Title:
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The stability and evolution of an intertidal flat in Venice Lagoon, Italy
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In this study, a multidisciplinary investigation was undertaken at two different spatial scales (regional and local) to determine the factors controlling the stability and evolution of Venice Lagoon. A 0-D numerical model, SLIM (Simulation of Littoral Morphodynamics), was constructed to predict factors responsible for the evolution of mudflats within the Lagoon. At the regional scale, seven sites were studied during two field campaigns in August 1998 and in February-March 1999 to investigate the temporal and spatial variation of surface sediment properties, sediment stability and environmental characteristics within a range of different habitats (subtidal and intertidal). A new version of the Mini Flume (an erosive device) was deployed in-situ for the first time, with the purpose of determining the critical erosion shear stress of surface sediments under controlled flows. At the local scale, Palude della Centrega, was chosen as a representative cohesive intertidal mudflat in the northern part of the Lagoon. Here sediment stability, sediment properties, elevation and habitat changes were monitored over a period of 16 months, from August 1998 until December 1999. The critical erosion threshold and shear strength of the intertidal sediments were derived using the Cohesive Strength Meter (CSM) and a Tor Vane Shear Meter (TSM), respectively. Relationships between the critical erosion threshold of the lagoonal sediments and their biological properties reveal that a complex feed-back mechanism exists which enhances the accretion of the intertidal areas in the northern part of the Lagoon. The sediment stability of Palude della Centrega is influenced by changes in sediment bulk density and water content. Palude della Centrega is accreting at a constant rate of 1.52 cm/a. This evolutionary trend is confirmed by investigations of the long-term morphological changes undertaken during the present study, as well as sediment dating carried out in the area by others and is in contrast with the general trend of intertidal mudflats in Venice Lagoon.
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