The Gulf of Finland is the most eutrophicated (over-fertilized) sub-basin of the Baltic Sea. Eutrophication leads to poor water quality, violent and toxic algae blooms, economical and possibly health problems. However, there are expectations of positive effects in the marine environment in this area due to decreasing nutrient (fertilizer) input from land. The input has decreased because of a collapsed agriculture in Russia and Estonia after "Perestrojka" and since the wastewater treatment plants around the Gulf have been generally improved. However, a large uncertainty still remains concerning the role of the sediments and the sediment held pool of nutrients in eutrophication. Information on the internal load processes and the magnitude of the nutrient fluxes from the sediments is of primary importance for understanding the system as a whole. Resuspension (stirred up particles from the bottom) of sediments, natural or man-induced, can play a major role in supplying nutrients or other solutes to the water. There are plans to commercially dredge areas of the Gulf for mineral nodules, which is likely to create important resuspension of sediments. This might enhance the water load of nutrients and consequently further deteriorate the aquatic conditions in the whole area. The overall goal of the proposed project is to gain and present a better understanding of the role of sediment held nutrients in eutrophication. This has general environmental interest since little is known on the subject. The most important goal is however to give urgently needed input which can help in the process of taking environmentally sustainable decisions to improve the "value" (ecological, economical and social) of the Gulf of Finland and the Baltic Sea. The objectives of the project are: - To investigate and gain a better understanding of the long (years) and short (weeks-months) term role of sediment held nutrients (silicate, phosphate, nitrate and ammonium) in eutrophication of the Gulf of Finland; - To improve the knowledge of the importance of periodic sediment re-suspension and anoxia (oxygen free bottom), of three different sediment types, for carbon, nitrogen, silicon and phosphorus recycling; - To make general, regional (for the Gulf of Finland) and local (for each station) models on the importance of sediments, sediment re-suspension and anoxia for the eutrophication and recycling/burial of organic material; - To "feed" data and relevant models into the larger "Baltic Sea eutrophication models" developed in previous and ongoing projects. Obtained data shall also be submitted to existing databases for the Baltic Sea (e.g. HELCOM and BED); - To communicate the environmental consequences of the obtained results to concerned decision-makers in the region by organizing three special INTAS sessions, at the end of the project. Presentations will also be made to the public and on the Internet. - To publish results in international reviewed scientific journals; - To collect high quality and quantity data by the use of state of the art in-situ and laboratory technology. - To maintain a significant transfer of technology, knowledge and new working methods between involved partners throughout the project.