210Pb and 137Cs as chronometers for salt marsh accretion in the Venice Lagoon – links to flooding frequency and climate change

Five salt marsh sediment cores from different parts of the Venice Lagoon were studied to determine their depositional history and its relationship with the environmental changes occurred during the past 100 years. X-radiographs of the cores show no disturbance related to particle mixing. Accretion rates were calculated using a constant flux model applied to excess 210Pb distributions in the cores. The record of 137Cs fluxes to the sites, determined from 137Cs profiles and the 210Pb chronologies, shows inputs from the global fallout of 137Cs in the late 1950s to early 1960s and the Chernobyl accident in 1986. Average accretion rates in the cores are comparable to the long-term average rate of mean sea level rise in the Venice Lagoon ( 0.25 cm y−1) except for a core collected in a marsh presumably affected by inputs from the Dese River. Short-term variations in accretion rate are correlated with the cumulative frequency of flooding, as determined by records of Acqua Alta, in four of the five cores, suggesting that variations in the phenomena causing flooding (such as wind patterns, storm frequency and NAO) are short-term driving forces for variations in marsh accretion rate.