First basin scale spatial-temporal characterization of underwater sound in the Mediterranean Sea.

Anthropogenic underwater noise is an emergent pollutant. Despite several worldwide monitoring programs, only few data are available for the Mediterranean Sea, one of the global biodiversity hotspots. The results of the first continuous acoustic programme run at a transnational basin scale in the Mediterranean Sea are here presented. Recordings were done from March 2020 to June 2021, including the COVID-19 lockdown, at nine stations in the Northern Adriatic Sea. Spatial-temporal variations of the underwater sound are described, having one third octave band sound pressure levels (SPLs) from 10 Hz to 20 kHz as metrics. Higher and more variable SPLs, mainly related to vessel traffic, were found close to harbours, whereas Natura 2000 stations experienced lower SPLs. Lower values were recorded during the lockdown in five stations. Median yearly SPLs ranged between 64 and 95 as well as 70 and 100 dB re 1 µPa for 63 and 125 Hz bands, respectively. These values are comparable with those previously found in busy shallow EU basins but higher levels are expected during a business-as-usual period. This is a baseline assessment for a highly impacted and environmental valuable area, that needs to be managed in a new sustainable blue growth strategy.

First assessment of underwater sound levels in the Northern Adriatic Sea at the basin scale.

The protection of marine habitats from human-generated underwater noise is an emerging challenge. Baseline information on sound levels, however, is poorly available, especially in the Mediterranean Sea. To bridge this knowledge gap, the SOUNDSCAPE project ran a basin-scale, cross-national, long-term underwater monitoring in the Northern Adriatic Sea. A network of nine monitoring stations, characterized by different natural conditions and anthropogenic pressures, ensured acoustic data collection from March 2020 to June 2021, including the full lockdown period related to the COVID-19 pandemic. Calibrated stationary recorders featured with an omnidirectional Neptune Sonar D60 Hydrophone recorded continuously 24 h a day (48 kHz sampling rate, 16 bit resolution). Data were analysed to Sound Pressure Levels (SPLs) with a specially developed and validated processing app. Here, we release the dataset composed of 20 and 60 seconds averaged SPLs (one-third octave, base 10) output files and a Python script to postprocess them. This dataset represents a benchmark for scientists and policymakers addressing the risk of noise impacts on marine fauna in the Mediterranean Sea and worldwide.

New evidence of a Roman road in the Venice Lagoon (Italy) based on high resolution seafloor reconstruction.

This study provides new evidence of the presence of an ancient Roman road in correspondence to a paleobeach ridge now submerged in the Venice Lagoon (Italy). New high resolution underwater seafloor data shed new light on the significance of the Roman remains in the lagoon. The interpretation of the data through archive and geo-archaeological research allowed a three-dimensional architectural reconstruction of the Roman road. The presence of the ancient Roman road confirms the hypothesis of a stable system of Roman settlements in the Venice Lagoon. The study highlights the significance of this road in the broader context of the Roman transport system, demonstrating once more the Roman ability to adapt and to handle complex dynamic environments that were often radically different from today.

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 human-impacted 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 · 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 · 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 45⋅103 m3/year and the disappearing of dune fields at a rate of 104⋅103 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.

Assessing the human footprint on the sea-floor of coastal systems: the case of the Venice Lagoon, Italy.

Coastal systems are among the most studied, most vulnerable, and economically most important ecosystems on Earth; nevertheless, little attention has been paid, so far, to the consequences of human activities on the shallow sea-floor of these environments. Here, we present a quantitative assessment of the effects of human actions on the floor of the tidal channels from the Venice Lagoon using 2500 kilometres of full coverage multibeam bathymetric mapping. Such extended dataset provides unprecedented evidence of pervasive human impacts, which extend far beyond the well known shrinking of salt marshes and artificial modifications of inlet geometries. Direct and indirect human imprints include dredging marks and fast-growing scours around anthropogenic structures built to protect the historical city of Venice from flooding. In addition, we document multiple effects of ship traffic (propeller-wash erosion, keel ploughing) and diffuse littering on the sea-floor. Particularly relevant, in view of the ongoing interventions on the lagoon morphology, is the evidence of the rapid morphological changes affecting the sea-floor and threatening the stability of anthropogenic structures.

High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon.

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system.