VARIABILITY OF NUTRIENT LIMITATION IN THE ARCHIPELAGO SEA, SW FINLAND

Eutrophication is the most acute environmental problem in the Archipel ago Sea, SW Finland. When analysing the factors behind this escalating eutrophication the determination of limiting nutrient at a given time is essential. Besides experimentations, nutrient limitation of plankt on has been extensively studied by direct chemical analyses. We used t he latter approach in this work. Nutrient limitation was studied by ca lculating different nutrient ratios - total nitrogen:phosphorus, inorg anic nitrogen:phosphorus, and nutrient balance ratio. Results showed t hat phosphorus usually limited primary production only near the coast line. In the middle zone of the Archipelago Sea the limiting factor va ried temporally. Outer in the open sea nitrogen limited primary produc tion during most of the year. Phosphorus limited phytoplankton growth especially in spring and in summer and nitrogen in late summer and in autumn. Our results suggested that nitrogen is an important limiting n utrient in the Archipelago Sea. In recent years when the eutrophicatio n has proceeded there has been a shift from.production limitation by b oth nutrients to limitation by nitrogen alone. But if we want to defin e and characterize the nutrient limitation of the entire ecosystem of the Archipelago Sea, budgets have to be calculated for both N and P an d internal recycling must be taken into account as well as external su pply of nutrients and loss processes.