Sedimentation and time-of-transition techniques for measuring grain-size distributions in lagoonal flats: comparability of results

A comparative study was performed of three instruments used to measure the grain-size distribution of thirty sediment samples from shallow lagoonal flats: the hydrometer, the Sedigraph 5100 and the CIS-1. The hydrometer and Sedigraph are based on sedimentation whereas the CIS-1 uses the time of transition. The percentage of the samples accounted for by the <8 lm fraction was not affected by the technique used, but this was not the case with the clay fraction (<2 lm). Due to its relative independence from the analytical method applied, the <8 lm fraction can be used in ternary diagram classifications. This fraction also has an environmental significance in coastal lagoons in terms of hydrodynamics, organic enrichment and macrozoobenthos assemblages. The linear relationships obtained in this study may provide useful operational indications for similar studies

Variazioni geomorfologiche nell’area centrale della Laguna di Venezia. Elaborazione di cartografia storica e foto aeree

Nel corso degli ultimi secoli l’evoluzione geomorfologica della Laguna di Venezia è stata notevolmente condizionata dai numerosi interventi antropici condotti in tutto il bacino e nelle zone limitrofe, i cui effetti si sono sommati a quelli indotti dai processi naturali costieri. L’analisi delle modificazioni avvenute nel settore centrale della laguna, particolarmente vulnerabile poiché sede della città di Venezia, del porto turistico e del polo industriale, è stata l’obiettivo di questo studio. A tal fine l’esame della cartografia storica (disponibile a partire dal 1500) ha assunto un ruolo fondamentale, fornendo informazioni uniche e precise sull’assetto passato del territorio, mentrele fotografie aeree (dal 1954) hanno reso un importante contributo al riconoscimento dei cambiamenti più recenti. L’interpretazione congiunta di dati preesistenti soprattutto di carattere geomorfologico e morfodinamico e di informazioni relative alle opere realizzate dall’uomo nei secoli ha permesso di ricostruire l’evoluzione dell’area e di conoscere i rapporti causa-effetto tra evoluzione del paesaggio e processi naturali e antropici. Lo studio è stato condotto con tecnologia GIS (Geographic Information System). Carte e immagini sono state quindi georeferenziate ed è stata creata una banca dati attraverso cui visualizzare ed elaborare diverse tipologie di informazioni geografiche all’interno di un unico progetto di analisi territoriale. Il lavoro ha permesso di mettere in evidenza: (a) i diversi tentativi di deviazione del tratto finale del Fiume Brenta per evitare che, con i suoi apparati deltizi endolagunari, potesse interrare la laguna centrale minacciando così l’integrità di Venezia, (b) gli effetti che tali diversioni hanno prodotto nella laguna stessa, (c) i processi erosivi intensificati dalla costruzione dei moli foranei alla bocca di Malamocco, (d) lo sviluppo del polo industriale di Porto Marghera, (e) lo scavo del canale Malamocco-Marghera, che ha incrementato l’energia e l’idrodinamicità dell’area, favorendo l’ulteriore erosione delle strutture morfologiche naturali e artificiali (barene e casse di colmata) adiacenti

Contribution of Saharan dust to the Central Mediterranean basin

The Mediterranean Basin receives sedimentary contributions from several sources with different geological characteristics. The most important natural source of dust is the Saharan desert. Data from aerosol dust samples collected in a remote site in the Central Mediterranean Basin were used to investigate incursions of Saharan dust during a seven-month period (October through April). This work is an attempt to trace source areas and transport of dust plumes by means of grain-size, mineralogical, and chemical analyses. Two sets of aerosol samples typical of "desert-dominated" and "anthropogenic- dominated" air masses were studied. We propose a model for assessing the effects of latitude on the chemistry and mineralogy of the Central Mediterranean aerosol. Calculations and measurements of insoluble fluxes, in particular for Al (80 μg/cm2 yr-1) and Ca (28μg/cm2 yr-1), were performed, and results were compared with fluxes from the literature calculated in other stations in the Mediterranean Basin

Time to teach post-normal science communication? Fostering the engagement of the extended peer community in an academic course of Environmental Sciences

In November 2016, within an Environmental studies course at the University of Venice, students carried out an experiment aimed at collecting scenarios of the Venetian coast’s future starting from lessons learnt during the episode of storm surge 50 years ago (Aqua Granda flood). The students built scenarios able to anticipate the effect of sea level rise on coastal areas in Venice, based not only on scientific input but also on a methodology called “Futurescape city Tours” (FCT) involving inhabitants of the barrier islands of Lido and Pellestrina. This paper will explore three main questions: (i) Can participatory and experiential methodologies, such as FCT help students behave in an anticipatory and inclusive way in their future professional activities? (ii) Can we talk about post-normal science teaching? — i.e. one that acknowledges and works with science and other knowledges to address societal issues? (iii) Can such an approach challenge students thinking in relation to knowledge hierarchies

Biogenic sediments from coastal ecosystems to beach-dune systems: implications for the adaptation of mixed and carbonate beaches to future sea level rise

