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Comparative studies

In contrast to Arcachon Bay the Sacca di Goro has a more limited tidal flushing and nitrogen inputs per unit area are greater by a factor of ca. 6. Important blooms occur of Gracilaria sp. and Ulva rigida and dystrophic crises occur on an annual basis. Peak values of Ulva biomass reach 800 g DW/m2 compared to a maximum of 150-200 g DW/m2 of Z. noltii in the Bassin d'Arcachon and a maximum of 400 g DW/m2 of Ruppia cirrhosa in the Valli di Comacchio. The system is net autotrophic during the growing season of the macroalgae, and becomes net heterotrophic during the algal crash which results in a dystrophic crisis. Inorganic nutrient concentrations in the water column show a negative correlation with plant biomass and a positive relation with riverine inputs. This shows that Ulva biomass represents clearly a temporal sink of N and P, but these elements are recycled during the algal crash. Very high concentrations of iron (200-500 µ occur in the sediment of the Sacca di Goro. The seasonal changes in the HS- - FeS - FeS2 system were monitored. As in the Bassin d'Arcachon, the total ratio of acid volatile sulphides to Fe(II), which is an indication of the saturation of the sedimentary iron buffer to sulphide, was always below 1.

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