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Venice 2014

The Lagoon: Health and Transformations

Comparisons between maps and surveys from the early 1800s and today reveal that the lagoon is and has been progressively shifting from a shallow marshy wetland towards a marine landscape.  The rate and progression of this shift is difficult to quantify and track because of the lack of data. What is known is that the problems associated with these changes are the result of the ‘sediment budget,’ the entering and leaving of sediment to and from the lagoon, which determine its physical habitats and health.[4] Disturbances resulting from the currents stirring-up and redistributing the sediments, which range from fine mud and fluvial silt to coarser sand, cause areas of higher sediment accumulation in the northern area of the lagoon and overall eroding of sediments in the remaining areas. The rate at which the lagoon is deepening coincides with the increasing volume of sediment swept out to sea. As the lagoon’s bed smoothes out and deepens and the dendritic creeks disappear, the currents become stronger, in turn draw more silt and sand into the navigational channels, which calls for costly dredging projects. With the erosion and reduction of sediment over the last century, the volume of water in the lagoon has doubled. 

The lagoon is inundated with a variety of pollutants from numerous sources, both on the mainland and on the islands.

What are these sources?

  • Factories – The refineries, chemical plants, and heavy metal factories constructed during the years 1950 to 1970 in the Marghera district, drained the majority of their liquid waste into the lagoon.

  • Dumps – Five million cubic yards of waste material distributed amongst 17 abandoned dumpsites was discovered by Venetian authorities.
  • Farms – The runoff from agricultural and livestock farms on the mainland contributes 53 percent of the phosphates and other pollutants in the lagoon, a roughly 700,000-square-mile drainage basin. The run-off from farms contains pesticides and fertilizers, which destroy the natural saltmarshes, vegetation along the banks of the mudflats, and algea covering the lagoon bed. 
  • People – The more than 100 municipalities in the basin surrounding the city center of Venice is home to approximately 1,400,000 citizens, the source of nearly half the pollutants in the lagoon.

  • Air and Road - Cruise ships, oil tankers, mainland cars, and factories release tons of pollutants and gases into the air, which cling to the exterior of buildings causing corrosion and foundation fragility.[5]

[4] Fletcher, Caroline and Jane Da Mosto. The Science of Saving Venice. Turin: Umberto Allemandi & Co., 2004. p.24.

[5] Permuda, Margherita, et al. “Evaluation of Vessel Emissions in a Lagoon Area with Ground Based Multi Axis DOAS Measurements.” Atmospheric Environment. no. 45 (2011): 5212-5219.