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Marine Ecology Progress Series

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MEPS 141:247-261 (1996)  -  doi:10.3354/meps141247

Study of the ecosystem of the lagoon of Venice, with emphasis on anthropogenic impact

Sorokin YuI, Sorokin PYu, Giovanardi O, Dalla Venezia L

The parameters of the structure and functioning of the ecosystem in the lagoon of Venice (Italy) were estimated in September-October 1993 at 36 stations. Phytoplankton was dominated by its nano- and pico-fractions, which comprised 60 to 99% of the total phytoplankton biomass. Phytoplankton wet biomass varied between 100 and 600 mg m-3 and its primary production between 30 and 90 mg C m-2 d-1. The numerical abundance of bacterioplankton (3 to 6 x 106 cells ml-1) and its wet biomass (0.3 to 1 g m-3) was 2 to 3 times greater than in adjacent waters of the Adriatic. Bacterial production was 20 to 40 mg C m-3 d-1. Microzooplankton was dominated by ciliates with biomasses of 30 to 700 mg m-3, while the density of rotifers and nauplii was low. The composition of mesozooplankton resembled that of the Adriatic complex only near the port entrances connecting the lagoon to the sea, while in polluted areas it was drastically depleted. Its average wet biomass was 80 to 300 mg m-3, attaining 700 to 1100 mg m-3 near the port entrances. The total plankton biomass was 0.8 to 2 g m-3, and was dominated by microplankton. The stock of labile organic matter in the lagoon was 2 to 3 times greater than in the waters of the adjacent Adriatic, with a turnover time which varied between 10 and 20 d. The stock of labile sulfides in the upper layer of the bottom sediments in the central basin of the lagoon was 1.5 to 2 g S dm-3 of wet silt. Data were generalized using the approach of energy balances and energy flows. The latter were used to evaluate the present state of the ecosystem of the lagoon of Venice, its changes due to anthropogenic impact, and its capability for self-purification.

Lagoon of Venice · Energy flows · Biomass · Primary production

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