PHOSPHORUS-METABOLISM IN ANTHROPOGENICALLY TRANSFORMED LAGOON ECOSYSTEMS - THE COMACCHIO LAGOONS (FERRARA, ITALY)

Inorganic phosphorus dynamics were investigated with the use of P-32 i n the hypertrophic Comacchio lagoons (NE Adriatic) during an extremely dense, quasi-permanent bloom of picocyanobacteria. Concentrations of dissolved inorganic phosphate (DIP) in waters of the blooming lagoons were usually near the detection limit (0.01 mu moles . dm(-3)). DIP up take rates by microplankton at near-ambient concentrations (0.01 to 0. 1 mu moles . dm(-3)) were in the range of 9.6 to 16.1 nmoles P . dm(-3 ). min(-1), and turnover times were 1.5 to 3 min. The turnover time wa s >40 h in the eutrophic coastal waters of the adjacent Adriatic Sea. The uptake rate of DIP depended on its initial concentration. in water samples artificially enriched with DIP, the uptake rate rose to its m aximum of 0.10 to 0.13 mu moles P . dm(-3). min(-1) (or similar to 6 t o 7 mu moles . dm(-3). h(-1)) when the initial concentration of DIP wa s elevated to 10 to 20 mu moles . dm(-3). The potential capacity of mi croplankton in the water samples to consume and retain DIP was estimat ed at similar to 25 mu moles . dm(-3). Specific features are discussed of phosphorus metabolism in the anthropogenically transformed lagoon ecosystem with an anomalous food web with few animals.