Eutrophication along the Emilia-Romagna coast: application of statistical analyses to 1984–1989 monitoring data

Eutrophication of the Northern Adriatic is a long-standing problem and in 1988 and 1989 a pale brown mucilage appeared in the sea, formed from extracellular polysaccharides produced by algae growing in the water. Data from the years 1984-89 from the extensive water quality data set collected by the M.N. Daphne was examined using the AARDVARK statistical software. The objective was to see if any features distinguished the years 1988 and 1989, in which mucilage was observed, from other years and whether any trends in water quality variables could be detected. Seasonal changes were observed in nitrate levels, but not in phosphate nor in chlorophyll a. No extreme values were observed in 1988 and 1989 but the peak nitrate concentrations in these years were only half the historical peak levels. Peaks in nitrate and phosphate concentration coincided with troughs in salinity but there was no correlation between phosphate and nitrate concentration, indicating that these two nutrients, although both associated with freshwater inputs, have different origins. In the first half of the year peaks in chlorophyll a correspond with peaks in dissolved oxygen but in the last half with troughs in dissolved oxygen. Chlorophyll a levels have fallen since 1984. No evidence of significant changes in nutrient levels between 1984 and 1989 was obtained.