The Lagoon of Venice (Italy) is a unique result of natural and anthropogenic changes. Through the centuries, human activities, steadily modified its environment creating the actual situation, to the point that the Lagoon of Venice is itself a signature of human activities. Moreover, he historical city of Venice, world heritage, is endangered by the relative sea level rise so that major modifications of the lagoon inlets are ongoing at the moment to protect it. For these reasons, the Lagoon of Venice is at the same time a paradigmatic case of a relatively circumscribed ecosystem in which the Anthropocene has started long ago, and a sensitive seismographer of the environmental changes that are taking place at the global level. In this context, a large geophysical survey was carried out to explore the Holocene sediments in order to establish the natural evolution of the lagoon and the impact of the human presence. The survey is the basis of an interdisciplinary study that has allowed the reconstruction of ancient landscapes of the lagoon from before its origin to present days. In particular, thanks to acoustic and geologic investigation of the lagoon sub-bottom, and by crossing our data with the environmental records provided by archeological findings and by the city's historical archives, we could distinguish different phases of the lagoon evolution and evaluate the weight of humans-induced changes We first mapped the position and the depth of the alluvial plain that was flooded during the last marine transgression, about 6000 years before present (BP),when the lagoon was originated. Successively, we mapped the areal extension of a dense network of palaeochannels and palaeosurfaces corresponding to different hydrologic conditions and relative mean sea levels. Thanks to many radiocarbon dating and to the acoustical sub-bottom reconstruction, we could establish an average sedimentation rate of of about 1 mm/year from 2500 and 1500 BP and 0.5 mm/year from 1500 BP up to present and an average migration rate of the natural channels ranging from 10 to 20 m/century with a filling rate between 0.5 and 2.5 mm/year. As a further result of this investigation, we found a general simplification of the morphologies over the centuries with a drastic reduction of the number of channels and salt marshes. This simplification can be explained by natural causes such as the general increase of the mean sea level and natural subsidence, and by human activities such as the artificial river diversion and inlet modifications resulting in a reduced sediment supply and in a change of the hydrodynamics. Finally, also by comparison with many historical maps, we observed that this tendency accelerated dramatically in the last century as a consequence of the construction of a deep industrial canal dredged between 1961 and 1969 to allow large containers navigation. The results of these researches can contribute to planning effective environmental strategies for the Lagoon of Venice.
The evolution of the Lagoon of Venice as a paradigm of anthropogenic alteration of ecosystems: a palaeoenvironmental reconstruction through wide-area acoustic surveys and core sampling
F Madricardo;S Donnici
2013
Abstract
The Lagoon of Venice (Italy) is a unique result of natural and anthropogenic changes. Through the centuries, human activities, steadily modified its environment creating the actual situation, to the point that the Lagoon of Venice is itself a signature of human activities. Moreover, he historical city of Venice, world heritage, is endangered by the relative sea level rise so that major modifications of the lagoon inlets are ongoing at the moment to protect it. For these reasons, the Lagoon of Venice is at the same time a paradigmatic case of a relatively circumscribed ecosystem in which the Anthropocene has started long ago, and a sensitive seismographer of the environmental changes that are taking place at the global level. In this context, a large geophysical survey was carried out to explore the Holocene sediments in order to establish the natural evolution of the lagoon and the impact of the human presence. The survey is the basis of an interdisciplinary study that has allowed the reconstruction of ancient landscapes of the lagoon from before its origin to present days. In particular, thanks to acoustic and geologic investigation of the lagoon sub-bottom, and by crossing our data with the environmental records provided by archeological findings and by the city's historical archives, we could distinguish different phases of the lagoon evolution and evaluate the weight of humans-induced changes We first mapped the position and the depth of the alluvial plain that was flooded during the last marine transgression, about 6000 years before present (BP),when the lagoon was originated. Successively, we mapped the areal extension of a dense network of palaeochannels and palaeosurfaces corresponding to different hydrologic conditions and relative mean sea levels. Thanks to many radiocarbon dating and to the acoustical sub-bottom reconstruction, we could establish an average sedimentation rate of of about 1 mm/year from 2500 and 1500 BP and 0.5 mm/year from 1500 BP up to present and an average migration rate of the natural channels ranging from 10 to 20 m/century with a filling rate between 0.5 and 2.5 mm/year. As a further result of this investigation, we found a general simplification of the morphologies over the centuries with a drastic reduction of the number of channels and salt marshes. This simplification can be explained by natural causes such as the general increase of the mean sea level and natural subsidence, and by human activities such as the artificial river diversion and inlet modifications resulting in a reduced sediment supply and in a change of the hydrodynamics. Finally, also by comparison with many historical maps, we observed that this tendency accelerated dramatically in the last century as a consequence of the construction of a deep industrial canal dredged between 1961 and 1969 to allow large containers navigation. The results of these researches can contribute to planning effective environmental strategies for the Lagoon of Venice.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
