Variability of nutrient limitation in the Archipelago Sea, SW Finland

Eutrophication is the most acute environmental problem in the Archipelago 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 plankton has been extensively studied by direct chemical analyses. We used the latter approach in this work. Nutrient limitation was studied by calculating different nutrient ratios - total nitrogen:phosphorus, inorganic nitrogen:phosphorus, and nutrient balance ratio. Results showed that phosphorus usually limited primary production only near the coast line. In the middle zone of the Archipelago Sea the limiting factor varied temporally. Outer in the open sea nitrogen limited primary production 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 nutrient in the Archipelago Sea. In recent years when the eutrophication has proceeded there has been a shift from.production limitation by both nutrients to limitation by nitrogen alone. But if we want to define and characterize the nutrient limitation of the entire ecosystem of the Archipelago Sea, budgets have to be calculated for both N and P and internal recycling must be taken into account as well as external supply of nutrients and loss processes.</p

Concentration ratios to aquatic plants at and near Olkiluoto repository site

In Finland, Olkiluoto Island on the western coast has been selected as a repository site for spent nuclear fuel disposal. With the approaching licensing steps (application for the nuclear construction licence in 2012), the biosphere assessment demonstrating the long-term safety of the repository is developed into more and more site specific. At the present coastal site, lakes will form in the future millennia due to the post-glacial crustal rebound, i.e. land uplift, which at least eventually will outrun the anthropogenic sea level rise. Both the brackish bays of Baltic Sea and the future lakes can be primary recipients of releases from the deep underground repository, and the aquatic plants can form a major pool of radionuclides with a rather rapid turnover. In some cases the aquatic plants are a relevant part of wildlife food web and possibly also a resource to human. To provide the biosphere assessment models with site-relevant input parameter data, samples of typical aquatic plants were collected from the sea area at the site and from two nearby lakes analogous to those expected to form at the site during the future millennia. This contribution presents water-to-plant concentration ratios of stable elements of high relevance to the biosphere assessment of the Olkiluoto spent fuel repository

Selection of real-life analogues for future lakes and mires at a repository site

In Finland, Olkiluoto Island on the western coast has been selected as a repository site for spent nuclear fuel. Due to the shallow sea areas around the island, the postglacial land uplift is going to change the landscape within the next millennia. For instance, new lakes and mires will develop on the present offshore areas. Concerning radionuclide transport models, the properties of the future ecosystems surrounding Olkiluoto Island can be forecast based on the properties of present lakes and mires. Due to the lack of site-specific data, lakes and mires of various successional stages were selected within a larger geographical area as analogues of the future ones. Here we present an example of a systematic process for selection of appropriate analogue sites