- Fish Assemblages in Different Shallow Water Habitats of the Venice Lagoon
Anita Franco, Piero Franzoi, Stefano Malavasi, Federico Riccato and Patrizia Torricelli.
Hydrobiologia, Vol. 555, No. 1, Feb 2006, pp. 159-174.
The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats (seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4-7 stations for each habitat type, by means of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness, fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as 'transition' habitats, with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both 'buffer zones' between the other habitats and migration routes for many fish species in the lagoon.
- Modeling the Venice Lagoon residence time
Andrea Cucco and Georg Umgiesser.
Ecological Modelling, Vol. 193, No. 1-2, 2006, pp. 34-51.
In this work the water residence time of the Venice Lagoon has been computed using a 2D hydrodynamic model. The model is based on the finite element method. It solves the shallow water equations on a spatial domain that represents the whole Adriatic Sea and the Venice Lagoon. The residence time has been defined through the remnant function of a passive tracer released inside the lagoon. The renewal capacity of the Venice Lagoon has been investigated when forced by the astronomic tide and by the two main local winds, bora and scirocco. The importance of the return flow from the Adriatic into the lagoon is shown. This influence has been quantified by the definition of the return flow factor that has been computed for each scenario.
- New geophysical knowledge of groundwater systems in Venice estuarine environment
E. Di Sipio, A. Galgaro and G. M. Zuppi.
Estuarine, Coastal and Shelf Science, Vol. 66, No. 1-2, Jan 2006, pp. 6-12.
Unconfined aquifers beneath the south sector of the Venice Lagoon are characterized by the presence of saline water. The results of this study allow the determination of the superficial extension of the salt water contamination in the direction of the mainland and the relationship between chemical analysis and conductivity, which reveals a complex lateral and vertical variability in both the permeability and textural pattern. Moreover, geophysical data validated by log data together with other physical and chemical results show a dislocation of the aquifer basement. This fact allows for the presumption that the salt groundwater distribution is affected by a regional tectonic lineament which extends towards the SE. Therefore salt contamination may be due to saline intrusion from the sea and the lagoon, and also from fossil brines mobilised by the combined action of tectonics and infiltration of fresh groundwater.
- Organochlorine compounds (polychlorinated biphenyls and pesticides) and polycyclic aromatic hydrocarbons in populations of Hexaplex trunculus affected by imposex in the lagoon of Venice, Italy
C. Maran, E. Centanni, F. Pellizzato and B. Pavoni.
Environmental Toxicology and Chemistry, Vol. 25, No. 2, Feb 2006, pp. 486-495.
Concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides, and polycyclic aromatic hydrocarbons (PAHs) were measured in gastropods from the Lagoon of Venice, Italy. The visceral coil and the rest of the soft body of organisms (Hexaplex trunculus) sampled at two stations inside the lagoon and three stations on the seaward side were analyzed to evaluate their contamination levels. Preferential accumulation of PCBs and pesticides in the visceral coil (>80%) compared with the rest of the soft body was observed, whereas on average, PAHs showed no preferential partitioning. Differences between levels of organochlorine contaminants in the gastropods highlighted a gradient of pollution from the stations inside the lagoon (PCBs, 45-363 ng/g; pesticides, 4-51 ng/g) to the sea (PCBs, 13-131 ng/g; pesticides, 2-29 ng/g). The possible role of the three classes of contaminants, in addition to that of organotin compounds (OTCs), previously analyzed in the same samples, in causing one of the anatomic modifications because of imposex in this gastropod also was studied. A modeling approach by partial least squares (PLS) in latent variables was applied to explain the penis length of imposex-affected females with concentrations of organic pollutants. The synergistic role of PCBs, pesticides, and OTCs was evidenced, whereas the contribution of PAHs appeared to be very low.
- PCBs and PAHs in sea-surface microlayer and sub-surface water samples of the Venice Lagoon (Italy)
L. Manodori, A. Gambaro and R. Piazza, et al.
Marine pollution bulletin, Vol. 52, No. 2, Feb 2006, pp. 184-192.
Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are two classes of micropollutants intensively monitored and regulated due to their toxicity, persistency and wide diffusion. Their concentrations have been investigated in sea-microlayer (SML) and sub-surface water (SSW) samples collected at two sites of the Venice Lagoon, a fragile ecosystem highly influenced by industrial and anthropogenic emissions. The total sPCB concentration varies from 0.45 ng/l to 2.1 ng/l in SSW while a clear enrichment is observed in the SML, where it ranges from 1.2 ng/l to 10.5 ng/l. The total sPAH concentration shows marked differences between the two stations and varies from 12.4 ng/l to 266.8 ng/l in SSW; in SML it is more uniform and ranges from 19.6 ng/l to 178.9 ng/l. The enrichment factors are not larger than 1 for both pollutants in the 'dissolved' phase, while they are most significant for the 'particulate' phase (sPCB: 5-9; sPAH: 4-14).
- Climatic oscillations influence the flooding of Venice
Sergio Fagherazzi, Giorgia Fosser, Luigi D'Alpaos and Paolo D'Odorico.
Geophysical Research Letters, Vol. 32, No. 19, Oct 2005
A detailed analysis of the tidal regime in Venice, Italy, during the last century shows that the frequency and magnitude of high tides are correlated to interdecadal climatic oscillations. The monthly high tide maxima and the average elevation of all high tides are negatively correlated to the North Atlantic Oscillation (NAO), to the Arctic Oscillation (AO), to the East Atlantic -West Russian oscillation (EA-WR), and to the Polar Eurasia teleconnection (POL). The correlation is high during winter months for all four indices, whereas in the fall, when most of the city floods occur, the AO and the EA-WR exert a stronger influence on the tidal regime. During negative phases of the climate indices both the average elevation of high tides and the frequency of flooding increase consistently, with negative effects on the city and its monuments.
- A combined wind wave-tidal model for the Venice lagoon, Italy
L. Carniello, A. Defina, S. Fagherazzi and L. D'Alpaos.
Journal of Geophysical Research.F.Earth Surface [J.Geophys.Res.(F
Earth Surf.)], Vol. 110, No. F4, Oct 2005
A numerical model that combines wind waves with tidal fluxes in a tidal basin is presented and validated. The model couples a hydrodynamic finite element module based on the shallow water equations with a finite volume module that accounts for the generation and propagation of wind waves. The wave module solves the wave action conservation on the same triangular mesh used in the hydrodynamic module, thus efficiently reproducing the physical relationships between waves and tide propagation. The combined wind wave-tidal model is applied to the Venice lagoon, Italy. The highly irregular bathymetry of this tidal environment, characterized by deep channels, emergent salt marshes, and extensive tidal flats, suggests the introduction of specific hypotheses that simplify the governing equations with a noteworthy increase in efficiency and robustness of the algorithm. Particular attention is devoted to the dissipation of wave energy at the steep boundaries between channels, tidal flats, and salt marshes. Simulations of wave fields generated under specific wind conditions are presented and discussed. The model results are compared, with good agreement, to field data collected in different stations inside the lagoon of Venice. Finally, evidence of the complementary effect of tidal currents and wind waves on bottom shear stresses is presented using the results of different simulations.
- Freshwater discharge from the drainage basin to the Venice Lagoon (Italy)
Aleardo Zuliani, Luca Zaggia, Flaviano Collavini and Roberto Zonta.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 929-938.
The twelve major tributaries of the Venice Lagoon (accounting for the 97% of the inputs from the drainage basin) were monitored in the framework of the DRAIN project (1998-2000) in order to obtain a detailed knowledge on the hydrological regimes and to measure the mean annual freshwater discharge from surface runoff. The study represents an essential step in the estimate of the pollutant load delivered to the lagoon that must necessarily be based on a solid understanding of the fluxes of material out of the drainage basin. Due to the influence of the tide in the majority of the gauging sections, a specific methodology for the measurement of the discharge was developed. The main results of the study are described, underlining the differences in the regime of the investigated streams. A rainfall-runoff analysis evidenced the different characteristics of the monitored tributaries, in terms of specific hydrological features, morphology of the individual sub-basins, management of the water resource and spatial distribution of rainfall. An estimate of the maximum peak discharge from the drainage basin is finally obtained from data of an extreme flood event occurred in November 1999.
