Increased eutrophication of the Northern Adriatic sea

The Northern Adriatic is one of the most productive regions of the Mediterranean, primarily due to the eutrophicating influence of Italian rivers, in particular the Po. In June 1977 unusually high phytoplankton standing crops (13 μg Chl a l.−1) occurred, together with extremely low dissolved oxygen concentrations in bottom waters (to 13%) which persisted for 4–6 months. Such conditions were associated with unusual climatic conditions creating increased discharge from the Po. The data indicate long term meteorological changes which may alter the biological characteristics of the region to a degree equal to, or exceeding, those created by anthropomorphic eutrophication. The 1977 data are presented, discussed, and contrasted with a 10 year data series.