Venice lagoon contains an ‘underwater dump’

A new study has revealed the precarious future of the famous lagoon in the historical Italian city of Venice.

The research, just published in the journal Scientific Reports, documents with unprecedented accuracy the imprint of multiple human activities on the sea-floor of the lagoon through mapping carried out with high-resolution geophysical instruments.

Lead researcher Fantina Madricardo from Italy’s Institute of Marine Sciences explains the results were obtained using multibeam echo-sounders (MBES) which provided “a sort of ultrasound of the sea-floor” that mapped the lagoon to centimetre-scale resolution.

The results revealed, she says, “the traces of dredging, grooves on shallow waters carved by off-course keelboats, or by their engines and the thruster of the ‘vaporetti’ (water buses) at the stops, which in low tide conditions ‘plow’ the sea-floor”.

This innovative approach, specifically designed for very low-depth environments, can be used in other shallow coastal areas to determine the impact and pervasiveness of human activities.

“Of great importance are the erosive structures generated by tidal currents around most of the coastal infrastructures built on an underwater basis, such as the piers which protect the port mouths from sea waves, where depressions of a few metres have formed within a few years after their construction,” explains Madricardo. 

“Making repeated surveys over the next few years with the same tools used in this study will allow us to identify early and, hopefully, prevent any collapses of the dams themselves.”

According to Fabio Trincardi, director of the Department of Sciences at Italy’s National Research Council (CNR) and designer of the MBES, the piers generate the tidal currents that, in turn, endanger their stability.

But the study also reveals another highly significant factor: the presence of a large quantity of marine litter in the lagoon channels.

“We chose the Venice lagoon to test this approach in order to make it clear that in all coastal areas and in the sea-floor we have not only the problem of pollution by chemicals but also that of solid waste, beyond the plastics and microplastics which are already subject to widespread attention,” Trincardi says.

He describes the litter as “a sort of neglected ‘underwater dump’ produced by malice and unawareness”.

“It leads many people to believe that what flows into the sea has no consequence on ecosystems and human health,” he continues, “just because this environment is not immediately visible, and leads us to pretend that the problem does not exist.”

Co-author Elisabetta Campiani says the subsurface litter needs to be recognised as a danger.

“We must not only worry about the increasingly invasive presence of anthropic waste on the surface of the sea or on the beaches, but also of those that accumulate on the sea-floor,” she says.

“In some ways, these are riskier precisely because they are invisible.”