Research Highlight: Saving Venice

There was something different about this project.

The fact struck geochemist Tony Rathburn while in the laboratory of Thetis SPA, an Italian environmental engineering firm and Scripps collaborating partner, as he examined research samples. He would do so while fine art lovers passed him by as they examined displays on the grounds of the same historic building that Thetis called home.

For Principal Development Engineer Bill Boyd, the uniqueness of the project became apparent while flying over the city’s masterful, centuries-old architecture and experiencing an “unbelievable” feeling of flying back into medieval times.

For microbiologist Doug Bartlett, it was the intriguing idea of studying sediment core samples that, with each deepening layer, would transport him back century by century and the notion of perhaps finding traces of the Black Plague that ravaged Europe in the Middle Ages.

Working in Venice, Italy, the celebrated city of romance, gondolas and Marco Polo, has presented rare opportunities and challenges for a handful of Scripps Institution of Oceanography, UC San Diego scientists.

The diverse team assembled for the Scripps Institution of Oceanography Sediment, or SIOSED, research group is probing the mix of processes dealing with dredging and reusing sediment lying beneath historic Venice’s lagoon. SIOSED was launched two years ago after the City of Venice’s Water Authority, through its concessionary, Consorzio Venezia Nuova, and Thetis approached Scripps for a scientific analysis of sediment ecotoxicology and related issues in the lagoon.

Venice officials must consistently grapple with environmental issues related to sediment processes, as the shallow lagoon—1 to 1.5 meters (3.3 to 5 feet) deep on average—must continually be dredged to allow a steady stream of commercial vessels and cruise ships.

The SIOSED team’s analysis will guide near-daily efforts to safely relocate tons of sediment as well as general coastal management projects. When sediment is dredged and transplanted to another part of the lagoon, how do the chemical properties of the water change? How do microscopic bacteria react? What about flora and fauna in the fragile lagoon ecosystem? And, apart from signs of plagues of bygone eras, what pathogens or other hazards might be lurking down deep?

The answers to these questions are vital for the maintenance and conservation of Venice’s environment. Beyond dredging, the SIOSED team’s findings could be applied to other estuary and wetland environments facing threats from flooding or sea level rise.

SIOSED’s project leaders hope their multidisciplinary approach becomes a new asset for policymakers, city planners, and environmental managers in coastal cities around the world in an era of unpredictable global change.

EXPLORING THE VENETIAN WORLD

First settled in the fifth century, Venice is a collection of dwellings and structures spread out among 117 islands in a coastal wetland. The lagoon that surrounds the city links directly with the Adriatic Sea through inlets. Declared a World Heritage site in 1987 by the United Nations, the city features some 150 canals and 400 bridges.

Scripps Oceanography has its own history of providing Venice with scientific expertise. In the 1970s, renowned Scripps oceanographer Walter Munk contributed his expertise when the idea of flood-limiting gates was being developed. Later, researcher Yehuda Bock used GPS technology to measure the precise rate of sinking in the city.

The unique qualities of a city crisscrossed by water boundaries can confound even the most experienced travelers. Even cosmopolitan SIOSED project leader Dimitri Deheyn, who hails from Belgium but was raised in Congo, Rwanda, and Peru, was surprised by aspects of the Venetian water world.

For example, while traveling around Venice lagoon he was surprised by the waterways’ similarities to a highway system, complete with stop signs, speed limits, and red lights. He was even more taken aback by the boats that correspond to land-based counterparts, including ambulances, firefighting vessels, and even a FedEx delivery vessel.

The most evident environmental threat for the city is flooding, a frequent occurrence at tourist epicenter St. Mark’s Square and on lower floors of countless buildings throughout the city. The flooding is attributed to several causes, most directly to the fact that Venice is sinking—nearly 23 centimeters (9 inches) in the last 100 years—into its soft marshland foundation.

Amplifying the problem are aqua alta, or high water, events, increasingly common flooding episodes triggered by a combination of seasonal high tides and Adriatic winds. Global climate change-induced sea-level rise also may be a contributing factor. The Intergovernmental Panel on Climate Change report released last month projected a rise in global sea levels of between 18 and 59 centimeters (7 and 23 inches) by the end of the century.

