Holocene evolution of the Venice Lagoon

The Venice Lagoon is characterized by a remarkable vertical and lateral variability of deposits, mainly produced by delta, tidal channels and sand bar migration. High resolution seismic surveys and coring analysis, carried out in the frame of the Co.Ri.La. research line 3.16, produced new insight in the evolution of the Venice Lagoon through the Holocene. Based on the new data, it has been possible, for the first time, to image and map the three main phases that characterized the formation and the evolution of the lagoon. Initially, the marine ingression, between 10,000 and 6,000 years B.P., produced the submersion by the Adriatic Sea of the Pleistocene alluvial plain. During this phase, longshore drift triggered the formation of the Venice palaeo lagoon. Then, the following sea level highstand recorded the predominance of sediment supply from rivers and the progressive advance of the coastline toward the sea. Finally, the more recent phase was characterized by the predominance of erosion and sediment exportation from the lagoon, as the consequence of human interventions on river mouths and inlets since historical time. These distinct phases are associated to sedimentary deposits with different geotechnical, sedimentological and geochemical characteristics, which play different roles in the erodibility of the sea floor and in the hydrogeological regime. In this paper we present the main results from the surveys carried between 2003 and 2006 in the southern portion of the lagoon, where the Holocene deposits reaches their maximum thickness

Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy

We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17-24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post-Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.Contiene material complementario: consultar en https://www.nature.com/articles/s41598-017-01483-z#Sec5Centro de Investigaciones Geológica

Late Quaternary transgressions and regressions in the Trieste Gulf (northeastern Adriatic Sea)

The integration of high-resolution seismic profiles, core data and radiocarbon plus U-Th datings, allows to document the late Quaternary succession of the Trieste Gulf, which represents the easternmost part of the northern Adriatic Sea. This succession consists of an alternation of shallow marine and continental deposits organized to compose four transgressive-regressive sequences down to ca. 90 m below present sea level. The sequences terminate landwards against a stepped surface bounding the Eocene Trieste Flysch and produced by alternating episodes of wave erosion during transgressions and subaerial exposure during stages of relative sea-level fall and lowstand. Two shallow-marine wedges, in addition to the Holocene one, have been recognized; they are associated with the Marine Isotopic Stage (MIS) 5.5 (Tyrrhenian) and probably at least one of the peaks of MIS 7. The recognized shallow-marine wedges typically prograde just seaward of a buried wave-cut platform lying in front of a receding paleo-coastal cliff. A previously unrecognized stratigraphic hiatus of ca. 25 ka duration, containing the whole Last Glacial Maximum (LGM) phase, was found at the top of palustrine deposits that accumulated on the MIS 5.5 marine sediments until ca. 40 cal ka B.P. and a post-LGM peat bed accumulated during the Younger Dryas stadial. The beginning of the Holocene was characterized by marked fluvial aggradation preceding the marine transgression at ca. 11-10 cal ka B.P. This new evidence is invaluable for better understanding late Quaternary sedimentary and erosional episodes that characterized the easternmost part of the norther Adriatic Sea, in the frame of the well-known glacio-eustatic sea-level changes

Hydrogeological effects of dredging navigable canals through lagoon shallows. A case study in Venice

For the first time a comprehensive investigation has been carried out to quantify the possible effects of dredging a navigable canal on the hydrogeological system underlying a coastal lagoon. The study is focused on the Venice Lagoon, Italy, where the port authority is planning to open a new 10m deep and 3km long canal to connect the city passenger terminal to the central lagoon inlet, thus avoiding the passage of large cruise ships through the historic center of Venice. A modeling study has been developed to evaluate the short (minutes), medium (months), and long (decades) term processes of water and pollutant exchange between the shallow aquifer system and the lagoon, possibly enhanced by the canal excavation, and ship wakes. An in-depth characterization of the lagoon subsurface along the channel has supported the numerical modeling. Piezometer and sea level records, geophysical acquisitions, laboratory analyses of groundwater and sediment samples (chemical analyses and ecotoxicity testing), and the outcome of 3-D hydrodynamic and computational fluid dynamic (CFD) models have been used to set up and calibrate the subsurface multi-model approach. The numerical outcomes allow us to quantify the groundwater volume and estimate the mass of anthropogenic contaminants (As, Cd, Cu, Cr, Hg, Pb, Se) likely leaked from the nearby industrial area over the past decades, and released into the lagoon from the canal bed by the action of depression waves generated by ships. Moreover, the model outcomes help to understand the effect of the hydrogeological layering on the propagation of the tidal fluctuation and salt concentration into the shallow brackish aquifers underlying the lagoon bottom.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy

We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17-24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post-Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.Contiene material complementario: consultar en https://www.nature.com/articles/s41598-017-01483-z#Sec5Centro de Investigaciones Geológica

Hydrogeological effects of dredging navigable canals through lagoon shallows. A case study in Venice

For the first time a comprehensive investigation has been carried out to quantify the possible effects of dredging a navigable canal on the hydrogeological system underlying a coastal lagoon. The study is focused on the Venice Lagoon, Italy, where the port authority is planning to open a new 10m deep and 3km long canal to connect the city passenger terminal to the central lagoon inlet, thus avoiding the passage of large cruise ships through the historic center of Venice. A modeling study has been developed to evaluate the short (minutes), medium (months), and long (decades) term processes of water and pollutant exchange between the shallow aquifer system and the lagoon, possibly enhanced by the canal excavation, and ship wakes. An in-depth characterization of the lagoon subsurface along the channel has supported the numerical modeling. Piezometer and sea level records, geophysical acquisitions, laboratory analyses of groundwater and sediment samples (chemical analyses and ecotoxicity testing), and the outcome of 3-D hydrodynamic and computational fluid dynamic (CFD) models have been used to set up and calibrate the subsurface multi-model approach. The numerical outcomes allow us to quantify the groundwater volume and estimate the mass of anthropogenic contaminants (As, Cd, Cu, Cr, Hg, Pb, Se) likely leaked from the nearby industrial area over the past decades, and released into the lagoon from the canal bed by the action of depression waves generated by ships. Moreover, the model outcomes help to understand the effect of the hydrogeological layering on the propagation of the tidal fluctuation and salt concentration into the shallow brackish aquifers underlying the lagoon bottom.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Measured and perceived environmental comfort: Field monitoring in an Italian school

Microclimatic conditions were recorded in an Italian school and Fanger's indexes PMV and PPD were calculated under different conditions. Students' sensations were investigated four times by means of two surveys, one related to actual microclimatic conditions and one on overall satisfaction, interaction occupant-building and reactions to discomfort. Pupils' classroom position was considered to look for possible influence on thermal comfort: a difference emerged from PMV and the survey, but the results obtained from the two approaches differ for both the entity of discomfort and its distribution within each classroom. Innovative multivariate nonparametric statistical techniques were applied to compare and rank the classrooms in accordance with students' subjective perceptions; a global ranking has been also calculated, considering thermal and visual comfort and air quality. Comparing pupil-sensation-based ranking with environmental parameters no clear correspondence was found, except for mid-season, where PMV, CO2 concentration and desk illuminance were similar in all the classrooms