- The interplay of eustasy, climate and human activity in the late Quaternary depositional evolution and sedimentary architecture of the Po Delta system
M. Stefani and S. Vincenzi.
Marine Geology, Vol. 222-223, 15 Nov 2005, pp. 19-48.
The late Pleistocene and Holocene environmental evolution and sequence stratigraphic architecture of the Po Delta region, Northern Italy, are examined. The study units record the depositional evolution from lowstand continental accumulation to marine transgression and highstand progradation. Interpretation of the high-resolution, three-dimension geological mapping of the central Po Delta area was framed within the evolution of the whole of the delta region, stretching from Venice Lagoon to the South of Ravenna. The development of the delta lobes was correlated with the fluvial drainage history. A discussion on the different auto and allocyclic mechanisms controlling the depositional evolution and a quantitative estimation of the changing depositional rates are also provided. Outcrop study was based on field surveying and on the analysis of aerial photography, topographic micro-relief, historical cartography, archaeological and historiographic data. Subsurface analysis was based on stratigraphic coring and cone penetration testing. During the last glacial lowstand, the modern coastal region was the site of middle alluvial plain sedimentation. Deglaciation and early transgression were associated with an erosive disconformity development. In the modern coastal area, transgressive accumulation started between 10 and 9000 yr BP. Back-stepping fluvial and brackish marsh deposits were followed by delta-estuarine sand bodies, influenced by the last important eustatic rise pulses. Transgression climaxed at about 5500 yr BP, during a warm climate phase. Early highstand saw the growth of large sand spits and barrier islands, progressively turning the previous bays into confined lagoons. At about 3500-3000 yr BP, a particularly active meteo-marine regime profoundly affected the depositional dynamics. Etruscan and Roman times were characterised by a warm climate and by riverine stability associated with the development of a large delta lobe. At around 1500 yr BP, transition toward moister and cooler conditions and the abandoning of the Roman Empire hydraulic works coincided with important drainage network instability. The modern delta lobe was induced 400 years ago by an artificial fluvial-mouth cut. The early evolution of the lobe recorded very high accumulation rates. The modern fragile environmental situation is characterised by strong coastal erosion and difficult management. stal erosion and difficult management.
- Introduction: Geological and environmental context
T. Spencer, J. da Mosto and CA Fletcher.
Books, 40 West 20th Street New York NY 10011-4211 USA, [URL:http://www.cup.org/]: Cambridge University Press, 2005, 17-19
The northern Adriatic basin is backed by the Alps to the north, the Apennines to the west and south and the Dinaric Alps to the east. The basin incorporates the remains of the Adriatic tectonic plate which is being subducted beneath the Apennines; the result is a long-term, regional subsidence rate in the Venice area of 1.0 mm a super(-1). Mesozoic basement limestones in the basin are overlain by alternating marls and limestones of Eocene - Oligocene age and Pliocene clays. Above the Plio - Pleistocene boundary are c. 800 m of clayey sands, sandy silts and clays and silts, characteristic of shallow sea and deltaic environments. The upper 300 m of these sediments consist of continental floodplain and marsh deposits and localized aeolian deposits, indicating cycles of sea level regression and transgression, associated with low glacial and high interglacial sea level stands respectively. During the last glaciation, the Venice Lagoon was characterized by fluvial and lacustrine environments, followed by extensive alluviation at the beginning of the post-glacial period. These clays were consolidated in the period between c. 10 000 and 6000 years ago and now form the patchily distributed 'caranto' beneath the city and the lagoon. The presence/absence of this deposit may help explain the variations in the degree of building subsidence seen across the city. The modern lagoon began to be formed c. 6000 years ago when rising sea levels flooded the easternmost part of the Po Plain, creating a coastline characterized by small cuspate deltas and the estuaries of the rivers Po, Adige, Brenta and Piave.