In order to address the flooding dilemma and a host of related issues, Venice has begun developing ways to safeguard the city and its lagoon. While some efforts call for raising buildings and piazzas brick by brick, the largest-scale solution is the Experimental Electromechanical Module, or MoSE project, a planned engineering effort to construct a series of immense lagoon barriers designed to block incoming waters when sea levels are dangerously high.

For SIOSED, Deheyn took on the task of assembling a diverse team able to provide deep insight on the complex mix of processes involved in Venice lagoon.

“The main focus of SIOSED is analyzing the dynamic processes involved in reusing sediment and in building subtidal sediment banks,” said Deheyn. “Will the physical chemistry of the sediment change? When we look at the dredged sediment layers, we are going back hundreds of years. What are we dealing with from decades past?”

Joining Deheyn’s expertise in ecological toxicity studies in SIOSED are Rathburn and Joris Gieskes, experts in geochemistry, along with Brad Tebo, who studies microbial geochemistry in the lagoon. To understand the role of disease-causing pathogens, the team includes Doug Bartlett. Phytotoxicity, the investigation of plant-derived poisons, is studied by Osmund Holm-Hansen. Understanding how changes in sediment might impact carbon levels and related cycling is being investigated by Farooq Azam. Lisa Levin and her colleagues are studying impacts of transplanted sediment on seafloor communities in the lagoon. Aspects related to sediment and water circulation, or hydrodynamics, are being analyzed by Hany Elwany.

To study dredging conditions, nearly 1,300 cubic meters (4,200 cubic feet) of sediment have been dredged and spread into six undersea banks. Along with SIOSED colleagues in Italy, the team collected sediment core and seawater samples roughly every six weeks over 15 field campaigns designed to track the changes in the sediment and lagoon over time.

Initial analyses are conducted at Thetis in order to establish baseline characteristics of the sediment, such as temperature and water conditions. The samples are then frozen to keep bacteria from changing and FedEx’d to Scripps for detailed examinations in the laboratories of the team’s investigators. Various analyses have been carried out by Italian partners in Venice and Trieste.

For Deheyn, the challenge has been not only managing the SIOSED program, but getting scientists from diverse backgrounds to collaborate cohesively so that they can answer the same questions about the Venetian sediment. Some scientists work on large scales of physical oceanography over tens of meters while others look at microorganisms at the millimeter level.

“We have all these people getting together and trying to speak the same scientific language—it’s challenging but it also makes it very exciting,” said Deheyn.

GLOBAL RESULTS

Initially slated as a two-year project, SIOSED was recently extended to 33 months to broaden the testing and analytical efforts. The project ends on Nov. 7, but Deheyn expects a series of research papers based on the data to be published in the months ahead and beyond.

Early results of the project show that dredged and translocated sediment will not have a negative impact on the lagoon ecosystem.

Bartlett’s group has searched for bacterial and viral pathogens using various molecular tests and has not seen substantial threats thus far, other than sites closer to sewage discharge areas that, not surprisingly, revealed high levels of certain bacteria and viruses. Nor has the group seen any traces of the plague.

For the benthic animals in the lagoon, Levin says the wetlands of Venice have exhibited surprising parallels with those of San Diego. Both, she says, are under pressure from humans and invasive species, have restoration efforts underway, and feature food webs fueled by algae.

“Our research studies the extent to which food webs have recovered in restored salt marshes and the speed with which invertebrate communities recover in artificial sediment banks,” said Levin. “So far in Venice we have seen that the banks recover faster than the salt marshes.”

Rathburn and Gieskes, meanwhile, have seen a possible relationship between tiny single-celled organisms called foraminifera and the level of contamination in lagoon sediment.

Historians of the storied city might remember the Scripps effort as part of the larger project that saved Venice. But for Deheyn, the public benefits may have a much wider reach.

“SIOSED is being developed in Italy but its lessons could be applied to other coastal cities around the world,” he said.

-- Mario C. Aguilera