Coastal ecosystems produce and store carbonate particles, which play a significant role in the carbonate dynamics of coastal areas and may contribute to the sediment budget of adjacent beaches. In the nearshore seabed of temperate zones (e.g. Mediterranean Sea and South Australia), marine biogenic carbonates are mainly produced inside sea-grass meadows. This study quantifies the contribution of biogenic sediments, mainly produced in Posidonia oceanica seagrass meadows and secondarily in photophilic algal communities, to the sediment budget of a Mediterranean beach-dune system (San Giovanni beach, western Sardinia, western Mediterranean Sea). A set of geophysical, petrographic and sedimentological data was used to estimate the sediment volume and composition of the beach-dune system as a whole. The San Giovanni beach-dune system contains 3797000 +/- 404000 t of sediment, 83% (3137000 +/- 404000 t) of which is located in the coastal wedge, 16% (619000 +/- 88000 t) in the dune fields and 1% (41000 +/- 15000 t) in the sub-aerial beach. The sediments are composed of mixed modern bioclastic and relict bioclastic and non-bioclastic grains from various sources. The system receives a large input of modern bioclastic grains, mainly composed of rhodophytes, molluscs and bryozoans, which derive from sediment production of present-day carbonate factories, particularly P. oceanica seagrass meadows. Radiocarbon dating of modern bioclastic grains indicated that they were produced during the last 4.37 kyr. This value was used to estimate the longterm deposition rates of modern bioclastic sediments in the various beach compartments. The total deposition rate of modern bioclastic grains is 46000 +/- 5000 t century 1, mainly deposited in the coastal wedge (39000 +/- 4000 t century(-1)) and dunes (7000 +/- 1000 t century(-1)), and 46 000 t represents similar to 1.2% of the total beach-dune sediment mass. Carbonate production from coastal ecosystems was estimated to be 132000/307000 t century(-1), 28% (15%/34 %) of which is transported to the beach-dune system, thus significantly contributing to the beach sediment budget.The contribution to the beach sediment budget represents a further ecosystem service, which our data can help quantify, provided by P. oceanica. The value of this sediment-supply service is in addition to the other important ecological services provided by seagrass meadows. The dependence of the beach sediment budget on carbonate production associated with coastal ecosystems has several implications for the adaptation of mixed and carbonate beaches to the loss of seagrass meadows due to local impacts and the changes expected to occur over the next few decades in coastal ecosystems following sea level rise

Tidal inlet seafloor changes induced by recently built hard structures

Tidal inlets are extremely dynamic environments that are often strongly modified by anthropogenic intervention. In this study, we describe the rapid evolution of a highly humanimpacted tidal inlet, studied through repeated high-resolution multibeam surveys and geomorphometric analysis. We document the rapid change induced by new hard coastal structures built to protect the historical city of Venice (Italy). A new breakwater erected between 2011 and 2013 induced the formation of large scour holes with the consequent erosion of about 170 x 103 ± 15.6% m3 of sediment until 2016. The construction of a new island in the middle of the inlet and the restriction of the inlet channel caused a general change of the inlet sedimentary regime from depositional to erosive with a net sediment loss of about 612 x 103 ± 42.7% m3, a reduction of the dune field area by more than 50% in about five years, and a coarsening in the sediment distribution. Our results give new insight on the tidal inlet resilience to changes, distinguishing two different phases in its recent evolution: (i) a very rapid response (from 2011 to 2013) of the seafloor morphology with scour-hole erosion at the new breakwater tips at a rate of about 45x103 m3/year and the disappearing of dune fields at a rate of 104x103 m2/year; and (ii) a general slowdown of the erosive processes from 2013 to 2016. Nevertheless, the erosion continues at the breakwater, though at a reduced rate, possibly representing a threat to the hard structure. In view of global mean sea level rise and consequent proliferation of hard structures along the coast all over the world, the combined use of very high resolution multibeam surveys and repeatable geomorphometric analysis proposed in this study will be crucial for the monitoring and future management of coastal environments

The Effects of Ship Wakes in the Venice Lagoon and Implications for the Sustainability of Shipping in Coastal Waters

We analyse the impact of ship traffic in the vicinity of navigation channels in a wide shallow waterbody. The crucial hydrodynamic driver in this situation is the depression (Bernoulli) wake that may be transferred into a long-living solitary wave of depression over the shoals. The analysis considers navigation channels in the Venice Lagoon using a new large dataset of approximately 600 measured wake events associated to specific ships whose data are provided by the AIS system. Since the development of the modern industrial port and the opening of the Malamocco–Marghera channel in the late 1960s, growing pressure on the lagoon caused by ship traffic has raised concerns about its physical integrity and habitat survival. The transit of large vessels has been shown to have serious impacts on the shallow water areas adjacent to waterways. Depression wakes created by such vessels can reach significant dimensions (water level dropdown of up to 2.45 m at the channel margin), causing unusually large retreat rates of several sections of the shoreline and which may adversely affect the lagoon morphology. The wakes are analysed in relation to ship and morphological parameters. A formulation is proposed to predict wake amplitude on the basis of ship characteristics and motion

Fast Shoreline Erosion Induced by Ship Wakes in a Coastal Lagoon: Field Evidence and Remote Sensing Analysis

An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3˗4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968˗2015 (1.19×106 m3). The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide