To reduce the effect of the “high water”, which involves mainly the City of Venice, a project is underway to install barriers in the three port channels which connect the Venice lagoon to the Northern Adriatic Sea. To have a basis on which to gauge any observed effects in the water quality as a consequence of the reduction of the exchange of water between the lagoon and the open sea, a survey on the most polluted area of the lagoon was carried out over the period of a year. The following parameters were determined: pH, temperature, salinity, transparency, dissolved oxygen, ammoniacal nitrogen, orthophosphate, zinc and total coliforms. The results, compared to those obtained from previous studies, show that situation improved for ammoniacal nitrogen, zinc and coliforms and remained fairly constant for the other parameters. The inner zones of the lagoon are much more exposed to eutrophication as a consequence of a lower circulation of water and higher accumulation of nutrients. Release from sediments appears to play an important role in controlling the water quality in the shallow areas. Frequent algae blooms have been observed during spring and summer seasons. There is no evidence of an attenuation of eutrophic phenomena in recent years.

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