Integrating culture-based and molecular methods provides an improved assessment of microbial quality in a coastal lagoon.

Faecal pollution in aquatic environments is a worldwide public health concern, yet the reliability and comprehensiveness of the methods used to assess faecal contamination are still debated. We compared three approaches, namely a culture-based method to enumerate Faecal Indicator Bacteria (FIB), a FIB-targeting qPCR assay, and High-Throughput Sequencing (HTS) to detect faeces- and sewage-associated taxa in water and sediment samples of an impacted model lagoon and its adjacent sea across one year. Despite at different levels, all approaches agreed in showing a higher contamination in the lagoon than in the sea, and higher in sediments than water. FIB significantly correlated when considering separately sediment and water, and when using both cultivation and qPCR. Similarly, FIB correlated between cultivation and qPCR, but qPCR provided consistently higher estimates of FIB. Faeces-associated bacteria positively correlated with cultivated FIB in both compartments, whereas sewage-associated bacteria did only in water. Considering their benefits and limitations, we conclude that, in our study site, improved quali-quantitative information on contamination is provided when at least two approaches are combined (e.g., cultivation and qPCR or HTS data). Our results provide insights to move beyond the use of FIB to improve faecal pollution management in aquatic environments and to incorporate HTS analysis into routine monitoring.

Partitioning and sources of microbial pollution in the Venice Lagoon.

Microbial pollutants are a serious threat to human and environmental health in coastal areas. Based on the hypothesis that pollution from multiple sources may produce a distinct microbial signature and that microbial pollutants seem to distribute between a free-living and a particle-attached fraction, we investigated the occurrence, partitioning and sources of microbial pollutants in water samples collected in the Venice Lagoon (Italy). The area was taken as a case study of an environment characterized by a long history of industrial pollution and by growing human pressure. We found a variety of pollutants from several sources, with sewage-associated and faecal bacteria accounting for up to 5.98% of microbial communities. Sewage-associated pollutants were most abundant close to the city centre. Faecal pollution was highest in the area of the industrial port and was dominated by human inputs, whereas contamination from animal faeces was mainly detected at the interface with the mainland. Microbial pollutants were almost exclusively associated with the particle-attached fraction. The samples also contained other potential pathogens. Our findings stress the need for monitoring and managing microbial pollution in highly urbanized lagoon and semi-enclosed systems and suggest that management plans to reduce microbial inputs to the waterways should include measures to reduce particulate matter inputs to the lagoon. Finally, High-Throughput Sequencing combined with computational approaches proved critical to assess water quality and appears to be a valuable tool to support the monitoring of waterborne diseases.

COVID-19 lockdown measures reveal human impact on water transparency in the Venice Lagoon.

The lagoon of Venice has always been affected by the regional geomorphological evolution, anthropogenic stressors and global changes. Different morphological settings and variable biogeophysical conditions characterize this continuously evolving system that rapidly responds to the anthropic impacts. When the lockdown measures were enforced in Italy to control the spread of the SARS-CoV-2 infection on March 10th 2020, the ordinary urban water traffic around Venice, one of the major pressures in the lagoon, came to a halt. This provided a unique opportunity to analyse the environmental effects of restrictions to mobility on water transparency. Pseudo true-colour composites Sentinel-2 satellite imagery proved useful for qualitative visual interpretation, showing the reduction of the vessel traffic and their wakes from the periods before and during the SARS-CoV-2 outbreak. A quantitative analysis of suspended matter patterns, based on satellite-derived turbidity, in the absence of traffic perturbations, allowed to focus on natural processes and the residual stress from human activities that continued throughout the lockdown. We conclude that the high water transparency can be considered as a transient condition determined by a combination of natural seasonal factors and the effects of COVID-19 restrictions.

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.

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.

Investigation of residence time and groundwater flux in Venice Lagoon: comparing radium isotope and hydrodynamic models.

The four naturally-occurring isotopes of radium were coupled with a previously evaluated hydrodynamic model to determine the apparent age of surface waters and to quantify submarine groundwater discharge (SGD) into the Venice Lagoon, Italy. Mean apparent age of water in the Venice Lagoon was calculated using the ratio of 224Ra to 228Ra determined from 30 monitoring stations and a mean pore water end member. Average apparent age was calculated to be 6.0 d using Ra ratios. This calculated age was very similar to average residence time calculated for the same period using a hydrodynamic model (5.8 d). A mass balance of Ra was accomplished by quantifying each of the sources and sinks of Ra in the lagoon, with the unknown variable being attributed to SGD. Total SGD were calculated to be 4.1 +/- 1.5, 3.8 +/- 0.7, 3.0 +/- 1.3, and 3.5 +/- 1.0 x 10(10) L d(-1) for (223,224,226, 228)Ra, respectively, which are an order of magnitude larger than total mean fluvial discharge into the Venice Lagoon (3.1 x 10(9) L d(-1)). The SGD as a source of nutrients in the Venice Lagoon is also discussed and, though significant to the nutrient budget, is likely to be less important as the dominant control on SGD is recirculated seawater rather than freshwater.

