Das Projekt "EROS 21: Biogeochemische Wechselwirkungen zwischen der Donau und dem nordwestlichen Schwarzen Meer" wird vom Umweltbundesamt gefördert und von Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz durchgeführt. EROS (European River Ocean System) is a long term interdisciplinary research project on biogeochemical processes in the European coastal environment. EROS 21 is a contribution to the Eloise integrated networking initiative and will focus on the interactions between the Danube, Dnestr and Dnepr rivers and the North-Western Black Sea. It constitutes a follow up of the ongoing Pilot project 'EROS 2000 - The interactions between the Danube river and the North Western Black Sea (1994-1996)' This area, indeed, corresponds to the largest catchment basin of european rivers, and represents one of the ultimate example of deterioration of the coastal marine environment, where dramatic eutrophication, pollution and erosion problems are observed. The extrapolation of the results obtained in this area will be of great value for determining measures to be taken to prevent such catastrophic situation in other semienclosed seas. It further represents a key environment for understanding the production of biogases of climatological significance such as methane. The geographical area under study is roughly the North-Western Black Sea continental shelf (offshore limit at the 200 m isobath, from Sebastopol to Burgas) but processes whose understanding requires and extension of the domain are examined at the appropriate scale (e.g. sediment dispersion, methane seepage, hydrodynamical circulation...). The scientific objectives are adressed by the four following key questions, which also determine the structure of the project: 1. What would be the consequences of a reduction of the river input of nutrients for the eutrophication and the ecosystem structure of the North Western Black Sea ? 2. What are the rivererine and atmospheric sources, levels and fates of key organic/inorganic contaminants in the North-Western Black Sea environment ? 3. What are likely to be the short - and long - term consequences of the regulation of river discharge for sediment erosion, transport, deposition and water stratification ? 4. What is the significance of the Black sea as a source of important greenhouse gases?