- Introduction: Large-scale engineering solutions to storm surge flooding
T. Spencer, PM Guthrie, J. da Mosto and CA Fletcher.
Books, 40 West 20th Street New York NY 10011-4211 USA, [URL:http://www.cup.org/]: Cambridge University Press, 2005, 241-243
There is no doubt that the most intensely debated element in the range of flood protection and environmental restoration measures being implemented and proposed for Venice is the plan to temporarily close off the inlets to the Venice Lagoon at times of high water levels by what have become known as 'mobile barriers'. These are retractable barriers which can be deployed rapidly. Proposals for an intervention of this kind have a long history; notably the 'competition of ideas' in 1971 which followed the 1966 flood; through the establishment of the Consorzio Venezia Nuova in 1984, charged with the sole responsibility for implementing the barrier solution; the design, construction and testing of the first experimental prototype, the MOSE ('MOdule Sperimentale Elecctromeccanico') between 1988 and 1992 near the Lido inlet; the construction of the physical scale model at Voltabarozzo (Padua); and other specialized and detailed design and modelling initiatives in collaboration with international experts. Throughout, the choice of construction has been driven by a diverse set of requirements: barrier performance (including speed of deployment, reliability and maintenance); aesthetics (in terms of the lack of visibility of the structures from the city); avoidance of interference with expanding port activities; and the need to meet environmental concerns with regard to impacts on lagoon morphology, ecology and water chemistry during both barrier construction and operation, the last condition still not satisfactorily met for some parties.
- Objectives and structure of the DRAIN project: An extensive study of the delivery from the drainage basin of the Venice Lagoon (Italy)
Roberto Zonta, Franco Costa, Flaviano Collavini and Luca Zaggia.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 923-928.
The Venice Lagoon and its drainage basin form a vast system, where historical and recent cities, large and medium-small industrial districts and intensive agricultural activities coexist within a peculiar environment. The drainage basin constituted of an ensemble of tributary sub-basins with contrasting characteristics and freshwater fluxes; the hydraulic pathways are generally complex and not univocally established. With the main objectives to measure the annual freshwater discharge into the Venice Lagoon and to estimate the related load of pollutants, an intense field activity was carried out in the ambit of the DRAIN project. The 12 main tributaries of the drainage basin were monitored for more than 2 years (1998-2000), obtaining a relevant data set of hydrodynamic, physico-chemical and chemical data. Integrative investigations were also developed in a multidisciplinary approach, covering the existing knowledge gaps on the hydrology and behaviour of such a complex system. The paper describes the characteristics of the system, the selected approach to investigate it, and the main project outcomes.
- Po River plume on the Adriatic continental shelf: Dispersion and sedimentation of dissolved and suspended matter during different river discharge rates
A. Boldrin, L. Langone, S. Miserocchi, M. Turchetto and F. Acri.
Marine Geology, Vol. 222-223, 15 Nov 2005, pp. 135-158.
Suspended matter and dissolved nutrients were studied in the prodelta of the Po River (northern Adriatic Sea) immediately after one of the greatest floods of the last century, which occurred in October 2000, and in four successive seasonal conditions. Hydrology, total suspended matter (TSM), particulate organic carbon (POC) and particulate nitrogen (PN) content, organic carbon stable isotopes ( delta super(1) super(3)C sub(P) sub(O) sub(C)), particle grain size spectra, phytoplankton, and dissolved inorganic nutrients (i.e., nitrate, nitrite, ammonium, phosphate, and silicate) were measured in different discharge conditions to describe processes occurring in the Po River delta. The main effect of high river discharge was a large volume of low salinity water at the surface that extended over the entire study area. The concentration of most sampled variables decreased along a dilution gradient from the Po River distributaries' mouths to the offshore. For TSM at the surface, riverine input and dilution were the main factors affecting its distribution. At the bottom, however, increased TSM in the nearshore was due to rapid sinking of suspended matter at the river mouth, while resuspension and advection dominated the transport of near bottom sediments offshore at 15-20 m depth. In the offshore where resuspension was active, an increase in ammonium and decrease in oxygen supported the presence of regeneration processes occurring at the bottom. During the October 2000 flood event, high nutrient concentrations promoted new production, triggering an algal bloom in the southern region of the study area. The origin of particulate organic carbon in the river delta was then estimated from a mixing model based on delta super(1) super(3)C sub(P) sub(O) sub(C) values and carbon:nitrogen (C/N) molar ratios, and as the contribution of three distinct sources of organic carbon were determined (i.e., marine, riverine, and terrestrial). The riverine end-member accounted for similar to 50% of the surface POC and generally decreased towards the offshore. The terrestrial carbon contribution was generally the least abundant (20-28% at the surface and at depth, respectively) and exhibited peak values (30-40%) during the October 2000 flood. Last, the marine contribution was the most abundant at the bottom ( similar to 40%) and generally increased offshore. During the October 2000 flood, the fluvial contribution of particulate organic carbon, that is the terrestrial and riverine fractions, represented approximately 80% of the total particulate organic carbon in the Po River delta.
