadmium, copper lead and zinc show clear decreases toward the sediment-water interface, suggesting recent reductions of contaminant inputs.