Michol Ghezzo

Comparative hydrodynamics of 10 Mediterranean lagoons by means of numerical modeling

A comparison study between 10 Mediterranean lagoons has been carried out by means of the 3-D numerical model SHYFEM. The investigated basins are the Venice and Marano-Grado lagoons in the Northern Adriatic Sea, the Lesina and Varano lagoons in the Southern Adriatic Sea, the Taranto basin in the Ionian Sea, the Cabras Lagoon in Sardinia, the Ganzirri and Faro lagoons in Sicily, the Mar Menor in Spain, and the Nador Lagoon in Morocco. This study has been focused on hydrodynamics in terms of exchange rates, transport time scale, and mixing. Water exchange depends mainly on the inlet shape and tidal range, but also on the wind regimes in the case of multi-inlet lagoons. Water renewal time, which is mostly determined by the exchange rate, is a powerful concept that allows lagoons to be characterized with a time scale. In the case of the studied lagoons, the renewal time ranged from few days in the Marano-Grado Lagoon up to 1 year in the case of the Mar Menor. The analysis of the renewal time frequency distribution allows identifying subbasins. The numerical study proved to be a useful tool for the intercomparison and classification of the lagoons. These environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the Mediterranean basin. Mixing efficiency turns out to be a function of the morphological complexity, but also of the forcings acting on the system.

Water circulation and transport timescales in the Gulf of Oristano

In this work, water circulation in the Gulf of Oristano was investigated using a 2D hydrodynamic model. The model is based on the finite-element method. This solves the shallow-water equations on a spatial domain representing the Gulf of Oristano and the surrounding coastal sea. The hydrodynamic features of the gulf were investigated when the basin is influenced by different wind regimes. In order to evaluate the renewal capacity of the basin, the residence and the transit times were computed for each scenario. The study reveals that the gulf is characterized by circulation patterns promoting strong trapping phenomena. The results obtained are partially confirmed by the heavy-metal distribution in the sediments. In particular, the southern part of the basin is characterized by the presence of high heavy-metal concentrations in the bottom sediment, in the same areas where model results reveal a strong trapping capacity. This study can be considered as a first attempt to investigate the wind-driven water circulation in the Gulf of Oristano, and the results obtained can help in planning hydrological campaigns in the basin.

Toward homogenization of Mediterranean lagoons and their loss of hydrodiversity

Lagoons are considered to be the most valuable systems of the Mediterranean coastal area, with crucial ecological, historical, economical, and social relevance. Climate change strongly affects coastal areas and can deeply change the status of transitional areas like lagoons. Herein we investigate the hydrological response of 10 Mediterranean lagoons to climate change by means of numerical models. Our results suggest that Mediterranean lagoons amplify the salinity and temperature changes expected for the open sea. Moreover, numerical simulations indicate that there will be a general loss of intralagoon and interlagoon variability of their physical properties. Therefore, as a result of climate change, we see on Mediterranean lagoons an example of a common process that in future may effect many coastal environments: that of homogenization of the physical characteristics with a tendency toward marinization.

Estuarine circulation in the Taranto Seas

The Taranto basin is a shallow water marine system in the South of Italy characterized by the presence of a lagoon environment together with a semi-enclosed bay connected to the Ionian Sea. This marine system experienced over the last few decades strong biochemical pollution and environmental degradation, and it is considered a hotspot study site for economic, ecological and scientific reasons. The aim of this study was to examine, on an annual temporal scale and with high spatial resolution, the main hydrodynamical processes and transport scales of the system by means of a 3D finite element numerical model application, adopting the most realistic forcing available. The model allowed us to assess the role played by baroclinic terms in the basin circulation, describing its estuarine nature. In particular, the main features of water circulation, salinity and temperature distribution, water renewal time and bottom stress were investigated. Our results allowed us to equate this system dynamic to that of a weakly stratified estuary, identifying the main driving sources of this mechanism. The vertical stratification over the whole year was proved to be stable, leading to a dual circulation flowing out on the surface, mainly through Porta Napoli channel, and inflowing on the bottom mainly through Navigabile channel. This process was responsible also for the renewal time faster on the bottom of the Mar Piccolo basin than the surface. Due to the great importance of the Taranto basin for what concerns sediment pollution, also the effect of currents in terms of bottom stress was investigated, leading to the conclusion that only in the inlets area the values of bottom stress can be high enough to cause erosion.

Connectivity in Three European Coastal Lagoons

The temporal variation and the spatial structure of marine populations strongly depend on the early life stages of the individuals and on their interaction with the environment. The physical dispersion of propagules (eggs and larvae) is a fundamental aspect, conditioning the successful recruitment of juveniles in the adult population. Coastal transitional ecosystems such as lagoons plays a role of nursery for species with economic relevance, such as demersal fishes, mollusks and crustaceans. Those environments promote the recruitment of the early stages for several organisms because they act as area of retention for propagules and concentration for resources. We applied in three different European coastal lagoon a lagrangian particle tracking model coupled with a hydrodynamic model, and developed a method to evaluate the connectivity inside a lagoon and between a lagoon and the sea. Each particle represents a generic passive pelagic larva with a duration of one month. The average connectivity has been estimated after two years of simulation under realistic tide and wind forcings. Our results allow to characterize the lagoons behavior considering different spatial scales and to compare the dynamics of different systems. This study is a first step toward a better knowledge of the factors influencing the ecological role of coastal lagoons.