- Pollutant loads from the drainage basin to the Venice Lagoon (Italy)
Flaviano Collavini, Cinzia Bettiol, Luca Zaggia and Roberto Zonta.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 939-947.
In order to assess the actual pollutant loads from the drainage basin, the twelve major tributaries of the Venice Lagoon were monitored and studied in the period 1998-2000 in the framework of the DRAIN project. A specific sampling scheme was designed to investigate the effects of the different regimes, including floods, in the transport of total and dissolved metals, nitrogen and phosphorous species as well as organic micropollutants. The loads were calculated from data collected during the year of 1999, since this year displayed a value close to the mean in terms of the distribution of total rainfall on the drainage basin. The annual values for the different pollutants are reported and discussed. A comparison with the estimates of previous investigations highlights the significant advancement provided by the DRAIN project results in the understanding of the drainage basin contribution to the pollution of the lagoon. Finally, the importance of flood events on the overall balance of materials and pollutants delivered to the lagoon is emphasized.
- Pollution historical trends as recorded by sediments at selected sites of the Venice Lagoon
Mauro Frignani, Luca G. Bellucci, Maurizio Favotto and Sonia Albertazzi.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 1011-1022.
Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and hexaclorobenzene (HCB) were determined in three sediment cores of the Venice Lagoon: I1, from the San Giuliano Canal that is likely the main source of pollutants for the study area; E, representing the lagoon sediment of the zone of Campalto; and M3, typical of a salt marsh environment and mostly subject to atmospheric inputs. Maximum concentrations were found in core I1: 25-1858 ngI-TE kg super(-) (PCDD/Fs), 1.7-13 mu g kg super(-) (HCB), and 107-717 mu g kg super(-) (PCBs) are surficial and peak values, respectively. The lagoon sediment (E), is much less contaminated: 24-47 ngI-TE kg super(-) for PCDD/Fs, 2.3-3.6 mu g kg super(-) for HCB, and 56-203 mu g kg super(-) for PCBs, whereas M3 shows the lowest values: 1.6-6.0 ngI-TE kg super(-) for PCDD/Fs, 0.3-0.6 mu g kg super(-) for HCB, and 7.1-39 mu g kg super(-) for PCBs. In any case, the recent trend is toward a decrease of pollutant concentration. The chronology of cores E and M3 is based on both super(210)Pb and super(137)Cs activity-depth profiles. The maximum concentrations of PCDD/Fs, HCB, and PCBs correspond to the years 1949, 1980, and 1968, respectively. The homologue profiles of PCDD/Fs confirm that I1 has been subject to an industrial source while the other sites also recorded significant contributions, changing over time, of octachlorinated dioxin from combustion. A comparison of the pollutant inventories, all normalised to super(210)Pb inventories, suggests that the atmospheric contribution to the contamination of the area of Campalto is low: the upper limits range from 6% (PCDD/Fs) to 17% (HCB).
- The seasonal distribution of dissolved inorganic nitrogen and phosphorous in the lagoon of Venice: A numerical analysis
R. Pastres, S. Ciavatta, G. Cossarini and C. Solidoro.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 1031-1039.
This paper investigates the seasonal evolution of the spatial distributions of dissolved inorganic nitrogen and phosphorus, in relation to the estimation of the N and P loads, which were obtained in the framework of the DRAIN project. Such investigation is carried out by using a 3D reaction-diffusion model which has been calibrated against salinity data and then used for obtaining the most likely scenario of the spatial and seasonal distribution of DIN and DIP. The consequences of different management policies are also discussed, in relation to the current Italian legislation, which sets quality standards for both DIN and DIP in the lagoon of Venice.
- Sedimentation rates and erosion processes in the lagoon of Venice
Sfriso Adriano, Facca Chiara and Marcomini Antonio.
Environment international, Vol. 31, No. 7, Sep 2005, pp. 983-992.
