Changes in Venice Lagoon dynamics due to construction of mobile barriers

The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon\u27s inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios. The results show that with the new structures the Lido sub-basin tends to increase its extension due the southward movement of the watershed, at the expense of the Chioggia sub-basin, whereas the Malamocco sub-basin changes its relative position, but not its extension. The residence time shows variations in agreement with this trend, decreasing in the southern part of the Lido sub-basin and increasing in the inner part of the Chioggia sub-basin. The variations in residence time and return fl ow factor indicate that they are caused by changes in both instantaneous current velocities and sea-lagoon interaction. In fact the new breakwaters in front of the Malamocco and Chioggia inlets modify the length and direction of the out fl ow jet (up to 1 ms− 1 ) and the patterns of the currents around the inlets and the nearby coast. The new arti fi cial island in the Lido inlet changes the current pattern and increases the current velocity on the southern side of the channel propagating this effect up to the Venice city. The risks and benefits individuated from our conclusion are that the Lido sub-basin can improve its renewal time, but the more intense current speeds can be a risk for the conservation of habitats and infrastructures. Finally the micro-circulation between the breakwater and the coast in Chioggia and Malamocco inlets can be a trap for pollutants or suspended sediment

Analisi modellistica delle caratteristiche idrologiche del tratto di mare costiero antistante Capo Altano (Sardegna sud-occidentale) finalizzato ad investigare i potenziali impatti di un impianto di maricoltura (Tonnare Sulcitane)

Il lavoro si propone di investigare i potenziali impatti derivanti dall’attività di maricoltura prevista nel tratto di mare antistante Capo Altano, Sardegna sud-occidentale, attraverso un’analisi correntometrica. Lo studio è finalizzato ad una stima dell’areale maggiormente soggetto all’accumulo di sostanza organica prodotta dagli impianti di produzione. Al fine di riprodurre la circolazione delle acque e del moto ondoso nell’area di indagine e di effettuare delle simulazioni in grado di stabilire quale siano le aree interessate al deposito di sostanza organica prodotta dall’attività di maricoltura, sono state implementati diverse classi di modelli numerici ed effettuati alcuni esperimenti in laboratorio. In particolare, sono stati sviluppati un modello numerico idrodinamico, agli elementi finiti, in grado di riprodurre il campo di moto bidimensionale; un modello ondametrico, agli elementi finiti, al fine di riprodurre lo stato del mare; nonché un modello numerico in grado di simulare il trasporto di sostanze disperse nella colonna d’acqua ad opera dei venti, correnti e moto ondoso finalizzato ad individuare l’estensione delle aree potenzialmente impattabili dai detriti organici prodotti. Tali strumenti numerici sono stati applicati all’area di interesse in modalità accoppiata al fine di simulare ed analizzare le dinamiche di interesse sia nell’arco di un intero anno solare sia per definiti scenari meteomarini di riferimento. Lo studio ha permesso di simulare la dinamica di trasporto e deposizione dei fecal pellets prodotti e dei mangimi utilizzati nell’ambito dell’attività prevista di maricoltura. Infine è stato possibile valutare l’estensione massima raggiunta dalla sostanza organica rilasciata dagli impianti di acquicoltura prima della deposizione sul fondale, in relazione a determinati scenari meteo-marini, ed individuare l’areale soggetto ad un potenziale impatto sulle comunità bentoniche

Studio sull’impatto ambientale delle attività di maricoltura nel Golfo di Oristano

L’obiettivo del presente lavoro è stato di simulare la dispersione e il tempo di residenza delle sostanze organiche immesse nell’ambiente a seguito delle attività di acquacoltura all’interno del Golfo di Oristano (Sardegna, Italia). A questo scopo è stato implementato un modello numerico di circolazione, con moduli di dispersione e diffusione euleriana e lagrangiana. Il modello ha evidenziato il ruolo fondamentale della direzione e dell’intensità del vento sulla dispersione dei rifiuti organici. A parità d’intensità, la direzione del vento influenza in maniera decisiva la distanza alla quale i rifiuti organici vengono trasportati e depositati. In tutti gli scenari di vento, il mangime non consumato, indipendentemente dalla sua dimensione, si deposita in un’area direttamente sotto le gabbie ma con una distribuzione spaziale che dipende dalle correnti indotte. In tutti i casi, la materia organica disciolta si diluisce ed è trasportata al di fuori del golfo. Con i venti da Maestrale i rifiuti organici sono spinti verso, l’interno del golfo per poi uscirne in forma disciolta da sud. Negli scenari di Libeccio e Scirocco i rifiuti organici disciolti tendono a diluirsi ed essere trasportati al di fuori del golfo dalla parte nord. In tutti gli scenari, la capacità di ricambio delle acque interne al golfo risulta elevata, con la maggior parte delle sostanze organiche disciolte presenti in concentrazioni molto basse dopo dieci ore dalla loro produzione. Dal punto di vista del ricambio d’acqua e conseguentemente per la dispersone di agenti inquinanti, quasi tutti i 13 siti simulati, ad esclusione dei due in prossimità dei capi, hanno tempi di residenza idonei per il posizionamento delle gabbie. Sono comunque da preferire le regioni più a sud perché i tempi di transito sono più bassi creando un impatto minore. Infine considerando che il golfo è ricoperto quasi interamente da Posidonia, i siti meno impattanti sono quelli che si trovano su un fondale fangoso e in prossimità del fiume Tirso (Sito 3 e 4). L’utilizzo di modelli numerici ha permesso di portare a termine studi a priori (tempi di transito, zone di deposizione, dispersioni inquinanti) per la pianificazione della disposizione ottimale delle gabbie, avente come conseguenza una più proficua produzione (maggiore redditività) e un minore impatto ambientale. Si può infine affermare che nonostante l’assenza di studi antecedenti al presente, le gabbie all’interno del Golfo di Oristano siano state posizionate correttamente, in una regione ottimale per produzione e impatto ambientale

