Variability of nutrient limitation in the Archipelago Sea,SW Finland

Eutrophication is the most acute environmentalproblem in the Archipelago Sea, SW Finland. Whenanalysing the factors behind this escalatingeutrophication the determination of limitingnutrient at a given time is essential. Besidesexperimentations, nutrient limitation of planktonhas been extensively studied by direct chemicalanalyses. We used the latter approach in this work.Nutrient limitation was studied by calculatingdifferent nutrient ratios – totalnitrogen:phosphorus, inorganic nitrogen:phosphorus,and nutrient balance ratio. Results showed thatphosphorus usually limited primary production onlynear the coast line. In the middle zone of theArchipelago Sea the limiting factor variedtemporally. Outer in the open sea nitrogen limitedprimary production during most of the year.Phosphorus limited phytoplankton growth especiallyin spring and in summer and nitrogen in late summerand in autumn. Our results suggested that nitrogenis an important limiting nutrient in the ArchipelagoSea. In recent years when the eutrophication hasproceeded there has been a shift from productionlimitation by both nutrients to limitation bynitrogen alone. But if we want to define andcharacterize the nutrient limitation of the entireecosystem of the Archipelago Sea, budgets have to becalculated for both N and P and internal recyclingmust be taken into account as well as externalsupply of nutrients and loss processes. This revised version was published online in July 2006 with corrections to the Cover Date.