Laura Carbognin

Distribution of Recent Benthic Foraminifera in the Southern Basin of the Venice Lagoon (Italy): Statistical Evaluation of Taxa Significance

The total benthic foraminiferal assemblage (living and dead) is analyzed for 95 samples collected in the southern basin of the Venice Lagoon [Chioggia Basin, Italy]. Quantitative results of the identified 48 species are statistically treated by correspondence analysis and Fuzzy c-means cluster analysis to define both the zonal environmental similarities (biotopes) and the faunal similarities (biofacies). In this lagoon basin, the biotopes delineate the area of marine influence, areas of mixed sea/lagoon, and zones of greater human impact that seem less heavily polluted with respect to the other two lagoon basins. The faunal similarities identified distinguish present sea and lagoon influences from the salt marsh assemblage, which are linked to the paleoenvironment. We show through statistical analyses that abundance is not the only factor governing the importance of the different taxa in defining biotopes. The important factor we found out is significance assumed as the ratio between abundance and distribution for both abundant and rare species. Results complete the knowledge on the present environmental condition of the Venice Lagoon and suggest limits of feasible simplifications to better define biotopes. These limits are given by the significant value of each taxon, which is greater, the smaller the equidistribution of the taxon itself.

Land subsidence monitoring service in the Lagoon of Venice

In order to provide the best knowledge of the subsidence process around the Lagoon of Venice to the authorities that manage the area, SAR-based monitoring techniques (differential SAR interferometry and the interferometric point target analysis) will be integrated with levelling and GPS surveys into an overall database and information system. In this contribution the different monitoring techniques are briefly introduced, the results presented and compared, and the integration concept explained.

Three-dimensional analysis of the Plio-Pleistocene seismic sequences in the Venice Lagoon (Italy)

Integrated seismic and well data provide for the first time a picture of the geological evolution of the Venice area over the last 5 Ma and a 3D subsoil model, which is fundamental to prediction of the anthropogenic uplift of Venice by seawater injection. A Pliocene southward prograding complex formed a shelf–slope system, whereas subsidence related to the Apennine foredeep development led to the establishment of a Early Pleistocene deep-water environment, favouring the accumulation of a thick turbidite succession. The NE progradation of the palaeo-Po river delta during the Middle Pleistocene promoted a drastic environmental revolution, followed by the deposition of cyclothems linked to glacio-eustatic changes. Supplementary material: Details of the seismic data and their relationship to the boreholes are available at http://www.geolsoc.org.uk/SUP18537.

Soil contamination and land subsidence raise concern in the Venice watershed, Italy

The southern catchment of the Venice watershed is threatened by shallow aquifer salinization and anthropogenic land subsidence due primarily to the microbial oxidation of organic soils that outcrop in the coastal farmland reclaimed from the Adriatic Sea over the last century. Recent hydrogeological and geophysical surveys provide documentary evidence that saltwater intrusion may extend inshore up to 20 km away from the Adriatic coastline with the contaminant plume from near ground surface down to 100 m depth in some areas. The actual salt distribution is the outcome of a number of factors, including the ground elevation markedly below the mean sea level (down to -4 m locally), the seawater encroachment along the final 10-15 km of the regional watercourses (Brenta, Bacchiglione, Adige, Gorzone), and the drainage practices implemented in the reclaimed area. The fresh-salt water interface is generally between 2 and 30 m deep and exhibits a pronounced seasonal variation. At the same time an ongoing settlement due to peat oxidation promoted by farming activities is observed in most of the area south of the Venice Lagoon that was reclaimed from 1892 to 1967 and is rich in organic matter. Overall land subsidence over the last 70 years ranges between 1.5-2 m and is still in progress at a rate of 1.5-2 cm/y. As a major result a large fraction of the reclaimed land lies below the mean sea level with an increasing exposure to flooding during severe winter storms and saltwater intrusion from the Adriatic Sea, the nearby Venice Lagoon, and the river beds that locally lie above the surrounding ground surface. To mitigate both hazards the implementation of a drainage strategy of the reclaimed area intended to maintain the water table as high as possible would be required. This could decelerate the peat oxidation (hence the related land subsidence) and oppose the inland subsurface salt convection and dispersion. Moreover the design of mobile gates at a few river mouths (e.g. the Brenta river) could create an effective barrier against the seawater migration upstream the watercourses in the hottest and driest summers.

Finite Element Modeling Of Saltwater Intrusion In The Venice Aquifer System

The Venice aquifer system is threatened by the intrusion of seawater from the overlying lagoon and of fossil saltwater from the deeper formations beneath the sea. A fully coupled flow and salt transport finite element model of the Venice system for the prediction of the expected maximum extent of saltwater intrusion in a vertical section of the system is presented. We obtain a steady state solution of the coupled flow and transport problem, which provides the potential largest extent of saltwater intrusion on condition that the present piezometry does not significantly change in the future. The results show that the salt intrusion concerns a restricted area extending few km inland from the coastline. In the upper part of this zone, down to a depth of 200 m, the predicted salt concentration varies between 3.5 and 7 g/1 and is mainly due to the seawater penetrating vertically from the lagoon. Below we find a higher concentration (3.5 - 14 g/1) caused by the lateral intrusion of fossil saltwater.

SAR interferometry confirms the present land stability of Venice

The city of Venice is very vulnerable to loss in land elevation as a result of subsidence and eustacy because of its small elevation above sea level. The alarm of the scientific community related to this persistent problem is increasing because of the forecasts of sea level rise caused by global warming. In order to evaluate the present relative settlement of Venice, a study has been performed by combining high precision levelling surveys and SAR interferometry. The analysis points out at an unprecedented detail the present ground stability of the city.

A new method to investigate the equality of bivariate dependence. Application to sediment samples study

In this paper a new method, termed BIDE (bivariate dependence), is described for testing the equality of the dependence structure, linear or nonlinear, among the variables of two or more samples. The BIDE method can be considered as a nonparametric extension of the z test by Rao that tests the equality of the correlation coefficients. The results of the application made on the mineralogical structures of two sediment samples from Holocene and Pleistocene cored in the lagoon of Venice, Italy, is discussed.

Correlation between percentage matrices: a new approach

Abstract This paper defines a correlation coefficient between two percentage matrices of the same order by the cosine of the angle between two hyperplanes properly associated with the two matrices. This procedure has been applied to 55 sediment samples collected from the Po River Delta area, Italy. The results obtained stress the goodness of this method, which offer a quick, simple, and effective tool for recognizing the depositional environment of sediments from their grain-size distribution.