engleski

The role of long-term monitoring of chemical parameters in the study of eutrophication, with special reference to the northern Adriatic

The northern Adriatic ecosystem undergoes marked fluctuations in phytoplankton crop from a combination of seasonal cycles and the influence of discharges from numerous freshwater sources, mainly the Po River (Gilmartin et al., 1990). A 26 years (1966-1992) database of temperature, salinity, dissolved oxygen, nutrient concentrations, phytoplankton biomass (Chl a), primary production (14C-"potential" photosynthetic activity), and phytoplankton count data was developed. Data were used to study fluctuations and changes in the eutrophication of the northern Adriatic. A number of changes were identified characterising the behaviour of the northern Adriatic ecosystem. For instance, a statistically significant decrease of orthosilicate concentration in the surface layer in May-June during the eighties should be related to an increasing domination of diatoms in the micro phytoplankton, particularly during the blooms (Degobbis et al., 1995). An increase of the surface assimilation number (PB) of 3-5 h-1 was observed in summer, which could be in part ascribed to a 1-2 C increase of the surface temperature. Those findings and some minor changes of nutrient concentrations, possibly related to modifications of the Po water composition (Ivančić, 1995), could not explain the changes observed in the dissolved oxygen cycle during the eighties. A decrease ( 25% in average) occurred in the bottom oxygen saturation minima in October- November, concurrently to an increase ( 10%) and enhanced variability in the surface layer in May-June. The long-term monitoring should be continued in the northern Adriatic to obtain more satisfactory answers to the problems related to eutrophication. Based on these examples a discussion was developed concerning the potentiality, as well as the limits of the chemical parameter monitoring to identify the causes and describe eutrophication trends in coastal regions similar to the northern Adriatic.

eutrophication ; nutrients ; long-term monitoring ; northern Adriatic Sea

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