Development of a novel tool to predict different water quality scenarios within a Marine Protected Area (MPA) in the Maltese Islands : the 2D SHYFEM-BFM model

Effective operational marine conservation and management is thwarted by a lack of financial and human resources. A coupled 2D hydrodynamic (SHYFEM) and ecological (BFM) model was developed in the current study as a Decision Support System (DSS) to spearhead good governance of a Marine Protected Area (MPA) in Dwejra (Maltese Islands) in the Central Mediterranean. Two scenarios were considered – one with the current levels of nutrient runoff from land and one in which such levels are increased as a result of a greater human activity within the area. Although the developed numerical modeling platform needs to be refined and to be run for a longer time -frame, its output suggests that it is a promising tool to assist in the operational management of an MPA.peer-reviewe

MORPHODYNAMICS PROCESSES IN THE LAGOON OF VENICE: THE SCANELLO SALT MARSH AREA

Geomorpholgical variations have been naturally occurring in the Lagoon of Venice since its formation. In recent times, however, complex morphodynamic changes, caused by natural processes and by the direct or indirect impact of man activities have been recognised. Moreover, there remains a lack of knowledge concerning sediment erosion, re-suspension, transport and sedimentation, sea-lagoon balance and the role played by the hydrodynamics. A detailed study of the Scanello salt marsh area, in the Northern part of the Venice Lagoon, was carried out, in order to better understand the erosion-transport-sedimentation processes and the hydrodynamics interaction. Understanding the role that the hydrodynamics plays in the erosion, transportation and deposition of sediments in this test area, is essential to the understanding the morphological variations, that are presently occurring in the Venice Lagoon and morphological and environmental restorations required. A 2D hydrodynamic finite element model was used to provide the circulation field of the entire Venice basin. Results obtained by different simulations allowed the investigation of the main hydrodynamic features of the Scanello area

A modelling study of the barotropic tidal dynamics in the Strait of Messina

This paper is devoted to a model case study of the barotropic tidal dynamics. A non-hydrostatic (i.e. fully three dimensional) ocean model, based on the finite-element method was applied in the Strait of Messina (Italy), where intense tidal flows interact with complex geometries of coasts and bathymetry. A simplified model configuration including only the tidal signal at the open boundaries was able to provide evidences that the barotropic tides, interacting with coastlines and bottom topography in such narrow sea strait, generate high amplitude overtones of the main tidal constituents as well as relatively intense tide-induced residual circulations. The spatial and temporal distribution of tidal flows was analysed with a numerical simulation of a whole synodic month. The vertical component of tidal flows, explicitly computed, was shown in cross-sections in order to emphasized the direct effect of boundaries constraints on the vertical acceleration. The presented model results endorse previous model approaches and observations and they remind the significance of the barotropic tidal dynamics in this domain of investigatio

Testing a novel aggregated methodology to assess hydrodynamic impacts on a high-resolution marine turtle trajectory

We designed a novel aggregated methodology to infer the impact of ocean motions on the movements of satellite-tracked marine turtles adopting available oceanographic observations and validated products of a numerical oceanographic forecasting system. The method was tested on an 11-months trajectory of a juvenile loggerhead turtle (LT) wandering in the Tyrrhenian Sea (Mediterranean Sea) that was reconstructed with a high-resolution GPS tracking system. The application of ad-hoc designed metrics revealed that the turtle's route shape, ground speed and periodicities of its explained variance mimic the inertial motions of the sea, showing that this methodology is able to reveal important details on the relation between turtle movements and oceanographic features. Inertial motions were also identified in the observed trajectory of a surface drifting buoy sampling the Tyrrhenian Sea in a common period. At each sampling point of the turtle trajectory, the sea current eddy kinetic energy (EKE) and a Sea Current Impact index were computed from a validated set of high-resolution ocean modeling products and their analysis showed the relevant effects of the highly variable local sea currents mechanical action. Specifically, the metric we adopted revealed that the turtle trajectory was favorably impacted by the encountered sea current advection for about 70% of its length. The presented oceanographic techniques in conjunction with high-resolution tracking system provide a practicable approach to study marine turtle movements, leading the way to discover further insights on turtle behavior in the ocean

Tide-surge-wave modelling and forecasting in the Mediterranean Sea with focus on the Italian coast

Abstract A tide-surge-wave modelling system, called Kassandra, was developed for the Mediterranean Sea. It consists of a 3-D finite element hydrodynamic model (SHYFEM), including a tidal model and a third generation finite element spectral wave model (WWMII) coupled to the hydrodynamic model. The numerical grid of the hydrodynamic and wave models covers the whole Mediterranean with variable resolution. The comparison with coastal tide gauge stations along the Italian peninsula results in a root sum square error for the main tidal components equal to 1.44 cm. The operational implementation of the Kassandra storm surge system through the use of a high resolution meteorological model chain (GFS, BOLAM, MOLOCH) allows accurate forecast of total water level and wave characteristics. The root mean square error for the first day of forecast is 5 cm for the total water level and 22 cm for the significant wave height. Simulation results indicate that the use of a 3-D approach with a depth-varying loading factor and the inclusion of the non-linear interaction between tides and surge improve significantly the model performance in the Italian coast