Since the early 1990s in the lagoon of Venice, especially in the central basin, the surface sediment underwent high re-suspension and sedimentation changes and water turbidity increased both because of the disappearance of the macroalgal coverage and the harvesting of the Manila clam Tapes philippinarum Adams and Reeve, which had rapidly colonised the bottom free of macrophytes. Clams are harvested with hydraulic and mechanical dredges which remove and re-suspend surface sediments causing the transport and loss of the finest materials. Sediment transport and re-deposition in the lagoon have been monitored with sediment traps placed onto the bottoms near the Malamocco mouth (st. A), the Lido watershed (st. B) and the mainland (sts. C and D). From 1989- 1993 to 1998-1999 sedimentation rates increased significantly at St. A (from 41 to 228 kg DW m super(-) super(2) year super(-) ), St. B (from 65 to 760 kg DW m super(-) super(2) year super(-) ) and St. C (from 140 to 721 kg DW m super(-) super(2) year super(-) ), while at St. D sedimentation rates increased only by ca. 20%. In parallel sediment grain- size changed with a loss of the finest fraction especially near the mainland. The erosion or sedimentation status, acquired by utilizing sedimentation devices placed onto the bottoms, showed that sts. B, C, D were affected by sediment losses, while St. A, populated by seagrasses and characterised by seasonal variations which depend on the shoot development, did not show any significant bathymetric change on an annual basis. The highest sediment erosion was recorded at St. D (ca. 3.6 cm year super(-) ) whereas a loss of ca. 1.5 and 0.5 cm year super(-) was found at sts. C and B, respectively, which accounted for a mean loss in the central lagoon of ca. 1.2 million tonnes year super(-) . Those data agree with the previous indirect estimation of sediment loss which was based on the number of fishing boats operating in the lagoon on an annual basis.
- Tidal regime, salinity and salt marsh plant zonation
S. Silvestri, A. Defina and M. Marani.
Estuarine, Coastal and Shelf Science, Vol. 62, No. 1-2, Jan 2005, pp. 119-130.
Salt marsh morphology is known to be strongly correlated to vegetation patterns through a complex interplay of biological and physical processes. This paper presents the results of field surveys at several study salt marshes within the Venice Lagoon (Italy), which indicate that salt-marsh macrophyte species may indeed be associated with narrow ranges of soil topographic elevation. Statistical analyses show that several properties of the frequency distributions of halophytes presence are sensitive not only to variations in soil elevation, but also to the specific marsh considered. Through direct in situ sampling and by use of a finite-element hydrodynamic model the role of plant submersion duration and frequency in determining the observed variability of vegetation species is then studied. Measurements of soil salinity have also been performed at selected salt marshes to address its influence on vegetation occurrence. With implications for tidal marshes in general, the distribution of halophytes in the salt marshes considered is found not to be responding to simple rules dictated by the tidal cycle or to salinity, and that such factors, when singularly considered, cannot explain the observed spatial distribution of halophytes. On the basis of observations and modelling results it is thus concluded that a combination of multiple factors, likely dominated by saturated/unsaturated flow in the soil, may be responsible for the observed macrophyte distribution.
- Venice and the Venice Lagoon: Creating a forum for international debate
T. Spencer, J. da Mosto, CA Fletcher and P. Campostrini.
Books, 40 West 20th Street New York NY 10011-4211 USA, [URL:http://www.cup.org/]: Cambridge University Press, 2005, 3-5
There really is no point in continuing to rescue and restore individual buildings in Venice if the city remains under increasing threat from flooding. Now what can be done about that wider issue?' With these words in late 2000, over lunch in the Master's Lodge at Churchill College, Cambridge, Anna Somers Cocks, the Chairman of Venice in Peril (The British Committee for the Preservation of Venice) set in train a broad series of research activities in Cambridge and Venice. One of several substantive outcomes of that process is this volume.
- A water-quality model for the Lagoon of Venice, Italy
G. Bendoricchio and G. De Boni.
Ecological Modelling, Vol. 184, No. 1, May 2005, pp. 69-81.
