Trophic Conditions in the Waters of the Venice Lagoon (Northern Adriatic Sea, Italy)

Data on nutrient concentrations and environmental parameters, recorded in the waters of the entire Venice lagoon (165 sites) in July 2003 and in two stations monthly sampled for two years (from April 1994 to March 1995 and from January to December 2005), are reported in order to compare the trophic conditions with the past situation. In summer 2003 the dissolved inorganic nitrogen varied between 0.66 and 41.2 μM, whereas the reactive phosphorus fluctuated between 0.01 and 1.75 μM. Values above the imperative values (nitrogen >25 μM, phosphorus >0.81 μM) established by the Italian law were not rare and they were found close to the mainland and the main river outflows. The comparison with previous data to update the knowledge on the trophic conditions of the lagoon showed that the overall trophic load is reducing. Only nitrate concentrations did not change. The seasonal samples allowed to confirm the above observations highlighting the behaviour of nutrients in relation to the weather conditions and to the primary producer fluctuations.