Multi-objective spatial tools to inform maritime spatial planning in the Adriatic Sea

This research presents a set of multi-objective spatial tools for sea planning and environmental management in the Adriatic Sea Basin. The tools address four objectives: 1) assessment of cumulative impacts from anthropogenic sea uses on environmental components of marine areas; 2) analysis of sea use conflicts; 3) 3-D hydrodynamic modelling of nutrient dispersion (nitrogen and phosphorus) from riverine sources in the Adriatic Sea Basin and 4) marine ecosystem services capacity assessment from seabed habitats based on an ES matrix approach. Geospatial modelling results were illustrated, analysed and compared on country level and for three biogeographic subdivisions, Northern-Central-Southern Adriatic Sea. The paper discusses model results for their spatial implications, relevance for sea planning, limitations and concludes with an outlook towards the need for more integrated, multi-functional tools development for sea planning.

Use of SHYFEM open source hydrodynamic model for time scales analysis in a semi-enclosed basin

In coastal semi-enclosed basins the knowledge about cleaning capacity of the system, related to the water transport and dilution process, can be crucial to decision makers in order of an aware management. This work aims to investigate the three-dimensional character of these transport time scales in the Taranto Seas (Apulia, Italy), through the application of a finite elements numerical model SHYFEM. In particular, a new Lagrangian module has been created in order to follow the 3D particles motion, computing three-dimensional Water Transit Time (WTT) and comparing it with the Water Renewal Time (WRT) of the basin. The results, summarized in the Trapping Index (TI) variable, allowed to identify the retention areas of the Taranto Seas both on the surface and on the bottom of the system.

Natural resources and climate change: A study of the potential impact on Manila clam in the Venice lagoon

A crucial aspect in climate change is to understand how an ecosystem will adapt under different environmental conditions and how it will influence the ecological resources and the connected human activities. In this study, a numerical model reproduces the growth dynamics, dispersion and settlement of clams larvae in the Venice lagoon. On the basis of the last IPCC scenarios for the years 2050 and 2100, the model simulates the changes in larval settlement, showing how the geographical distribution and, consequently, the nursery area changes over time. Our results indicate that climate change will modify, not only the timing of the settlements (from spring-summer to winter autumn) and the spatial distribution of nursery areas (from central to southern lagoon), but also the absolute quantity of settled larvae in the lagoon. This can strongly affect aquaculture in terms of availability of seed and farming practice. Given that these changes are due to the variations in temperature and circulation, similar processes are likely to happen in other transitional environments all over the world affecting the global aquaculture resources. In this regard, the tool we developed could support local policymakers in the knowledge-based planning and sustainable management of clam aquaculture in vulnerable environments.

A toolkit to study seabird–fishery interactions

A toolkit to study seabird–fishery interactions Tangi Le Bot*, Amélie Lescroël, and David Grémillet Centre d’Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS—Université de Montpellier—Université Paul-Valéry Montpellier EPHE, Montpellier, France Point Blue Conservation Science, 3820 Cypress Drive, Suite 11, Petaluma, CA 94954, USA Percy FitzPatrick Institute and DST-NRF Centre of Excellence at the University of Cape Town, Rondebosch 7701, South Africa *Corresponding author: tel: þ33 (0) 467 613 309; e-mail: tangi.lebot@cefe.cnrs.fr. Le Bot, T., Lescroël, A., and Grémillet, D. A toolkit to study seabird–fishery interactions. – ICES Journal of Marine Science, 75: 1513– 1525.

Modelling as decision support for the localisation of submarine urban wastewater outfall: Venice lagoon (Italy) as a case study

Microbiological impact is critical in coastal areas where tourism is particularly important for both the local and regional economy. Submarine outfalls are commonly used to enhance the dispersion of treated sewage thus avoiding pollution along the coast. The Venice lagoon (North Italy) has a very sensitive ecosystem, due to the morphological and natural characteristics of the basin and the co-existence of human activities. To preserve the lagoon, the discharge from the treatment plant for urban wastewater collected from the Venezia-Mestre agglomeration, neighbouring areas and local industries (total of 400,000 population equivalent—PE) has been moved from the lagoon to the open Adriatic Sea since November 2013 by means of an approximately 20-km pipeline. Microbiological pollution inside the lagoon can affect shellfish breeding areas instead, along the coast it affects the quality of bathing waters. In this study, and for the first time, a 3D hydrodynamic SHYFEM model (shallow water finite element model) with high spatial resolution coupled with a microbiological module has been applied to the lagoon and to the Adriatic Sea, to evaluate the effectiveness of the location of the submarine outfall. Microbiological data have been produced by the control Authority according to official analytic methods and by the plant operator. The module of survival of free Escherichia coli follows a variable rate in dependence of UV radiation, temperature and salinity in the water. Two scenarios were modelled: final discharge into the lagoon before November 2013 and after into the open sea. In the latter case, two situations have been considered, one with “Bora” and the other with “Scirocco” winds. Our results indicate that the model correctly simulates microbiological decay and dispersion. The transferral of the final discharge point far from the shoreline improves pollution dispersion, thus preserving the lagoon without evidence of impacts on the bathing waters in all meteorological conditions.