Sediment chemical contamination of a shallow water area close to the industrial zone of Porto Marghera (Venice Lagoon, Italy).

The industrial zone of Porto Marghera is one the most important "contaminated sites of national interest" (SIN) in Italy, being identified as an area of high environmental risk. The site includes a wide shallow water area of the Venice Lagoon extending toward the city of Venice, which was investigated in order to acquire information on the pollutant level and distribution. Grain-size, heavy metal, nutrient, and organic micropollutant concentrations were determined in the surface sediment layers (0-5 and 5-10 cm depths) of 51 sites. A generally low contamination was found, except for Hg concentration, which increases the toxicological risk in most of the sites of the area, according to the results of a comparison with Sediment Quality Guidelines. A heavy pollution fingerprint (Cd, Cu, Hg, Pb, and Zn up to 15.2, 257, 11.9, 248, and 3010 mg/kg d.w., respectively) was instead found near the Tresse Island, which is ascribed to the spill of pollutants from the contaminated sediment disposed therein. Grain-size and heavy metal profiles down to a depth of 40 cm in eight selected sites, finally show a probable decrease of the pollution affecting the area in recent years.

Sulphate reduction in the sediment of the Venice canals (Italy).

The sulphur cycle in the sediment of the Venice canal network was investigated by considering the sulphate reduction rate (SRR) and the distribution of sulphur compounds, in both pore water and sediment. Sulphate reduction (SR) is the main process in the metabolism of the organic matter supplied to the network by untreated urban effluents. Although it might account for the decomposition of only a limited percentage of the total organic-C inputs, the estimated rates are among the highest observed in coastal sediments. Measured rates range from 0.26 to 0.99 micromolcm(-3)d(-1), while mean annual values, estimated by a diagenetic model, vary from 0.16 to 0.43 micromolcm(-3)d(-1). The speciation of S in the sediment reveals that pyrite-S is the most abundant component of the total reduced S pool, whereas acid volatile sulphides and elemental sulphur together account for less than 45%. A preliminary budget indicates that the rate of burial of solid-phase S is small compared to the S produced by SR (from 10 to 25%). A large amount of reduced S is then lost from the canal deposits to be re-oxidised at the sediment-water interface or in the overlying water column.

The effect of floods on the transport of suspended sediments and contaminants: a case study from the estuary of the Dese River (Venice Lagoon, Italy).

A flood event was investigated in a measurement section of the estuary of the Dese River, the major tributary of the Venice Lagoon (mean annual discharge=7.5 m3/s), to observe the variations induced by the flow on the physico-chemistry of the water column and the transport of particles and pollutants. The flood was generated by a typical summer storm, which had a return period of 2 years. The study was based on the continuous recording of the discharge and the measurement of both current speed and physico-chemical variables along the vertical profile. Water samples were also collected for the analysis of total and dissolved heavy metals (As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn), and nutrients (TKN, N-NO3-, N-NO2-, N-NH3, total phosphorous, P-PO43-). The suspended particle matter (SPM) concentration increased in the water column during the flood, and the discharge versus SPM relationship showed a counterclockwise hysteresis. The occurrence of hysteresis was related to the delayed response of the load, deriving from the runoff on the basin soils with respect to materials mobilized from the streambed in the initial phases of the flood. The transport of most of the analysed heavy metals was driven by the SPM. The increase in concentration of this parameter significantly affected the amount of Fe, Cu, Pb, Cr, Ni, and partially Zn transported by the stream. Among nutrients, N-NO3- concentration also increased significantly during the flood, due to the runoff on agricultural surfaces. The study allowed describing the mechanisms of load generation with high flow magnitudes, highlighting the importance of floods in the transport of materials and pollutants from the drainage basin to the Venice Lagoon.

Freshwater discharge from the drainage basin to the Venice Lagoon (Italy).

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.

Objectives and structure of the DRAIN project: an extensive study of the delivery from the drainage basin of the Venice Lagoon (Italy).

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.

Pollutant loads from the drainage basin to the Venice Lagoon (Italy).

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.