Venice has never maintained a main sewage system (Zonta, et al., 2005). For this reason, a large portion of the wastes generated in the historic center of Venice have always been discharge directly into its channels. Recently, an increasing number of septic systems have been installed. Also, plans are now underway to improve water quality by decreasing sewage flow, improving standards of water treatment, reusing water, and dispersing effluents offshore into the Adriatic Sea (Casarin et al., 2005).
Currently, water quality, particularly near the city, is extremely poor. The lagoon faces eutrophication, chemical pollution, and contamination by endocrine disrupters (Fletcher et al., 2005). During the 1970s and '80s eutrophication frequently lead to large algal blooms and anoxic events (Marcomini et al., 2005). In 1990 phosphates, an important limiting nutrient for algal growth, were banned from use in detergents in Italy (Zirino, 2005). Since that time, algal blooms have declined, though it is uncertain if the cause of decline can be traced to decreased phosphates or increased turbidity within the lagoon.
More recent concerns have focused on the levels of heavy metals and concentrations of chemical pollutants such as dioxins, PCBs, DDT, aromatic hydrocarbons, herbicides, and pesticides (Zirino, 2005 and pesticides Zonta et al., 2005). Both water and sediment pollution is widely distributed within the lagoon. Pollutants not only originate within the city, but from aerosols (Capodaglio et al., 2005) and to a greater extent from the lagoon's watershed (Zonta et al., 2005). About 70% of the drainage basin that empties into the lagoon is used either for agriculture or raising livestock. Substantial pollution from these sources can reach the lagoon, particularly during April and November flooding.
Lagoon sediments can serve as a reservoir for pollutants. If sediments become resuspended during activities such as fishing (Solidoro et al., 2005) or by the wakes caused by motor boats (Dabala et al., 2005) pollution can be reintroduced to the water column. Sediment pollution within the lagoon represents such a significant problem that most of the sediments currently removed during periodic dredging to clear the channels are not considered fit for recycling within the lagoon (Zonta et al., 2005).
Go To Subsidence,
sea level rise, and storm surge
List of Visuals
- Aerial photograph of dredging and sediment remediation in Venice lagoon
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