On the changing ecology of Venice lagoon

Abstract

The parameters characterizing the state of the Venice lagoon environment and its biota were measured at 70 stations covering all its three basins in August–October 1996. These observations repeated those accomplished in the lagoon in 1993 during a previous survey. Comparison of the results for 1993 and 1996 showed that a drastic change in the ecological situation had occurred in the lagoon during that period. In 1993, it was critical in its central and northern basins, while the southern basin was still preserving its less perturbed ecological status. In 1996, the ecosystems of the former two basins were found to be rapidly recovering, but the ecosystem at the southern basin was found to be in a state of catastrophic collapse regarding its biota, especially in its southern part. This change was attributed to the change in the direction of waste discharges by the Marghera refinery complex from the central basin to the southern basin under the pressure of public opinion. The phenomenon of the rapid ecological recovery of the central and northern basins released from the detrimental industrial pollution impact of the Marghera wastes is investigated in detail, as is also the ecological distress in the southern basin. Among the parameters measured at the stations were: contents of labile organic matter and suspended organic matter in water column, standing stock of acid-volatile sulfides in bottom sediments, abundance and composition of all plankton components, whole plankton biomass, primary production by phytoplankton, bacterial production and decomposition rate of organic matter. The comparison of parameters measured in 1993 and in 1996 in the areas considered is presented as well as the basic ratios and examples of energy balances. The problems of monitoring the Venice lagoon ecology are discussed.