Biodiversity losses and nutrient loading are considered as two major factors affecting the boundaries of a proposed safe operating space for humanity. Whereas there is knowledge about individual effects of biodiversity and eutrophication on aquatic systems, the strong interactions between these factors were only recently shown. The aim of this proposal is to develop an understanding of the complex interactions between phytoplankton biodiversity and nutrient loading in aquatic systems. The key research challenge is to determine thresholds for nutrient loading critical to maintain community stability (resiliance), and important aquatic ecosystem services in dependence of phytoplankton diversity. The planned project includes field and laboratory experiments complemented by theoretical modelling to investigate the interactions between eutrophication and biodiversity.Experiments will be performed covering a gradient from highly controlled laboratory investigations up to natural, large scale studies. To broaden the general importance of findings, the project will investigate the interaction between eutrophication and biodiversity for different European aquatic systems, including a variety of freshwater lakes but also study sites at the North Atlantic and the Baltic.One major result of this project will be to integrate key drivers of eutrophication and biodiversity loss and their impacts and interactions within a common logic. Thereby the project will gain the attention of key stakeholders by offering a framework that contributes to generate information and awareness of threats to biodiversity in Europe and beyond. The expected findings will allow analysts to explore plausible future developments that may have important implications for current and future decision making. Publication of the results from this project will be disseminated in scientific journals and will be used by scientists to plan and conduct further studies.