Links between hydrology and sedimentology in the Lagoon of Venice, Italy

A textural classification of sediments collected in input channels, shallow lagoon beds and navigation channels of the Lagoon of Venice is presented. Some variables describing both the hydrodynamics and the transport time scales of the Lagoon are compared with bottom sediment distribution inside the basin. A high correlation between residence time (REST) and the silt fraction (4-31 mu m) was only found for REST values <20 days. A good correlation was also found between root mean square velocity (RMSV) and the fine sand fraction (63-105 mu m) for RMSV > 10 cm s(-1). The distribution of the various sediment types was explained by the use of PCA applied to both grain-size and hydrological parameters, which extracted two principal factors and formed four groups of clustered samples. Groups 1 (clayey silt) and 2 (very silty slightly sandy mud) comprise samples located mainly in the nor-them and central lagoon and inshore. The samples of group 3 (very silty sandy mud) seem to show stabilisation, reflected in the reduction of sand and the sedimentation of silt with respect to samples in group 4 (slightly silty sand), some of which were collected on a previous seagrass bed which has now disappeared and/or been reduced in size.