RESUMEN
The sediment phase of the Venice lagoon within an area of shallow water, the Palude della Rosa, was studied and three insoluble enzymatic activities (cellulase, phosphatase and urease) were found to be linked to the inorganic phase. These immobilized enzymes were more resistant to environmental changes, even extreme ones, compared to their soluble counterparts. The evolution of their activity with pH, temperature and seasonal variation was investigated. While pH related activities showed the usual behaviour, the resistance to temperature was extremely high and seasonal variation was dependent on immobilization. These enzymatic activities could be used as a diagnostic factor for the ecosystem, since their presence is related to the nature of the waste products.