A water-quality model for the Lagoon of Venice is proposed. The model is based on the results of an existing, deterministic, hydraulic-dispersive model of the Lagoon to provide the distribution of salinity and residence time in the Lagoon of Venice. This model has been implemented by Magistrato alle Acque di Venezia and Consorzio Venezia Nuova to evaluate the environmental impact of the MOSE Project, that has the aim to defend the city of Venice from extraordinary high tides [CVN, 1997. Allegato allo studio di impatto ambientale del progetto di massima delle opere mobili per la difesa dei centri abitati lagunari dagli allagamenti, vol. 2. CVN, 2002. Studio di nuove configurazioni dei canali di bocca e del relativo adeguamento progettuale delle opere mobili alle bocche di porto]. The water-quality is simulated by statistic analysis on water-quality data, monthly collected in 30 stations. The data-set covers a period of 2 years, and has been collected in the framework of MELa1, the institutional water- quality monitoring program (Magistrato alle Acque di Venezia, Consorzio Venezia Nuova). The Spearman correlation index of salinity and residence time versus the water-quality variables (nitrogen, phosphorus, chlorophyll-a and the trophic index TRIX) has been studied on a yearly average basis and for the spring-summer periods. The spatial distribution of the water-quality variables, based on the yearly average of nutrients, is mostly driven by the dispersive processes and is well correlated to salinity [Bianchi, F. Acri, F. Alberghi, M. Bastianini, M. Boldrin, A. Cavalloni, B. Cioce, F. Comaschi, A. Rabitti, S. Socal, G. Turchetto M.M. 1999. Biologocal variability in the Venice Lagoon. In: Lasserre, P. Marzollo, A. (Eds.), The Venice Lagoon Ecosystem. Input Interaction between Land and Sea, UNESCO, Man and Biosphere Series, vol. 25, pp. 97-125]. The model has been applied to simulate the variation of nutrients and trophic index distribution in the Lagoon as a consequence of an increase of hydraulic dissipation at the Lagoon outlets. The work presented in this paper shows that, coupling a deterministic, distributed-parameters, dynamic, hydraulic-dispersive model to a statistic one that accounts for the correlation between hydraulic related forcing functions (salinity, residence time) and water-quality data is a promising and simple way to evaluate the water-quality of the Lagoon of Venice. Of course, this methodology is applicable because a very large data-set is now available. The usual limitations of the statistical model methodology are present in this application too. E.g. it cannot precisely estimate the values of the water-quality variables, but it can indicate how they react when the system hydrological features change. Besides, the outcomes depend strongly on site characteristics and on the actual ecosystem state. The model has not been validated yet, due to the short data time lag, but the aim of this work is to suggest a simple simulation tool whose reliability is at least the same of that obtained by complex, deterministic, dynamic water-quality models. These models, accounting for several processes and hence including a lot of parameters, require for calibration a much more detailed data-set not yet available. The increase of dissipation is altering nutrient concentrations in the Lagoon of an average +3.2%, while the average variation for TRIX is +0.4%, and for chlorophyll-a is +3.0%. These variations are small enough to confirm a posteriori the validity of the adopted statistical approach.
- Short-term simulations under winter conditions in the Lagoon of Venice: a contribution to the environmental impact assessment of temporary closure of the inlets
D. M. Canu, G. Umgiesser and C. Solidoro.
Ecological Modelling, Vol. 138, No. 1-3, 15 Mar 2001, pp. 215-230.
A primitive equation finite element hydrodynamic model developed for the Lagoon of Venice some years ago has been internally coupled with the Streeter-Phelps module of Water Quality Analysis Simulation Program (WASP). The coupled model (VELFEEM) has been applied for a first evaluation of the impact on water quality of the Lagoon of Venice induced by a reduction in the exchange with the Adriatic Sea, which could be caused by the temporary closure of the inlets. Such closures have been proposed to prevent the flooding (acqua-alta) of the historical city occurring in winter time and would be obtained by specifically designed mobile gates (MOSE). Short-term simulations of biochemical oxygen-dissolved oxygen (BOD-DO) dynamics are performed under winter conditions, in both the presence and the absence of the mobile closure. Results suggest that the mobile closures do not significantly affect the water quality of the lagoon, even in the case of repeated closures, and that, in any case, the lagoon seems to be able to return rather easily to its unperturbed condition when the inlets are open again.